408 lines
12 KiB
XML
408 lines
12 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
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<!ENTITY ENCRYPT_METHOD SYSTEM "login.defs.d/ENCRYPT_METHOD.xml">
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<!ENTITY MD5_CRYPT_ENAB SYSTEM "login.defs.d/MD5_CRYPT_ENAB.xml">
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<!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">
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<!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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]>
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<refentry id='passwd.1'>
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<!-- $Id$ -->
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<refmeta>
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<refentrytitle>passwd</refentrytitle>
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<manvolnum>1</manvolnum>
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<refmiscinfo class="sectdesc">User Commands</refmiscinfo>
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</refmeta>
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<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'>
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<cmdsynopsis>
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<command>passwd</command>
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<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>
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</cmdsynopsis>
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</refsynopsisdiv>
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<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 for user accounts.
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A normal user may only change the password for his/her own account, while
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the superuser may change the password for any account.
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<command>passwd</command> also changes account information, such as
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the full name of the user, the user's login shell, or his/her password
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expiry date and interval.
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</para>
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<refsect2 id='password_changes'>
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<title>Password Changes</title>
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<para>
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The user is first prompted for his/her old password, if one is
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present. This password is then encrypted and compared against the
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stored password. The user has only one chance to enter the correct
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password. The superuser is permitted to bypass this step so that
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forgotten passwords may be changed.
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</para>
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<para>
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After the password has been entered, password aging information is
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checked to see 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.
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</para>
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<para>
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The user is then prompted twice for a replacement password. The
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second entry is compared against the first and both are required to
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match in order for the password to be changed.
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</para>
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<para>
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Then, the password is tested for complexity. As a general guideline,
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passwords should consist of 6 to 8 characters including one or more
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characters from each of the following sets:
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</para>
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<itemizedlist mark='bullet'>
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<listitem>
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<para>lower case alphabetics</para>
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</listitem>
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<listitem>
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<para>digits 0 thru 9</para>
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</listitem>
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<listitem>
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<para>punctuation marks</para>
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</listitem>
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</itemizedlist>
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<para>
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Care must be taken not to include the system default erase or kill
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characters. <command>passwd</command> will reject any password which
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is not suitably complex.
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</para>
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</refsect2>
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<refsect2 id='hints_for_user_passwords'>
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<title>Hints for user passwords</title>
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<para>
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The security of a password depends upon the strength of the
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encryption algorithm and the size of the key space. The
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<emphasis>UNIX</emphasis> System encryption method is based on the
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NBS DES algorithm and is very secure. The size of the key space
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depends upon the randomness of the password which is selected.
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</para>
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<para>
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Compromises in password security normally result from careless
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password selection or handling. For this reason, you should not
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select a password which appears in a dictionary or which must be
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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
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used as guesses to violate system security.
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</para>
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<para>
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You can find advices on how to choose a strong password on
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http://en.wikipedia.org/wiki/Password_strength
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</para>
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</refsect2>
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</refsect1>
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<refsect1 id='options'>
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<title>OPTIONS</title>
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<para>
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The options which apply to the <command>passwd</command> command are:
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</para>
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<variablelist remap='IP'>
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<varlistentry>
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<term>
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<option>-a</option>, <option>--all</option>
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</term>
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<listitem>
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<para>
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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>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<option>-d</option>, <option>--delete</option>
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</term>
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<listitem>
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<para>
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Delete a user's password (make it empty). This is a quick way
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to disable a password for an account. It will set the named
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account passwordless.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<option>-e</option>, <option>--expire</option>
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</term>
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<listitem>
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<para>
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Immediately expire an account's password. This in effect can
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force a user to change his/her password at the user's next login.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><option>-h</option>, <option>--help</option></term>
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<listitem>
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<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>
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<option>-i</option>, <option>--inactive</option> <replaceable>INACTIVE</replaceable>
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</term>
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<listitem>
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<para>
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This option is used to disable an account after the password has
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been expired for a number of days. After a user account has had
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an expired password for <replaceable>INACTIVE</replaceable>
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days, the user may no longer sign on to the account.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<option>-k</option>, <option>--keep-tokens</option>
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</term>
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<listitem>
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<para>
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Indicate password change should be performed only for expired
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authentication tokens (passwords). The user wishes to keep their
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non-expired tokens as before.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<option>-l</option>, <option>--lock</option>
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</term>
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<listitem>
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<para>
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Lock the named account. This option disables an account by changing
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the password to a value which matches no possible encrypted value,
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and by setting the account expiry field to 1.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<option>-m</option>, <option>--mindays</option> <replaceable>MIN_DAYS</replaceable>
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</term>
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<listitem>
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<para>
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Set the minimum number of days between password changes to
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<replaceable>MIN_DAYS</replaceable>. A value of zero for this field
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indicates that the user may change his/her password at any time.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<option>-q</option>, <option>--quiet</option>
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</term>
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<listitem>
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<para>
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Quiet mode.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<option>-r</option>, <option>--repository</option> <replaceable>REPOSITORY</replaceable>
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</term>
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<listitem>
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<para>
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change password in <replaceable>REPOSITORY</replaceable> repository
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<option>-S</option>, <option>--status</option>
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</term>
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<listitem>
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<para>
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Display account status information. The status information
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consists of 7 fields. The first field is the user's login name.
