SULOGIN(8)                     Linux System Administrator's Manual                     SULOGIN(8)



NAME
       sulogin - Single-user login

SYNOPSIS
       sulogin [ -e ] [ -p ] [ -t SECONDS ] [ TTY ]

DESCRIPTION
       sulogin  is  invoked by init(8) when the system goes into single user mode.  (This is done
       through an entry in inittab(5).)  Init also tries to execute sulogin when the boot  loader
       (e.g., grub(8)) passes it the -b option.

       The user is prompted

            Give root password for system maintenance
            (or type Control-D for normal startup):

       If  the  root account is locked, no password prompt is displayed and sulogin behaves as if
       the correct password were entered.

       sulogin will be connected to the current terminal, or to the optional device that  can  be
       specified on the command line (typically /dev/console).

       If  the -t option is used then the program only waits the given number of seconds for user
       input.

       If the -p option is used then the single-user shell is invoked with a dash  as  the  first
       character  in  argv[0].   This  causes  the shell process to behave as a login shell.  The
       default is not to do this, so that the shell will not read /etc/profile or  $HOME/.profile
       at startup.

       After the user exits the single-user shell, or presses control-D at the prompt, the system
       will (continue to) boot to the default runlevel.

ENVIRONMENT VARIABLES
       sulogin looks for the environment variable SUSHELL or sushell to determine what  shell  to
       start.  If  the  environment variable is not set, it will try to execute root's shell from
       /etc/passwd. If that fails it will fall back to /bin/sh.

       This is very valuable together with the -b option to init. To boot the system into  single
       user mode, with the root file system mounted read/write, using a special "fail safe" shell
       that is statically linked (this example is valid for the LILO bootprompt)

       boot: linux -b rw sushell=/sbin/sash

FALLBACK METHODS
       sulogin checks the root password using the standard method (getpwnam) first.  Then, if the
       -e option was specified, sulogin examines these files directly to find the root password:

       /etc/passwd,
       /etc/shadow (if present)

       If  they  are damaged or nonexistent, sulogin will start a root shell without asking for a
       password. Only use the -e option if you are  sure  the  console  is  physically  protected
       against unauthorized access.

AUTHOR
       Miquel van Smoorenburg <miquels AT cistron.nl>

SEE ALSO
       init(8), inittab(5).



                                           17 Jan 2006                                 SULOGIN(8)