531 lines
16 KiB
XML
531 lines
16 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
|
||
<!--
|
||
SPDX-FileCopyrightText: 1989 - 1994, Julianne Frances Haugh
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||
SPDX-FileCopyrightText: 2007 - 2011, Nicolas François
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||
SPDX-License-Identifier: BSD-3-Clause
|
||
-->
|
||
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook V4.5//EN"
|
||
"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
|
||
<!ENTITY BCRYPT_MIN_ROUNDS SYSTEM "login.defs.d/BCRYPT_MIN_ROUNDS.xml">
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||
<!ENTITY ENCRYPT_METHOD SYSTEM "login.defs.d/ENCRYPT_METHOD.xml">
|
||
<!ENTITY MD5_CRYPT_ENAB SYSTEM "login.defs.d/MD5_CRYPT_ENAB.xml">
|
||
<!ENTITY OBSCURE_CHECKS_ENAB SYSTEM "login.defs.d/OBSCURE_CHECKS_ENAB.xml">
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||
<!ENTITY PASS_ALWAYS_WARN SYSTEM "login.defs.d/PASS_ALWAYS_WARN.xml">
|
||
<!ENTITY PASS_CHANGE_TRIES SYSTEM "login.defs.d/PASS_CHANGE_TRIES.xml">
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||
<!ENTITY PASS_MAX_LEN SYSTEM "login.defs.d/PASS_MAX_LEN.xml">
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||
<!ENTITY SHA_CRYPT_MIN_ROUNDS SYSTEM "login.defs.d/SHA_CRYPT_MIN_ROUNDS.xml">
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||
<!ENTITY YESCRYPT_COST_FACTOR SYSTEM "login.defs.d/YESCRYPT_COST_FACTOR.xml">
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||
<!-- SHADOW-CONFIG-HERE -->
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||
]>
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||
<refentry id='passwd.1'>
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||
<!-- $Id$ -->
|
||
<refentryinfo>
|
||
<author>
|
||
<firstname>Julianne Frances</firstname>
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||
<surname>Haugh</surname>
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||
<contrib>Creation, 1989</contrib>
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||
</author>
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||
<author>
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||
<firstname>Thomas</firstname>
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||
<surname>Kłoczko</surname>
|
||
<email>kloczek@pld.org.pl</email>
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||
<contrib>shadow-utils maintainer, 2000 - 2007</contrib>
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||
</author>
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||
<author>
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||
<firstname>Nicolas</firstname>
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||
<surname>François</surname>
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||
<email>nicolas.francois@centraliens.net</email>
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||
<contrib>shadow-utils maintainer, 2007 - now</contrib>
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||
</author>
|
||
</refentryinfo>
|
||
<refmeta>
|
||
<refentrytitle>passwd</refentrytitle>
|
||
<manvolnum>1</manvolnum>
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||
<refmiscinfo class="sectdesc">User Commands</refmiscinfo>
|
||
<refmiscinfo class="source">shadow-utils</refmiscinfo>
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||
<refmiscinfo class="version">&SHADOW_UTILS_VERSION;</refmiscinfo>
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||
</refmeta>
|
||
<refnamediv id='name'>
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||
<refname>passwd</refname>
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||
<refpurpose>change user password</refpurpose>
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||
</refnamediv>
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||
|
||
<refsynopsisdiv id='synopsis'>
|
||
<cmdsynopsis>
|
||
<command>passwd</command>
|
||
<arg choice='opt'>
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||
<replaceable>options</replaceable>
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||
</arg>
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||
<arg choice='opt'>
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||
<replaceable>LOGIN</replaceable>
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||
</arg>
|
||
</cmdsynopsis>
|
||
</refsynopsisdiv>
|
||
|
||
<refsect1 id='description'>
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||
<title>DESCRIPTION</title>
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||
<para>
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||
The <command>passwd</command> command changes passwords
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||
for user accounts.
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||
A regular user can only change the password for their own account,
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||
while the superuser can change the password for any account.
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||
The <command>passwd</command> also changes the account
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||
or associated password validity period.
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||
</para>
|
||
|
||
<refsect2 id='password_changes'>
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||
<title>Password Changes</title>
|
||
<para>
|
||
If the account has a non-empty password,
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||
the user is first prompted to enter their current password.
