LOGIN(1) User Commands LOGIN(1)NAMElogin - begin session on the system
SYNOPSISlogin [-p] [-h host] [username] [ENV=VAR...]
login [-p] [-h host] -f username
login [-p] -r host
DESCRIPTION
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.
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 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.
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, /etc/motd, by creating a zero-length file .hushlogin in
your login directory. The mail message will be one of "You have new
mail.", "You have mail.", or "No Mail." according to the condition of
your mailbox.
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.
On some installations, the environmental variable $TERM will be
initialized to the terminal type on your tty line, as specified in
/etc/ttytype.
An initialization script for your command interpreter may also be
executed. Please see the appropriate manual section for more
information on this function.
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.
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".
OPTIONS-f
Do not perform authentication, user is preauthenticated.
Note: In that case, username is mandatory.
-h
Name of the remote host for this login.
-p
Preserve environment.
-r
Perform autologin protocol for rlogin.
The -r, -h and -f options are only used when login is invoked by root.
CAVEATS
This version of login has many compilation options, only some of which
may be in use at any particular site.
The location of files is subject to differences in system
configuration.
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".
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.
CONFIGURATION
The following configuration variables in /etc/login.defs change the
behavior of this tool:
CONSOLE (string)
If defined, either full pathname of a file containing device names
(one per line) or a ":" delimited list of device names. Root logins
will be allowed only upon these devices.
If not defined, root will be allowed on any device.
The device should be specified without the /dev/ prefix.
CONSOLE_GROUPS (string)
List of groups to add to the user's supplementary groups set when
logging in on the console (as determined by the CONSOLE setting).
Default is none.
Use with caution - it is possible for users to gain permanent
access to these groups, even when not logged in on the console.
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_HZ (string)
If set, it will be used to define the HZ environment variable when
a user login. The value must be preceded by HZ=. A common value on
Linux is HZ=100.
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.
ENV_TZ (string)
If set, it will be used to define the TZ environment variable when
a user login. The value can be the name of a timezone preceded by
TZ= (for example TZ=CST6CDT), or the full path to the file
containing the timezone specification (for example /etc/tzname).
If a full path is specified but the file does not exist or cannot
be read, the default is to use TZ=CST6CDT.
ENVIRON_FILE (string)
If this file exists and is readable, login environment will be read
from it. Every line should be in the form name=value.
Lines starting with a # are treated as comment lines and ignored.
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.
FAILLOG_ENAB (boolean)
Enable logging and display of /var/log/faillog login failure info.
FAKE_SHELL (string)
If set, login will execute this shell instead of the users' shell
specified in /etc/passwd.
FTMP_FILE (string)
If defined, login failures will be logged in this file in a utmp
format.
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.
ISSUE_FILE (string)
If defined, this file will be displayed before each login prompt.
KILLCHAR (number)
Terminal KILL character (025 = CTRL/U).
The value can be prefixed "0" for an octal value, or "0x" for an
hexadecimal value.
LASTLOG_ENAB (boolean)
Enable logging and display of /var/log/lastlog login time info.
LOGIN_RETRIES (number)
Maximum number of login retries in case of bad password.
LOGIN_STRING (string)
The string used for prompting a password. The default is to use
"Password: ", or a translation of that string. If you set this
variable, the prompt will not be translated.
If the string contains %s, this will be replaced by the user's
name.
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.
MAIL_CHECK_ENAB (boolean)
Enable checking and display of mailbox status upon login.
You should disable it if the shell startup files already check for
mail ("mailx -e" or equivalent).
MAIL_DIR (string)
The mail spool directory. This is needed to manipulate the mailbox
when its corresponding user account is modified or deleted. If not
specified, a compile-time default is used.
MAIL_FILE (string)
Defines the location of the users mail spool files relatively to
their home directory.
The MAIL_DIR and MAIL_FILE variables are used by useradd, usermod, and
userdel to create, move, or delete the user's mail spool.
If MAIL_CHECK_ENAB is set to yes, they are also used to define the MAIL
environment variable.
MOTD_FILE (string)
If defined, ":" delimited list of "message of the day" files to be
displayed upon login.
NOLOGINS_FILE (string)
If defined, name of file whose presence will inhibit non-root
logins. The contents of this file should be a message indicating
why logins are inhibited.
PORTTIME_CHECKS_ENAB (boolean)
Enable checking of time restrictions specified in /etc/porttime.
QUOTAS_ENAB (boolean)
Enable setting of resource limits from /etc/limits and ulimit,
umask, and niceness from the user's passwd gecos field.
TTYGROUP (string), TTYPERM (string)
The terminal permissions: the login tty will be owned by the
TTYGROUP group, and the permissions will be set to TTYPERM.
By default, the ownership of the terminal is set to the user's
primary group and the permissions are set to 0600.
TTYGROUP can be either the name of a group or a numeric group
identifier.
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".
ULIMIT (number)
Default ulimit value.
UMASK (number)
The file mode creation mask is initialized to this value. If not
specified, the mask will be initialized to 022.
useradd and newusers use this mask to set the mode of the home
directory they create
It is also used by login to define users' initial umask. Note that
this mask can be overridden by the user's GECOS line (if
QUOTAS_ENAB is set) or by the specification of a limit with the K
identifier in limits(5).
USERGROUPS_ENAB (boolean)
Enable setting of the umask group bits to be the same as owner bits
(examples: 022 -> 002, 077 -> 007) for non-root users, if the uid
is the same as gid, and username is the same as the primary group
name.
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.
FILES
/var/run/utmp
List of current login sessions.
/var/log/wtmp
List of previous login sessions.
/etc/passwd
User account information.
/etc/shadow
Secure user account information.
/etc/motd
System message of the day file.
/etc/nologin
Prevent non-root users from logging in.
/etc/ttytype
List of terminal types.
$HOME/.hushlogin
Suppress printing of system messages.
/etc/login.defs
Shadow password suite configuration.
SEE ALSOmail(1), passwd(1), sh(1), su(1), login.defs(5), nologin(5), passwd(5),
securetty(5), getty(8).
shadow-utils 4.1.5.1 05/25/2012 LOGIN(1)
