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<?xml version="1.0" encoding="UTF-8"?>
<!--
SPDX-FileCopyrightText: 1989 - 1994, Julianne Frances Haugh
SPDX-FileCopyrightText: 2007 - 2009, Nicolas François
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 CONSOLE SYSTEM "login.defs.d/CONSOLE.xml">
<!ENTITY CONSOLE_GROUPS SYSTEM "login.defs.d/CONSOLE_GROUPS.xml">
<!ENTITY DEFAULT_HOME SYSTEM "login.defs.d/DEFAULT_HOME.xml">
<!ENTITY ENV_HZ SYSTEM "login.defs.d/ENV_HZ.xml">
<!ENTITY ENV_PATH SYSTEM "login.defs.d/ENV_PATH.xml">
<!ENTITY ENV_SUPATH SYSTEM "login.defs.d/ENV_SUPATH.xml">
<!ENTITY ENV_TZ SYSTEM "login.defs.d/ENV_TZ.xml">
<!ENTITY ENVIRON_FILE SYSTEM "login.defs.d/ENVIRON_FILE.xml">
<!ENTITY ERASECHAR SYSTEM "login.defs.d/ERASECHAR.xml">
<!ENTITY FAIL_DELAY SYSTEM "login.defs.d/FAIL_DELAY.xml">
<!ENTITY FAILLOG_ENAB SYSTEM "login.defs.d/FAILLOG_ENAB.xml">
<!ENTITY FAKE_SHELL SYSTEM "login.defs.d/FAKE_SHELL.xml">
<!ENTITY FTMP_FILE SYSTEM "login.defs.d/FTMP_FILE.xml">
<!ENTITY HUSHLOGIN_FILE SYSTEM "login.defs.d/HUSHLOGIN_FILE.xml">
<!ENTITY ISSUE_FILE SYSTEM "login.defs.d/ISSUE_FILE.xml">
<!ENTITY KILLCHAR SYSTEM "login.defs.d/KILLCHAR.xml">
<!ENTITY LASTLOG_ENAB SYSTEM "login.defs.d/LASTLOG_ENAB.xml">
<!ENTITY LOGIN_RETRIES SYSTEM "login.defs.d/LOGIN_RETRIES.xml">
<!ENTITY LOGIN_STRING SYSTEM "login.defs.d/LOGIN_STRING.xml">
<!ENTITY LOGIN_TIMEOUT SYSTEM "login.defs.d/LOGIN_TIMEOUT.xml">
<!ENTITY LOG_OK_LOGINS SYSTEM "login.defs.d/LOG_OK_LOGINS.xml">
<!ENTITY LOG_UNKFAIL_ENAB SYSTEM "login.defs.d/LOG_UNKFAIL_ENAB.xml">
<!ENTITY MAIL_CHECK_ENAB SYSTEM "login.defs.d/MAIL_CHECK_ENAB.xml">
<!ENTITY MAIL_DIR SYSTEM "login.defs.d/MAIL_DIR.xml">
<!ENTITY MOTD_FILE SYSTEM "login.defs.d/MOTD_FILE.xml">
<!ENTITY NOLOGINS_FILE SYSTEM "login.defs.d/NOLOGINS_FILE.xml">
<!ENTITY PORTTIME_CHECKS_ENAB SYSTEM "login.defs.d/PORTTIME_CHECKS_ENAB.xml">
<!ENTITY QUOTAS_ENAB SYSTEM "login.defs.d/QUOTAS_ENAB.xml">
<!ENTITY TTYGROUP SYSTEM "login.defs.d/TTYGROUP.xml">
<!ENTITY TTYTYPE_FILE SYSTEM "login.defs.d/TTYTYPE_FILE.xml">
<!ENTITY ULIMIT SYSTEM "login.defs.d/ULIMIT.xml">
<!ENTITY UMASK SYSTEM "login.defs.d/UMASK.xml">
<!ENTITY USERGROUPS_ENAB SYSTEM "login.defs.d/USERGROUPS_ENAB.xml">
<!-- SHADOW-CONFIG-HERE -->
]>
<refentry id='login.1'>
<!-- $Id$ -->
<refentryinfo>
<author>
<firstname>Julianne Frances</firstname>
<surname>Haugh</surname>
<contrib>Creation, 1989</contrib>
</author>
<author>
<firstname>Thomas</firstname>
<surname>Kłoczko</surname>
<email>kloczek@pld.org.pl</email>
<contrib>shadow-utils maintainer, 2000 - 2007</contrib>
</author>
<author>
<firstname>Nicolas</firstname>
<surname>François</surname>
<email>nicolas.francois@centraliens.net</email>
<contrib>shadow-utils maintainer, 2007 - now</contrib>
</author>
</refentryinfo>
<refmeta>
<refentrytitle>login</refentrytitle>
<manvolnum>1</manvolnum>
<refmiscinfo class="sectdesc">User Commands</refmiscinfo>
<refmiscinfo class="source">shadow-utils</refmiscinfo>
<refmiscinfo class="version">&SHADOW_UTILS_VERSION;</refmiscinfo>
</refmeta>
<refnamediv id='name'>
<refname>login</refname>
<refpurpose>begin session on the system</refpurpose>
</refnamediv>
<!-- body begins here -->
<refsynopsisdiv id='synopsis'>
<cmdsynopsis>
<command>login</command>
<arg choice='opt'>-p</arg>
<arg choice='opt'>-h <replaceable>host</replaceable></arg>
<arg choice='opt'>
<replaceable>username</replaceable></arg>
<arg choice='opt' rep='repeat'> <replaceable>ENV=VAR</replaceable></arg>
</cmdsynopsis>
<cmdsynopsis>
<command>login</command>
<arg choice='opt'>-p</arg>
<arg choice='opt'>-h <replaceable>host</replaceable></arg>
<arg choice='plain'>-f</arg>
<arg choice='plain'><replaceable>username</replaceable></arg>
</cmdsynopsis>
<cmdsynopsis>
<command>login</command>
<arg choice='opt'>-p</arg>
<arg choice='plain'>-r <replaceable>host</replaceable></arg>
</cmdsynopsis>
</refsynopsisdiv>
<refsect1 id='description'>
<title>DESCRIPTION</title>
<para>
The <command>login</command> program is used to establish a new session
with the system. It is normally invoked automatically by responding to
