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The Linux-PAM System Administrators' Guide
Andrew G. Morgan
<morgan@kernel.org>
Thorsten Kukuk
<kukuk@thkukuk.de>
Version 1.1.2, 31. August 2010
Abstract
This manual documents what a system-administrator needs to know about the
Linux-PAM library. It covers the correct syntax of the PAM configuration
file and discusses strategies for maintaining a secure system.
--------------------------------------------------------------------------
1. Introduction
2. Some comments on the text
3. Overview
4. The Linux-PAM configuration file
4.1. Configuration file syntax
4.2. Directory based configuration
4.3. Example configuration file entries
5. Security issues
5.1. If something goes wrong
5.2. Avoid having a weak `other' configuration
6. A reference guide for available modules
6.1. pam_access - logdaemon style login access control
6.2. pam_cracklib - checks the password against dictionary
words
6.3. pam_debug - debug the PAM stack
6.4. pam_deny - locking-out PAM module
6.5. pam_echo - print text messages
6.6. pam_env - set/unset environment variables
6.7. pam_exec - call an external command
6.8. pam_faildelay - change the delay on failure
per-application
6.9. pam_filter - filter module
6.10. pam_ftp - module for anonymous access
6.11. pam_group - module to modify group access
6.12. pam_issue - add issue file to user prompt
6.13. pam_keyinit - display the keyinit file
6.14. pam_lastlog - display date of last login
6.15. pam_limits - limit resources
6.16. pam_listfile - deny or allow services based on an
arbitrary file
6.17. pam_localuser - require users to be listed in
/etc/passwd
6.18. pam_loginuid - record user's login uid to the process
attribute
6.19. pam_mail - inform about available mail
6.20. pam_mkhomedir - create users home directory
6.21. pam_motd - display the motd file
6.22. pam_namespace - setup a private namespace
6.23. pam_nologin - prevent non-root users from login
6.24. pam_permit - the promiscuous module
6.25. pam_pwhistory - grant access using .pwhistory file
6.26. pam_rhosts - grant access using .rhosts file
6.27. pam_rootok - gain only root access
6.28. pam_securetty - limit root login to special devices
6.29. pam_selinux - set the default security context
6.30. pam_shells - check for valid login shell
6.31. pam_succeed_if - test account characteristics
6.32. pam_tally - login counter (tallying) module
6.33. pam_tally2 - login counter (tallying) module
6.34. pam_time - time controled access
6.35. pam_timestamp - authenticate using cached successful
authentication attempts
6.36. pam_umask - set the file mode creation mask
6.37. pam_unix - traditional password authentication
6.38. pam_userdb - authenticate against a db database
6.39. pam_warn - logs all PAM items
6.40. pam_wheel - only permit root access to members of group
wheel
6.41. pam_xauth - forward xauth keys between users
7. See also
8. Author/acknowledgments
9. Copyright information for this document
Chapter 1. Introduction
Linux-PAM (Pluggable Authentication Modules for Linux) is a suite of
shared libraries that enable the local system administrator to choose how
applications authenticate users.
In other words, without (rewriting and) recompiling a PAM-aware
application, it is possible to switch between the authentication
mechanism(s) it uses. Indeed, one may entirely upgrade the local
authentication system without touching the applications themselves.
Historically an application that has required a given user to be
authenticated, has had to be compiled to use a specific authentication
mechanism. For example, in the case of traditional UN*X systems, the
identity of the user is verified by the user entering a correct password.
This password, after being prefixed by a two character ``salt'', is
encrypted (with crypt(3)). The user is then authenticated if this
encrypted password is identical to the second field of the user's entry in
the system password database (the /etc/passwd file). On such systems, most
if not all forms of privileges are granted based on this single
authentication scheme. Privilege comes in the form of a personal
user-identifier (UID) and membership of various groups. Services and
applications are available based on the personal and group identity of the
user. Traditionally, group membership has been assigned based on entries
in the /etc/group file.
It is the purpose of the Linux-PAM project to separate the development of
privilege granting software from the development of secure and appropriate
authentication schemes. This is accomplished by providing a library of
functions that an application may use to request that a user be
authenticated. This PAM library is configured locally with a system file,
/etc/pam.conf (or a series of configuration files located in /etc/pam.d/)
to authenticate a user request via the locally available authentication
modules. The modules themselves will usually be located in the directory
/lib/security or /lib64/security and take the form of dynamically loadable
object files (see dlopen(3)).
Chapter 2. Some comments on the text
Before proceeding to read the rest of this document, it should be noted
that the text assumes that certain files are placed in certain
directories. Where they have been specified, the conventions we adopt here
for locating these files are those of the relevant RFC (RFC-86.0, see
bibliography"). If you are using a distribution of Linux (or some other
operating system) that supports PAM but chooses to distribute these files
in a different way you should be careful when copying examples directly
from the text.
As an example of the above, where it is explicit, the text assumes that
PAM loadable object files (the modules) are to be located in the following
directory: /lib/security/ or /lib64/security depending on the
architecture. This is generally the location that seems to be compatible
with the Filesystem Hierarchy Standard (FHS). On Solaris, which has its
own licensed version of PAM, and some other implementations of UN*X, these
files can be found in /usr/lib/security. Please be careful to perform the
necessary transcription when using the examples from the text.
Chapter 3. Overview
For the uninitiated, we begin by considering an example. We take an
application that grants some service to users; login is one such program.
Login does two things, it first establishes that the requesting user is
whom they claim to be and second provides them with the requested service:
in the case of login the service is a command shell (bash, tcsh, zsh,
etc.) running with the identity of the user.
Traditionally, the former step is achieved by the login application
prompting the user for a password and then verifying that it agrees with
that located on the system; hence verifying that as far as the system is
concerned the user is who they claim to be. This is the task that is
delegated to Linux-PAM.
From the perspective of the application programmer (in this case the
person that wrote the login application), Linux-PAM takes care of this
authentication task -- verifying the identity of the user.
The flexibility of Linux-PAM is that you, the system administrator, have
the freedom to stipulate which authentication scheme is to be used. You
have the freedom to set the scheme for any/all PAM-aware applications on
your Linux system. That is, you can authenticate from anything as naive as
simple trust (pam_permit) to something as paranoid as a combination of a
retinal scan, a voice print and a one-time password!
To illustrate the flexibility you face, consider the following situation:
a system administrator (parent) wishes to improve the mathematical ability
of her users (children). She can configure their favorite ``Shoot 'em up
game'' (PAM-aware of course) to authenticate them with a request for the
product of a couple of random numbers less than 12. It is clear that if
the game is any good they will soon learn their multiplication tables. As
they mature, the authentication can be upgraded to include (long)
division!
Linux-PAM deals with four separate types of (management) task. These are:
authentication management; account management; session management; and
password management. The association of the preferred management scheme
with the behavior of an application is made with entries in the relevant
Linux-PAM configuration file. The management functions are performed by
modules specified in the configuration file. The syntax for this file is
discussed in the section below.
Here is a figure that describes the overall organization of Linux-PAM:
+----------------+
| application: X |
+----------------+ / +----------+ +================+
| authentication-[---->--\--] Linux- |--<--| PAM config file|
| + [----<--/--] PAM | |================|
|[conversation()][--+ \ | | | X auth .. a.so |
+----------------+ | / +-n--n-----+ | X auth .. b.so |
| | | __| | | _____/
| service user | A | | |____,-----'
| | | V A
+----------------+ +------|-----|---------+ -----+------+
+---u-----u----+ | | |
| auth.... |--[ a ]--[ b ]--[ c ]
+--------------+
| acct.... |--[ b ]--[ d ]
+--------------+
| password |--[ b ]--[ c ]
+--------------+
| session |--[ e ]--[ c ]
+--------------+
By way of explanation, the left of the figure represents the application;
application X. Such an application interfaces with the Linux-PAM library
and knows none of the specifics of its configured authentication method.
The Linux-PAM library (in the center) consults the contents of the PAM
configuration file and loads the modules that are appropriate for
application-X. These modules fall into one of four management groups
(lower-center) and are stacked in the order they appear in the
configuration file. These modules, when called by Linux-PAM, perform the
various authentication tasks for the application. Textual information,
required from/or offered to the user, can be exchanged through the use of
the application-supplied conversation function.
If a program is going to use PAM, then it has to have PAM functions
explicitly coded into the program. If you have access to the source code
you can add the appropriate PAM functions. If you do not have access to
the source code, and the binary does not have the PAM functions included,
then it is not possible to use PAM.
Chapter 4. The Linux-PAM configuration file
When a PAM aware privilege granting application is started, it activates
its attachment to the PAM-API. This activation performs a number of tasks,
the most important being the reading of the configuration file(s):
/etc/pam.conf. Alternatively, this may be the contents of the /etc/pam.d/
directory. The presence of this directory will cause Linux-PAM to ignore
/etc/pam.conf.
These files list the PAMs that will do the authentication tasks required
by this service, and the appropriate behavior of the PAM-API in the event
that individual PAMs fail.
4.1. Configuration file syntax
The syntax of the /etc/pam.conf configuration file is as follows. The file
is made up of a list of rules, each rule is typically placed on a single
line, but may be extended with an escaped end of line: `\<LF>'. Comments
are preceded with `#' marks and extend to the next end of line.
The format of each rule is a space separated collection of tokens, the
first three being case-insensitive:
service type control module-path module-arguments
The syntax of files contained in the /etc/pam.d/ directory, are identical
except for the absence of any service field. In this case, the service is
the name of the file in the /etc/pam.d/ directory. This filename must be
in lower case.
An important feature of PAM, is that a number of rules may be stacked to
combine the services of a number of PAMs for a given authentication task.
The service is typically the familiar name of the corresponding
application: login and su are good examples. The service-name, other, is
reserved for giving default rules. Only lines that mention the current
service (or in the absence of such, the other entries) will be associated
with the given service-application.
The type is the management group that the rule corresponds to. It is used
to specify which of the management groups the subsequent module is to be
associated with. Valid entries are:
account
this module type performs non-authentication based account
management. It is typically used to restrict/permit access to a
service based on the time of day, currently available system
resources (maximum number of users) or perhaps the location of the
applicant user -- 'root' login only on the console.
auth
this module type provides two aspects of authenticating the user.
Firstly, it establishes that the user is who they claim to be, by
instructing the application to prompt the user for a password or
other means of identification. Secondly, the module can grant
group membership or other privileges through its credential
granting properties.
password
this module type is required for updating the authentication token
associated with the user. Typically, there is one module for each
'challenge/response' based authentication (auth) type.
session
this module type is associated with doing things that need to be
done for the user before/after they can be given service. Such
things include the logging of information concerning the
opening/closing of some data exchange with a user, mounting
directories, etc.
If the type value from the list above is prepended with a - character the
PAM library will not log to the system log if it is not possible to load
the module because it is missing in the system. This can be useful
especially for modules which are not always installed on the system and
are not required for correct authentication and authorization of the login
session.
The third field, control, indicates the behavior of the PAM-API should the
module fail to succeed in its authentication task. There are two types of
syntax for this control field: the simple one has a single simple keyword;
the more complicated one involves a square-bracketed selection of
value=action pairs.
For the simple (historical) syntax valid control values are:
required
failure of such a PAM will ultimately lead to the PAM-API
returning failure but only after the remaining stacked modules
(for this service and type) have been invoked.
requisite
like required, however, in the case that such a module returns a
failure, control is directly returned to the application or to the
superior PAM stack. The return value is that associated with the
first required or requisite module to fail. Note, this flag can be
used to protect against the possibility of a user getting the
opportunity to enter a password over an unsafe medium. It is
conceivable that such behavior might inform an attacker of valid
accounts on a system. This possibility should be weighed against
the not insignificant concerns of exposing a sensitive password in
a hostile environment.
sufficient
if such a module succeeds and no prior required module has failed
the PAM framework returns success to the application or to the
superior PAM stack immediately without calling any further modules
in the stack. A failure of a sufficient module is ignored and
processing of the PAM module stack continues unaffected.
optional
the success or failure of this module is only important if it is
the only module in the stack associated with this service+type.
include
include all lines of given type from the configuration file
specified as an argument to this control.
substack
include all lines of given type from the configuration file
specified as an argument to this control. This differs from
include in that evaluation of the done and die actions in a
substack does not cause skipping the rest of the complete module
stack, but only of the substack. Jumps in a substack also can not
make evaluation jump out of it, and the whole substack is counted
as one module when the jump is done in a parent stack. The reset
action will reset the state of a module stack to the state it was
in as of beginning of the substack evaluation.
For the more complicated syntax valid control values have the following
form:
[value1=action1 value2=action2 ...]
Where valueN corresponds to the return code from the function invoked in
the module for which the line is defined. It is selected from one of
these: success, open_err, symbol_err, service_err, system_err, buf_err,
perm_denied, auth_err, cred_insufficient, authinfo_unavail, user_unknown,
maxtries, new_authtok_reqd, acct_expired, session_err, cred_unavail,
cred_expired, cred_err, no_module_data, conv_err, authtok_err,
authtok_recover_err, authtok_lock_busy, authtok_disable_aging, try_again,
ignore, abort, authtok_expired, module_unknown, bad_item, conv_again,
incomplete, and default.
The last of these, default, implies 'all valueN's not mentioned
explicitly. Note, the full list of PAM errors is available in
/usr/include/security/_pam_types.h. The actionN can take one of the
following forms:
ignore
when used with a stack of modules, the module's return status will
not contribute to the return code the application obtains.
bad
this action indicates that the return code should be thought of as
indicative of the module failing. If this module is the first in
the stack to fail, its status value will be used for that of the
whole stack.
die
equivalent to bad with the side effect of terminating the module
stack and PAM immediately returning to the application.
ok
this tells PAM that the administrator thinks this return code
should contribute directly to the return code of the full stack of
modules. In other words, if the former state of the stack would
lead to a return of PAM_SUCCESS, the module's return code will
override this value. Note, if the former state of the stack holds
some value that is indicative of a modules failure, this 'ok'
value will not be used to override that value.
done
equivalent to ok with the side effect of terminating the module
stack and PAM immediately returning to the application.
N (an unsigned integer)
equivalent to ok with the side effect of jumping over the next N
modules in the stack. Note that N equal to 0 is not allowed (and
it would be identical to ok in such case).
reset
clear all memory of the state of the module stack and start again
with the next stacked module.
Each of the four keywords: required; requisite; sufficient; and optional,
have an equivalent expression in terms of the [...] syntax. They are as
follows:
required
[success=ok new_authtok_reqd=ok ignore=ignore default=bad]
requisite
[success=ok new_authtok_reqd=ok ignore=ignore default=die]
sufficient
[success=done new_authtok_reqd=done default=ignore]
optional
[success=ok new_authtok_reqd=ok default=ignore]
module-path is either the full filename of the PAM to be used by the
application (it begins with a '/'), or a relative pathname from the
default module location: /lib/security/ or /lib64/security/, depending on
the architecture.
module-arguments are a space separated list of tokens that can be used to
modify the specific behavior of the given PAM. Such arguments will be
documented for each individual module. Note, if you wish to include spaces
in an argument, you should surround that argument with square brackets.
squid auth required pam_mysql.so user=passwd_query passwd=mada \
db=eminence [query=select user_name from internet_service \
where user_name='%u' and password=PASSWORD('%p') and \
service='web_proxy']
When using this convention, you can include `[' characters inside the
string, and if you wish to include a `]' character inside the string that
will survive the argument parsing, you should use `\]'. In other words:
[..[..\]..] --> ..[..]..
Any line in (one of) the configuration file(s), that is not formatted
correctly, will generally tend (erring on the side of caution) to make the
authentication process fail. A corresponding error is written to the
system log files with a call to syslog(3).
4.2. Directory based configuration
More flexible than the single configuration file is it to configure libpam
via the contents of the /etc/pam.d/ directory. In this case the directory
is filled with files each of which has a filename equal to a service-name
(in lower-case): it is the personal configuration file for the named
service.
The syntax of each file in /etc/pam.d/ is similar to that of the
/etc/pam.conf file and is made up of lines of the following form:
type control module-path module-arguments
The only difference being that the service-name is not present. The
service-name is of course the name of the given configuration file. For
example, /etc/pam.d/login contains the configuration for the login
service.
4.3. Example configuration file entries
In this section, we give some examples of entries that can be present in
the Linux-PAM configuration file. As a first attempt at configuring your
system you could do worse than to implement these.
If a system is to be considered secure, it had better have a reasonably
secure 'other entry. The following is a paranoid setting (which is not a
bad place to start!):
#
# default; deny access
#
other auth required pam_deny.so
other account required pam_deny.so
other password required pam_deny.so
other session required pam_deny.so
Whilst fundamentally a secure default, this is not very sympathetic to a
misconfigured system. For example, such a system is vulnerable to locking
everyone out should the rest of the file become badly written.
The module pam_deny (documented in a later section) is not very
sophisticated. For example, it logs no information when it is invoked so
unless the users of a system contact the administrator when failing to
execute a service application, the administrator may go for a long while
in ignorance of the fact that his system is misconfigured.
The addition of the following line before those in the above example would
provide a suitable warning to the administrator.
