Unix for Beginners
Unix Shell Programming
Unix Useful References
Unix Useful Resources
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sulogin - Unix, Linux Command
sulogin -- Single-user login
sulogin [ -e ] [ -p ] [ -t timeout ] [ tty-device ]
sulogin can be 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 it is passed the -b flag
from the bootmonitor (eg, LILO).
The user is prompted
sulogin will be connected to the current terminal, or to the
optional device that can be specified on the command line
Give root password for system maintenance
(or type Control-D for normal startup):
If the -p flag was set, the single-user shell will be invoked
with a dash as the first character in argv. That will
cause most shells 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 roots shell from /etc/passwd. If that
fails it will fall back to /bin/sh.
This is very valuable together with the -b flag to init. To boot
the system into single user mode, with the root file system mounted read/write,
using a special "failsafe" 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)
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 non-existant, 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 <email@example.com>