the <emphasis remap='I'>login:</emphasis> prompt on the user's
terminal. <command>login</command> may be special to the shell and may
not be invoked as a sub-process. When called from a shell,
<command>login</command> should be executed as
<emphasis remap='B'>exec login</emphasis> which will cause the user
to exit from the current shell (and thus will prevent the new logged
in user to return to the session of the caller). Attempting to
execute <command>login</command> from any shell but the login shell
will produce an error message.
</para>
<para>
The user is then prompted for a password, where appropriate. Echoing
is disabled to prevent revealing the password. Only a small number of
password failures are permitted before <command>login</command> exits
and the communications link is severed.
</para>
<para>
If password aging has been enabled for your account, you may be
prompted for a new password before proceeding. You will be forced to
provide your old password and the new password before continuing.
Please refer to <citerefentry>
<refentrytitle>passwd</refentrytitle><manvolnum>1</manvolnum>
</citerefentry> for more information.
</para>
<para condition="no_pam">
After a successful login, you will be informed of any system messages
and the presence of mail. You may turn off the printing of the system
message file, <filename>/etc/motd</filename>, by creating a
zero-length file <filename>.hushlogin</filename> in your login directory.
The mail message will be one of "<emphasis>You have new
mail.</emphasis>", "<emphasis>You have mail.</emphasis>", or
"<emphasis>No Mail.</emphasis>" according to the condition of your
mailbox.
</para>
<para>
Your user and group ID will be set according to their values in the
<filename>/etc/passwd</filename> file. The value for
<envar>$HOME</envar>, <envar>$SHELL</envar>, <envar>$PATH</envar>,
<envar>$LOGNAME</envar>, and <envar>$MAIL</envar> are set according
to the appropriate fields in the password entry. Ulimit, umask and nice
values may also be set according to entries in the GECOS field.
</para>
<para>
On some installations, the environmental variable
<envar>$TERM</envar> will be initialized to the terminal type on
your tty line, as specified in <filename>/etc/ttytype</filename>.
</para>
<para>
An initialization script for your command interpreter may also be
executed. Please see the appropriate manual section for more
information on this function.
</para>
<para>
A subsystem login is indicated by the presence of a "*" as the first
character of the login shell. The given home directory will be used as
the root of a new file system which the user is actually logged into.
</para>
<para>
The <command>login</command> program is NOT responsible for removing
users from the utmp file. It is the responsibility of
<citerefentry><refentrytitle>getty</refentrytitle>
<manvolnum>8</manvolnum></citerefentry> and
<citerefentry><refentrytitle>init</refentrytitle>
<manvolnum>8</manvolnum></citerefentry> to clean up apparent ownership
of a terminal session. If you use <command>login</command> from the
shell prompt without <command>exec</command>, the user you use will
continue to appear to be logged in even after you log out of the
"subsession".
</para>
</refsect1>
<refsect1 id='options'>
<title>OPTIONS</title>
<variablelist remap='IP'>
<varlistentry>
<term>
<option>-f</option>
</term>
<listitem>
<para>
Do not perform authentication, user is preauthenticated.
</para>
<para>
Note: In that case, <replaceable>username</replaceable> is
mandatory.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<option>-h</option>
</term>
<listitem>
<para>Name of the remote host for this login.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<option>-p</option>
</term>
<listitem>
<para>Preserve environment.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<option>-r</option>
</term>
<listitem>
<para>Perform autologin protocol for rlogin.</para>
</listitem>
</varlistentry>
</variablelist>
<para>
The <option>-r</option>, <option>-h</option> and <option>-f</option>
options are only used when <command>login</command> is invoked by
root.
