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 appropriate. Echoing is
disabled to prevent revealing the password. Only a number of password
failures are permitted before login exits and the communications link is
severed. See LOGIN_RETRIES in the CONFIG FILE ITEMS section.
If password aging has been enabled for the account, the user may be
prompted for a new password before proceeding. In such case old password
must be provided and the new password entered 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 administrator to login even in case of network problems. The
environment variable values 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 otherwise configured.
The environment variable $TERM will be preserved, if it exists, else it
will be initialized to the terminal type on your tty. Other environment
variables are preserved if the -p option is given.
The environment variables defined by PAM are always preserved.
Then the user’s shell is started. If no shell is specified for the user
in /etc/passwd, then /bin/sh is used. If the specified shell contains a
space, it is treated as a shell script. If there is no home directory
specified in /etc/passwd, then / is used, followed by .hushlogin check
as 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 to preserve the environment. See also
LOGIN_ENV_SAFELIST config file item.
-f
Used to skip a login authentication. This option is usually used by
the getty(8) autologin feature.
-h
Used by other servers (such as telnetd(8) to pass the name of the
remote host to login so that it can be placed in utmp and wtmp. Only
the superuser is allowed use this option.
Note that the -h option has an impact on the PAM service name. The
standard service name is login, but with the -h option, the name is
remote. It is necessary to create proper PAM config files (for
example, /etc/pam.d/login and /etc/pam.d/remote).
-H
Used by other servers (for example, telnetd(8)) to tell login that
printing the hostname should be suppressed in the login: prompt. See
also LOGIN_PLAIN_PROMPT below.
-h, --help
Display help text and exit.
-V, --version
Display version and exit.
CONFIG FILE ITEMS
login reads the /etc/login.defs configuration file (see login.defs(5)).
Note that the configuration file could be distributed with another
package (usually shadow-utils). The following configuration items are
relevant for login:
MOTD_FILE (string)
Specifies a ":" delimited list of "message of the day" files and
directories to be displayed upon login. If the specified path is a
directory then displays all files with .motd file extension in
version-sort order from the directory.
The default value is /usr/share/misc/motd:/run/motd:/etc/motd. If
the MOTD_FILE item is empty or a quiet login is enabled, then the
message of the day is not displayed. Note that the same
functionality is also provided by the pam_motd(8) PAM module.
The directories in the MOTD_FILE are supported since version 2.36.
Note that login does not implement any filenames overriding behavior
like pam_motd (see also MOTD_FIRSTONLY), but all content from all
files is displayed. It is recommended to keep extra logic in content
generators and use /run/motd.d rather than rely on overriding
behavior hardcoded in system tools.
MOTD_FIRSTONLY (boolean)
Forces login to stop display content specified by MOTD_FILE after
the first accessible item in the list. Note that a directory is one
item in this case. This option allows login semantics to be
configured to be more compatible with pam_motd. The default value is
no.
LOGIN_ENV_SAFELIST (string)
Forces login to protect the specified environment variables if -p is
not used. The string value is a comma-separated list of variable
names. For example: "LANG,LC_MESSAGES,LC_COLLATE". The safelist is
ignored for the environment variables HOME, SHELL and USER.
LOGIN_PLAIN_PROMPT (boolean)
Tell login that printing the hostname should be suppressed in the
login: prompt. This is an alternative to the -H command line option.
The default value is no.
LOGIN_TIMEOUT (number)
Maximum time in seconds for login. The default value is 60.
LOGIN_RETRIES (number)
Maximum number of login retries in case of a bad password. The
default value is 3.
LOGIN_KEEP_USERNAME (boolean)
Tell login to only re-prompt for the password if authentication
failed, but the username is valid. The default value is no.
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. See also mesg(1).
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
terminal is set to the user’s primary group.
The TTYGROUP can be either the name of a group or a numeric group
identifier. See also mesg(1).
HUSHLOGIN_FILE (string)
If defined, this file can inhibit all the usual chatter during the
login sequence. If a full pathname (for example, /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 a full pathname is not 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 it does not exist
then ~/.hushlogin.
If the HUSHLOGIN_FILE item is empty, then all the checks are
disabled.
DEFAULT_HOME (boolean)
Indicate if login is allowed if we cannot 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 their home.
The default value is yes.
LASTLOG_UID_MAX (unsigned number)
Highest user ID number for which the lastlog entries should be
updated. As higher user IDs are usually tracked by remote user
identity and authentication services there is no need to create a
huge sparse lastlog file for them. No LASTLOG_UID_MAX option present
in the configuration means that there is no user ID limit for
writing lastlog entries. The default value is ULONG_MAX.
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 a
user enters their password instead of their login name.
ENV_PATH (string)
If set, it will be used to define the PATH environment variable when
a regular user logs in. 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 logs in. ENV_ROOTPATH takes precedence. 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, $HOME/.hushlogin
CREDENTIALS
login supports configuration via systemd credentials (see
https://systemd.io/CREDENTIALS/). login reads the following systemd
credentials:
login.noauth (boolean)
If set, configures login to skip login authentication, similarly to
the -f option.
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(2) 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(2) 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.
AUTHORS
Derived from BSD login 5.40 (5/9/89) by Michael Glad <glad@daimi.dk> for
HP-UX. Ported to Linux 0.12: Peter Orbaek <poe@daimi.aau.dk>. Rewritten
to a PAM-only version by Karel Zak <kzak@redhat.com>
SEE ALSO
mail(1), passwd(1), passwd(5), utmp(5), environ(7), getty(8), init(8),
lastlog(8), shutdown(8)
REPORTING BUGS
For bug reports, use the issue tracker
<https://github.com/util-linux/util-linux/issues>.
AVAILABILITY
The login command is part of the util-linux package which can be
downloaded from Linux Kernel Archive
<https://www.kernel.org/pub/linux/utils/util-linux/>.
util-linux 2.41 2025-02-26 LOGIN(1)
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