| .TH SULOGIN 8 "17 Jan 2006" "" "Linux System Administrator's Manual" |
| .SH NAME |
| sulogin \- Single-user login |
| .SH SYNOPSIS |
| .B sulogin |
| [ \fB\-e\fP ] |
| [ \fB\-p\fP ] |
| [ \fB\-t\fP \fISECONDS\fP ] |
| [ \fITTY\fP ] |
| .SH DESCRIPTION |
| .I sulogin |
| is invoked by \fBinit(8)\fP when the system goes into single user mode. |
| (This is done through an entry in \fIinittab(5)\fP.) |
| \fBInit\fP also |
| tries to execute \fIsulogin\fP when |
| the boot loader (e.g., \fBgrub\fP(8)) |
| passes it the \fB\-b\fP option. |
| .PP |
| The user is prompted |
| .IP "" .5i |
| Give root password for system maintenance |
| .br |
| (or type Control\-D for normal startup): |
| .PP |
| \fIsulogin\fP will be connected to the current terminal, or to the |
| optional device that can be specified on the command line |
| (typically \fB/dev/console\fP). |
| .PP |
| If the \fB\-t\fP option is used then the program only waits |
| the given number of seconds for user input. |
| .PP |
| If the \fB\-p\fP option is used then the single-user shell is invoked |
| with a \fIdash\fP as the first character in \fIargv[0]\fP. |
| This causes the shell process to behave as a login shell. |
| The default is \fInot\fP to do this, |
| so that the shell will \fInot\fP read \fB/etc/profile\fP |
| or \fB$HOME/.profile\fP at startup. |
| .PP |
| 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. |
| .SH ENVIRONMENT VARIABLES |
| \fIsulogin\fP looks for the environment variable \fBSUSHELL\fP or |
| \fBsushell\fP 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 \fB/bin/sh\fP. |
| .PP |
| This is very valuable together with the \fB\-b\fP 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) |
| .PP |
| boot: linux \-b rw sushell=/sbin/sash |
| .SH FALLBACK METHODS |
| \fIsulogin\fP checks the root password using the standard method (getpwnam) |
| first. |
| Then, if the \fB\-e\fP option was specified, |
| \fIsulogin\fP examines these files directly to find the root password: |
| .PP |
| /etc/passwd, |
| .br |
| /etc/shadow (if present) |
| .PP |
| If they are damaged or nonexistent, sulogin will start a root shell |
| without asking for a password. Only use the \fB\-e\fP option if you |
| are sure the console is physically protected against unauthorized access. |
| .SH AUTHOR |
| Miquel van Smoorenburg <miquels@cistron.nl> |
| .SH SEE ALSO |
| init(8), inittab(5). |