#
# default; wake up! This application is not configured
#
other auth required pam_warn.so
other password required pam_warn.so
Having two 'other auth' lines is an example of stacking.
On a system that uses the /etc/pam.d/ configuration, the corresponding
default setup would be achieved with the following file:
#
# default configuration: /etc/pam.d/other
#
auth required pam_warn.so
auth required pam_deny.so
account required pam_deny.so
password required pam_warn.so
password required pam_deny.so
session required pam_deny.so
This is the only explicit example we give for an /etc/pam.d/ file. In
general, it should be clear how to transpose the remaining examples to
this configuration scheme.
On a less sensitive computer, one on which the system administrator wishes
to remain ignorant of much of the power of Linux-PAM, the following
selection of lines (in /etc/pam.d/other) is likely to mimic the
historically familiar Linux setup.
#
# default; standard UN*X access
#
auth required pam_unix.so
account required pam_unix.so
password required pam_unix.so
session required pam_unix.so
In general this will provide a starting place for most applications.
Chapter 5. Security issues
5.1. If something goes wrong
Linux-PAM has the potential to seriously change the security of your
system. You can choose to have no security or absolute security (no access
permitted). In general, Linux-PAM errs towards the latter. Any number of
configuration errors can disable access to your system partially, or
completely.
The most dramatic problem that is likely to be encountered when
configuring Linux-PAM is that of deleting the configuration file(s):
/etc/pam.d/* and/or /etc/pam.conf. This will lock you out of your own
system!
To recover, your best bet is to restore the system from a backup or boot
the system into a rescue system and correct things from there.
5.2. Avoid having a weak `other' configuration
It is not a good thing to have a weak default (other) entry. This service
is the default configuration for all PAM aware applications and if it is
weak, your system is likely to be vulnerable to attack.
Here is a sample "other" configuration file. The pam_deny module will deny
access and the pam_warn module will send a syslog message to auth.notice:
#
# The PAM configuration file for the `other' service
#
auth required pam_deny.so
auth required pam_warn.so
account required pam_deny.so
account required pam_warn.so
password required pam_deny.so
password required pam_warn.so
session required pam_deny.so
session required pam_warn.so
Chapter 6. A reference guide for available modules
Here, we collect together the descriptions of the various modules coming
with Linux-PAM.
6.1. pam_access - logdaemon style login access control
pam_access.so [ debug ] [ nodefgroup ] [ noaudit ] [ accessfile=file ] [
fieldsep=sep ] [ listsep=sep ]
6.1.1. DESCRIPTION
The pam_access PAM module is mainly for access management. It provides
logdaemon style login access control based on login names, host or domain
names, internet addresses or network numbers, or on terminal line names, X
$DISPLAY values, or PAM service names in case of non-networked logins.
By default rules for access management are taken from config file
/etc/security/access.conf if you don't specify another file. Then
individual *.conf files from the /etc/security/access.d/ directory are
read. The files are parsed one after another in the order of the system
locale. The effect of the individual files is the same as if all the files
were concatenated together in the order of parsing. This means that once a
pattern is matched in some file no further files are parsed. If a config
file is explicitly specified with the accessfile option the files in the
above directory are not parsed.
If Linux PAM is compiled with audit support the module will report when it
denies access based on origin (host, tty, etc.).
6.1.2. DESCRIPTION
The /etc/security/access.conf file specifies (user/group, host),
(user/group, network/netmask), (user/group, tty), (user/group,
X-$DISPLAY-value), or (user/group, pam-service-name) combinations for
which a login will be either accepted or refused.
When someone logs in, the file access.conf is scanned for the first entry
that matches the (user/group, host) or (user/group, network/netmask)
combination, or, in case of non-networked logins, the first entry that
matches the (user/group, tty) combination, or in the case of non-networked
logins without a tty, the first entry that matches the (user/group,
X-$DISPLAY-value) or (user/group, pam-service-name/) combination. The
permissions field of that table entry determines whether the login will be
accepted or refused.
Each line of the login access control table has three fields separated by
a ":" character (colon):
permission:users/groups:origins
The first field, the permission field, can be either a "+" character
(plus) for access granted or a "-" character (minus) for access denied.
The second field, the users/group field, should be a list of one or more
login names, group names, or ALL (which always matches). To differentiate
user entries from group entries, group entries should be written with
brackets, e.g. (group).
The third field, the origins field, should be a list of one or more tty
names (for non-networked logins), X $DISPLAY values or PAM service names
(for non-networked logins without a tty), host names, domain names (begin
with "."), host addresses, internet network numbers (end with "."),
internet network addresses with network mask (where network mask can be a
decimal number or an internet address also), ALL (which always matches) or
LOCAL. The LOCAL keyword matches if and only if pam_get_item(3), when
called with an item_type of PAM_RHOST, returns NULL or an empty string
(and therefore the origins field is compared against the return value of
pam_get_item(3) called with an item_type of PAM_TTY or, absent that,
PAM_SERVICE).
If supported by the system you can use @netgroupname in host or user
patterns. The @@netgroupname syntax is supported in the user pattern only
and it makes the local system hostname to be passed to the netgroup match
call in addition to the user name. This might not work correctly on some
libc implementations causing the match to always fail.
The EXCEPT operator makes it possible to write very compact rules.
If the nodefgroup is not set, the group file is searched when a name does
not match that of the logged-in user. Only groups are matched in which
users are explicitly listed. However the PAM module does not look at the
primary group id of a user.
The "#" character at start of line (no space at front) can be used to mark
this line as a comment line.
6.1.3. OPTIONS
accessfile=/path/to/access.conf
Indicate an alternative access.conf style configuration file to
override the default. This can be useful when different services
need different access lists.
debug
A lot of debug information is printed with syslog(3).
noaudit
Do not report logins from disallowed hosts and ttys to the audit
subsystem.
fieldsep=separators
This option modifies the field separator character that pam_access
will recognize when parsing the access configuration file. For
example: fieldsep=| will cause the default `:' character to be
treated as part of a field value and `|' becomes the field
separator. Doing this may be useful in conjunction with a system
that wants to use pam_access with X based applications, since the
PAM_TTY item is likely to be of the form "hostname:0" which
includes a `:' character in its value. But you should not need
this.
listsep=separators
This option modifies the list separator character that pam_access
will recognize when parsing the access configuration file. For
example: listsep=, will cause the default ` ' (space) and `\t'
(tab) characters to be treated as part of a list element value and
`,' becomes the only list element separator. Doing this may be
useful on a system with group information obtained from a Windows
domain, where the default built-in groups "Domain Users", "Domain
Admins" contain a space.
nodefgroup
User tokens which are not enclosed in parentheses will not be
matched against the group database. The backwards compatible
default is to try the group database match even for tokens not
enclosed in parentheses.
6.1.4. MODULE TYPES PROVIDED
All module types (auth, account, password and session) are provided.
6.1.5. RETURN VALUES
PAM_SUCCESS
Access was granted.
PAM_PERM_DENIED
Access was not granted.
PAM_IGNORE
pam_setcred was called which does nothing.
PAM_ABORT
Not all relevant data or options could be gotten.
PAM_USER_UNKNOWN
The user is not known to the system.
6.1.6. FILES
/etc/security/access.conf
Default configuration file
6.1.7. EXAMPLES
These are some example lines which might be specified in
/etc/security/access.conf.
User root should be allowed to get access via cron, X11 terminal :0, tty1,
..., tty5, tty6.
+:root:crond :0 tty1 tty2 tty3 tty4 tty5 tty6
User root should be allowed to get access from hosts which own the IPv4
addresses. This does not mean that the connection have to be a IPv4 one, a
IPv6 connection from a host with one of this IPv4 addresses does work,
too.
+:root:192.168.200.1 192.168.200.4 192.168.200.9
+:root:127.0.0.1
User root should get access from network 192.168.201. where the term will
be evaluated by string matching. But it might be better to use
network/netmask instead. The same meaning of 192.168.201. is
192.168.201.0/24 or 192.168.201.0/255.255.255.0.
+:root:192.168.201.
User root should be able to have access from hosts foo1.bar.org and
foo2.bar.org (uses string matching also).
+:root:foo1.bar.org foo2.bar.org
User root should be able to have access from domain foo.bar.org (uses
string matching also).
+:root:.foo.bar.org
User root should be denied to get access from all other sources.
-:root:ALL
User foo and members of netgroup admins should be allowed to get access
from all sources. This will only work if netgroup service is available.
+:@admins foo:ALL
User john and foo should get access from IPv6 host address.
+:john foo:2001:db8:0:101::1
User john should get access from IPv6 net/mask.
+:john:2001:db8:0:101::/64
Disallow console logins to all but the shutdown, sync and all other
accounts, which are a member of the wheel group.
-:ALL EXCEPT (wheel) shutdown sync:LOCAL
All other users should be denied to get access from all sources.
-:ALL:ALL
6.1.8. AUTHORS
The logdaemon style login access control scheme was designed and
implemented by Wietse Venema. The pam_access PAM module was developed by
Alexei Nogin <alexei@nogin.dnttm.ru>. The IPv6 support and the
network(address) / netmask feature was developed and provided by Mike
Becher <mike.becher@lrz-muenchen.de>.
6.2. pam_cracklib - checks the password against dictionary words
pam_cracklib.so [ ... ]
6.2.1. DESCRIPTION
This module can be plugged into the password stack of a given application
to provide some plug-in strength-checking for passwords.
The action of this module is to prompt the user for a password and check
its strength against a system dictionary and a set of rules for
identifying poor choices.
The first action is to prompt for a single password, check its strength
and then, if it is considered strong, prompt for the password a second
time (to verify that it was typed correctly on the first occasion). All
being well, the password is passed on to subsequent modules to be
installed as the new authentication token.
The strength checks works in the following manner: at first the Cracklib
routine is called to check if the password is part of a dictionary; if
this is not the case an additional set of strength checks is done. These
checks are:
Palindrome
Is the new password a palindrome?
Case Change Only
Is the new password the the old one with only a change of case?
Similar
Is the new password too much like the old one? This is primarily
controlled by one argument, difok which is a number of character
changes (inserts, removals, or replacements) between the old and
new password that are enough to accept the new password. This
defaults to 5 changes.
Simple
Is the new password too small? This is controlled by 6 arguments
minlen, maxclassrepeat, dcredit, ucredit, lcredit, and ocredit.
See the section on the arguments for the details of how these work
and there defaults.
Rotated
Is the new password a rotated version of the old password?
Same consecutive characters
Optional check for same consecutive characters.
Too long monotonic character sequence
Optional check for too long monotonic character sequence.
Contains user name
Optional check whether the password contains the user's name in
some form.
This module with no arguments will work well for standard unix password
encryption. With md5 encryption, passwords can be longer than 8 characters
and the default settings for this module can make it hard for the user to
choose a satisfactory new password. Notably, the requirement that the new
password contain no more than 1/2 of the characters in the old password
becomes a non-trivial constraint. For example, an old password of the form
"the quick brown fox jumped over the lazy dogs" would be difficult to
change... In addition, the default action is to allow passwords as small
as 5 characters in length. For a md5 systems it can be a good idea to
increase the required minimum size of a password. One can then allow more
credit for different kinds of characters but accept that the new password
may share most of these characters with the old password.
6.2.2. OPTIONS
debug
This option makes the module write information to syslog(3)
indicating the behavior of the module (this option does not write
password information to the log file).
authtok_type=XXX
The default action is for the module to use the following prompts
when requesting passwords: "New UNIX password: " and "Retype UNIX
password: ". The example word UNIX can be replaced with this
option, by default it is empty.
retry=N
Prompt user at most N times before returning with error. The
default is 1.
difok=N
This argument will change the default of 5 for the number of
character changes in the new password that differentiate it from
the old password.
minlen=N
The minimum acceptable size for the new password (plus one if
credits are not disabled which is the default). In addition to the
number of characters in the new password, credit (of +1 in length)
is given for each different kind of character (other, upper, lower
and digit). The default for this parameter is 9 which is good for
a old style UNIX password all of the same type of character but
may be too low to exploit the added security of a md5 system. Note
that there is a pair of length limits in Cracklib itself, a "way
too short" limit of 4 which is hard coded in and a defined limit
(6) that will be checked without reference to minlen. If you want
to allow passwords as short as 5 characters you should not use
this module.
dcredit=N
(N >= 0) This is the maximum credit for having digits in the new
password. If you have less than or N digits, each digit will count
+1 towards meeting the current minlen value. The default for
dcredit is 1 which is the recommended value for minlen less than
10.
(N < 0) This is the minimum number of digits that must be met for
a new password.
ucredit=N
(N >= 0) This is the maximum credit for having upper case letters
in the new password. If you have less than or N upper case letters
each letter will count +1 towards meeting the current minlen
value. The default for ucredit is 1 which is the recommended value
for minlen less than 10.
(N < 0) This is the minimum number of upper case letters that must
be met for a new password.
lcredit=N
(N >= 0) This is the maximum credit for having lower case letters
in the new password. If you have less than or N lower case
letters, each letter will count +1 towards meeting the current
minlen value. The default for lcredit is 1 which is the
recommended value for minlen less than 10.
(N < 0) This is the minimum number of lower case letters that must
be met for a new password.
ocredit=N
(N >= 0) This is the maximum credit for having other characters in
the new password. If you have less than or N other characters,
each character will count +1 towards meeting the current minlen
value. The default for ocredit is 1 which is the recommended value
for minlen less than 10.
(N < 0) This is the minimum number of other characters that must
be met for a new password.
minclass=N
The minimum number of required classes of characters for the new
password. The default number is zero. The four classes are digits,
upper and lower letters and other characters. The difference to
the credit check is that a specific class if of characters is not
required. Instead N out of four of the classes are required.
maxrepeat=N
Reject passwords which contain more than N same consecutive
characters. The default is 0 which means that this check is
disabled.
maxsequence=N
Reject passwords which contain monotonic character sequences
longer than N. The default is 0 which means that this check is
disabled. Examples of such sequence are '12345' or 'fedcb'. Note
that most such passwords will not pass the simplicity check unless
the sequence is only a minor part of the password.
maxclassrepeat=N
Reject passwords which contain more than N consecutive characters
of the same class. The default is 0 which means that this check is
disabled.
reject_username
Check whether the name of the user in straight or reversed form is
contained in the new password. If it is found the new password is
rejected.
gecoscheck
Check whether the words from the GECOS field (usualy full name of
the user) longer than 3 characters in straight or reversed form
are contained in the new password. If any such word is found the
new password is rejected.
enforce_for_root
The module will return error on failed check also if the user
changing the password is root. This option is off by default which
means that just the message about the failed check is printed but
root can change the password anyway. Note that root is not asked
for an old password so the checks that compare the old and new
password are not performed.
use_authtok
This argument is used to force the module to not prompt the user
for a new password but use the one provided by the previously
stacked password module.
dictpath=/path/to/dict
Path to the cracklib dictionaries.
6.2.3. MODULE TYPES PROVIDED
Only the password module type is provided.
6.2.4. RETURN VALUES
PAM_SUCCESS
The new password passes all checks.
PAM_AUTHTOK_ERR
No new password was entered, the username could not be determined
or the new password fails the strength checks.
PAM_AUTHTOK_RECOVERY_ERR
The old password was not supplied by a previous stacked module or
got not requested from the user. The first error can happen if
use_authtok is specified.
PAM_SERVICE_ERR
A internal error occurred.
6.2.5. EXAMPLES
For an example of the use of this module, we show how it may be stacked
with the password component of pam_unix(8)
#
# These lines stack two password type modules. In this example the
# user is given 3 opportunities to enter a strong password. The
# "use_authtok" argument ensures that the pam_unix module does not
# prompt for a password, but instead uses the one provided by
# pam_cracklib.
#
passwd password required pam_cracklib.so retry=3
passwd password required pam_unix.so use_authtok
Another example (in the /etc/pam.d/passwd format) is for the case that you
want to use md5 password encryption:
#%PAM-1.0
#
# These lines allow a md5 systems to support passwords of at least 14
# bytes with extra credit of 2 for digits and 2 for others the new
# password must have at least three bytes that are not present in the
# old password
#
password required pam_cracklib.so \
difok=3 minlen=15 dcredit= 2 ocredit=2
password required pam_unix.so use_authtok nullok md5
And here is another example in case you don't want to use credits:
#%PAM-1.0
#
# These lines require the user to select a password with a minimum
# length of 8 and with at least 1 digit number, 1 upper case letter,
# and 1 other character
#
password required pam_cracklib.so \
dcredit=-1 ucredit=-1 ocredit=-1 lcredit=0 minlen=8
password required pam_unix.so use_authtok nullok md5
6.2.6. AUTHOR
pam_cracklib was written by Cristian Gafton <gafton@redhat.com>
6.3. pam_debug - debug the PAM stack
pam_debug.so [ auth=value ] [ cred=value ] [ acct=value ] [
prechauthtok=value ] [ chauthtok=value ] [ auth=value ] [
open_session=value ] [ close_session=value ]
6.3.1. DESCRIPTION
The pam_debug PAM module is intended as a debugging aide for determining
how the PAM stack is operating. This module returns what its module
arguments tell it to return.
