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<html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>6.37. pam_unix - traditional password authentication</title><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot"><link rel="home" href="Linux-PAM_SAG.html" title="The Linux-PAM System Administrators' Guide"><link rel="up" href="sag-module-reference.html" title="Chapter 6. A reference guide for available modules"><link rel="prev" href="sag-pam_umask.html" title="6.36. pam_umask - set the file mode creation mask"><link rel="next" href="sag-pam_userdb.html" title="6.38. pam_userdb - authenticate against a db database"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">6.37. pam_unix - traditional password authentication</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="sag-pam_umask.html">Prev</a> </td><th width="60%" align="center">Chapter 6. A reference guide for available modules</th><td width="20%" align="right"> <a accesskey="n" href="sag-pam_userdb.html">Next</a></td></tr></table><hr></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="sag-pam_unix"></a>6.37. pam_unix - traditional password authentication</h2></div></div></div><div class="cmdsynopsis"><p><code class="command">pam_unix.so</code> [
...
]</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="sag-pam_unix-description"></a>6.37.1. DESCRIPTION</h3></div></div></div><p>
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.
</p><p>
The account component performs the task of establishing the status
of the user's account and password based on the following
<span class="emphasis"><em>shadow</em></span> 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
<span class="emphasis"><em>PAM_AUTHTOKEN_REQD</em></span> return, delay
giving service to the user until they have established a new password.
The entries listed above are documented in the <span class="citerefentry"><span class="refentrytitle">shadow</span>(5)</span> manual page. Should the user's record not contain
one or more of these entries, the corresponding
<span class="emphasis"><em>shadow</em></span> check is not performed.
</p><p>
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.
</p><p>
A helper binary, <span class="citerefentry"><span class="refentrytitle">unix_chkpwd</span>(8)</span>, 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 <span class="citerefentry"><span class="refentrytitle">xlock</span>(1)</span> 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 <code class="function">fork()</code>d. The <code class="option">noreap</code> module
argument can be used to suppress this temporary shielding and may be
needed for use with certain applications.
</p><p>
The maximum length of a password supported by the pam_unix module
via the helper binary is <span class="emphasis"><em>PAM_MAX_RESP_SIZE</em></span>
- currently 512 bytes. The rest of the password provided by the
conversation function to the module will be ignored.
</p><p>
The password component of this module performs the task of updating
the user's password. The default encryption hash is taken from the
<span class="emphasis"><em>ENCRYPT_METHOD</em></span> variable from
<span class="emphasis"><em>/etc/login.defs</em></span>
</p><p>
The session component of this module logs when a user logins
or leave the system.
</p><p>
Remaining arguments, supported by others functions of this
module, are silently ignored. Other arguments are logged as
errors through <span class="citerefentry"><span class="refentrytitle">syslog</span>(3)</span>.
</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="sag-pam_unix-options"></a>6.37.2. OPTIONS</h3></div></div></div><div class="variablelist"><dl class="variablelist"><dt><span class="term">
<code class="option">debug</code>
</span></dt><dd><p>
Turns on debugging via
<span class="citerefentry"><span class="refentrytitle">syslog</span>(3)</span>.
</p></dd><dt><span class="term">
<code class="option">audit</code>
</span></dt><dd><p>
A little more extreme than debug.
</p></dd><dt><span class="term">
<code class="option">quiet</code>
</span></dt><dd><p>
Turns off informational messages namely messages about
session open and close via
<span class="citerefentry"><span class="refentrytitle">syslog</span>(3)</span>.
</p></dd><dt><span class="term">
<code class="option">nullok</code>
</span></dt><dd><p>
The default action of this module is to not permit the
user access to a service if their official password is blank.
The <code class="option">nullok</code> argument overrides this default.
</p></dd><dt><span class="term">
<code class="option">try_first_pass</code>
</span></dt><dd><p>
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.
</p></dd><dt><span class="term">
<code class="option">use_first_pass</code>
</span></dt><dd><p>
The argument <code class="option">use_first_pass</code> 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.
</p></dd><dt><span class="term">
<code class="option">nodelay</code>
</span></dt><dd><p>
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.
</p></dd><dt><span class="term">
<code class="option">use_authtok</code>
</span></dt><dd><p>
When password changing enforce the module to set the new
password to the one provided by a previously stacked
<code class="option">password</code> module (this is used in the
example of the stacking of the <span class="command"><strong>pam_cracklib</strong></span>
module documented below).
</p></dd><dt><span class="term">
<code class="option">authtok_type=<em class="replaceable"><code>type</code></em></code>
</span></dt><dd><p>
This argument can be used to modify the password prompt
when changing passwords to include the type of the password.
Empty by default.
