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



NAME
       sulogin - Single-user login

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

DESCRIPTION
       sulogin  can  be  invoked by init(8) when the system goes into single user mode.  (This is done through an entry in init-
       tab(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):

       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  vari-
       able 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, sulo-
       gin 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 <miquelsATcistron.nl>

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



                                                           17 Jan 2006                                                SULOGIN(8)