6.3.2. OPTIONS
auth=value
The pam_sm_authenticate(3) function will return value.
cred=value
The pam_sm_setcred(3) function will return value.
acct=value
The pam_sm_acct_mgmt(3) function will return value.
prechauthtok=value
The pam_sm_chauthtok(3) function will return value if the
PAM_PRELIM_CHECK flag is set.
chauthtok=value
The pam_sm_chauthtok(3) function will return value if the
PAM_PRELIM_CHECK flag is not set.
open_session=value
The pam_sm_open_session(3) function will return value.
close_session=value
The pam_sm_close_session(3) function will return value.
Where value can be one of: success, open_err, symbol_err, service_err,
system_err, buf_err, perm_denied, auth_err, cred_insufficient,
authinfo_unavail, user_unknown, maxtries, new_authtok_reqd, acct_expired,
session_err, cred_unavail, cred_expired, cred_err, no_module_data,
conv_err, authtok_err, authtok_recover_err, authtok_lock_busy,
authtok_disable_aging, try_again, ignore, abort, authtok_expired,
module_unknown, bad_item, conv_again, incomplete.
6.3.3. MODULE TYPES PROVIDED
All module types (auth, account, password and session) are provided.
6.3.4. RETURN VALUES
PAM_SUCCESS
Default return code if no other value was specified, else
specified return value.
6.3.5. EXAMPLES
auth requisite pam_permit.so
auth [success=2 default=ok] pam_debug.so auth=perm_denied cred=success
auth [default=reset] pam_debug.so auth=success cred=perm_denied
auth [success=done default=die] pam_debug.so
auth optional pam_debug.so auth=perm_denied cred=perm_denied
auth sufficient pam_debug.so auth=success cred=success
6.3.6. AUTHOR
pam_debug was written by Andrew G. Morgan <morgan@kernel.org>.
6.4. pam_deny - locking-out PAM module
pam_deny.so
6.4.1. DESCRIPTION
This module can be used to deny access. It always indicates a failure to
the application through the PAM framework. It might be suitable for using
for default (the OTHER) entries.
6.4.2. OPTIONS
This module does not recognise any options.
6.4.3. MODULE TYPES PROVIDED
All module types (account, auth, password and session) are provided.
6.4.4. RETURN VALUES
PAM_AUTH_ERR
This is returned by the account and auth services.
PAM_CRED_ERR
This is returned by the setcred function.
PAM_AUTHTOK_ERR
This is returned by the password service.
PAM_SESSION_ERR
This is returned by the session service.
6.4.5. EXAMPLES
#%PAM-1.0
#
# If we don't have config entries for a service, the
# OTHER entries are used. To be secure, warn and deny
# access to everything.
other auth required pam_warn.so
other auth required pam_deny.so
other account required pam_warn.so
other account required pam_deny.so
other password required pam_warn.so
other password required pam_deny.so
other session required pam_warn.so
other session required pam_deny.so
6.4.6. AUTHOR
pam_deny was written by Andrew G. Morgan <morgan@kernel.org>
6.5. pam_echo - print text messages
pam_echo.so [ file=/path/message ]
6.5.1. DESCRIPTION
The pam_echo PAM module is for printing text messages to inform user about
special things. Sequences starting with the % character are interpreted in
the following way:
%H
The name of the remote host (PAM_RHOST).
%h
The name of the local host.
%s
The service name (PAM_SERVICE).
%t
The name of the controlling terminal (PAM_TTY).
%U
The remote user name (PAM_RUSER).
%u
The local user name (PAM_USER).
All other sequences beginning with % expands to the characters following
the % character.
6.5.2. OPTIONS
file=/path/message
The content of the file /path/message will be printed with the PAM
conversion function as PAM_TEXT_INFO.
6.5.3. MODULE TYPES PROVIDED
All module types (auth, account, password and session) are provided.
6.5.4. RETURN VALUES
PAM_BUF_ERR
Memory buffer error.
PAM_SUCCESS
Message was successful printed.
PAM_IGNORE
PAM_SILENT flag was given or message file does not exist, no
message printed.
6.5.5. EXAMPLES
For an example of the use of this module, we show how it may be used to
print information about good passwords:
password optional pam_echo.so file=/usr/share/doc/good-password.txt
password required pam_unix.so
6.5.6. AUTHOR
Thorsten Kukuk <kukuk@thkukuk.de>
6.6. pam_env - set/unset environment variables
pam_env.so [ debug ] [ conffile=conf-file ] [ envfile=env-file ] [
readenv=0|1 ] [ user_envfile=env-file ] [ user_readenv=0|1 ]
6.6.1. DESCRIPTION
The pam_env PAM module allows the (un)setting of environment variables.
Supported is the use of previously set environment variables as well as
PAM_ITEMs such as PAM_RHOST.
By default rules for (un)setting of variables are taken from the config
file /etc/security/pam_env.conf. An alternate file can be specified with
the conffile option.
Second a file (/etc/environment by default) with simple KEY=VAL pairs on
separate lines will be read. With the envfile option an alternate file can
be specified. And with the readenv option this can be completly disabled.
Third it will read a user configuration file ($HOME/.pam_environment by
default). The default file file can be changed with the user_envfile
option and it can be turned on and off with the user_readenv option.
Since setting of PAM environment variables can have side effects to other
modules, this module should be the last one on the stack.
6.6.2. DESCRIPTION
The /etc/security/pam_env.conf file specifies the environment variables to
be set, unset or modified by pam_env(8). When someone logs in, this file
is read and the environment variables are set according.
Each line starts with the variable name, there are then two possible
options for each variable DEFAULT and OVERRIDE. DEFAULT allows and
administrator to set the value of the variable to some default value, if
none is supplied then the empty string is assumed. The OVERRIDE option
tells pam_env that it should enter in its value (overriding the default
value) if there is one to use. OVERRIDE is not used, "" is assumed and no
override will be done.
VARIABLE [DEFAULT=[value]] [OVERRIDE=[value]]
(Possibly non-existent) environment variables may be used in values using
the ${string} syntax and (possibly non-existent) PAM_ITEMs as well as HOME
and SHELL may be used in values using the @{string} syntax. Both the $ and
@ characters can be backslash escaped to be used as literal values values
can be delimited with "", escaped " not supported. Note that many
environment variables that you would like to use may not be set by the
time the module is called. For example, ${HOME} is used below several
times, but many PAM applications don't make it available by the time you
need it. The special variables @{HOME} and @{SHELL} are expanded to the
values for the user from his passwd entry.
The "#" character at start of line (no space at front) can be used to mark
this line as a comment line.
The /etc/environment file specifies the environment variables to be set.
The file must consist of simple NAME=VALUE pairs on separate lines. The
pam_env(8) module will read the file after the pam_env.conf file.
6.6.3. OPTIONS
conffile=/path/to/pam_env.conf
Indicate an alternative pam_env.conf style configuration file to
override the default. This can be useful when different services
need different environments.
debug
A lot of debug information is printed with syslog(3).
envfile=/path/to/environment
Indicate an alternative environment file to override the default.
The syntax are simple KEY=VAL pairs on separate lines. The export
instruction can be specified for bash compatibility, but will be
ignored. This can be useful when different services need different
environments.
readenv=0|1
Turns on or off the reading of the file specified by envfile (0 is
off, 1 is on). By default this option is on.
user_envfile=filename
Indicate an alternative .pam_environment file to override the
default.The syntax is the same as for /etc/environment. The
filename is relative to the user home directory. This can be
useful when different services need different environments.
user_readenv=0|1
Turns on or off the reading of the user specific environment file.
0 is off, 1 is on. By default this option is off as user supplied
environment variables in the PAM environment could affect behavior
of subsequent modules in the stack without the consent of the
system administrator.
6.6.4. MODULE TYPES PROVIDED
The auth and session module types are provided.
6.6.5. RETURN VALUES
PAM_ABORT
Not all relevant data or options could be gotten.
PAM_BUF_ERR
Memory buffer error.
PAM_IGNORE
No pam_env.conf and environment file was found.
PAM_SUCCESS
Environment variables were set.
6.6.6. FILES
/etc/security/pam_env.conf
Default configuration file
/etc/environment
Default environment file
$HOME/.pam_environment
User specific environment file
6.6.7. EXAMPLES
These are some example lines which might be specified in
/etc/security/pam_env.conf.
Set the REMOTEHOST variable for any hosts that are remote, default to
"localhost" rather than not being set at all
REMOTEHOST DEFAULT=localhost OVERRIDE=@{PAM_RHOST}
Set the DISPLAY variable if it seems reasonable
DISPLAY DEFAULT=${REMOTEHOST}:0.0 OVERRIDE=${DISPLAY}
Now some simple variables
PAGER DEFAULT=less
MANPAGER DEFAULT=less
LESS DEFAULT="M q e h15 z23 b80"
NNTPSERVER DEFAULT=localhost
PATH DEFAULT=${HOME}/bin:/usr/local/bin:/bin\
:/usr/bin:/usr/local/bin/X11:/usr/bin/X11
XDG_DATA_HOME @{HOME}/share/
Silly examples of escaped variables, just to show how they work.
DOLLAR DEFAULT=\$
DOLLARDOLLAR DEFAULT= OVERRIDE=\$${DOLLAR}
DOLLARPLUS DEFAULT=\${REMOTEHOST}${REMOTEHOST}
ATSIGN DEFAULT="" OVERRIDE=\@
6.6.8. AUTHOR
pam_env was written by Dave Kinchlea <kinch@kinch.ark.com>.
6.7. pam_exec - call an external command
pam_exec.so [ debug ] [ expose_authtok ] [ seteuid ] [ quiet ] [ stdout ]
[ log=file ] [ type=type ] command [ ... ]
6.7.1. DESCRIPTION
pam_exec is a PAM module that can be used to run an external command.
The child's environment is set to the current PAM environment list, as
returned by pam_getenvlist(3) In addition, the following PAM items are
exported as environment variables: PAM_RHOST, PAM_RUSER, PAM_SERVICE,
PAM_TTY, PAM_USER and PAM_TYPE, which contains one of the module types:
account, auth, password, open_session and close_session.
Commands called by pam_exec need to be aware of that the user can have
controll over the environment.
6.7.2. OPTIONS
debug
Print debug information.
expose_authtok
During authentication the calling command can read the password
from stdin(3). Only first PAM_MAX_RESP_SIZE bytes of a password
are provided to the command.
log=file
The output of the command is appended to file
type=type
Only run the command if the module type matches the given type.
stdout
Per default the output of the executed command is written to
/dev/null. With this option, the stdout output of the executed
command is redirected to the calling application. It's in the
responsibility of this application what happens with the output.
The log option is ignored.
quiet
Per default pam_exec.so will echo the exit status of the external
command if it fails. Specifying this option will suppress the
message.
seteuid
Per default pam_exec.so will execute the external command with the
real user ID of the calling process. Specifying this option means
the command is run with the effective user ID.
6.7.3. MODULE TYPES PROVIDED
All module types (auth, account, password and session) are provided.
6.7.4. RETURN VALUES
PAM_SUCCESS
The external command was run successfully.
PAM_SERVICE_ERR
No argument or a wrong number of arguments were given.
PAM_SYSTEM_ERR
A system error occurred or the command to execute failed.
PAM_IGNORE
pam_setcred was called, which does not execute the command. Or,
the value given for the type= parameter did not match the module
type.
6.7.5. EXAMPLES
Add the following line to /etc/pam.d/passwd to rebuild the NIS database
after each local password change:
password optional pam_exec.so seteuid /usr/bin/make -C /var/yp
This will execute the command
make -C /var/yp
with effective user ID.
6.7.6. AUTHOR
pam_exec was written by Thorsten Kukuk <kukuk@thkukuk.de> and Josh
Triplett <josh@joshtriplett.org>.
6.8. pam_faildelay - change the delay on failure per-application
pam_faildelay.so [ debug ] [ delay=microseconds ]
6.8.1. DESCRIPTION
pam_faildelay is a PAM module that can be used to set the delay on failure
per-application.
If no delay is given, pam_faildelay will use the value of FAIL_DELAY from
/etc/login.defs.
6.8.2. OPTIONS
debug
Turns on debugging messages sent to syslog.
delay=N
Set the delay on failure to N microseconds.
6.8.3. MODULE TYPES PROVIDED
Only the auth module type is provided.
6.8.4. RETURN VALUES
PAM_IGNORE
Delay was successful adjusted.
PAM_SYSTEM_ERR
The specified delay was not valid.
6.8.5. EXAMPLES
The following example will set the delay on failure to 10 seconds:
auth optional pam_faildelay.so delay=10000000
6.8.6. AUTHOR
pam_faildelay was written by Darren Tucker <dtucker@zip.com.au>.
6.9. pam_filter - filter module
pam_filter.so [ debug ] [ new_term ] [ non_term ] run1|run2 filter [ ... ]
6.9.1. DESCRIPTION
This module is intended to be a platform for providing access to all of
the input/output that passes between the user and the application. It is
only suitable for tty-based and (stdin/stdout) applications.
To function this module requires filters to be installed on the system.
The single filter provided with the module simply transposes upper and
lower case letters in the input and output streams. (This can be very
annoying and is not kind to termcap based editors).
Each component of the module has the potential to invoke the desired
filter. The filter is always execv(2) with the privilege of the calling
application and not that of the user. For this reason it cannot usually be
killed by the user without closing their session.
6.9.2. OPTIONS
debug
Print debug information.
new_term
The default action of the filter is to set the PAM_TTY item to
indicate the terminal that the user is using to connect to the
application. This argument indicates that the filter should set
PAM_TTY to the filtered pseudo-terminal.
non_term
don't try to set the PAM_TTY item.
runX
In order that the module can invoke a filter it should know when
to invoke it. This argument is required to tell the filter when to
do this.
Permitted values for X are 1 and 2. These indicate the precise
time that the filter is to be run. To understand this concept it
will be useful to have read the pam(3) manual page. Basically, for
each management group there are up to two ways of calling the
module's functions. In the case of the authentication and session
components there are actually two separate functions. For the case
of authentication, these functions are pam_authenticate(3) and
pam_setcred(3), here run1 means run the filter from the
pam_authenticate function and run2 means run the filter from
pam_setcred. In the case of the session modules, run1 implies that
the filter is invoked at the pam_open_session(3) stage, and run2
for pam_close_session(3).
For the case of the account component. Either run1 or run2 may be
used.
For the case of the password component, run1 is used to indicate
that the filter is run on the first occasion of pam_chauthtok(3)
(the PAM_PRELIM_CHECK phase) and run2 is used to indicate that the
filter is run on the second occasion (the PAM_UPDATE_AUTHTOK
phase).
filter
The full pathname of the filter to be run and any command line
arguments that the filter might expect.
6.9.3. MODULE TYPES PROVIDED
All module types (auth, account, password and session) are provided.
6.9.4. RETURN VALUES
PAM_SUCCESS
The new filter was set successfully.
PAM_ABORT
Critical error, immediate abort.
6.9.5. EXAMPLES
Add the following line to /etc/pam.d/login to see how to configure login
to transpose upper and lower case letters once the user has logged in:
session required pam_filter.so run1 /lib/security/pam_filter/upperLOWER
6.9.6. AUTHOR
pam_filter was written by Andrew G. Morgan <morgan@kernel.org>.
6.10. pam_ftp - module for anonymous access
pam_ftp.so [ debug ] [ ignore ] [ users=XXX,YYY, ...]
6.10.1. DESCRIPTION
pam_ftp is a PAM module which provides a pluggable anonymous ftp mode of
access.
This module intercepts the user's name and password. If the name is ftp or
anonymous, the user's password is broken up at the @ delimiter into a
PAM_RUSER and a PAM_RHOST part; these pam-items being set accordingly. The
username (PAM_USER) is set to ftp. In this case the module succeeds.
Alternatively, the module sets the PAM_AUTHTOK item with the entered
password and fails.
This module is not safe and easily spoofable.
6.10.2. OPTIONS
debug
Print debug information.
ignore
Pay no attention to the email address of the user (if supplied).
ftp=XXX,YYY,...
Instead of ftp or anonymous, provide anonymous login to the comma
separated list of users: XXX,YYY,.... Should the applicant enter
one of these usernames the returned username is set to the first
in the list: XXX.
6.10.3. MODULE TYPES PROVIDED
Only the auth module type is provided.
6.10.4. RETURN VALUES
PAM_SUCCESS
The authentication was successful.
PAM_USER_UNKNOWN
User not known.
6.10.5. EXAMPLES
Add the following line to /etc/pam.d/ftpd to handle ftp style anonymous
login:
#
# ftpd; add ftp-specifics. These lines enable anonymous ftp over
# standard UN*X access (the listfile entry blocks access to
# users listed in /etc/ftpusers)
#
auth sufficient pam_ftp.so
auth required pam_unix.so use_first_pass
auth required pam_listfile.so \
onerr=succeed item=user sense=deny file=/etc/ftpusers
6.10.6. AUTHOR
pam_ftp was written by Andrew G. Morgan <morgan@kernel.org>.
6.11. pam_group - module to modify group access
pam_group.so
6.11.1. DESCRIPTION
The pam_group PAM module does not authenticate the user, but instead it
grants group memberships (in the credential setting phase of the
authentication module) to the user. Such memberships are based on the
service they are applying for.
