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NAME | SYNOPSIS | DESCRIPTION | OPTIONS | MODULE TYPES PROVIDED | RETURN VALUES | EXAMPLES | SEE ALSO | AUTHOR | COLOPHON |
PAM_UNIX(8) Linux-PAM Manual PAM_UNIX(8)
pam_unix - Module for traditional password authentication
pam_unix.so [...]
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).
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. If the SHA256 algorithm is not known to the
crypt(3) function, fall back to MD5.
sha512
When a user changes their password next, encrypt it with the
SHA512 algorithm. If the SHA512 algorithm is not known to the
crypt(3) function, fall back to MD5.
blowfish
When a user changes their password next, encrypt it with the
blowfish algorithm. If the blowfish algorithm is not known to the
crypt(3) function, fall back to MD5.
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).
All module types (account, auth, password and session) are provided.
PAM_IGNORE
Ignore this module.
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
login.defs(5), pam.conf(5), pam.d(5), pam(8)
pam_unix was written by various people.
This page is part of the linux-pam (Pluggable Authentication Modules
for Linux) project. Information about the project can be found at
⟨http://www.linux-pam.org/⟩. If you have a bug report for this manual
page, see ⟨//www.linux-pam.org/⟩. This page was obtained from the
tarball Linux-PAM-1.3.0.tar.gz fetched from
⟨http://www.linux-pam.org/library/⟩ on 2017-07-05. If you discover
any rendering problems in this HTML version of the page, or you
believe there is a better or more up-to-date source for the page, or
you have corrections or improvements to the information in this
COLOPHON (which is not part of the original manual page), send a mail
to man-pages@man7.org
Linux-PAM Manual 04/19/2016 PAM_UNIX(8)
Pages that refer to this page: pam_cracklib(8), unix_chkpwd(8), unix_update(8)