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The second field indicates if the user account is locked (L),
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has no password (NP), or has a usable password (P). The third
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field gives the date of the last password change. The next four
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fields are the minimum age, maximum age, warning period, and
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inactivity period for the password. These ages are expressed in
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days.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<option>-u</option>, <option>--unlock</option>
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</term>
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<listitem>
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<para>
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Unlock the named account. This option re-enables an account by
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changing the password back to its previous value (to value before
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using <option>-l</option> option), and by resetting the account
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expiry field.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<option>-w</option>, <option>--warndays</option> <replaceable>WARN_DAYS</replaceable>
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</term>
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<listitem>
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<para>
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Set the number of days of warning before a password change is
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required. The <replaceable>WARN_DAYS</replaceable> option is
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the number of days prior to the password expiring that a user
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will be warned that his/her password is about to expire.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<option>-x</option>, <option>--maxdays</option> <replaceable>MAX_DAYS</replaceable>
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</term>
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<listitem>
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<para>
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Set the maximum number of days a password remains valid. After
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<replaceable>MAX_DAYS</replaceable>, the password is required
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to be changed.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1 id='caveats'>
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<title>CAVEATS</title>
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<para>
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Not all options may be supported. Password complexity checking may
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vary from site to site. The user is urged to select a password as
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complex as he or she feels comfortable with. Users may not be able to
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change their password on a system if NIS is enabled and they are not
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logged into the NIS server.
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</para>
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</refsect1>
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<refsect1 id='configuration' condition="no_pam">
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<title>CONFIGURATION</title>
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<para>
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The following configuration variables in
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<filename>/etc/login.defs</filename> change the behavior of this
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tool:
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</para>
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<variablelist>
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&ENCRYPT_METHOD;
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&MD5_CRYPT_ENAB;
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&OBSCURE_CHECKS_ENAB;
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&PASS_ALWAYS_WARN;
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&PASS_CHANGE_TRIES;
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&PASS_MAX_LEN; <!-- documents also PASS_MIN_LEN -->
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&SHA_CRYPT_MIN_ROUNDS;
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</variablelist>
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</refsect1>
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<refsect1 id='files'>
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<title>FILES</title>
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<variablelist>
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<varlistentry>
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<term><filename>/etc/passwd</filename></term>
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<listitem>
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<para>User account information.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><filename>/etc/shadow</filename></term>
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<listitem>
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<para>Secure user account information.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1 id='exit_values'>
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<title>EXIT VALUES</title>
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<para>
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The <command>passwd</command> command exits with the following values:
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<variablelist>
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<varlistentry>
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<term><replaceable>0</replaceable></term>
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<listitem>
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<para>success</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable>1</replaceable></term>
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<listitem>
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<para>permission denied</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable>2</replaceable></term>
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<listitem>
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<para>invalid combination of options</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable>3</replaceable></term>
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<listitem>
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<para>unexpected failure, nothing done</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable>4</replaceable></term>
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<listitem>
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<para>unexpected failure, <filename>passwd</filename> file missing</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable>5</replaceable></term>
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<listitem>
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<para><filename>passwd</filename> file busy, try again</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable>6</replaceable></term>
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<listitem>
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<para>invalid argument to option</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</para>
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</refsect1>
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<refsect1 id='see_also'>
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<title>SEE ALSO</title>
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<para>
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<citerefentry>
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<refentrytitle>group</refentrytitle><manvolnum>5</manvolnum>
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</citerefentry>,
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<citerefentry>
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<refentrytitle>passwd</refentrytitle><manvolnum>5</manvolnum>
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</citerefentry>,
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<citerefentry>
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<refentrytitle>shadow</refentrytitle><manvolnum>5</manvolnum>
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</citerefentry>.
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</para>
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</refsect1>
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</refentry>
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