By default rules for group memberships are taken from config file
/etc/security/group.conf.
This module's usefulness relies on the file-systems accessible to the
user. The point being that once granted the membership of a group, the
user may attempt to create a setgid binary with a restricted group
ownership. Later, when the user is not given membership to this group,
they can recover group membership with the precompiled binary. The reason
that the file-systems that the user has access to are so significant, is
the fact that when a system is mounted nosuid the user is unable to create
or execute such a binary file. For this module to provide any level of
security, all file-systems that the user has write access to should be
mounted nosuid.
The pam_group module functions in parallel with the /etc/group file. If
the user is granted any groups based on the behavior of this module, they
are granted in addition to those entries /etc/group (or equivalent).
6.11.2. DESCRIPTION
The pam_group PAM module does not authenticate the user, but instead it
grants group memberships (in the credential setting phase of the
authentication module) to the user. Such memberships are based on the
service they are applying for.
For this module to function correctly there must be a correctly formatted
/etc/security/group.conf file present. White spaces are ignored and lines
maybe extended with '\' (escaped newlines). Text following a '#' is
ignored to the end of the line.
The syntax of the lines is as follows:
services;ttys;users;times;groups
The first field, the services field, is a logic list of PAM service names
that the rule applies to.
The second field, the tty field, is a logic list of terminal names that
this rule applies to.
The third field, the users field, is a logic list of users, or a UNIX
group, or a netgroup of users to whom this rule applies. Group names are
preceded by a '%' symbol, while netgroup names are preceded by a '@'
symbol.
For these items the simple wildcard '*' may be used only once. With UNIX
groups or netgroups no wildcards or logic operators are allowed.
The times field is used to indicate "when" these groups are to be given to
the user. The format here is a logic list of day/time-range entries. The
days are specified by a sequence of two character entries, MoTuSa for
example is Monday Tuesday and Saturday. Note that repeated days are unset
MoMo = no day, and MoWk = all weekdays bar Monday. The two character
combinations accepted are Mo Tu We Th Fr Sa Su Wk Wd Al, the last two
being week-end days and all 7 days of the week respectively. As a final
example, AlFr means all days except Friday.
Each day/time-range can be prefixed with a '!' to indicate "anything but".
The time-range part is two 24-hour times HHMM, separated by a hyphen,
indicating the start and finish time (if the finish time is smaller than
the start time it is deemed to apply on the following day).
The groups field is a comma or space separated list of groups that the
user inherits membership of. These groups are added if the previous fields
are satisfied by the user's request.
For a rule to be active, ALL of service+ttys+users must be satisfied by
the applying process.
6.11.3. OPTIONS
This module does not recognise any options.
6.11.4. MODULE TYPES PROVIDED
Only the auth module type is provided.
6.11.5. RETURN VALUES
PAM_SUCCESS
group membership was granted.
PAM_ABORT
Not all relevant data could be gotten.
PAM_BUF_ERR
Memory buffer error.
PAM_CRED_ERR
Group membership was not granted.
PAM_IGNORE
pam_sm_authenticate was called which does nothing.
PAM_USER_UNKNOWN
The user is not known to the system.
6.11.6. FILES
/etc/security/group.conf
Default configuration file
6.11.7. EXAMPLES
These are some example lines which might be specified in
/etc/security/group.conf.
Running 'xsh' on tty* (any ttyXXX device), the user 'us' is given access
to the floppy (through membership of the floppy group)
xsh;tty*&!ttyp*;us;Al0000-2400;floppy
Running 'xsh' on tty* (any ttyXXX device), the users 'sword', 'pike' and
'shield' are given access to games (through membership of the floppy
group) after work hours.
xsh; tty* ;sword|pike|shield;!Wk0900-1800;games, sound
xsh; tty* ;*;Al0900-1800;floppy
Any member of the group 'admin' running 'xsh' on tty*, is granted access
(at any time) to the group 'plugdev'
xsh; tty* ;%admin;Al0000-2400;plugdev
6.11.8. AUTHORS
pam_group was written by Andrew G. Morgan <morgan@kernel.org>.
6.12. pam_issue - add issue file to user prompt
pam_issue.so [ noesc ] [ issue=issue-file-name ]
6.12.1. DESCRIPTION
pam_issue is a PAM module to prepend an issue file to the username prompt.
It also by default parses escape codes in the issue file similar to some
common getty's (using \x format).
Recognized escapes:
\d
current day
\l
name of this tty
\m
machine architecture (uname -m)
\n
machine's network node hostname (uname -n)
\o
domain name of this system
\r
release number of operating system (uname -r)
\t
current time
\s
operating system name (uname -s)
\u
number of users currently logged in
\U
same as \u except it is suffixed with "user" or "users" (eg. "1
user" or "10 users")
\v
operating system version and build date (uname -v)
6.12.2. OPTIONS
noesc
Turns off escape code parsing.
issue=issue-file-name
The file to output if not using the default.
6.12.3. MODULE TYPES PROVIDED
Only the auth module type is provided.
6.12.4. RETURN VALUES
PAM_BUF_ERR
Memory buffer error.
PAM_IGNORE
The prompt was already changed.
PAM_SERVICE_ERR
A service module error occurred.
PAM_SUCCESS
The new prompt was set successfully.
6.12.5. EXAMPLES
Add the following line to /etc/pam.d/login to set the user specific issue
at login:
auth optional pam_issue.so issue=/etc/issue
6.12.6. AUTHOR
pam_issue was written by Ben Collins <bcollins@debian.org>.
6.13. pam_keyinit - display the keyinit file
pam_keyinit.so [ debug ] [ force ] [ revoke ]
6.13.1. DESCRIPTION
The pam_keyinit PAM module ensures that the invoking process has a session
keyring other than the user default session keyring.
The session component of the module checks to see if the process's session
keyring is the user default, and, if it is, creates a new anonymous
session keyring with which to replace it.
If a new session keyring is created, it will install a link to the user
common keyring in the session keyring so that keys common to the user will
be automatically accessible through it.
The session keyring of the invoking process will thenceforth be inherited
by all its children unless they override it.
This module is intended primarily for use by login processes. Be aware
that after the session keyring has been replaced, the old session keyring
and the keys it contains will no longer be accessible.
This module should not, generally, be invoked by programs like su, since
it is usually desirable for the key set to percolate through to the
alternate context. The keys have their own permissions system to manage
this.
This module should be included as early as possible in a PAM
configuration, so that other PAM modules can attach tokens to the keyring.
The keyutils package is used to manipulate keys more directly. This can be
obtained from:
Keyutils
6.13.2. OPTIONS
debug
Log debug information with syslog(3).
force
Causes the session keyring of the invoking process to be replaced
unconditionally.
revoke
Causes the session keyring of the invoking process to be revoked
when the invoking process exits if the session keyring was created
for this process in the first place.
6.13.3. MODULE TYPES PROVIDED
Only the session module type is provided.
6.13.4. RETURN VALUES
PAM_SUCCESS
This module will usually return this value
PAM_AUTH_ERR
Authentication failure.
PAM_BUF_ERR
Memory buffer error.
PAM_IGNORE
The return value should be ignored by PAM dispatch.
PAM_SERVICE_ERR
Cannot determine the user name.
PAM_SESSION_ERR
This module will return this value if its arguments are invalid or
if a system error such as ENOMEM occurs.
PAM_USER_UNKNOWN
User not known.
6.13.5. EXAMPLES
Add this line to your login entries to start each login session with its
own session keyring:
session required pam_keyinit.so
This will prevent keys from one session leaking into another session for
the same user.
6.13.6. AUTHOR
pam_keyinit was written by David Howells, <dhowells@redhat.com>.
6.14. pam_lastlog - display date of last login
pam_lastlog.so [ debug ] [ silent ] [ never ] [ nodate ] [ nohost ] [
noterm ] [ nowtmp ] [ noupdate ] [ showfailed ] [ inactive=<days> ] [
unlimited ]
6.14.1. DESCRIPTION
pam_lastlog is a PAM module to display a line of information about the
last login of the user. In addition, the module maintains the
/var/log/lastlog file.
Some applications may perform this function themselves. In such cases,
this module is not necessary.
If the module is called in the auth or account phase, the accounts that
were not used recently enough will be disallowed to log in. The check is
not performed for the root account so the root is never locked out.
6.14.2. OPTIONS
debug
Print debug information.
silent
Don't inform the user about any previous login, just update the
/var/log/lastlog file. This option does not affect display of bad
login attempts.
never
If the /var/log/lastlog file does not contain any old entries for
the user, indicate that the user has never previously logged in
with a welcome message.
nodate
Don't display the date of the last login.
noterm
Don't display the terminal name on which the last login was
attempted.
nohost
Don't indicate from which host the last login was attempted.
nowtmp
Don't update the wtmp entry.
noupdate
Don't update any file.
showfailed
Display number of failed login attempts and the date of the last
failed attempt from btmp. The date is not displayed when nodate is
specified.
inactive=<days>
This option is specific for the auth or account phase. It
specifies the number of days after the last login of the user when
the user will be locked out by the module. The default value is
90.
unlimited
If the fsize limit is set, this option can be used to override it,
preventing failures on systems with large UID values that lead
lastlog to become a huge sparse file.
6.14.3. MODULE TYPES PROVIDED
The auth and account module type allows to lock out users which did not
login recently enough. The session module type is provided for displaying
the information about the last login and/or updating the lastlog and wtmp
files.
6.14.4. RETURN VALUES
PAM_SUCCESS
Everything was successful.
PAM_SERVICE_ERR
Internal service module error.
PAM_USER_UNKNOWN
User not known.
PAM_AUTH_ERR
User locked out in the auth or account phase due to inactivity.
PAM_IGNORE
There was an error during reading the lastlog file in the auth or
account phase and thus inactivity of the user cannot be
determined.
6.14.5. EXAMPLES
Add the following line to /etc/pam.d/login to display the last login time
of an user:
session required pam_lastlog.so nowtmp
To reject the user if he did not login during the previous 50 days the
following line can be used:
auth required pam_lastlog.so inactive=50
6.14.6. AUTHOR
pam_lastlog was written by Andrew G. Morgan <morgan@kernel.org>.
Inactive account lock out added by Tomas Mraz <tm@t8m.info>.
6.15. pam_limits - limit resources
pam_limits.so [ conf=/path/to/limits.conf ] [ debug ] [ set_all ] [
utmp_early ] [ noaudit ]
6.15.1. DESCRIPTION
The pam_limits PAM module sets limits on the system resources that can be
obtained in a user-session. Users of uid=0 are affected by this limits,
too.
By default limits are taken from the /etc/security/limits.conf config
file. Then individual *.conf files from the /etc/security/limits.d/
directory are read. The files are parsed one after another in the order of
"C" locale. The effect of the individual files is the same as if all the
files were concatenated together in the order of parsing. If a config file
is explicitly specified with a module option then the files in the above
directory are not parsed.
The module must not be called by a multithreaded application.
If Linux PAM is compiled with audit support the module will report when it
denies access based on limit of maximum number of concurrent login
sessions.
6.15.2. DESCRIPTION
The pam_limits.so module applies ulimit limits, nice priority and number
of simultaneous login sessions limit to user login sessions. This
description of the configuration file syntax applies to the
/etc/security/limits.conf file and *.conf files in the
/etc/security/limits.d directory.
The syntax of the lines is as follows:
<domain> <type> <item> <value>
The fields listed above should be filled as follows:
<domain>
* a username
* a groupname, with @group syntax. This should not be confused
with netgroups.
* the wildcard *, for default entry.
* the wildcard %, for maxlogins limit only, can also be used
with %group syntax. If the % wildcard is used alone it is
identical to using * with maxsyslogins limit. With a group
specified after % it limits the total number of logins of all
users that are member of the group.
* an uid range specified as <min_uid>:<max_uid>. If min_uid is
omitted, the match is exact for the max_uid. If max_uid is
omitted, all uids greater than or equal min_uid match.
* a gid range specified as @<min_gid>:<max_gid>. If min_gid is
omitted, the match is exact for the max_gid. If max_gid is
omitted, all gids greater than or equal min_gid match. For
the exact match all groups including the user's supplementary
groups are examined. For the range matches only the user's
primary group is examined.
* a gid specified as %:<gid> applicable to maxlogins limit
only. It limits the total number of logins of all users that
are member of the group with the specified gid.
<type>
hard
for enforcing hard resource limits. These limits are
set by the superuser and enforced by the Kernel. The
user cannot raise his requirement of system resources
above such values.
soft
for enforcing soft resource limits. These limits are
ones that the user can move up or down within the
permitted range by any pre-existing hard limits. The
values specified with this token can be thought of as
default values, for normal system usage.
-
for enforcing both soft and hard resource limits
together.
Note, if you specify a type of '-' but neglect to
supply the item and value fields then the module will
never enforce any limits on the specified user/group
etc. .
<item>
core
limits the core file size (KB)
data
maximum data size (KB)
fsize
maximum filesize (KB)
memlock
maximum locked-in-memory address space (KB)
nofile
maximum number of open file descriptors
rss
maximum resident set size (KB) (Ignored in Linux
2.4.30 and higher)
stack
maximum stack size (KB)
cpu
maximum CPU time (minutes)
nproc
maximum number of processes
as
address space limit (KB)
maxlogins
maximum number of logins for this user (this limit
does not apply to user with uid=0)
maxsyslogins
maximum number of all logins on system; user is not
allowed to log-in if total number of all user logins
is greater than specified number (this limit does not
apply to user with uid=0)
priority
the priority to run user process with (negative
values boost process priority)
locks
maximum locked files (Linux 2.4 and higher)
sigpending
maximum number of pending signals (Linux 2.6 and
higher)
msgqueue
maximum memory used by POSIX message queues (bytes)
(Linux 2.6 and higher)
nice
maximum nice priority allowed to raise to (Linux
2.6.12 and higher) values: [-20,19]
rtprio
maximum realtime priority allowed for non-privileged
processes (Linux 2.6.12 and higher)
All items support the values -1, unlimited or infinity indicating no
limit, except for priority and nice. If nofile is to be set to one of
these values, it will be set to the contents of /proc/sys/fs/nr_open
instead (see setrlimit(3)).
If a hard limit or soft limit of a resource is set to a valid value, but
outside of the supported range of the local system, the system may reject
the new limit or unexpected behavior may occur. If the control value
required is used, the module will reject the login if a limit could not be
set.
In general, individual limits have priority over group limits, so if you
impose no limits for admin group, but one of the members in this group
have a limits line, the user will have its limits set according to this
line.
Also, please note that all limit settings are set per login. They are not
global, nor are they permanent; existing only for the duration of the
session. One exception is the maxlogin option, this one is system wide.
But there is a race, concurrent logins at the same time will not always be
detect as such but only counted as one.
In the limits configuration file, the '#' character introduces a comment -
after which the rest of the line is ignored.
The pam_limits module does report configuration problems found in its
configuration file and errors via syslog(3).
6.15.3. OPTIONS
conf=/path/to/limits.conf
Indicate an alternative limits.conf style configuration file to
override the default.
debug
Print debug information.
set_all
Set the limits for which no value is specified in the
configuration file to the one from the process with the PID 1.
utmp_early
Some broken applications actually allocate a utmp entry for the
user before the user is admitted to the system. If some of the
services you are configuring PAM for do this, you can selectively
use this module argument to compensate for this behavior and at
the same time maintain system-wide consistency with a single
limits.conf file.
noaudit
Do not report exceeded maximum logins count to the audit
subsystem.
6.15.4. MODULE TYPES PROVIDED
Only the session module type is provided.
6.15.5. RETURN VALUES
PAM_ABORT
Cannot get current limits.
PAM_IGNORE
No limits found for this user.
PAM_PERM_DENIED
New limits could not be set.
PAM_SERVICE_ERR
Cannot read config file.
PAM_SESSION_ERR
Error recovering account name.
PAM_SUCCESS
Limits were changed.
PAM_USER_UNKNOWN
The user is not known to the system.
6.15.6. FILES
/etc/security/limits.conf
Default configuration file
6.15.7. EXAMPLES
These are some example lines which might be specified in
/etc/security/limits.conf.
* soft core 0
* hard nofile 512
@student hard nproc 20
@faculty soft nproc 20
@faculty hard nproc 50
ftp hard nproc 0
@student - maxlogins 4
:123 hard cpu 5000
@500: soft cpu 10000
600:700 hard locks 10
6.15.8. AUTHORS
pam_limits was initially written by Cristian Gafton <gafton@redhat.com>
6.16. pam_listfile - deny or allow services based on an arbitrary file
pam_listfile.so item=[tty|user|rhost|ruser|group|shell] sense=[allow|deny]
file=/path/filename onerr=[succeed|fail] [ apply=[user|@group] ] [ quiet ]
6.16.1. DESCRIPTION
pam_listfile is a PAM module which provides a way to deny or allow
services based on an arbitrary file.
The module gets the item of the type specified -- user specifies the
username, PAM_USER; tty specifies the name of the terminal over which the
request has been made, PAM_TTY; rhost specifies the name of the remote
host (if any) from which the request was made, PAM_RHOST; and ruser
specifies the name of the remote user (if available) who made the request,
PAM_RUSER -- and looks for an instance of that item in the file=filename.
filename contains one line per item listed. If the item is found, then if
sense=allow, PAM_SUCCESS is returned, causing the authorization request to
succeed; else if sense=deny, PAM_AUTH_ERR is returned, causing the
authorization request to fail.
