#Bash 的 login 命令

LOGIN(1)                         User Commands                        LOGIN(1)

NAME
       login - begin session on the system

SYNOPSIS

       login [-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.

       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_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_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.

       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.

       FAKE_SHELL (string)
           If set, login will execute this shell instead of the users' shell
           specified in /etc/passwd.

       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.

       KILLCHAR (number)
           Terminal KILL character (025 = CTRL/U).

           The value can be prefixed "0" for an octal value, or "0x" for an
           hexadecimal value.

       LOGIN_RETRIES (number)
           Maximum number of login retries in case of bad password.

           This will most likely be overridden by PAM, since the default
           pam_unix module has its own built in of 3 retries. However, this is
           a safe fallback in case you are using an authentication module that
           does not enforce PAM_MAXTRIES.

       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.

       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".

       USERGROUPS_ENAB (boolean)
           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 ALSO
       mail(1), passwd(1), sh(1), su(1), login.defs(5), nologin(5), passwd(5),
       securetty(5), getty(8).

shadow-utils 4.13                 05/30/2024                          LOGIN(1)