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       sulogin - Single-user login


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


       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, as is the default on Ubuntu, no password
       prompt is displayed and sulogin behaves as if the correct password were

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

       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.


       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


       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/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.


       Miquel van Smoorenburg <>


       init(8), inittab(5).

                                  17 Jan 2006