If an error is encountered (for instance, if filename does not exist, or a
poorly-constructed argument is encountered), then if onerr=succeed,
PAM_SUCCESS is returned, otherwise if onerr=fail, PAM_AUTH_ERR or
PAM_SERVICE_ERR (as appropriate) will be returned.
An additional argument, apply=, can be used to restrict the application of
the above to a specific user (apply=username) or a given group
(apply=@groupname). This added restriction is only meaningful when used
with the tty, rhost and shell items.
Besides this last one, all arguments should be specified; do not count on
any default behavior.
No credentials are awarded by this module.
6.16.2. OPTIONS
item=[tty|user|rhost|ruser|group|shell]
What is listed in the file and should be checked for.
sense=[allow|deny]
Action to take if found in file, if the item is NOT found in the
file, then the opposite action is requested.
file=/path/filename
File containing one item per line. The file needs to be a plain
file and not world writable.
onerr=[succeed|fail]
What to do if something weird happens like being unable to open
the file.
apply=[user|@group]
Restrict the user class for which the restriction apply. Note that
with item=[user|ruser|group] this does not make sense, but for
item=[tty|rhost|shell] it have a meaning.
quiet
Do not treat service refusals or missing list files as errors that
need to be logged.
6.16.3. MODULE TYPES PROVIDED
All module types (auth, account, password and session) are provided.
6.16.4. RETURN VALUES
PAM_AUTH_ERR
Authentication failure.
PAM_BUF_ERR
Memory buffer error.
PAM_IGNORE
The rule does not apply to the apply option.
PAM_SERVICE_ERR
Error in service module.
PAM_SUCCESS
Success.
6.16.5. EXAMPLES
Classic 'ftpusers' authentication can be implemented with this entry in
/etc/pam.d/ftpd:
#
# deny ftp-access to users listed in the /etc/ftpusers file
#
auth required pam_listfile.so \
onerr=succeed item=user sense=deny file=/etc/ftpusers
Note, users listed in /etc/ftpusers file are (counterintuitively) not
allowed access to the ftp service.
To allow login access only for certain users, you can use a
/etc/pam.d/login entry like this:
#
# permit login to users listed in /etc/loginusers
#
auth required pam_listfile.so \
onerr=fail item=user sense=allow file=/etc/loginusers
For this example to work, all users who are allowed to use the login
service should be listed in the file /etc/loginusers. Unless you are
explicitly trying to lock out root, make sure that when you do this, you
leave a way for root to log in, either by listing root in /etc/loginusers,
or by listing a user who is able to su to the root account.
6.16.6. AUTHOR
pam_listfile was written by Michael K. Johnson <johnsonm@redhat.com> and
Elliot Lee <sopwith@cuc.edu>.
6.17. pam_localuser - require users to be listed in /etc/passwd
pam_localuser.so [ debug ] [ file=/path/passwd ]
6.17.1. DESCRIPTION
pam_localuser is a PAM module to help implementing site-wide login
policies, where they typically include a subset of the network's users and
a few accounts that are local to a particular workstation. Using
pam_localuser and pam_wheel or pam_listfile is an effective way to
restrict access to either local users and/or a subset of the network's
users.
This could also be implemented using pam_listfile.so and a very short awk
script invoked by cron, but it's common enough to have been separated out.
6.17.2. OPTIONS
debug
Print debug information.
file=/path/passwd
Use a file other than /etc/passwd.
6.17.3. MODULE TYPES PROVIDED
All module types (account, auth, password and session) are provided.
6.17.4. RETURN VALUES
PAM_SUCCESS
The new localuser was set successfully.
PAM_SERVICE_ERR
No username was given.
PAM_PERM_DENIED
The user is not listed in the passwd file.
6.17.5. EXAMPLES
Add the following lines to /etc/pam.d/su to allow only local users or
group wheel to use su.
account sufficient pam_localuser.so
account required pam_wheel.so
6.17.6. AUTHOR
pam_localuser was written by Nalin Dahyabhai <nalin@redhat.com>.
6.18. pam_loginuid - record user's login uid to the process attribute
pam_loginuid.so [ require_auditd ]
6.18.1. DESCRIPTION
The pam_loginuid module sets the loginuid process attribute for the
process that was authenticated. This is necessary for applications to be
correctly audited. This PAM module should only be used for entry point
applications like: login, sshd, gdm, vsftpd, crond and atd. There are
probably other entry point applications besides these. You should not use
it for applications like sudo or su as that defeats the purpose by
changing the loginuid to the account they just switched to.
6.18.2. OPTIONS
require_auditd
This option, when given, will cause this module to query the audit
daemon status and deny logins if it is not running.
6.18.3. MODULE TYPES PROVIDED
Only the session module type is provided.
6.18.4. RETURN VALUES
PAM_SUCCESS
The loginuid value is set and auditd is running if check
requested.
PAM_IGNORE
The /proc/self/loginuid file is not present on the system or the
login process runs inside uid namespace and kernel does not
support overwriting loginuid.
PAM_SESSION_ERR
Any other error prevented setting loginuid or auditd is not
running.
6.18.5. EXAMPLES
#%PAM-1.0
auth required pam_unix.so
auth required pam_nologin.so
account required pam_unix.so
password required pam_unix.so
session required pam_unix.so
session required pam_loginuid.so
6.18.6. AUTHOR
pam_loginuid was written by Steve Grubb <sgrubb@redhat.com>
6.19. pam_mail - inform about available mail
pam_mail.so [ close ] [ debug ] [ dir=maildir ] [ empty ] [ hash=count ] [
noenv ] [ nopen ] [ quiet ] [ standard ]
6.19.1. DESCRIPTION
The pam_mail PAM module provides the "you have new mail" service to the
user. It can be plugged into any application that has credential or
session hooks. It gives a single message indicating the newness of any
mail it finds in the user's mail folder. This module also sets the PAM
environment variable, MAIL, to the user's mail directory.
If the mail spool file (be it /var/mail/$USER or a pathname given with the
dir= parameter) is a directory then pam_mail assumes it is in the Maildir
format.
6.19.2. OPTIONS
close
Indicate if the user has any mail also on logout.
debug
Print debug information.
dir=maildir
Look for the user's mail in an alternative location defined by
maildir/<login>. The default location for mail is
/var/mail/<login>. Note, if the supplied maildir is prefixed by a
'~', the directory is interpreted as indicating a file in the
user's home directory.
empty
Also print message if user has no mail.
hash=count
Mail directory hash depth. For example, a hashcount of 2 would
make the mail file be /var/spool/mail/u/s/user.
noenv
Do not set the MAIL environment variable.
nopen
Don't print any mail information on login. This flag is useful to
get the MAIL environment variable set, but to not display any
information about it.
quiet
Only report when there is new mail.
standard
Old style "You have..." format which doesn't show the mail spool
being used. This also implies "empty".
6.19.3. MODULE TYPES PROVIDED
The session and auth (on establishment and deletion of credentials) module
types are provided.
6.19.4. RETURN VALUES
PAM_BUF_ERR
Memory buffer error.
PAM_SERVICE_ERR
Badly formed arguments.
PAM_SUCCESS
Success.
PAM_USER_UNKNOWN
User not known.
6.19.5. EXAMPLES
Add the following line to /etc/pam.d/login to indicate that the user has
new mail when they login to the system.
session optional pam_mail.so standard
6.19.6. AUTHOR
pam_mail was written by Andrew G. Morgan <morgan@kernel.org>.
6.20. pam_mkhomedir - create users home directory
pam_mkhomedir.so [ silent ] [ umask=mode ] [ skel=skeldir ]
6.20.1. DESCRIPTION
The pam_mkhomedir PAM module will create a users home directory if it does
not exist when the session begins. This allows users to be present in
central database (such as NIS, kerberos or LDAP) without using a
distributed file system or pre-creating a large number of directories. The
skeleton directory (usually /etc/skel/) is used to copy default files and
also sets a umask for the creation.
The new users home directory will not be removed after logout of the user.
6.20.2. OPTIONS
silent
Don't print informative messages.
umask=mask
The user file-creation mask is set to mask. The default value of
mask is 0022.
skel=/path/to/skel/directory
Indicate an alternative skel directory to override the default
/etc/skel.
6.20.3. MODULE TYPES PROVIDED
Only the session module type is provided.
6.20.4. RETURN VALUES
PAM_BUF_ERR
Memory buffer error.
PAM_CRED_INSUFFICIENT
Insufficient credentials to access authentication data.
PAM_PERM_DENIED
Not enough permissions to create the new directory or read the
skel directory.
PAM_USER_UNKNOWN
User not known to the underlying authentication module.
PAM_SUCCESS
Environment variables were set.
6.20.5. EXAMPLES
A sample /etc/pam.d/login file:
auth requisite pam_securetty.so
auth sufficient pam_ldap.so
auth required pam_unix.so
auth required pam_nologin.so
account sufficient pam_ldap.so
account required pam_unix.so
password required pam_unix.so
session required pam_mkhomedir.so skel=/etc/skel/ umask=0022
session required pam_unix.so
session optional pam_lastlog.so
session optional pam_mail.so standard
6.20.6. AUTHOR
pam_mkhomedir was written by Jason Gunthorpe <jgg@debian.org>.
6.21. pam_motd - display the motd file
pam_motd.so [ motd=/path/filename ] [ motd_dir=/path/dirname.d ]
6.21.1. DESCRIPTION
pam_motd is a PAM module that can be used to display arbitrary motd
(message of the day) files after a successful login. By default, pam_motd
shows files in the following locations:
/etc/motd
/run/motd
/usr/lib/motd
/etc/motd.d/
/run/motd.d/
/usr/lib/motd.d/
Each message size is limited to 64KB.
If /etc/motd does not exist, then /run/motd is shown. If /run/motd does
not exist, then /usr/lib/motd is shown.
Similar overriding behavior applies to the directories. Files in
/etc/motd.d/ override files with the same name in /run/motd.d/ and
/usr/lib/motd.d/. Files in /run/motd.d/ override files with the same name
in /usr/lib/motd.d/.
Files in the directories listed above are displayed in lexicographic order
by name. Moreover, the files are filtered by reading them with the
credentials of the target user authenticating on the system.
To silence a message, a symbolic link with target /dev/null may be placed
in /etc/motd.d with the same filename as the message to be silenced.
Example: Creating a symbolic link as follows silences
/usr/lib/motd.d/my_motd.
ln -s /dev/null /etc/motd.d/my_motd
6.21.2. OPTIONS
motd=/path/filename
The /path/filename file is displayed as message of the day.
Multiple paths to try can be specified as a colon-separated list.
By default this option is set to
/etc/motd:/run/motd:/usr/lib/motd.
motd_dir=/path/dirname.d
The /path/dirname.d directory is scanned and each file contained
inside of it is displayed. Multiple directories to scan can be
specified as a colon-separated list. By default this option is set
to /etc/motd.d:/run/motd.d:/usr/lib/motd.d.
When no options are given, the default behavior applies for both options.
Specifying either option (or both) will disable the default behavior for
both options.
6.21.3. MODULE TYPES PROVIDED
Only the session module type is provided.
6.21.4. RETURN VALUES
PAM_IGNORE
This is the only return value of this module.
6.21.5. EXAMPLES
The suggested usage for /etc/pam.d/login is:
session optional pam_motd.so
To use a motd file from a different location:
session optional pam_motd.so motd=/elsewhere/motd
To use a motd file from elsewhere, along with a corresponding .d
directory:
session optional pam_motd.so motd=/elsewhere/motd motd_dir=/elsewhere/motd.d
6.21.6. AUTHOR
pam_motd was written by Ben Collins <bcollins@debian.org>.
The motd_dir= option was added by Allison Karlitskaya
<allison.karlitskaya@redhat.com>.
6.22. pam_namespace - setup a private namespace
pam_namespace.so [ debug ] [ unmnt_remnt ] [ unmnt_only ] [
require_selinux ] [ gen_hash ] [ ignore_config_error ] [
ignore_instance_parent_mode ] [ unmount_on_close ] [ use_current_context ]
[ use_default_context ] [ mount_private ]
6.22.1. DESCRIPTION
The pam_namespace PAM module sets up a private namespace for a session
with polyinstantiated directories. A polyinstantiated directory provides a
different instance of itself based on user name, or when using SELinux,
user name, security context or both. If an executable script
/etc/security/namespace.init exists, it is used to initialize the instance
directory after it is set up and mounted on the polyinstantiated
directory. The script receives the polyinstantiated directory path, the
instance directory path, flag whether the instance directory was newly
created (0 for no, 1 for yes), and the user name as its arguments.
The pam_namespace module disassociates the session namespace from the
parent namespace. Any mounts/unmounts performed in the parent namespace,
such as mounting of devices, are not reflected in the session namespace.
To propagate selected mount/unmount events from the parent namespace into
the disassociated session namespace, an administrator may use the special
shared-subtree feature. For additional information on shared-subtree
feature, please refer to the mount(8) man page and the shared-subtree
description at http://lwn.net/Articles/159077 and
http://lwn.net/Articles/159092.
6.22.2. DESCRIPTION
The pam_namespace.so module allows setup of private namespaces with
polyinstantiated directories. Directories can be polyinstantiated based on
user name or, in the case of SELinux, user name, sensitivity level or
complete security context. If an executable script
/etc/security/namespace.init exists, it is used to initialize the
namespace every time an instance directory is set up and mounted. The
script receives the polyinstantiated directory path and the instance
directory path as its arguments.
The /etc/security/namespace.conf file specifies which directories are
polyinstantiated, how they are polyinstantiated, how instance directories
would be named, and any users for whom polyinstantiation would not be
performed.
When someone logs in, the file namespace.conf is scanned. Comments are
marked by # characters. Each non comment line represents one
polyinstantiated directory. The fields are separated by spaces but can be
quoted by " characters also escape sequences \b, \n, and \t are
recognized. The fields are as follows:
polydir instance_prefix method list_of_uids
The first field, polydir, is the absolute pathname of the directory to
polyinstantiate. The special string $HOME is replaced with the user's home
directory, and $USER with the username. This field cannot be blank.
The second field, instance_prefix is the string prefix used to build the
pathname for the instantiation of <polydir>. Depending on the
polyinstantiation method it is then appended with "instance
differentiation string" to generate the final instance directory path.
This directory is created if it did not exist already, and is then bind
mounted on the <polydir> to provide an instance of <polydir> based on the
<method> column. The special string $HOME is replaced with the user's home
directory, and $USER with the username. This field cannot be blank.
The third field, method, is the method used for polyinstantiation. It can
take these values; "user" for polyinstantiation based on user name,
"level" for polyinstantiation based on process MLS level and user name,
"context" for polyinstantiation based on process security context and user
name, "tmpfs" for mounting tmpfs filesystem as an instance dir, and
"tmpdir" for creating temporary directory as an instance dir which is
removed when the user's session is closed. Methods "context" and "level"
are only available with SELinux. This field cannot be blank.
The fourth field, list_of_uids, is a comma separated list of user names
for whom the polyinstantiation is not performed. If left blank,
polyinstantiation will be performed for all users. If the list is preceded
with a single "~" character, polyinstantiation is performed only for users
in the list.
The method field can contain also following optional flags separated by :
characters.
create=mode,owner,group - create the polyinstantiated directory. The mode,
owner and group parameters are optional. The default for mode is
determined by umask, the default owner is the user whose session is
opened, the default group is the primary group of the user.
iscript=path - path to the instance directory init script. The base
directory for relative paths is /etc/security/namespace.d.
noinit - instance directory init script will not be executed.
shared - the instance directories for "context" and "level" methods will
not contain the user name and will be shared among all users.
mntopts=value - value of this flag is passed to the mount call when the
tmpfs mount is done. It allows for example the specification of the
maximum size of the tmpfs instance that is created by the mount call. In
addition to options specified in the tmpfs(5) manual the nosuid, noexec,
and nodev flags can be used to respectively disable setuid bit effect,
disable running executables, and disable devices to be interpreted on the
mounted tmpfs filesystem.
The directory where polyinstantiated instances are to be created, must
exist and must have, by default, the mode of 0000. The requirement that
the instance parent be of mode 0000 can be overridden with the command
line option ignore_instance_parent_mode
In case of context or level polyinstantiation the SELinux context which is
used for polyinstantiation is the context used for executing a new process
as obtained by getexeccon. This context must be set by the calling
application or pam_selinux.so module. If this context is not set the
polyinstatiation will be based just on user name.
The "instance differentiation string" is <user name> for "user" method and
<user name>_<raw directory context> for "context" and "level" methods. If
the whole string is too long the end of it is replaced with md5sum of
itself. Also when command line option gen_hash is used the whole string is
replaced with md5sum of itself.
