LOGIN
Section: User Commands (1)
Updated: June 2012
Page Index
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 small number
of password failures are permitted before
login
exits and the communications 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 administrator 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 otherwise configured.
The environment variable
$TERM
will be preserved, if it exists (other environment variables are
preserved if the
-p
option is given), else it will be initialized 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 login authentication. This option is usually
used by the
getty(8)
autologin feature.
- -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 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 (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 the
login
command line to be configured.
- --help
-
Display help text and exit.
- -V, --version
-
Display version information 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:
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.
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.
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 terminal 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 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 her 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.
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 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 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
.hushlogin
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
for HP-UX
Ported to Linux 0.12:
Peter Orbaek
Rewritten to a PAM-only version by
Karel Zak
SEE ALSO
mail(1),
passwd(1),
passwd(5),
utmp(5),
environ(7),
getty(8),
init(8),
lastlog(8)
shutdown(8)
AVAILABILITY
The login command is part of the util-linux package and is
available from
Linux Kernel Archive