LOGIN(1) User Commands LOGIN(1)
NAME
login - begin session on the system
SYNOPSIS
login [ -p ] [ -h host ] [ -H ] [ -f username | username ]
DESCRIPTION
login is used when signing onto a system. If no argument is given,
login prompts for the username.
The user is then prompted for a password, where approprate. Echoing is
disabled to prevent revealing the password. Only a small number of
password failures are permitted before login exits and the communica-
tions link is severed.
If password aging has been enabled for the account, the user may be
prompted for a new password before proceeding. He will be forced to
provide his old password and the new password before continuing.
Please refer to passwd(1) for more information.
The user and group ID will be set according to their values in the
/etc/passwd file. There is one exception if the user ID is zero: in
this case, only the primary group ID of the account is set. This
should allow the system adminitrator to login even in case of network
problems. The value for $HOME, $USER, $SHELL, $PATH, $LOGNAME, and
$MAIL are set according to the appropriate fields in the password
entry. $PATH defaults to /usr/local/bin:/bin:/usr/bin for normal
users, and to /usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr
/bin for root if not other configured.
The environment variable $TERM will be preserved, if it exists (other
environment variables are preserved if the -p option is given) or be
initialize to the terminal type on your tty.
Then the user's shell is started. If no shell is specified for the
user in /etc/passwd, then /bin/sh is used. If there is no directory
specified in /etc/passwd, then / is used (the home directory is checked
for the .hushlogin file described below).
If the file .hushlogin exists, then a "quiet" login is performed (this
disables the checking of mail and the printing of the last login time
and message of the day). Otherwise, if /var/log/lastlog exists, the
last login time is printed (and the current login is recorded).
OPTIONS
-p Used by getty(8) to tell login not to destroy the environment.
-f Used to skip a second login authentication. This specifically
does not work for root, and does not appear to work well under
Linux.
-h Used by other servers (i.e., telnetd(8)) to pass the name of the
remote host to login so that it may be placed in utmp and wtmp.
Only the superuser may use this option.
Note that the -h option has impact on the PAM service name. The
standard service name is login, with the -h option the name is
remote. It is necessary to create a proper PAM config files
(e.g. /etc/pam.d/login and /etc/pam.d/remote).
-H Used by other servers (i.e., telnetd(8)) to tell login that
printing the hostname should be suppressed in the login: prompt.
See also LOGIN_PLAIN_PROMPT below if your server does not allow
to configure login command line.
-V Print version and exit.
CONFIG FILE ITEMS
login reads the /etc/login.defs(5) configuration file. Note that the
configuration file could be distributed with another package (e.g.
shadow-utils). The following configuration items are relevant for
login(1):
MOTD_FILE (string)
If defined, ":" delimited list of "message of the day" files to be
displayed upon login. The default value is /etc/motd. If the
MOTD_FILE item is empty or quiet login is enabled then the message
of the day is not displayed. Note that the same functionality is
also provided by pam_motd(8) PAM module.
LOGIN_PLAIN_PROMPT (boolean)
Tell login that printing the hostname should be suppressed in the
login: prompt. This is alternative to the -H command line option.
The default value is no.
LOGIN_TIMEOUT (number)
Max time in seconds for login. The default value is 60.
LOGIN_RETRIES (number)
Maximum number of login retries in case of bad password. The
default value is 3.
FAIL_DELAY (number)
Delay in seconds before being allowed another three tries after a
login failure. The default value is 5.
TTYPERM (string)
The terminal permissions. The default value is 0600 or 0620 if tty
group is used.
TTYGROUP (string)
The login tty will be owned by the TTYGROUP. The default value is
tty. If the TTYGROUP does not exist then the ownership of the ter-
minal is set to the user's primary group.
The TTYGROUP can be either the name of a group or a numeric group
identifier.
HUSHLOGIN_FILE (string)
If defined, this file can inhibit all the usual chatter during the
login sequence. If a full pathname (e.g. /etc/hushlogins) is
specified, then hushed mode will be enabled if the user's name or
shell are found in the file. If this global hush login file is
empty then the hushed mode will be enabled for all users.
If not a full pathname is specified, then hushed mode will be
enabled if the file exists in the user's home directory.
The default is to check /etc/hushlogins and if does not exist then
~/.hushlogin
If the HUSHLOGIN_FILE item is empty then all checks are disabled.
DEFAULT_HOME (boolean)
Indicate if login is allowed if we can not change directory to the
home directory. If set to yes, the user will login in the root (/)
directory if it is not possible to change directory to her home.
The default value is yes.
LOG_UNKFAIL_ENAB (boolean)
Enable display of unknown usernames when login failures are
recorded. The default value is no.
Note that logging unknown usernames may be a security issue if an
user enter her password instead of her login name.
ENV_PATH (string)
If set, it will be used to define the PATH environment variable
when a regular user login. The default value is /usr/local/bin:
/bin:/usr/bin
ENV_ROOTPATH (string)
ENV_SUPATH (string)
If set, it will be used to define the PATH environment variable
when the superuser login. The default value is /usr/local/sbin:
/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin
FILES
/var/run/utmp
/var/log/wtmp
/var/log/lastlog
/var/spool/mail/*
/etc/motd
/etc/passwd
/etc/nologin
/etc/pam.d/login
/etc/pam.d/remote
/etc/hushlogins
.hushlogin
SEE ALSO
init(8), getty(8), mail(1), passwd(1), passwd(5), environ(7), shut-
down(8)
BUGS
The undocumented BSD -r option is not supported. This may be required
by some rlogind(8) programs.
A recursive login, as used to be possible in the good old days, no
longer works; for most purposes su(1) is a satisfactory substitute.
Indeed, for security reasons, login does a vhangup() system call to
remove any possible listening processes on the tty. This is to avoid
password sniffing. If one uses the command login, then the surrounding
shell gets killed by vhangup() because it's no longer the true owner of
the tty. This can be avoided by using exec login in a top-level shell
or xterm.
AUTHOR
Derived from BSD login 5.40 (5/9/89) by Michael Glad <glad AT daimi.dk>
for HP-UX
Ported to Linux 0.12: Peter Orbaek <poe AT daimi.dk>
Rewritten to PAM-only version by Karel Zak <kzak AT redhat.com>
AVAILABILITY
The login command is part of the util-linux package and is available
from Linux Kernel Archive <ftp://ftp.kernel.org/pub/linux/utils/util-
linux/>.
util-linux June 2012 LOGIN(1)
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