login man page
login — begin session on the system
login [ -p ] [ -h host ] [ -H ] [ -f username | username ]
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).
Used by getty(8) to tell login not to destroy the environment.
Used to skip a second login authentication. This specifically does not work for root, and does not appear to work well under Linux.
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 impact on the PAM service name. The standard service name is login, 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).
Used by other servers (i.e., telnetd(8)) to tell login that printing the hostname should be suppressed in the login: prompt.
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(1):
- MOTD_FILE (string)
If defined, a ":" delimited list of "message of the day" files to be displayed upon login. The default value is /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 pam_motd(8) PAM module.
- LOGIN_TIMEOUT (number)
Max 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.
- 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. The default value is /usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin
/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
mail(1), passwd(1), passwd(5), environ(7), getty(8), init(8), shutdown(8)
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() 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() 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.
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
The login command is part of the util-linux package and is available from Linux Kernel Archive.
ac(1), agetty(8), bash(1), chsh(1), clogin(1), crypt(3), dash(1), dump-utmp(8), efax(1), environ(7), group(5), in.rlogind(8), in.telnetd(8), intro(1), ksh(1), last(1), login.defs(5), makepasswd(1), mesg(1), mgettydefs(4), motd(5), newgrp(1), nologin(5), nologin(8), openvt(1), pam(3), PAM(8), passwd(5), proc(5), rz(1), securetty(5), sg(1), sge_queue_conf(5), sge_types(1), shadow(5), shellinaboxd(1), systemd.exec(5), ttyslot(3), ul(1), utmp(5).