SYNOPSIS
login [ -p ] [ username ]
login [ -p ] [ -h host ] [ -f username ] host
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 appro
prate. Echoing is disabled to prevent revealing the pass
word. Only a small number of password failures are permit
ted before login exits and the communications link is sev
ered.
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 val
ues in the 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 prevent that the system
adminitrator cannot login in case of network problems.
The value for $HOME, $SHELL, $PATH, $LOGNAME, and $MAIL
are set according to the appropriate fields in the pass
word entry. $PATH defaults to
/usr/local/bin:/bin:/usr/bin:. for normal users, and to
/sbin:/bin:/usr/sbin:/usr/bin for root if not other con
figured. Ulimit, umask and nice values may also be set
according to entries in the GECOS field. The environment
variable $TERM will be preserved, if it exists (other
environment variables are preserved if the -p option is
given) or be initialize to the terminal type on your tty
line, as specified in /etc/ttytype.
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 above).
This login implementation does ignore /etc/nologin and
/etc/securetty. You need to configure this in the PAM
configuration file for login in /etc/pam.d/login.
login reads the /etc/login.defs(5) configuration file.
Please refer to this documenation for options which could
be set.
SPECIAL ACCESS RESTRICTIONS
The file /etc/securetty lists the names of the ttys where
root is allowed to log in. One name of a tty device with
out the /dev/ prefix must be specified on each line. If
the file does not exist, root is allowed to log in on any
tty. You need to add the /lib/security/pam_securetty.so
module in /etc/pam.d/login for activating.
FILES
/var/run/utmp - list of current login sessins
/var/log/wtmp - list of previous login sessions
/var/log/lastlog - list of times of previous user logins
/etc/passwd - user account information
/etc/shadow - encrypted passwords and age information
/etc/motd - system message file
/etc/ttytype - list of terminal types (/etc/login.defs)
SEE ALSO
init(8), getty(8), mail(1), passwd(1), passwd(5), envi
ron(7), shutdown(8), login.defs(5)
BUGS
A recursive login, as used to be possible in the good old
days, no longer works; for most purposes su(1) is a satis
factory substitute. Indeed, for security reasons, login
does a vhangup() system call to remove any possible lis
tening processes on the tty. This is to avoid password
sniffing. If one uses the command "login", then the sur
rounding shell gets killed by vhangup() 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.
AUTHOR
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)
Added new features: Thorsten Kukuk (kukuk@suse.de)
PAM Login 3.8 15. July 2002 LOGIN(1)
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