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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 | <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 V1.76.1"><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" title="6.37. pam_unix - traditional password authentication"><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" title="6.37.1. DESCRIPTION"><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 password component of this module performs the task of updating
the user's password.
</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" title="6.37.2. OPTIONS"><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><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">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
and allows any user with a blank password to access the
service.
</p></dd><dt><span class="term">
<code class="option">nullok_secure</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_secure</code> argument overrides this
default and allows any user with a blank password to access
the service as long as the value of PAM_TTY is set to one of
the values found in /etc/securetty.
</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">not_set_pass</code>
</span></dt><dd><p>
This argument is used to inform the module that it is not to
pay attention to/make available the old or new passwords from/to
other (stacked) password modules.
</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.
</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. If the
SHA256 algorithm is not known to the <span class="citerefentry"><span class="refentrytitle">crypt</span>(3)</span> function,
fall back to MD5.
</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. If the
SHA512 algorithm is not known to the <span class="citerefentry"><span class="refentrytitle">crypt</span>(3)</span> function,
fall back to MD5.
</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. If the
blowfish algorithm is not known to the <span class="citerefentry"><span class="refentrytitle">crypt</span>(3)</span> function,
fall back to MD5.
</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 default value is 6. The maximum for DES
crypt-based passwords is 8 characters.
</p></dd><dt><span class="term">
<code class="option">obscure</code>
</span></dt><dd><p>
Enable some extra checks on password strength. These checks
are based on the "obscure" checks in the original shadow
package. The behavior is similar to the pam_cracklib
module, but for non-dictionary-based checks. The following
checks are implemented:
</p><div class="variablelist"><dl><dt><span class="term">
<code class="option">Palindrome</code>
</span></dt><dd><p>
Verifies that the new password is not a palindrome
of (i.e., the reverse of) the previous one.
</p></dd><dt><span class="term">
<code class="option">Case Change Only</code>
</span></dt><dd><p>
Verifies that the new password isn't the same as the
old one with a change of case.
</p></dd><dt><span class="term">
<code class="option">Similar</code>
</span></dt><dd><p>
Verifies that the new password isn't too much like
the previous one.
</p></dd><dt><span class="term">
<code class="option">Simple</code>
</span></dt><dd><p>
Is the new password too simple? This is based on
the length of the password and the number of
different types of characters (alpha, numeric, etc.)
used.
</p></dd><dt><span class="term">
<code class="option">Rotated</code>
</span></dt><dd><p>
Is the new password a rotated version of the old
password? (E.g., "billy" and "illyb")
</p></dd></dl></div><p>
</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" title="6.37.3. MODULE TYPES PROVIDED"><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" title="6.37.4. RETURN VALUES"><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><dt><span class="term">PAM_IGNORE</span></dt><dd><p>
Ignore this module.
</p></dd></dl></div></div><div class="section" title="6.37.5. EXAMPLES"><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 users 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" title="6.37.6. AUTHOR"><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>
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