CentOS 7.0 - man page for login (centos section 1)

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LOGIN(1)				  User Commands 				 LOGIN(1)

       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

       The user is then prompted for a password, where approprate.  Echoing is disabled  to  pre-
       vent  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 adminitrator 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 other configured.

       The environment variable $TERM will be preserved, if it exists  (other  environment  vari-
       ables  are  preserved  if the -p option is given) or be initialize 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 check-
       ing  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

       -p     Used by getty(8) to tell login not to destroy the environment.

       -f     Used  to	skip  a second login authentication.  This specifically does not work for
	      root, and does not appear to work well under Linux.

       -h     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

	      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 a
	      proper PAM config files (e.g.  /etc/pam.d/login and /etc/pam.d/remote).

       -H     Used by other servers (i.e., telnetd(8)) to tell login that printing  the  hostname
	      should be suppressed in the login: prompt.

       -V     Print version and exit.

       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  configura-
       tion items are relevant for login(1):

       MOTD_FILE (string)
	   If  defined,  ":"  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 quiet login
	   is enabled then the message of the day is not displayed.  Note that the same function-
	   ality 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 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 TTY-
	   GROUP does not exist then the ownership of the terminal is set to the  user's  primary

	   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 not a full pathname is 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 does not exist then ~/.hushlogin

	   If the HUSHLOGIN_FILE item is empty then all checks are disabled.

       DEFAULT_HOME (boolean)
	   Indicate if login is allowed if we can not 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 an user enter her pass-
	   word instead of her login name.

       ENV_PATH (string)
	   If  set,  it  will be used to define the PATH environment variable when a regular user
	   login.  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
	   login.   The default value is /usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr


       init(8), getty(8), mail(1), passwd(1), passwd(5), environ(7), shutdown(8)

       The undocumented BSD -r option is not supported.  This may be required by some  rlogind(8)

       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 <glad@daimi.dk> for HP-UX
       Ported to Linux 0.12: Peter Orbaek <poe@daimi.aau.dk>
       Rewritten to PAM-only version by Karel Zak <kzak@redhat.com>

       The login command is part of the util-linux package and is  available  from  Linux  Kernel
       Archive <ftp://ftp.kernel.org/pub/linux/utils/util-linux/>.

util-linux				    June 2012					 LOGIN(1)
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