| LOGIN(1) | User Commands | LOGIN(1) |
.SH "NAME" login - begin session on the system
.SH "SYNOPSIS"
.HP 144u
login
[-p]
[-h host]
[username]
[ENV=VAR...]
.HP 144u
login
[-p]
[-h host]
-f
username
.HP 144u
login
[-p]
-r host
.SH "DESCRIPTION"
.PP The login program is used to establish a new session with the
system. It is normally invoked automatically by responding to the
login: prompt on the user's terminal. login may be special to
the shell and may not be invoked as a sub-process. When called from a shell,
login should be executed as exec login 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
login from any shell but the login shell will produce an error
message.
.PP 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 login exits and the communications link
is severed.
.PP 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
passwd(1) for more information.
.PP Your user and group ID will be set according to their values in the
/etc/passwd file. The value for $HOME, $SHELL, $PATH,
$LOGNAME, and $MAIL 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.
.PP On some installations, the environmental variable $TERM will be
initialized to the terminal type on your tty line, as specified in
/etc/ttytype.
.PP An initialization script for your command interpreter may also be
executed. Please see the appropriate manual section for more information on
this function.
.PP 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.
.PP The login program is NOT responsible for removing users from the
utmp file. It is the responsibility of getty(8) and init(8) to
clean up apparent ownership of a terminal session. If you use login
from the shell prompt without exec, the user you use will continue to
appear to be logged in even after you log out of the
"subsession".
.SH "OPTIONS"
.PP -f
Do not perform authentication, user is preauthenticated.
Note: in that case, username is mandatory.
.RE
.PP -h
Name of the remote host for this login.
.RE
.PP -p
Preserve environment.
.RE
.PP The -r, -h and -f options are only used when
login is invoked by root.
.SH "CAVEATS"
.PP This version of login has many compilation options, only some of
which may be in use at any particular site.
.PP The location of files is subject to differences in system
configuration.
.PP The login program is NOT responsible for removing users from the
utmp file. It is the responsibility of getty(8) and init(8) to
clean up apparent ownership of a terminal session. If you use login
from the shell prompt without exec, the user you use will continue to
appear to be logged in even after you log out of the
"subsession".
.PP As with any program, login'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.
.SH "CONFIGURATION"
.PP The following configuration variables in /etc/login.defs change the
behavior of this tool:
DEFAULT_HOME (boolean)
Indicate if login is allowed if we can't cd to the home directory. Default is
no.
If set to yes, the user will login in the root (/) directory if it is
not possible to cd to her home directory.
ENV_PATH (string)
If set, it will be used to define the PATH environment variable when a
regular user login. The value is a colon separated list of paths (for
example /bin:/usr/bin) and can be preceded by PATH=. The
default value is PATH=/bin:/usr/bin.
ENV_SUPATH (string)
If set, it will be used to define the PATH environment variable when the
superuser login. The value is a colon separated list of paths (for example
/sbin:/bin:/usr/sbin:/usr/bin) and can be preceded by PATH=.
The default value is PATH=/sbin:/bin:/usr/sbin:/usr/bin.
ERASECHAR (number)
Terminal ERASE character (010 = backspace, 0177 = DEL).
The value can be prefixed "0" for an octal value, or "0x"
for an hexadecimal value.
FAIL_DELAY (number)
Delay in seconds before being allowed another attempt after a login
failure.
FAKE_SHELL (string)
If set, login will execute this shell instead of the users' shell
specified in /etc/passwd.
HUSHLOGIN_FILE (string)
If defined, this file can inhibit all the usual chatter during the login
sequence. If a full pathname is specified, then hushed mode will be enabled
if the user's name or shell are found in the file. If not a full pathname,
then hushed mode will be enabled if the file exists in the user's home
directory.
KILLCHAR (number)
Terminal KILL character (025 = CTRL/U).
The value can be prefixed "0" for an octal value, or "0x"
for an hexadecimal value.
LOGIN_RETRIES (number)
Maximum number of login retries in case of bad password.
This will most likely be overridden by PAM, since the default pam_unix module
has its own built in of 3 retries. However, this is a safe fallback in case
you are using an authentication module that does not enforce
PAM_MAXTRIES.
LOGIN_TIMEOUT (number)
Max time in seconds for login.
LOG_OK_LOGINS (boolean)
Enable logging of successful logins.
LOG_UNKFAIL_ENAB (boolean)
Enable display of unknown usernames when login failures are recorded.
Note: logging unknown usernames may be a security issue if an user enter her
password instead of her login name.
TTYGROUP (string), TTYPERM (number)
The terminal permissions: the login tty will be owned by the TTYGROUP
group, and the permissions will be set to TTYPERM.
TTYGROUP can be either the name of a group or a numeric group
identifier.
If TTYGROUP is not defined, then the group ownership of the terminal is set
to the user's primary group. If TTYPERM is not defined, then the permissions
are set to 0600.
If you have a write program which is "setgid" to a special
group which owns the terminals, define TTYGROUP to the group number and
TTYPERM to 0620. Otherwise leave TTYGROUP commented out and assign TTYPERM
to either 622 or 600.
TTYTYPE_FILE (string)
If defined, file which maps tty line to TERM environment parameter. Each line
of the file is in a format something like "vt100 tty01".
USERGROUPS_ENAB (boolean)
If set to yes, userdel will remove the user's group if it
contains no more members, and useradd will create by default a group
with the name of the user.
.SH "FILES"
.PP /var/run/utmp
List of current login sessions.
.RE
.PP /var/log/wtmp
List of previous login sessions.
.RE
.PP /etc/passwd
User account information.
.RE
.PP /etc/shadow
Secure user account information.
.RE
.PP /etc/motd
System message of the day file.
.RE
.PP /etc/nologin
Prevent non-root users from logging in.
.RE
.PP /etc/ttytype
List of terminal types.
.RE
.PP $HOME/.hushlogin
Suppress printing of system messages.
.RE
.PP /etc/login.defs
Shadow password suite configuration.
.RE
.SH "SEE ALSO"
.PP mail(1), passwd(1), sh(1), su(1),
login.defs(5), nologin(5), passwd(5),
securetty(5), getty(8).
| 10/26/2026 | shadow-utils 4.20.3 |