</p></dd><dt><span class="term">
<code class="option">nis</code>
</span></dt><dd><p>
NIS RPC is used for setting new passwords.
</p></dd><dt><span class="term">
<code class="option">remember=<em class="replaceable"><code>n</code></em></code>
</span></dt><dd><p>
The last <em class="replaceable"><code>n</code></em> passwords for each
user are saved in <code class="filename">/etc/security/opasswd</code>
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 <span class="command"><strong>pam_pwhistory</strong></span>
module should be used.
</p></dd><dt><span class="term">
<code class="option">shadow</code>
</span></dt><dd><p>
Try to maintain a shadow based system.
</p></dd><dt><span class="term">
<code class="option">md5</code>
</span></dt><dd><p>
When a user changes their password next, encrypt
it with the MD5 algorithm.
</p></dd><dt><span class="term">
<code class="option">bigcrypt</code>
</span></dt><dd><p>
When a user changes their password next,
encrypt it with the DEC C2 algorithm.
</p></dd><dt><span class="term">
<code class="option">sha256</code>
</span></dt><dd><p>
When a user changes their password next,
encrypt it with the SHA256 algorithm. The
SHA256 algorithm must be supported by the <span class="citerefentry"><span class="refentrytitle">crypt</span>(3)</span> function.
</p></dd><dt><span class="term">
<code class="option">sha512</code>
</span></dt><dd><p>
When a user changes their password next,
encrypt it with the SHA512 algorithm. The
SHA512 algorithm must be supported by the <span class="citerefentry"><span class="refentrytitle">crypt</span>(3)</span> function.
</p></dd><dt><span class="term">
<code class="option">blowfish</code>
</span></dt><dd><p>
When a user changes their password next,
encrypt it with the blowfish algorithm. The
blowfish algorithm must be supported by the <span class="citerefentry"><span class="refentrytitle">crypt</span>(3)</span> function.
</p></dd><dt><span class="term">
<code class="option">rounds=<em class="replaceable"><code>n</code></em></code>
</span></dt><dd><p>
Set the optional number of rounds of the SHA256, SHA512
and blowfish password hashing algorithms to
<em class="replaceable"><code>n</code></em>.
</p></dd><dt><span class="term">
<code class="option">broken_shadow</code>
</span></dt><dd><p>
Ignore errors reading shadow information for
users in the account management module.
</p></dd><dt><span class="term">
<code class="option">minlen=<em class="replaceable"><code>n</code></em></code>
</span></dt><dd><p>
Set a minimum password length of <em class="replaceable"><code>n</code></em>
characters. The max. for DES crypt based passwords are 8
characters.
</p></dd><dt><span class="term">
<code class="option">no_pass_expiry</code>
</span></dt><dd><p>
When set ignore password expiration as defined by the
<span class="emphasis"><em>shadow</em></span> entry of the user. The option has an
effect only in case <span class="emphasis"><em>pam_unix</em></span> 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
<span class="emphasis"><em>sshd</em></span>. The module will return
<span class="emphasis"><em>PAM_SUCCESS</em></span> instead of eventual
<span class="emphasis"><em>PAM_NEW_AUTHTOK_REQD</em></span> or
<span class="emphasis"><em>PAM_AUTHTOK_EXPIRED</em></span>.
</p></dd></dl></div><p>
Invalid arguments are logged with <span class="citerefentry"><span class="refentrytitle">syslog</span>(3)</span>.
</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="sag-pam_unix-types"></a>6.37.3. MODULE TYPES PROVIDED</h3></div></div></div><p>
All module types (<code class="option">account</code>, <code class="option">auth</code>,
<code class="option">password</code> and <code class="option">session</code>) are provided.
</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="sag-pam_unix-return_values"></a>6.37.4. RETURN VALUES</h3></div></div></div><div class="variablelist"><dl class="variablelist"><dt><span class="term">PAM_IGNORE</span></dt><dd><p>
Ignore this module.
</p></dd></dl></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="sag-pam_unix-examples"></a>6.37.5. EXAMPLES</h3></div></div></div><p>
An example usage for <code class="filename">/etc/pam.d/login</code>
would be:
</p><pre class="programlisting">
# 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
</pre><p>
</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="sag-pam_unix-author"></a>6.37.6. AUTHOR</h3></div></div></div><p>
pam_unix was written by various people.
</p></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="sag-pam_umask.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="sag-module-reference.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="sag-pam_userdb.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">6.36. pam_umask - set the file mode creation mask </td><td width="20%" align="center"><a accesskey="h" href="Linux-PAM_SAG.html">Home</a></td><td width="40%" align="right" valign="top"> 6.38. pam_userdb - authenticate against a db database</td></tr></table></div></body></html>