vlock: tty session lock program

If we want to lock current virtual console without logout.we can use vlock to lock console and use it like the situation follow.

jerry@jerry-P5Q-office:~$ vlock

This TTY is now locked.

Please press [ENTER] to unlock.
jerry's Password:
jerry@jerry-P5Q-office:~$

man of vlock

VLOCK(1)                                      Linux User's Manual                                     VLOCK(1)

NAME
       vlock - Virtual Console lock program

SYNOPSIS
       vlock [ -hv ]

       vlock [ -acns ] [ -t <timeout> ] [ plugins... ]

DESCRIPTION
       vlock  is  a  program to lock one or more sessions on the Linux console.  This is especially useful for
       Linux machines which have multiple users with access to the console.  One user may lock his or her ses‐
       sion(s)  while still allowing other users to use the system on other virtual consoles.  If desired, the
       entire console may be locked and virtual console switching disabled.

       By default, only the current VC (virtual console) is locked.  With the  -a,--all  option  all  VCs  are
       locked.   The  locked  VCs cannot be unlocked without the invoker's password or the root password.  The
       root password will always be able to unlock any or all sessions, unless disabled at compile time.

       Please note that it is entirely possible to completely lock  yourself  out  of  the  console  with  the
       -a,--all  option if you cannot remember your password!  Unless you are able to kill vlock by logging in
       remotely via a serial terminal or network, a hard reset is the only method of  ``unlocking''  the  dis‐
       play.

       When  locking  the entire console display it is sometimes still possible to kill vlock using the Secure
       Access Key (SAK) or other commands that are available through the SysRq mechanism.  When the  -s,--dis‐
       able-sysrq  and -a,--all options are given the SysRq mechanism is disabled while vlock is running.  See
       /usr/src/linux/Documentation/sysrq.txt for more details.

       vlock works for console sessions primarily.  To lock the entire console display from an X  session  use
       the -n,--new option.  This will make vlock switch to an empty virtual console to lock the display.

       The  options  -n,--new, -s,--disable-sysrq, and -t,--timeout only work if vlock is compiled with plugin
       support.  See the PLUGINS section for more information.

OPTIONS
       -a,--all

              Lock all console sessions and disable VC switching.

       -c,--current

              Lock the current session (this is the default).

       -n,--new

              Switch to a new virtual console before locking all console sessions.

       -s,--disable-sysrq

              Disable the SysRq mechanism while consoles are locked.  This option only works if  the  -a,--all
              option given.

       -t,--timeout <seconds>

              Specify the timeout for the screensaver plugins.  See vlock-plugins(5) for more information.

       -h,--help

              Print a brief help message.

       -v,--version

              Print the version number.

ENVIRONMENT VARIABLES
       The following environment variables can be used to change vlock's behavior:

       USER

              If  this  variable  is  when  vlock  is  run as root (uid 0) vlock locks the screen as this user
              instead of root.  The root password will still be able to unlock the session, unless disabled at
              compile time.

       VLOCK_ALL_MESSAGE

              If  this  variable  is  set and all consoles are locked its contents will be used as the locking
              message instead of the default message.

       VLOCK_CURRENT_MESSAGE

              If this variable is set and only the current consoles is locked its contents will be used as the
              locking message instead of the default message.

       VLOCK_MESSAGE

              If this variable is set its contents will be used as the locking message instead of the default.
              This overrides the former two variables.

       VLOCK_PLUGINS

              If this variable is set it is interpreted as a space separated list  of  plugins  that  will  be
              loaded when vlock starts additionally to the ones listed on the command line.

       VLOCK_TIMEOUT

              Set  this  variable to specify the timeout (in seconds) after which the screen saver plugins (if
              any) will be invoked.  If this variable is unset or set to an invalid value or 0 no  timeout  is
              used.  See vlock-plugins(5) for more information about plugins.

       VLOCK_PROMPT_TIMEOUT

              Set  this  variable to specify the amount of time (in seconds) you will have to enter your pass‐
              word at the password prompt.  If this variable is unset or set to an invalid value or 0 no time‐
              out is used.  Warning: If this value is too low, you may not be able to unlock your session.

FILES
       ~/.vlockrc

              This  file  is  read by vlock on startup if it exists.  All the variables mentioned above can be
              set here.

SECURITY
       See the SECURITY file in the vlock distribution for more information.

SEE ALSO
       vlock-main(8), vlock-plugins(5)

AUTHORS
       Michael K. Johnson <http://danlj.org/mkj/>

       Frank Benkstein <frank-vlock@benkstein.net>

Linux                                            28 July 2007                                         VLOCK(1)

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