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||
The entered password is encrypted and compared to the stored value.
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||
The user has only one attempt to enter the correct password.
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||
The superuser can bypass this step to allow changing forgotten passwords.
|
||
</para>
|
||
|
||
<para>
|
||
After the password has been entered, password aging information is
|
||
checked to determine if the user is permitted to change the password at
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||
this time. If not, <command>passwd</command> refuses to change the
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||
password and exits.
|
||
</para>
|
||
|
||
<para>
|
||
The user is then prompted twice for a replacement password. The
|
||
second entry is compared against the first and both are required to
|
||
match for the password to be changed.
|
||
</para>
|
||
|
||
<para>
|
||
Then, the password is tested for complexity.
|
||
<command>passwd</command> rejects passwords that do not meet
|
||
the complexity requirements.
|
||
Do not include the system default erase or kill characters.
|
||
</para>
|
||
|
||
</refsect2>
|
||
|
||
<refsect2 id='hints_for_user_passwords'>
|
||
<title>Hints for user passwords</title>
|
||
<para>
|
||
The security of a password depends on the strength of the
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||
encryption algorithm and the size of the key space. The legacy
|
||
<emphasis>UNIX</emphasis> System encryption method is based on the
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||
NBS DES algorithm. More recent methods are now recommended (see
|
||
<option>ENCRYPT_METHOD</option>). The size of the key space
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||
depends on the randomness of the selected password.
|
||
</para>
|
||
|
||
<para>
|
||
Compromises in password security normally result from careless
|
||
password selection or handling. For this reason, you should not
|
||
select a password which appears in a dictionary or one that must be
|
||
written down. The password should also not be a proper name, your
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||
license number, birth date, or street address. Any of these may be
|
||
used as guesses to violate system security.
|
||
</para>
|
||
|
||
<para>
|
||
As a general guideline, passwords should be long and random. It's
|
||
fine to use simple character sets, such as passwords consisting
|
||
only of lowercase letters, if that helps memorizing longer
|
||
passwords. For a password consisting only of lowercase English
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||
letters randomly chosen, and a length of 32, there are 26^32
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||
(approximately 2^150) different possible combinations. Being an
|
||
exponential equation, it's apparent that the exponent (the length)
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||
is more important than the base (the size of the character set).
|
||
</para>
|
||
|
||
<para>
|
||
You can find advice on how to choose a strong password on
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||
https://en.wikipedia.org/wiki/Password_strength
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||
</para>
|
||
</refsect2>
|
||
</refsect1>
|
||
|
||
<refsect1 id='options'>
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||
<title>OPTIONS</title>
|
||
<para>
|
||
The options which apply to the <command>passwd</command> command are:
|
||
</para>
|
||
<variablelist remap='IP'>
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||
<varlistentry>
|
||
<term>
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||
<option>-a</option>, <option>--all</option>
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||
</term>
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||
<listitem>
|
||
<para>
|
||
This option can be used only with <option>-S</option> and causes show
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||
status for all users.
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||
</para>
|
||
</listitem>
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||
</varlistentry>
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||
<varlistentry>
|
||
<term>
|
||
<option>-d</option>, <option>--delete</option>
|
||
</term>
|
||
<listitem>
|
||
<para>
|
||
Deletes a user's password, making it empty.
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||
This command sets the account to be passwordless.
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||
</para>
|
||
</listitem>
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||
</varlistentry>
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||
<varlistentry>
|
||
<term>
|
||
<option>-e</option>, <option>--expire</option>
|
||
</term>
|
||
<listitem>
|
||
<para>
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||
Immediately expire an account's password. This in effect can
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||
force a user to change their password at the user's next login.
