login-utils/login.1

.\" Copyright 1993 Rickard E. Faith (faith@cs.unc.edu)
.\" May be distributed under the GNU General Public License
.TH LOGIN "1" "June 2012" "util-linux" "User Commands"
.SH NAME
login \- begin session on the system
.SH SYNOPSIS
.B login
[
.BR \-p
] [
.BR \-h
.IR host
] [
.BR \-H
] [
.BR \-f
.IR username
|
.IR username
]
.SH DESCRIPTION
.B login
is used when signing onto a system.  If no argument is given,
.B login
prompts for the username.
.PP
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
.B login
exits and the communications link is severed.
.PP
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
.BR passwd (1)
for more information.
.PP
The user and group ID will be set according to their values in the
.I /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
.BR $HOME ,
.BR $USER ,
.BR $SHELL ,
.BR $PATH ,
.BR $LOGNAME ,
and
.B $MAIL
are set according to the appropriate fields in the password entry.
.B $PATH
defaults to
.I /usr\:/local\:/bin:\:/bin:\:/usr\:/bin
for normal users, and to
.I /usr\:/local\:/sbin:\:/usr\:/local\:/bin:\:/sbin:\:/bin:\:/usr\:/sbin:\:/usr\:/bin
for root, if not otherwise configured.
.P
The environment variable
.B $TERM
will be preserved, if it exists (other environment variables are
preserved if the
.B \-p
option is given), else it will be initialized to the terminal type on your tty.
.PP
Then the user's shell is started.  If no shell is specified for the
user in
.BR /etc\:/passwd ,
then
.B /bin\:/sh
is used.  If there is no directory specified in
.IR /etc\:/passwd ,
then
.I /
is used (the home directory is checked for the
.I .hushlogin
file described below).
.PP
If the file
.I .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
.I /var\:/log\:/lastlog
exists, the last login time is printed (and the current login is
recorded).
.SH OPTIONS
.TP
.B \-p
Used by
.BR getty (8)
to tell
.B login
not to destroy the environment.
.TP
.B \-f
Used to skip a second login authentication.  This specifically does
.B not
work for root, and does not appear to work well under Linux.
.TP
.B \-h
Used by other servers (i.e.,
.BR telnetd (8))
to pass the name of the remote host to
.B login
so that it may be placed in utmp and wtmp.  Only the superuser may
use this option.
.IP
Note that the
.B \-h
option has impact on the
.B PAM service
.BR name .
The standard service name is
.IR login ,
with the
.B \-h
option the name is
.IR remote .
It is necessary to create proper PAM config files (e.g.
.I /etc\:/pam.d\:/login
and
.IR /etc\:/pam.d\:/remote ).
.TP
.B \-H
Used by other servers (i.e.,
.BR telnetd (8))
to tell
.B login
that printing the hostname should be suppressed in the login: prompt.
.TP
.B \-V
Display version information and exit.
.SH CONFIG FILE ITEMS
.B login
reads the
.IR /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
.BR login (1):
.PP
.B MOTD_FILE
(string)
.RS 4
If defined, a ":" delimited list of "message of the day" files to be
displayed upon login.  The default value is
.IR /etc\:/motd .
If the
.B 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
.BR pam_motd (8)
PAM module.
.RE
.PP
.B LOGIN_TIMEOUT
(number)
.RS 4
Max time in seconds for login.  The default value is
.IR 60 .
.RE
.PP
.B LOGIN_RETRIES
(number)
.RS 4
Maximum number of login retries in case of a bad password.  The default
value is
.IR 3 .
.RE
.PP
.B FAIL_DELAY
(number)
.RS 4
Delay in seconds before being allowed another three tries after a
login failure.  The default value is
.IR 5 .
.RE
.PP
.B TTYPERM
(string)
.RS 4
The terminal permissions.  The default value is
.IR 0600
or
.IR 0620
if tty group is used.
.RE
.PP
.B TTYGROUP
(string)
.RS 4
The login tty will be owned by the
.BR TTYGROUP .
The default value is
.IR tty .
If the
.B TTYGROUP
does not exist, then the ownership of the terminal is set to the
user\'s primary group.
.PP
The
.B TTYGROUP
can be either the name of a group or a numeric group identifier.
.RE
.PP
.B HUSHLOGIN_FILE
(string)
.RS 4
If defined, this file can inhibit all the usual chatter during the
login sequence.  If a full pathname (e.g.
.IR /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.
.PP
If a full pathname is not specified, then hushed mode will be enabled
if the file exists in the user\'s home directory.
.PP
The default is to check
.I /etc\:/hushlogins
and if it does not exist then
.I ~/.hushlogin
.PP
If the
.B HUSHLOGIN_FILE
item is empty, then all the checks are disabled.
.RE
.PP
.B DEFAULT_HOME
(boolean)
.RS 4
Indicate if login is allowed if we can not change directory to the
home directory.  If set to
.IR yes ,
the user will login in the root (/) directory if it is not possible
to change directory to her home.  The default value is
.IR yes .
.RE
.PP
.B LOG_UNKFAIL_ENAB
(boolean)
.RS 4
Enable display of unknown usernames when login failures are recorded.
The default value is
.IR no .
.PP
Note that logging unknown usernames may be a security issue if a
user enters her password instead of her login name.
.RE
.PP
.B ENV_PATH
(string)
.RS 4
If set, it will be used to define the PATH environment variable when
a regular user logs in.  The default value is
.I /usr\:/local\:/bin:\:/bin:\:/usr\:/bin
.RE
.PP
.B ENV_ROOTPATH
(string)
.br
.B ENV_SUPATH
(string)
.RS 4
If set, it will be used to define the PATH environment variable when
the superuser logs in.  The default value is
.I /usr\:/local\:/sbin:\:/usr\:/local\:/bin:\:/sbin:\:/bin:\:/usr\:/sbin:\:/usr\:/bin
.RE
.SH FILES
.nf
.I /var/run/utmp
.I /var/log/wtmp
.I /var/log/lastlog
.I /var/spool/mail/*
.I /etc/motd
.I /etc/passwd
.I /etc/nologin
.I /etc/pam.d/login
.I /etc/pam.d/remote
.I /etc/hushlogins
.I .hushlogin
.fi
.SH "SEE ALSO"
.BR init (8),
.BR getty (8),
.BR mail (1),
.BR passwd (1),
.BR passwd (5),
.BR environ (7),
.BR shutdown (8)
.SH BUGS
The undocumented BSD
.B \-r
option is not supported.  This may be required by some
.BR rlogind (8)
programs.
.PP
A recursive login, as used to be possible in the good old days, no
longer works; for most purposes
.BR 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
.BR 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
.B exec login
in a top-level shell or xterm.
.SH AUTHOR
Derived from BSD login 5.40 (5/9/89) by
.MT glad@\:daimi.\:dk
Michael Glad
.ME
for HP-UX
.br
Ported to Linux 0.12:
.MT poe@\:daimi.\:aau.\:dk
Peter Orbaek
.ME
.br
Rewritten to a PAM-only version by
.MT kzak@\:redhat.\:com
Karel Zak
.ME
.SH AVAILABILITY
The login command is part of the util-linux package and is
available from
.UR ftp:\://ftp.kernel.org\:/pub\:/linux\:/utils\:/util-linux/
Linux Kernel Archive
.UE .