6.22.3. OPTIONS
debug
A lot of debug information is logged using syslog
unmnt_remnt
For programs such as su and newrole, the login session has already
setup a polyinstantiated namespace. For these programs,
polyinstantiation is performed based on new user id or security
context, however the command first needs to undo the
polyinstantiation performed by login. This argument instructs the
command to first undo previous polyinstantiation before proceeding
with new polyinstantiation based on new id/context
unmnt_only
For trusted programs that want to undo any existing bind mounts
and process instance directories on their own, this argument
allows them to unmount currently mounted instance directories
require_selinux
If selinux is not enabled, return failure
gen_hash
Instead of using the security context string for the instance
name, generate and use its md5 hash.
ignore_config_error
If a line in the configuration file corresponding to a
polyinstantiated directory contains format error, skip that line
process the next line. Without this option, pam will return an
error to the calling program resulting in termination of the
session.
ignore_instance_parent_mode
Instance parent directories by default are expected to have the
restrictive mode of 000. Using this option, an administrator can
choose to ignore the mode of the instance parent. This option
should be used with caution as it will reduce security and
isolation goals of the polyinstantiation mechanism.
unmount_on_close
Explicitly unmount the polyinstantiated directories instead of
relying on automatic namespace destruction after the last process
in a namespace exits. This option should be used only in case it
is ensured by other means that there cannot be any processes
running in the private namespace left after the session close. It
is also useful only in case there are multiple pam session calls
in sequence from the same process.
use_current_context
Useful for services which do not change the SELinux context with
setexeccon call. The module will use the current SELinux context
of the calling process for the level and context
polyinstantiation.
use_default_context
Useful for services which do not use pam_selinux for changing the
SELinux context with setexeccon call. The module will use the
default SELinux context of the user for the level and context
polyinstantiation.
mount_private
This option can be used on systems where the / mount point or its
submounts are made shared (for example with a mount --make-rshared
/ command). The module will mark the whole directory tree so any
mount and unmount operations in the polyinstantiation namespace
are private. Normally the pam_namespace will try to detect the
shared / mount point and make the polyinstantiated directories
private automatically. This option has to be used just when only a
subtree is shared and / is not.
Note that mounts and unmounts done in the private namespace will
not affect the parent namespace if this option is used or when the
shared / mount point is autodetected.
6.22.4. MODULE TYPES PROVIDED
Only the session module type is provided. The module must not be called
from multithreaded processes.
6.22.5. RETURN VALUES
PAM_SUCCESS
Namespace setup was successful.
PAM_SERVICE_ERR
Unexpected system error occurred while setting up namespace.
PAM_SESSION_ERR
Unexpected namespace configuration error occurred.
6.22.6. FILES
/etc/security/namespace.conf
Main configuration file
/etc/security/namespace.d
Directory for additional configuration files
/etc/security/namespace.init
Init script for instance directories
6.22.7. EXAMPLES
These are some example lines which might be specified in
/etc/security/namespace.conf.
# The following three lines will polyinstantiate /tmp,
# /var/tmp and user's home directories. /tmp and /var/tmp
# will be polyinstantiated based on the security level
# as well as user name, whereas home directory will be
# polyinstantiated based on the full security context and user name.
# Polyinstantiation will not be performed for user root
# and adm for directories /tmp and /var/tmp, whereas home
# directories will be polyinstantiated for all users.
#
# Note that instance directories do not have to reside inside
# the polyinstantiated directory. In the examples below,
# instances of /tmp will be created in /tmp-inst directory,
# where as instances of /var/tmp and users home directories
# will reside within the directories that are being
# polyinstantiated.
#
/tmp /tmp-inst/ level root,adm
/var/tmp /var/tmp/tmp-inst/ level root,adm
$HOME $HOME/$USER.inst/inst- context
For the <service>s you need polyinstantiation (login for example) put the
following line in /etc/pam.d/<service> as the last line for session group:
session required pam_namespace.so [arguments]
This module also depends on pam_selinux.so setting the context.
6.22.8. AUTHORS
The namespace setup scheme was designed by Stephen Smalley, Janak Desai
and Chad Sellers. The pam_namespace PAM module was developed by Janak
Desai <janak@us.ibm.com>, Chad Sellers <csellers@tresys.com> and Steve
Grubb <sgrubb@redhat.com>. Additional improvements by Xavier Toth
<txtoth@gmail.com> and Tomas Mraz <tmraz@redhat.com>.
6.23. pam_nologin - prevent non-root users from login
pam_nologin.so [ file=/path/nologin ] [ successok ]
6.23.1. DESCRIPTION
pam_nologin is a PAM module that prevents users from logging into the
system when /var/run/nologin or /etc/nologin exists. The contents of the
file are displayed to the user. The pam_nologin module has no effect on
the root user's ability to log in.
6.23.2. OPTIONS
file=/path/nologin
Use this file instead the default /var/run/nologin or
/etc/nologin.
successok
Return PAM_SUCCESS if no file exists, the default is PAM_IGNORE.
6.23.3. MODULE TYPES PROVIDED
The auth and acct module types are provided.
6.23.4. RETURN VALUES
PAM_AUTH_ERR
The user is not root and /etc/nologin exists, so the user is not
permitted to log in.
PAM_BUF_ERR
Memory buffer error.
PAM_IGNORE
This is the default return value.
PAM_SUCCESS
Success: either the user is root or the nologin file does not
exist.
PAM_USER_UNKNOWN
User not known to the underlying authentication module.
6.23.5. EXAMPLES
The suggested usage for /etc/pam.d/login is:
auth required pam_nologin.so
6.23.6. AUTHOR
pam_nologin was written by Michael K. Johnson <johnsonm@redhat.com>.
6.24. pam_permit - the promiscuous module
pam_permit.so
6.24.1. DESCRIPTION
pam_permit is a PAM module that always permit access. It does nothing
else.
In the case of authentication, the user's name will be set to nobody if
the application didn't set one. Many applications and PAM modules become
confused if this name is unknown.
This module is very dangerous. It should be used with extreme caution.
6.24.2. OPTIONS
This module does not recognise any options.
6.24.3. MODULE TYPES PROVIDED
The auth, account, password and session module types are provided.
6.24.4. RETURN VALUES
PAM_SUCCESS
This module always returns this value.
6.24.5. EXAMPLES
Add this line to your other login entries to disable account management,
but continue to permit users to log in.
account required pam_permit.so
6.24.6. AUTHOR
pam_permit was written by Andrew G. Morgan, <morgan@kernel.org>.
6.25. pam_pwhistory - grant access using .pwhistory file
pam_pwhistory.so [ debug ] [ use_authtok ] [ enforce_for_root ] [
remember=N ] [ retry=N ] [ authtok_type=STRING ] [
conf=/path/to/config-file ]
6.25.1. DESCRIPTION
This module saves the last passwords for each user in order to force
password change history and keep the user from alternating between the
same password too frequently.
This module does not work together with kerberos. In general, it does not
make much sense to use this module in conjunction with NIS or LDAP, since
the old passwords are stored on the local machine and are not available on
another machine for password history checking.
6.25.2. OPTIONS
debug
Turns on debugging via syslog(3).
use_authtok
When password changing enforce the module to use the new password
provided by a previously stacked password module (this is used in
the example of the stacking of the pam_cracklib module documented
below).
enforce_for_root
If this option is set, the check is enforced for root, too.
remember=N
The last N passwords for each user are saved. The default is 10.
Value of 0 makes the module to keep the existing contents of the
opasswd file unchanged.
retry=N
Prompt user at most N times before returning with error. The
default is 1.
authtok_type=STRING
See pam_get_authtok(3) for more details.
conf=/path/to/config-file
Use another configuration file instead of the default
/etc/security/pwhistory.conf.
The options for configuring the module behavior are described in the
pwhistory.conf(5) manual page. The options specified on the module command
line override the values from the configuration file.
6.25.3. MODULE TYPES PROVIDED
Only the password module type is provided.
6.25.4. RETURN VALUES
PAM_AUTHTOK_ERR
No new password was entered, the user aborted password change or
new password couldn't be set.
PAM_IGNORE
Password history was disabled.
PAM_MAXTRIES
Password was rejected too often.
PAM_USER_UNKNOWN
User is not known to system.
6.25.5. FILES
/etc/security/opasswd
File with password history
6.25.6. EXAMPLES
An example password section would be:
#%PAM-1.0
password required pam_pwhistory.so
password required pam_unix.so use_authtok
In combination with pam_cracklib:
#%PAM-1.0
password required pam_cracklib.so retry=3
password required pam_pwhistory.so use_authtok
password required pam_unix.so use_authtok
6.25.7. AUTHOR
pam_pwhistory was written by Thorsten Kukuk <kukuk@thkukuk.de>
6.26. pam_rhosts - grant access using .rhosts file
pam_rhosts.so
6.26.1. DESCRIPTION
This module performs the standard network authentication for services, as
used by traditional implementations of rlogin and rsh etc.
The authentication mechanism of this module is based on the contents of
two files; /etc/hosts.equiv (or and ~/.rhosts. Firstly, hosts listed in
the former file are treated as equivalent to the localhost. Secondly,
entries in the user's own copy of the latter file is used to map
"remote-host remote-user" pairs to that user's account on the current
host. Access is granted to the user if their host is present in
/etc/hosts.equiv and their remote account is identical to their local one,
or if their remote account has an entry in their personal configuration
file.
The module authenticates a remote user (internally specified by the item
PAM_RUSER connecting from the remote host (internally specified by the
item PAM_RHOST). Accordingly, for applications to be compatible this
authentication module they must set these items prior to calling
pam_authenticate(). The module is not capable of independently probing the
network connection for such information.
6.26.2. OPTIONS
debug
Print debug information.
silent
Don't print informative messages.
superuser=account
Handle account as root.
6.26.3. MODULE TYPES PROVIDED
Only the auth module type is provided.
6.26.4. RETURN VALUES
PAM_AUTH_ERR
The remote host, remote user name or the local user name couldn't
be determined or access was denied by .rhosts file.
PAM_USER_UNKNOWN
User is not known to system.
6.26.5. EXAMPLES
To grant a remote user access by /etc/hosts.equiv or .rhosts for rsh add
the following lines to /etc/pam.d/rsh:
#%PAM-1.0
#
auth required pam_rhosts.so
auth required pam_nologin.so
auth required pam_env.so
auth required pam_unix.so
6.26.6. AUTHOR
pam_rhosts was written by Thorsten Kukuk <kukuk@thkukuk.de>
6.27. pam_rootok - gain only root access
pam_rootok.so [ debug ]
6.27.1. DESCRIPTION
pam_rootok is a PAM module that authenticates the user if their UID is 0.
Applications that are created setuid-root generally retain the UID of the
user but run with the authority of an enhanced effective-UID. It is the
real UID that is checked.
6.27.2. OPTIONS
debug
Print debug information.
6.27.3. MODULE TYPES PROVIDED
The auth, acct and password module types are provided.
6.27.4. RETURN VALUES
PAM_SUCCESS
The UID is 0.
PAM_AUTH_ERR
The UID is not 0.
6.27.5. EXAMPLES
In the case of the su(1) application the historical usage is to permit the
superuser to adopt the identity of a lesser user without the use of a
password. To obtain this behavior with PAM the following pair of lines are
needed for the corresponding entry in the /etc/pam.d/su configuration
file:
# su authentication. Root is granted access by default.
auth sufficient pam_rootok.so
auth required pam_unix.so
6.27.6. AUTHOR
pam_rootok was written by Andrew G. Morgan, <morgan@kernel.org>.
6.28. pam_securetty - limit root login to special devices
pam_securetty.so [ debug ]
6.28.1. DESCRIPTION
pam_securetty is a PAM module that allows root logins only if the user is
logging in on a "secure" tty, as defined by the listing in /etc/securetty.
pam_securetty also checks to make sure that /etc/securetty is a plain file
and not world writable. It will also allow root logins on the tty
specified with console= switch on the kernel command line and on ttys from
the /sys/class/tty/console/active.
This module has no effect on non-root users and requires that the
application fills in the PAM_TTY item correctly.
For canonical usage, should be listed as a required authentication method
before any sufficient authentication methods.
6.28.2. OPTIONS
debug
Print debug information.
noconsole
Do not automatically allow root logins on the kernel console
device, as specified on the kernel command line or by the sys
file, if it is not also specified in the /etc/securetty file.
6.28.3. MODULE TYPES PROVIDED
Only the auth module type is provided.
6.28.4. RETURN VALUES
PAM_SUCCESS
The user is allowed to continue authentication. Either the user is
not root, or the root user is trying to log in on an acceptable
device.
PAM_AUTH_ERR
Authentication is rejected. Either root is attempting to log in
via an unacceptable device, or the /etc/securetty file is world
writable or not a normal file.
PAM_INCOMPLETE
An application error occurred. pam_securetty was not able to get
information it required from the application that called it.
PAM_SERVICE_ERR
An error occurred while the module was determining the user's name
or tty, or the module could not open /etc/securetty.
PAM_USER_UNKNOWN
The module could not find the user name in the /etc/passwd file to
verify whether the user had a UID of 0. Therefore, the results of
running this module are ignored.
6.28.5. EXAMPLES
auth required pam_securetty.so
auth required pam_unix.so
6.28.6. AUTHOR
pam_securetty was written by Elliot Lee <sopwith@cuc.edu>.
6.29. pam_selinux - set the default security context
pam_selinux.so [ open ] [ close ] [ restore ] [ nottys ] [ debug ] [
verbose ] [ select_context ] [ env_params ] [ use_current_range ]
6.29.1. DESCRIPTION
pam_selinux is a PAM module that sets up the default SELinux security
context for the next executed process.
When a new session is started, the open_session part of the module
computes and sets up the execution security context used for the next
execve(2) call, the file security context for the controlling terminal,
and the security context used for creating a new kernel keyring.
When the session is ended, the close_session part of the module restores
old security contexts that were in effect before the change made by the
open_session part of the module.
Adding pam_selinux into the PAM stack might disrupt behavior of other PAM
modules which execute applications. To avoid that, pam_selinux.so open
should be placed after such modules in the PAM stack, and pam_selinux.so
close should be placed before them. When such a placement is not feasible,
pam_selinux.so restore could be used to temporary restore original
security contexts.
6.29.2. OPTIONS
open
Only execute the open_session part of the module.
close
Only execute the close_session part of the module.
restore
In open_session part of the module, temporarily restore the
security contexts as they were before the previous call of the
module. Another call of this module without the restore option
will set up the new security contexts again.
nottys
Do not setup security context of the controlling terminal.
debug
Turn on debug messages via syslog(3).
verbose
Attempt to inform the user when security context is set.
select_context
Attempt to ask the user for a custom security context role. If MLS
is on, ask also for sensitivity level.
env_params
Attempt to obtain a custom security context role from PAM
environment. If MLS is on, obtain also sensitivity level. This
option and the select_context option are mutually exclusive. The
respective PAM environment variables are SELINUX_ROLE_REQUESTED,
SELINUX_LEVEL_REQUESTED, and SELINUX_USE_CURRENT_RANGE. The first
two variables are self describing and the last one if set to 1
makes the PAM module behave as if the use_current_range was
specified on the command line of the module.
use_current_range
Use the sensitivity level of the current process for the user
context instead of the default level. Also suppresses asking of
the sensitivity level from the user or obtaining it from PAM
environment.
6.29.3. MODULE TYPES PROVIDED
Only the session module type is provided.
6.29.4. RETURN VALUES
PAM_SUCCESS
The security context was set successfully.
PAM_SESSION_ERR
Unable to get or set a valid context.
PAM_USER_UNKNOWN
The user is not known to the system.
PAM_BUF_ERR
Memory allocation error.
6.29.5. EXAMPLES
auth required pam_unix.so
session required pam_permit.so
session optional pam_selinux.so
6.29.6. AUTHOR
pam_selinux was written by Dan Walsh <dwalsh@redhat.com>.
6.30. pam_shells - check for valid login shell
pam_shells.so
6.30.1. DESCRIPTION
pam_shells is a PAM module that only allows access to the system if the
user's shell is listed in /etc/shells.
It also checks if /etc/shells is a plain file and not world writable.
6.30.2. OPTIONS
This module does not recognise any options.
6.30.3. MODULE TYPES PROVIDED
The auth and account module types are provided.
6.30.4. RETURN VALUES
PAM_AUTH_ERR
Access to the system was denied.
PAM_SUCCESS
The user's login shell was listed as valid shell in /etc/shells.
PAM_SERVICE_ERR
The module was not able to get the name of the user.
6.30.5. EXAMPLES
auth required pam_shells.so
6.30.6. AUTHOR
pam_shells was written by Erik Troan <ewt@redhat.com>.
6.31. pam_succeed_if - test account characteristics
pam_succeed_if.so [flag...] [condition...]
6.31.1. DESCRIPTION
pam_succeed_if.so is designed to succeed or fail authentication based on
characteristics of the account belonging to the user being authenticated
or values of other PAM items. One use is to select whether to load other
modules based on this test.
The module should be given one or more conditions as module arguments, and
authentication will succeed only if all of the conditions are met.
6.31.2. OPTIONS
The following flags are supported:
debug
Turns on debugging messages sent to syslog.
use_uid
Evaluate conditions using the account of the user whose UID the
application is running under instead of the user being
authenticated.
quiet
Don't log failure or success to the system log.
quiet_fail
Don't log failure to the system log.
quiet_success
Don't log success to the system log.
audit
Log unknown users to the system log.
Conditions are three words: a field, a test, and a value to test for.