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||
</para>
|
||
</listitem>
|
||
</varlistentry>
|
||
<varlistentry>
|
||
<term><option>-h</option>, <option>--help</option></term>
|
||
<listitem>
|
||
<para>Display help message and exit.</para>
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||
</listitem>
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||
</varlistentry>
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||
<varlistentry>
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||
<term>
|
||
<option>-i</option>, <option>--inactive</option> <replaceable>INACTIVE</replaceable>
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||
</term>
|
||
<listitem>
|
||
<para>
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||
This option is used to disable an account after the password has
|
||
been expired for a number of days. After a user account has had
|
||
an expired password for <replaceable>INACTIVE</replaceable>
|
||
days, the user may no longer sign on to the account.
|
||
</para>
|
||
</listitem>
|
||
</varlistentry>
|
||
<varlistentry>
|
||
<term>
|
||
<option>-k</option>, <option>--keep-tokens</option>
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||
</term>
|
||
<listitem>
|
||
<para>
|
||
Indicate password change should be performed only for expired
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||
authentication tokens (passwords). The user wishes to keep their
|
||
non-expired tokens as before.
|
||
</para>
|
||
</listitem>
|
||
</varlistentry>
|
||
<varlistentry>
|
||
<term>
|
||
<option>-l</option>, <option>--lock</option>
|
||
</term>
|
||
<listitem>
|
||
<para>
|
||
Lock the password of the named account. This option disables a
|
||
password by changing it to a value which matches no possible
|
||
encrypted value (it adds a ´!´ at the beginning of the
|
||
password).
|
||
</para>
|
||
<para>
|
||
Note that this does not disable the account. The user may
|
||
still be able to login using another authentication token
|
||
(e.g. an SSH key). To disable the account, administrators
|
||
should use <command>usermod --expiredate 1</command>
|
||
(this sets the account's expire date to 1970-01-02).
|
||
</para>
|
||
<para>
|
||
Users with a locked password are not allowed to change their
|
||
password.
|
||
</para>
|
||
</listitem>
|
||
</varlistentry>
|
||
<varlistentry>
|
||
<term>
|
||
<option>-n</option>, <option>--mindays</option> <replaceable>MIN_DAYS</replaceable>
|
||
</term>
|
||
<listitem>
|
||
<para>
|
||
Set the minimum number of days between password changes to
|
||
<replaceable>MIN_DAYS</replaceable>. A value of zero for this field
|
||
indicates that the user may change their password at any time.
|
||
</para>
|
||
</listitem>
|
||
</varlistentry>
|
||
<varlistentry>
|
||
<term>
|
||
<option>-q</option>, <option>--quiet</option>
|
||
</term>
|
||
<listitem>
|
||
<para>
|
||
Quiet mode.
|
||
</para>
|
||
</listitem>
|
||
</varlistentry>
|
||
<varlistentry>
|
||
<term>
|
||
<option>-r</option>, <option>--repository</option> <replaceable>REPOSITORY</replaceable>
|
||
</term>
|
||
<listitem>
|
||
<para>
|
||
change password in <replaceable>REPOSITORY</replaceable> repository
|
||
</para>
|
||
</listitem>
|
||
</varlistentry>
|
||
<varlistentry>
|
||
<term>
|
||
<option>-R</option>, <option>--root</option> <replaceable>CHROOT_DIR</replaceable>
|
||
</term>
|
||
<listitem>
|
||
<para>
|
||
Apply changes in the <replaceable>CHROOT_DIR</replaceable>
|
||
directory and use the configuration files from the
|
||
<replaceable>CHROOT_DIR</replaceable> directory.
|
||
Only absolute paths are supported.
|
||
No SELINUX support.
|
||
</para>
|
||
</listitem>
|
||
</varlistentry>
|
||
<varlistentry>
|
||
<term>
|
||
<option>-P</option>, <option>--prefix</option> <replaceable>PREFIX_DIR</replaceable>
|
||
</term>
|
||
<listitem>
|
||
<para>
|
||
Apply changes to configuration files under the root filesystem
|
||
found under the directory <replaceable>PREFIX_DIR</replaceable>.
|
||
This option does not chroot and is intended for preparing a cross-compilation
|
||
target. Some limitations: NIS and LDAP users/groups are
|
||
not verified. No PAM support. No SELINUX support.
|
||
</para>
|
||
</listitem>
|
||
</varlistentry>
|
||
<varlistentry>
|
||
<term>
|
||
<option>-S</option>, <option>--status</option>
|
||
</term>
|
||
<listitem>
|
||
<para>
|
||
Display account status information. The status information
|
||
consists of 7 fields. The first field is the user's login name.