</para>
</refsect1>
<refsect1 id='caveats'>
<title>CAVEATS</title>
<para>
This version of <command>login</command> has many compilation options,
only some of which may be in use at any particular site.
</para>
<para>The location of files is subject to differences in system
configuration.
</para>
<para>
The <command>login</command> program is NOT responsible for removing
users from the utmp file. It is the responsibility of <citerefentry>
<refentrytitle>getty</refentrytitle><manvolnum>8</manvolnum>
</citerefentry> and <citerefentry>
<refentrytitle>init</refentrytitle><manvolnum>8</manvolnum>
</citerefentry> to clean up apparent ownership of a terminal session.
If you use <command>login</command> from the shell prompt without
<command>exec</command>, the user you use will continue to appear to
be logged in even after you log out of the "subsession".
</para>
<para>
As with any program, <command>login</command>'s appearance can be faked.
If non-trusted users have physical access to a machine, an
attacker could use this to obtain the password of the next person
coming to sit in front of the machine. Under Linux, the SAK mechanism can be
used by users to initiate a trusted path and prevent this kind of
attack.
</para>
</refsect1>
<refsect1 id='configuration'>
<title>CONFIGURATION</title>
<para>
The following configuration variables in
<filename>/etc/login.defs</filename> change the behavior of this
tool:
</para>
<variablelist>
&CONSOLE;
&CONSOLE_GROUPS;
&DEFAULT_HOME;
<phrase condition="no_pam">&ENV_HZ;</phrase>
<phrase>&ENV_PATH;</phrase>
<phrase>&ENV_SUPATH;</phrase>
&ENV_TZ;
&ENVIRON_FILE;
&ERASECHAR;
&FAIL_DELAY;
&FAILLOG_ENAB;
&FAKE_SHELL;
&FTMP_FILE;
&HUSHLOGIN_FILE;
&ISSUE_FILE;
&KILLCHAR;
&LASTLOG_ENAB;
&LOGIN_RETRIES;
&LOGIN_STRING;
&LOGIN_TIMEOUT;
&LOG_OK_LOGINS;
&LOG_UNKFAIL_ENAB;
&MAIL_CHECK_ENAB;
<phrase condition="no_pam">&MAIL_DIR;</phrase>
&MOTD_FILE;
&NOLOGINS_FILE;
&PORTTIME_CHECKS_ENAB;
&QUOTAS_ENAB;
&TTYGROUP; <!-- documents also TTYPERM -->
&TTYTYPE_FILE;
&ULIMIT;
<phrase condition="no_pam">&UMASK;</phrase>
&USERGROUPS_ENAB;
</variablelist>
</refsect1>
<refsect1 id='files'>
<title>FILES</title>
<variablelist>
<varlistentry>
<term><filename>/var/run/utmp</filename></term>
<listitem>
<para>List of current login sessions.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><filename>/var/log/wtmp</filename></term>
<listitem>
<para>List of previous login sessions.</para>
</listitem>
</varlistentry>
<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>
<term><filename>/etc/motd</filename></term>
<listitem>
<para>System message of the day file.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><filename>/etc/nologin</filename></term>
<listitem>
<para>Prevent non-root users from logging in.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><filename>/etc/ttytype</filename></term>
<listitem>
<para>List of terminal types.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><filename>$HOME/.hushlogin</filename></term>
<listitem>
<para>Suppress printing of system messages.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><filename>/etc/login.defs</filename></term>
<listitem>
<para>Shadow password suite configuration.</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1 id='see_also'>
<title>SEE ALSO</title>
<para>
<citerefentry>
<refentrytitle>mail</refentrytitle><manvolnum>1</manvolnum>
</citerefentry>,
<citerefentry>
<refentrytitle>passwd</refentrytitle><manvolnum>1</manvolnum>
</citerefentry>,
<citerefentry>
<refentrytitle>sh</refentrytitle><manvolnum>1</manvolnum>
</citerefentry>,
<citerefentry>
<refentrytitle>su</refentrytitle><manvolnum>1</manvolnum>
</citerefentry>,
<citerefentry>
<refentrytitle>login.defs</refentrytitle><manvolnum>5</manvolnum>
</citerefentry>,
<citerefentry>
<refentrytitle>nologin</refentrytitle><manvolnum>5</manvolnum>
</citerefentry>,
<citerefentry>
<refentrytitle>passwd</refentrytitle><manvolnum>5</manvolnum>
</citerefentry>,
<citerefentry>
<refentrytitle>securetty</refentrytitle><manvolnum>5</manvolnum>
</citerefentry>,
<citerefentry>
<refentrytitle>getty</refentrytitle><manvolnum>8</manvolnum>
</citerefentry>.
</para>
</refsect1>
</refentry>
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