Available fields are user, uid, gid, shell, home, ruser, rhost, tty and
service:
field < number
Field has a value numerically less than number.
field <= number
Field has a value numerically less than or equal to number.
field eq number
Field has a value numerically equal to number.
field >= number
Field has a value numerically greater than or equal to number.
field > number
Field has a value numerically greater than number.
field ne number
Field has a value numerically different from number.
field = string
Field exactly matches the given string.
field != string
Field does not match the given string.
field =~ glob
Field matches the given glob.
field !~ glob
Field does not match the given glob.
field in item:item:...
Field is contained in the list of items separated by colons.
field notin item:item:...
Field is not contained in the list of items separated by colons.
user ingroup group
User is in given group.
user notingroup group
User is not in given group.
user innetgr netgroup
(user,host) is in given netgroup.
user notinnetgr group
(user,host) is not in given netgroup.
6.31.3. MODULE TYPES PROVIDED
All module types (account, auth, password and session) are provided.
6.31.4. RETURN VALUES
PAM_SUCCESS
The condition was true.
PAM_AUTH_ERR
The condition was false.
PAM_SERVICE_ERR
A service error occurred or the arguments can't be parsed
correctly.
6.31.5. EXAMPLES
To emulate the behaviour of pam_wheel, except there is no fallback to
group 0:
auth required pam_succeed_if.so quiet user ingroup wheel
Given that the type matches, only loads the othermodule rule if the UID is
over 500. Adjust the number after default to skip several rules.
type [default=1 success=ignore] pam_succeed_if.so quiet uid > 500
type required othermodule.so arguments...
6.31.6. AUTHOR
Nalin Dahyabhai <nalin@redhat.com>
6.32. pam_tally - login counter (tallying) module
pam_tally.so [ file=/path/to/counter ] [ onerr=[fail|succeed] ] [
magic_root ] [ even_deny_root_account ] [ deny=n ] [ lock_time=n ] [
unlock_time=n ] [ per_user ] [ no_lock_time ] [ no_reset ] [ audit ] [
silent ] [ no_log_info ]
pam_tally [ --file /path/to/counter ] [ --user username ] [ --reset[=n] ]
[ --quiet ]
6.32.1. DESCRIPTION
This module maintains a count of attempted accesses, can reset count on
success, can deny access if too many attempts fail.
pam_tally has several limitations, which are solved with pam_tally2. For
this reason pam_tally is deprecated and will be removed in a future
release.
pam_tally comes in two parts: pam_tally.so and pam_tally. The former is
the PAM module and the latter, a stand-alone program. pam_tally is an
(optional) application which can be used to interrogate and manipulate the
counter file. It can display user counts, set individual counts, or clear
all counts. Setting artificially high counts may be useful for blocking
users without changing their passwords. For example, one might find it
useful to clear all counts every midnight from a cron job. The faillog(8)
command can be used instead of pam_tally to to maintain the counter file.
Normally, failed attempts to access root will not cause the root account
to become blocked, to prevent denial-of-service: if your users aren't
given shell accounts and root may only login via su or at the machine
console (not telnet/rsh, etc), this is safe.
6.32.2. OPTIONS
GLOBAL OPTIONS
This can be used for auth and account module types.
onerr=[fail|succeed]
If something weird happens (like unable to open the
file), return with PAM_SUCCESS if onerr=succeed is
given, else with the corresponding PAM error code.
file=/path/to/counter
File where to keep counts. Default is
/var/log/faillog.
audit
Will log the user name into the system log if the
user is not found.
silent
Don't print informative messages.
no_log_info
Don't log informative messages via syslog(3).
AUTH OPTIONS
Authentication phase first checks if user should be denied access
and if not it increments attempted login counter. Then on call to
pam_setcred(3) it resets the attempts counter.
deny=n
Deny access if tally for this user exceeds n.
lock_time=n
Always deny for n seconds after failed attempt.
unlock_time=n
Allow access after n seconds after failed attempt. If
this option is used the user will be locked out for
the specified amount of time after he exceeded his
maximum allowed attempts. Otherwise the account is
locked until the lock is removed by a manual
intervention of the system administrator.
magic_root
If the module is invoked by a user with uid=0 the
counter is not incremented. The sysadmin should use
this for user launched services, like su, otherwise
this argument should be omitted.
no_lock_time
Do not use the .fail_locktime field in
/var/log/faillog for this user.
no_reset
Don't reset count on successful entry, only
decrement.
even_deny_root_account
Root account can become unavailable.
per_user
If /var/log/faillog contains a non-zero
.fail_max/.fail_locktime field for this user then use
it instead of deny=n/ lock_time=n parameter.
no_lock_time
Don't use .fail_locktime filed in /var/log/faillog
for this user.
ACCOUNT OPTIONS
Account phase resets attempts counter if the user is not magic
root. This phase can be used optionally for services which don't
call pam_setcred(3) correctly or if the reset should be done
regardless of the failure of the account phase of other modules.
magic_root
If the module is invoked by a user with uid=0 the
counter is not incremented. The sysadmin should use
this for user launched services, like su, otherwise
this argument should be omitted.
no_reset
Don't reset count on successful entry, only
decrement.
6.32.3. MODULE TYPES PROVIDED
The auth and account module types are provided.
6.32.4. RETURN VALUES
PAM_AUTH_ERR
A invalid option was given, the module was not able to retrieve
the user name, no valid counter file was found, or too many failed
logins.
PAM_SUCCESS
Everything was successful.
PAM_USER_UNKNOWN
User not known.
6.32.5. EXAMPLES
Add the following line to /etc/pam.d/login to lock the account after too
many failed logins. The number of allowed fails is specified by
/var/log/faillog and needs to be set with pam_tally or faillog(8) before.
auth required pam_securetty.so
auth required pam_tally.so per_user
auth required pam_env.so
auth required pam_unix.so
auth required pam_nologin.so
account required pam_unix.so
password required pam_unix.so
session required pam_limits.so
session required pam_unix.so
session required pam_lastlog.so nowtmp
session optional pam_mail.so standard
6.32.6. AUTHOR
pam_tally was written by Tim Baverstock and Tomas Mraz.
6.33. pam_tally2 - login counter (tallying) module
pam_tally2.so [ file=/path/to/counter ] [ onerr=[fail|succeed] ] [
magic_root ] [ even_deny_root ] [ deny=n ] [ lock_time=n ] [ unlock_time=n
] [ root_unlock_time=n ] [ serialize ] [ audit ] [ silent ] [ no_log_info
] [ debug ]
pam_tally2 [ --file /path/to/counter ] [ --user username ] [ --reset[=n] ]
[ --quiet ]
6.33.1. DESCRIPTION
This module maintains a count of attempted accesses, can reset count on
success, can deny access if too many attempts fail.
pam_tally2 comes in two parts: pam_tally2.so and pam_tally2. The former is
the PAM module and the latter, a stand-alone program. pam_tally2 is an
(optional) application which can be used to interrogate and manipulate the
counter file. It can display user counts, set individual counts, or clear
all counts. Setting artificially high counts may be useful for blocking
users without changing their passwords. For example, one might find it
useful to clear all counts every midnight from a cron job.
Normally, failed attempts to access root will not cause the root account
to become blocked, to prevent denial-of-service: if your users aren't
given shell accounts and root may only login via su or at the machine
console (not telnet/rsh, etc), this is safe.
6.33.2. OPTIONS
GLOBAL OPTIONS
This can be used for auth and account module types.
onerr=[fail|succeed]
If something weird happens (like unable to open the
file), return with PAM_SUCCESS if onerr=succeed is
given, else with the corresponding PAM error code.
file=/path/to/counter
File where to keep counts. Default is
/var/log/tallylog.
audit
Will log the user name into the system log if the
user is not found.
silent
Don't print informative messages.
no_log_info
Don't log informative messages via syslog(3).
debug
Always log tally count when it is incremented as a
debug level message to the system log.
AUTH OPTIONS
Authentication phase first increments attempted login counter and
checks if user should be denied access. If the user is
authenticated and the login process continues on call to
pam_setcred(3) it resets the attempts counter.
deny=n
Deny access if tally for this user exceeds n.
lock_time=n
Always deny for n seconds after failed attempt.
unlock_time=n
Allow access after n seconds after failed attempt. If
this option is used the user will be locked out for
the specified amount of time after he exceeded his
maximum allowed attempts. Otherwise the account is
locked until the lock is removed by a manual
intervention of the system administrator.
magic_root
If the module is invoked by a user with uid=0 the
counter is not incremented. The sysadmin should use
this for user launched services, like su, otherwise
this argument should be omitted.
even_deny_root
Root account can become unavailable.
root_unlock_time=n
This option implies even_deny_root option. Allow
access after n seconds to root account after failed
attempt. If this option is used the root user will be
locked out for the specified amount of time after he
exceeded his maximum allowed attempts.
serialize
Serialize access to the tally file using locks. This
option might be used only for non-multithreaded
services because it depends on the fcntl locking of
the tally file. Also it is a good idea to use this
option only in such configurations where the time
between auth phase and account or setcred phase is
not dependent on the authenticating client. Otherwise
the authenticating client will be able to prevent
simultaneous authentications by the same user by
simply artificially prolonging the time the file
record lock is held.
ACCOUNT OPTIONS
Account phase resets attempts counter if the user is not magic
root. This phase can be used optionally for services which don't
call pam_setcred(3) correctly or if the reset should be done
regardless of the failure of the account phase of other modules.
magic_root
If the module is invoked by a user with uid=0 the
counter is not changed. The sysadmin should use this
for user launched services, like su, otherwise this
argument should be omitted.
6.33.3. MODULE TYPES PROVIDED
The auth and account module types are provided.
6.33.4. RETURN VALUES
PAM_AUTH_ERR
A invalid option was given, the module was not able to retrieve
the user name, no valid counter file was found, or too many failed
logins.
PAM_SUCCESS
Everything was successful.
PAM_USER_UNKNOWN
User not known.
6.33.5. NOTES
pam_tally2 is not compatible with the old pam_tally faillog file format.
This is caused by requirement of compatibility of the tallylog file format
between 32bit and 64bit architectures on multiarch systems.
There is no setuid wrapper for access to the data file such as when the
pam_tally2.so module is called from xscreensaver. As this would make it
impossible to share PAM configuration with such services the following
workaround is used: If the data file cannot be opened because of
insufficient permissions (EACCES) the module returns PAM_IGNORE.
6.33.6. EXAMPLES
Add the following line to /etc/pam.d/login to lock the account after 4
failed logins. Root account will be locked as well. The accounts will be
automatically unlocked after 20 minutes. The module does not have to be
called in the account phase because the login calls pam_setcred(3)
correctly.
auth required pam_securetty.so
auth required pam_tally2.so deny=4 even_deny_root unlock_time=1200
auth required pam_env.so
auth required pam_unix.so
auth required pam_nologin.so
account required pam_unix.so
password required pam_unix.so
session required pam_limits.so
session required pam_unix.so
session required pam_lastlog.so nowtmp
session optional pam_mail.so standard
6.33.7. FILES
/var/log/tallylog
failure count logging file
6.33.8. AUTHOR
pam_tally2 was written by Tim Baverstock and Tomas Mraz.
6.34. pam_time - time controled access
pam_time.so [ debug ] [ noaudit ]
6.34.1. DESCRIPTION
The pam_time PAM module does not authenticate the user, but instead it
restricts access to a system and or specific applications at various times
of the day and on specific days or over various terminal lines. This
module can be configured to deny access to (individual) users based on
their name, the time of day, the day of week, the service they are
applying for and their terminal from which they are making their request.
By default rules for time/port access are taken from config file
/etc/security/time.conf.
If Linux PAM is compiled with audit support the module will report when it
denies access.
6.34.2. DESCRIPTION
The pam_time PAM module does not authenticate the user, but instead it
restricts access to a system and or specific applications at various times
of the day and on specific days or over various terminal lines. This
module can be configured to deny access to (individual) users based on
their name, the time of day, the day of week, the service they are
applying for and their terminal from which they are making their request.
For this module to function correctly there must be a correctly formatted
/etc/security/time.conf file present. White spaces are ignored and lines
maybe extended with '\' (escaped newlines). Text following a '#' is
ignored to the end of the line.
The syntax of the lines is as follows:
services;ttys;users;times
In words, each rule occupies a line, terminated with a newline or the
beginning of a comment; a '#'. It contains four fields separated with
semicolons, ';'.
The first field, the services field, is a logic list of PAM service names
that the rule applies to.
The second field, the tty field, is a logic list of terminal names that
this rule applies to.
The third field, the users field, is a logic list of users or a netgroup
of users to whom this rule applies.
For these items the simple wildcard '*' may be used only once. With
netgroups no wildcards or logic operators are allowed.
The times field is used to indicate the times at which this rule applies.
The format here is a logic list of day/time-range entries. The days are
specified by a sequence of two character entries, MoTuSa for example is
Monday Tuesday and Saturday. Note that repeated days are unset MoMo = no
day, and MoWk = all weekdays bar Monday. The two character combinations
accepted are Mo Tu We Th Fr Sa Su Wk Wd Al, the last two being week-end
days and all 7 days of the week respectively. As a final example, AlFr
means all days except Friday.
Each day/time-range can be prefixed with a '!' to indicate "anything but".
The time-range part is two 24-hour times HHMM, separated by a hyphen,
indicating the start and finish time (if the finish time is smaller than
the start time it is deemed to apply on the following day).
For a rule to be active, ALL of service+ttys+users must be satisfied by
the applying process.
Note, currently there is no daemon enforcing the end of a session. This
needs to be remedied.
Poorly formatted rules are logged as errors using syslog(3).
6.34.3. OPTIONS
debug
Some debug information is printed with syslog(3).
noaudit
Do not report logins at disallowed time to the audit subsystem.
6.34.4. MODULE TYPES PROVIDED
Only the account type is provided.
6.34.5. RETURN VALUES
PAM_SUCCESS
Access was granted.
PAM_ABORT
Not all relevant data could be gotten.
PAM_BUF_ERR
Memory buffer error.
PAM_PERM_DENIED
Access was not granted.
PAM_USER_UNKNOWN
The user is not known to the system.
6.34.6. FILES
/etc/security/time.conf
Default configuration file
6.34.7. EXAMPLES
These are some example lines which might be specified in
/etc/security/time.conf.
All users except for root are denied access to console-login at all times:
login ; tty* & !ttyp* ; !root ; !Al0000-2400
Games (configured to use PAM) are only to be accessed out of working
hours. This rule does not apply to the user waster:
games ; * ; !waster ; Wd0000-2400 | Wk1800-0800
6.34.8. AUTHOR
pam_time was written by Andrew G. Morgan <morgan@kernel.org>.
6.35. pam_timestamp - authenticate using cached successful authentication
attempts
pam_timestamp.so [ timestampdir=directory ] [ timestamp_timeout=number ] [
verbose ] [ debug ]
6.35.1. DESCRIPTION
In a nutshell, pam_timestamp caches successful authentication attempts,
and allows you to use a recent successful attempt as the basis for
authentication. This is similar mechanism which is used in sudo.
When an application opens a session using pam_timestamp, a timestamp file
is created in the timestampdir directory for the user. When an application
attempts to authenticate the user, a pam_timestamp will treat a
sufficiently recent timestamp file as grounds for succeeding.
6.35.2. OPTIONS
timestampdir=directory
Specify an alternate directory where pam_timestamp creates
timestamp files.
timestamp_timeout=number
How long should pam_timestamp treat timestamp as valid after their
last modification date (in seconds). Default is 300 seconds.
verbose
Attempt to inform the user when access is granted.
debug
Turns on debugging messages sent to syslog(3).
6.35.3. MODULE TYPES PROVIDED
The auth and session module types are provided.
6.35.4. RETURN VALUES
PAM_AUTH_ERR
The module was not able to retrieve the user name or no valid
timestamp file was found.
PAM_SUCCESS
Everything was successful.
PAM_SESSION_ERR
Timestamp file could not be created or updated.
6.35.5. NOTES
Users can get confused when they are not always asked for passwords when
running a given program. Some users reflexively begin typing information
before noticing that it is not being asked for.
6.35.6. EXAMPLES
auth sufficient pam_timestamp.so verbose
auth required pam_unix.so
session required pam_unix.so
session optional pam_timestamp.so
6.35.7. FILES
/var/run/pam_timestamp/...
timestamp files and directories
6.35.8. AUTHOR
pam_timestamp was written by Nalin Dahyabhai.
6.36. pam_umask - set the file mode creation mask
pam_umask.so [ debug ] [ silent ] [ usergroups ] [ umask=mask ]
6.36.1. DESCRIPTION
pam_umask is a PAM module to set the file mode creation mask of the
current environment. The umask affects the default permissions assigned to
newly created files.
The PAM module tries to get the umask value from the following places in
the following order:
* umask= entry in the user's GECOS field
* umask= argument
* UMASK entry from /etc/login.defs
* UMASK= entry from /etc/default/login
The GECOS field is split on comma ',' characters. The module also in
addition to the umask= entry recognizes pri= entry, which sets the nice
priority value for the session, and ulimit= entry, which sets the maximum
size of files the processes in the session can create.