|
||
The second field indicates if the user account has a locked
|
||
password (L),
|
||
has no password (NP), or has a usable password (P). The third
|
||
field gives the date of the last password change. The next four
|
||
fields are the minimum age, maximum age, warning period, and
|
||
inactivity period for the password. These ages are expressed in
|
||
days.
|
||
</para>
|
||
</listitem>
|
||
</varlistentry>
|
||
<varlistentry>
|
||
<term>
|
||
<option>-u</option>, <option>--unlock</option>
|
||
</term>
|
||
<listitem>
|
||
<para>
|
||
Unlock the password of the named account. This option
|
||
re-enables a password by changing the password back to its
|
||
previous value (to the value before using the
|
||
<option>-l</option> option).
|
||
</para>
|
||
</listitem>
|
||
</varlistentry>
|
||
<varlistentry>
|
||
<term>
|
||
<option>-w</option>, <option>--warndays</option> <replaceable>WARN_DAYS</replaceable>
|
||
</term>
|
||
<listitem>
|
||
<para>
|
||
Set the number of days of warning before a password change is required.
|
||
The <replaceable>WARN_DAYS</replaceable> option is
|
||
the number of days prior to password expiration
|
||
during which the user is warned
|
||
that their password is about to expire.
|
||
</para>
|
||
</listitem>
|
||
</varlistentry>
|
||
<varlistentry>
|
||
<term>
|
||
<option>-x</option>, <option>--maxdays</option> <replaceable>MAX_DAYS</replaceable>
|
||
</term>
|
||
<listitem>
|
||
<para>
|
||
Set the maximum number of days a password remains valid. After
|
||
<replaceable>MAX_DAYS</replaceable>, the password is required
|
||
to be changed.
|
||
</para>
|
||
<para>
|
||
Passing the number <emphasis remap='I'>-1</emphasis> as
|
||
<replaceable>MAX_DAYS</replaceable> will remove checking a
|
||
password's validity.
|
||
</para>
|
||
</listitem>
|
||
</varlistentry>
|
||
<varlistentry>
|
||
<term>
|
||
<option>-s</option>, <option>--stdin</option>
|
||
</term>
|
||
<listitem>
|
||
<para>
|
||
This option is used to indicate that passwd should read the new password from standard
|
||
input, which can be a pipe.
|
||
</para>
|
||
</listitem>
|
||
</varlistentry>
|
||
</variablelist>
|
||
</refsect1>
|
||
|
||
<refsect1 id='caveats'>
|
||
<title>CAVEATS</title>
|
||
<para>
|
||
Password complexity checking may
|
||
vary from site to site. The user is urged to select a password as
|
||
complex as he or she feels comfortable with.
|
||
</para>
|
||
<para>
|
||
Users may not be able to
|
||
change their password on a system if NIS is enabled and they are not
|
||
logged into the NIS server.
|
||
</para>
|
||
<para condition="pam">
|
||
<command>passwd</command> uses PAM to authenticate users and to
|
||
change their passwords.
|
||
</para>
|
||
</refsect1>
|
||
|
||
<refsect1 id='configuration' condition="no_pam">
|
||
<title>CONFIGURATION</title>
|
||
<para>
|
||
The following configuration variables in
|
||
<filename>/etc/login.defs</filename> change the behavior of this
|
||
tool:
|
||
</para>
|
||
<variablelist>
|
||
&ENCRYPT_METHOD;
|
||
&MD5_CRYPT_ENAB;
|
||
&OBSCURE_CHECKS_ENAB;
|
||
&PASS_ALWAYS_WARN;
|
||
&PASS_CHANGE_TRIES;
|
||
&PASS_MAX_LEN; <!-- documents also PASS_MIN_LEN -->
|
||
&SHA_CRYPT_MIN_ROUNDS;
|
||
</variablelist>
|
||
</refsect1>
|
||
|
||
<refsect1 id='files'>
|
||
<title>FILES</title>
|
||
<variablelist>
|
||
<varlistentry>
|
||
<term><filename>/etc/passwd</filename></term>
|
||
<listitem>