6.36.2. OPTIONS
debug
Print debug information.
silent
Don't print informative messages.
usergroups
If the user is not root and the username is the same as primary
group name, the umask group bits are set to be the same as owner
bits (examples: 022 -> 002, 077 -> 007).
umask=mask
Sets the calling process's file mode creation mask (umask) to mask
& 0777. The value is interpreted as Octal.
6.36.3. MODULE TYPES PROVIDED
Only the session type is provided.
6.36.4. RETURN VALUES
PAM_SUCCESS
The new umask was set successfully.
PAM_SERVICE_ERR
No username was given.
PAM_USER_UNKNOWN
User not known.
6.36.5. EXAMPLES
Add the following line to /etc/pam.d/login to set the user specific umask
at login:
session optional pam_umask.so umask=0022
6.36.6. AUTHOR
pam_umask was written by Thorsten Kukuk <kukuk@thkukuk.de>.
6.37. pam_unix - traditional password authentication
pam_unix.so [ ... ]
6.37.1. DESCRIPTION
This is the standard Unix authentication module. It uses standard calls
from the system's libraries to retrieve and set account information as
well as authentication. Usually this is obtained from the /etc/passwd and
the /etc/shadow file as well if shadow is enabled.
The account component performs the task of establishing the status of the
user's account and password based on the following shadow elements:
expire, last_change, max_change, min_change, warn_change. In the case of
the latter, it may offer advice to the user on changing their password or,
through the PAM_AUTHTOKEN_REQD return, delay giving service to the user
until they have established a new password. The entries listed above are
documented in the shadow(5) manual page. Should the user's record not
contain one or more of these entries, the corresponding shadow check is
not performed.
The authentication component performs the task of checking the users
credentials (password). The default action of this module is to not permit
the user access to a service if their official password is blank.
A helper binary, unix_chkpwd(8), is provided to check the user's password
when it is stored in a read protected database. This binary is very simple
and will only check the password of the user invoking it. It is called
transparently on behalf of the user by the authenticating component of
this module. In this way it is possible for applications like xlock(1) to
work without being setuid-root. The module, by default, will temporarily
turn off SIGCHLD handling for the duration of execution of the helper
binary. This is generally the right thing to do, as many applications are
not prepared to handle this signal from a child they didn't know was
fork()d. The noreap module argument can be used to suppress this temporary
shielding and may be needed for use with certain applications.
The maximum length of a password supported by the pam_unix module via the
helper binary is PAM_MAX_RESP_SIZE - currently 512 bytes. The rest of the
password provided by the conversation function to the module will be
ignored.
The password component of this module performs the task of updating the
user's password. The default encryption hash is taken from the
ENCRYPT_METHOD variable from /etc/login.defs
The session component of this module logs when a user logins or leave the
system.
Remaining arguments, supported by others functions of this module, are
silently ignored. Other arguments are logged as errors through syslog(3).
6.37.2. OPTIONS
debug
Turns on debugging via syslog(3).
audit
A little more extreme than debug.
quiet
Turns off informational messages namely messages about session
open and close via syslog(3).
nullok
The default action of this module is to not permit the user access
to a service if their official password is blank. The nullok
argument overrides this default.
try_first_pass
Before prompting the user for their password, the module first
tries the previous stacked module's password in case that
satisfies this module as well.
use_first_pass
The argument use_first_pass forces the module to use a previous
stacked modules password and will never prompt the user - if no
password is available or the password is not appropriate, the user
will be denied access.
nodelay
This argument can be used to discourage the authentication
component from requesting a delay should the authentication as a
whole fail. The default action is for the module to request a
delay-on-failure of the order of two second.
use_authtok
When password changing enforce the module to set the new password
to the one provided by a previously stacked password module (this
is used in the example of the stacking of the pam_cracklib module
documented below).
authtok_type=type
This argument can be used to modify the password prompt when
changing passwords to include the type of the password. Empty by
default.
nis
NIS RPC is used for setting new passwords.
remember=n
The last n passwords for each user are saved in
/etc/security/opasswd in order to force password change history
and keep the user from alternating between the same password too
frequently. The MD5 password hash algorithm is used for storing
the old passwords. Instead of this option the pam_pwhistory module
should be used.
shadow
Try to maintain a shadow based system.
md5
When a user changes their password next, encrypt it with the MD5
algorithm.
bigcrypt
When a user changes their password next, encrypt it with the DEC
C2 algorithm.
sha256
When a user changes their password next, encrypt it with the
SHA256 algorithm. The SHA256 algorithm must be supported by the
crypt(3) function.
sha512
When a user changes their password next, encrypt it with the
SHA512 algorithm. The SHA512 algorithm must be supported by the
crypt(3) function.
blowfish
When a user changes their password next, encrypt it with the
blowfish algorithm. The blowfish algorithm must be supported by
the crypt(3) function.
rounds=n
Set the optional number of rounds of the SHA256, SHA512 and
blowfish password hashing algorithms to n.
broken_shadow
Ignore errors reading shadow information for users in the account
management module.
minlen=n
Set a minimum password length of n characters. The max. for DES
crypt based passwords are 8 characters.
no_pass_expiry
When set ignore password expiration as defined by the shadow entry
of the user. The option has an effect only in case pam_unix was
not used for the authentication or it returned authentication
failure meaning that other authentication source or method
succeeded. The example can be public key authentication in sshd.
The module will return PAM_SUCCESS instead of eventual
PAM_NEW_AUTHTOK_REQD or PAM_AUTHTOK_EXPIRED.
Invalid arguments are logged with syslog(3).
6.37.3. MODULE TYPES PROVIDED
All module types (account, auth, password and session) are provided.
6.37.4. RETURN VALUES
PAM_IGNORE
Ignore this module.
6.37.5. EXAMPLES
An example usage for /etc/pam.d/login would be:
# Authenticate the user
auth required pam_unix.so
# Ensure users account and password are still active
account required pam_unix.so
# Change the user's password, but at first check the strength
# with pam_cracklib(8)
password required pam_cracklib.so retry=3 minlen=6 difok=3
password required pam_unix.so use_authtok nullok md5
session required pam_unix.so
6.37.6. AUTHOR
pam_unix was written by various people.
6.38. pam_userdb - authenticate against a db database
pam_userdb.so db=/path/database [ debug ] [ crypt=[crypt|none] ] [ icase ]
[ dump ] [ try_first_pass ] [ use_first_pass ] [ unknown_ok ] [ key_only ]
6.38.1. DESCRIPTION
The pam_userdb module is used to verify a username/password pair against
values stored in a Berkeley DB database. The database is indexed by the
username, and the data fields corresponding to the username keys are the
passwords.
6.38.2. OPTIONS
crypt=[crypt|none]
Indicates whether encrypted or plaintext passwords are stored in
the database. If it is crypt, passwords should be stored in the
database in crypt(3) form. If none is selected, passwords should
be stored in the database as plaintext.
db=/path/database
Use the /path/database database for performing lookup. There is no
default; the module will return PAM_IGNORE if no database is
provided. Note that the path to the database file should be
specified without the .db suffix.
debug
Print debug information. Note that password hashes, both from db
and computed, will be printed to syslog.
dump
Dump all the entries in the database to the log. Don't do this by
default!
icase
Make the password verification to be case insensitive (ie when
working with registration numbers and such). Only works with
plaintext password storage.
try_first_pass
Use the authentication token previously obtained by another module
that did the conversation with the application. If this token can
not be obtained then the module will try to converse. This option
can be used for stacking different modules that need to deal with
the authentication tokens.
use_first_pass
Use the authentication token previously obtained by another module
that did the conversation with the application. If this token can
not be obtained then the module will fail. This option can be used
for stacking different modules that need to deal with the
authentication tokens.
unknown_ok
Do not return error when checking for a user that is not in the
database. This can be used to stack more than one pam_userdb
module that will check a username/password pair in more than a
database.
key_only
The username and password are concatenated together in the
database hash as 'username-password' with a random value. if the
concatenation of the username and password with a dash in the
middle returns any result, the user is valid. this is useful in
cases where the username may not be unique but the username and
password pair are.
6.38.3. MODULE TYPES PROVIDED
The auth and account module types are provided.
6.38.4. RETURN VALUES
PAM_AUTH_ERR
Authentication failure.
PAM_AUTHTOK_RECOVERY_ERR
Authentication information cannot be recovered.
PAM_BUF_ERR
Memory buffer error.
PAM_CONV_ERR
Conversation failure.
PAM_SERVICE_ERR
Error in service module.
PAM_SUCCESS
Success.
PAM_USER_UNKNOWN
User not known to the underlying authentication module.
6.38.5. EXAMPLES
auth sufficient pam_userdb.so icase db=/etc/dbtest
6.38.6. AUTHOR
pam_userdb was written by Cristian Gafton >gafton@redhat.com<.
6.39. pam_warn - logs all PAM items
pam_warn.so
6.39.1. DESCRIPTION
pam_warn is a PAM module that logs the service, terminal, user, remote
user and remote host to syslog(3). The items are not probed for, but
instead obtained from the standard PAM items. The module always returns
PAM_IGNORE, indicating that it does not want to affect the authentication
process.
6.39.2. OPTIONS
This module does not recognise any options.
6.39.3. MODULE TYPES PROVIDED
The auth, account, password and session module types are provided.
6.39.4. RETURN VALUES
PAM_IGNORE
This module always returns PAM_IGNORE.
6.39.5. EXAMPLES
#%PAM-1.0
#
# If we don't have config entries for a service, the
# OTHER entries are used. To be secure, warn and deny
# access to everything.
other auth required pam_warn.so
other auth required pam_deny.so
other account required pam_warn.so
other account required pam_deny.so
other password required pam_warn.so
other password required pam_deny.so
other session required pam_warn.so
other session required pam_deny.so
6.39.6. AUTHOR
pam_warn was written by Andrew G. Morgan <morgan@kernel.org>.
6.40. pam_wheel - only permit root access to members of group wheel
pam_wheel.so [ debug ] [ deny ] [ group=name ] [ root_only ] [ trust ] [
use_uid ]
6.40.1. DESCRIPTION
The pam_wheel PAM module is used to enforce the so-called wheel group. By
default it permits root access to the system if the applicant user is a
member of the wheel group. If no group with this name exist, the module is
using the group with the group-ID 0.
6.40.2. OPTIONS
debug
Print debug information.
deny
Reverse the sense of the auth operation: if the user is trying to
get UID 0 access and is a member of the wheel group (or the group
of the group option), deny access. Conversely, if the user is not
in the group, return PAM_IGNORE (unless trust was also specified,
in which case we return PAM_SUCCESS).
group=name
Instead of checking the wheel or GID 0 groups, use the name group
to perform the authentication.
root_only
The check for wheel membership is done only when the target user
UID is 0.
trust
The pam_wheel module will return PAM_SUCCESS instead of PAM_IGNORE
if the user is a member of the wheel group (thus with a little
play stacking the modules the wheel members may be able to su to
root without being prompted for a passwd).
use_uid
The check will be done against the real uid of the calling
process, instead of trying to obtain the user from the login
session associated with the terminal in use.
6.40.3. MODULE TYPES PROVIDED
The auth and account module types are provided.
6.40.4. RETURN VALUES
PAM_AUTH_ERR
Authentication failure.
PAM_BUF_ERR
Memory buffer error.
PAM_IGNORE
The return value should be ignored by PAM dispatch.
PAM_PERM_DENY
Permission denied.
PAM_SERVICE_ERR
Cannot determine the user name.
PAM_SUCCESS
Success.
PAM_USER_UNKNOWN
User not known.
6.40.5. EXAMPLES
The root account gains access by default (rootok), only wheel members can
become root (wheel) but Unix authenticate non-root applicants.
su auth sufficient pam_rootok.so
su auth required pam_wheel.so
su auth required pam_unix.so
6.40.6. AUTHOR
pam_wheel was written by Cristian Gafton <gafton@redhat.com>.
6.41. pam_xauth - forward xauth keys between users
pam_xauth.so [ debug ] [ xauthpath=/path/to/xauth ] [ systemuser=UID ] [
targetuser=UID ]
6.41.1. DESCRIPTION
The pam_xauth PAM module is designed to forward xauth keys (sometimes
referred to as "cookies") between users.
Without pam_xauth, when xauth is enabled and a user uses the su(1) command
to assume another user's privileges, that user is no longer able to access
the original user's X display because the new user does not have the key
needed to access the display. pam_xauth solves the problem by forwarding
the key from the user running su (the source user) to the user whose
identity the source user is assuming (the target user) when the session is
created, and destroying the key when the session is torn down.
This means, for example, that when you run su(1) from an xterm session,
you will be able to run X programs without explicitly dealing with the
xauth(1) xauth command or ~/.Xauthority files.
pam_xauth will only forward keys if xauth can list a key connected to the
$DISPLAY environment variable.
Primitive access control is provided by ~/.xauth/export in the invoking
user's home directory and ~/.xauth/import in the target user's home
directory.
If a user has a ~/.xauth/import file, the user will only receive cookies
from users listed in the file. If there is no ~/.xauth/import file, the
user will accept cookies from any other user.
If a user has a .xauth/export file, the user will only forward cookies to
users listed in the file. If there is no ~/.xauth/export file, and the
invoking user is not root, the user will forward cookies to any other
user. If there is no ~/.xauth/export file, and the invoking user is root,
the user will not forward cookies to other users.
Both the import and export files support wildcards (such as *). Both the
import and export files can be empty, signifying that no users are
allowed.
6.41.2. OPTIONS
debug
Print debug information.
xauthpath=/path/to/xauth
Specify the path the xauth program (it is expected in
/usr/X11R6/bin/xauth, /usr/bin/xauth, or /usr/bin/X11/xauth by
default).
systemuser=UID
Specify the highest UID which will be assumed to belong to a
"system" user. pam_xauth will refuse to forward credentials to
users with UID less than or equal to this number, except for root
and the "targetuser", if specified.
targetuser=UID
Specify a single target UID which is exempt from the systemuser
check.
6.41.3. MODULE TYPES PROVIDED
Only the session type is provided.
6.41.4. RETURN VALUES
PAM_BUF_ERR
Memory buffer error.
PAM_PERM_DENIED
Permission denied by import/export file.
PAM_SESSION_ERR
Cannot determine user name, UID or access users home directory.
PAM_SUCCESS
Success.
PAM_USER_UNKNOWN
User not known.
6.41.5. EXAMPLES
Add the following line to /etc/pam.d/su to forward xauth keys between
users when calling su:
session optional pam_xauth.so
6.41.6. AUTHOR
pam_xauth was written by Nalin Dahyabhai <nalin@redhat.com>, based on
original version by Michael K. Johnson <johnsonm@redhat.com>.
Chapter 7. See also
* The Linux-PAM Application Writers' Guide.
* The Linux-PAM Module Writers' Guide.
* The V. Samar and R. Schemers (SunSoft), ``UNIFIED LOGIN WITH PLUGGABLE
AUTHENTICATION MODULES'', Open Software Foundation Request For
Comments 86.0, October 1995.
Chapter 8. Author/acknowledgments
This document was written by Andrew G. Morgan (morgan@kernel.org) with
many contributions from Chris Adams, Peter Allgeyer, Tim Baverstock, Tim
Berger, Craig S. Bell, Derrick J. Brashear, Ben Buxton, Seth Chaiklin,
Oliver Crow, Chris Dent, Marc Ewing, Cristian Gafton, Emmanuel Galanos,
Brad M. Garcia, Eric Hester, Michel D'Hooge, Roger Hu, Eric Jacksch,
Michael K. Johnson, David Kinchlea, Olaf Kirch, Marcin Korzonek, Thorsten
Kukuk, Stephen Langasek, Nicolai Langfeldt, Elliot Lee, Luke Kenneth
Casson Leighton, Al Longyear, Ingo Luetkebohle, Marek Michalkiewicz,
Robert Milkowski, Aleph One, Martin Pool, Sean Reifschneider, Jan
Rekorajski, Erik Troan, Theodore Ts'o, Jeff Uphoff, Myles Uyema, Savochkin
Andrey Vladimirovich, Ronald Wahl, David Wood, John Wilmes, Joseph S. D.
Yao and Alex O. Yuriev.
Thanks are also due to Sun Microsystems, especially to Vipin Samar and
Charlie Lai for their advice. At an early stage in the development of
Linux-PAM, Sun graciously made the documentation for their implementation
of PAM available. This act greatly accelerated the development of
Linux-PAM.
Chapter 9. Copyright information for this document
Copyright (c) 2006 Thorsten Kukuk <kukuk@thkukuk.de>
Copyright (c) 1996-2002 Andrew G. Morgan <morgan@kernel.org>
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are
met:
1. Redistributions of source code must retain the above copyright
notice, and the entire permission notice in its entirety,
including the disclaimer of warranties.
2. Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in the
documentation and/or other materials provided with the distribution.
3. The name of the author may not be used to endorse or promote
products derived from this software without specific prior
written permission.
Alternatively, this product may be distributed under the terms of the GNU
General Public License (GPL), in which case the provisions of the GNU GPL
are required instead of the above restrictions. (This clause is necessary
due to a potential bad interaction between the GNU GPL and the
restrictions contained in a BSD-style copyright.)
THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED
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IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
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