|
||
<para>User account information.</para>
|
||
</listitem>
|
||
</varlistentry>
|
||
<varlistentry>
|
||
<term><filename>/etc/shadow</filename></term>
|
||
<listitem>
|
||
<para>Secure user account information.</para>
|
||
</listitem>
|
||
</varlistentry>
|
||
<varlistentry condition="no_pam">
|
||
<term><filename>/etc/login.defs</filename></term>
|
||
<listitem>
|
||
<para>Shadow password suite configuration.</para>
|
||
</listitem>
|
||
</varlistentry>
|
||
<varlistentry condition="pam">
|
||
<term><filename>/etc/pam.d/passwd</filename></term>
|
||
<listitem>
|
||
<para>PAM configuration for <command>passwd</command>.</para>
|
||
</listitem>
|
||
</varlistentry>
|
||
</variablelist>
|
||
</refsect1>
|
||
|
||
<refsect1 id='exit_values'>
|
||
<title>EXIT VALUES</title>
|
||
<para>
|
||
The <command>passwd</command> command exits with the following values:
|
||
<variablelist>
|
||
<varlistentry>
|
||
<term><replaceable>0</replaceable></term>
|
||
<listitem>
|
||
<para>success</para>
|
||
</listitem>
|
||
</varlistentry>
|
||
<varlistentry>
|
||
<term><replaceable>1</replaceable></term>
|
||
<listitem>
|
||
<para>permission denied</para>
|
||
</listitem>
|
||
</varlistentry>
|
||
<varlistentry>
|
||
<term><replaceable>2</replaceable></term>
|
||
<listitem>
|
||
<para>invalid combination of options</para>
|
||
</listitem>
|
||
</varlistentry>
|
||
<varlistentry>
|
||
<term><replaceable>3</replaceable></term>
|
||
<listitem>
|
||
<para>unexpected failure, nothing done</para>
|
||
</listitem>
|
||
</varlistentry>
|
||
<varlistentry>
|
||
<term><replaceable>4</replaceable></term>
|
||
<listitem>
|
||
<para>unexpected failure, <filename>passwd</filename> file missing</para>
|
||
</listitem>
|
||
</varlistentry>
|
||
<varlistentry>
|
||
<term><replaceable>5</replaceable></term>
|
||
<listitem>
|
||
<para><filename>passwd</filename> file busy, try again</para>
|
||
</listitem>
|
||
</varlistentry>
|
||
<varlistentry>
|
||
<term><replaceable>6</replaceable></term>
|
||
<listitem>
|
||
<para>invalid argument to option</para>
|
||
</listitem>
|
||
</varlistentry>
|
||
<varlistentry>
|
||
<term><replaceable>10</replaceable></term>
|
||
<listitem>
|
||
<para>an error was returned by <refentrytitle>pam</refentrytitle><manvolnum>3</manvolnum></para>
|
||
</listitem>
|
||
</varlistentry>
|
||
</variablelist>
|
||
</para>
|
||
</refsect1>
|
||
|
||
<refsect1 id='see_also'>
|
||
<title>SEE ALSO</title>
|
||
<para>
|
||
<citerefentry>
|
||
<refentrytitle>chpasswd</refentrytitle><manvolnum>8</manvolnum>
|
||
</citerefentry>,
|
||
<citerefentry>
|
||
<refentrytitle>makepasswd</refentrytitle><manvolnum>1</manvolnum>
|
||
</citerefentry>,
|
||
<citerefentry>
|
||
<refentrytitle>passwd</refentrytitle><manvolnum>5</manvolnum>
|
||
</citerefentry>,
|
||
<citerefentry>
|
||
<refentrytitle>shadow</refentrytitle><manvolnum>5</manvolnum>
|
||
</citerefentry>,
|
||
<phrase condition="no_pam">
|
||
<citerefentry>
|
||
<refentrytitle>login.defs</refentrytitle><manvolnum>5</manvolnum>
|
||
</citerefentry>,
|
||
</phrase>
|
||
<citerefentry>
|
||
<refentrytitle>usermod</refentrytitle><manvolnum>8</manvolnum>
|
||
</citerefentry>.
|
||
</para>
|
||
|
||
<para>
|
||
The following web page comically (yet correctly) compares the
|
||
strength of two different methods for choosing a password:
|
||
"https://xkcd.com/936/"
|
||
</para>
|
||
</refsect1>
|
||
</refentry>
|