SIMPLEINIT(8)

NAME
simpleinit - process control initialization

SYNOPSIS
init [ single ]

DESCRIPTION
init is invoked as the last step in the Linux boot sequence. If the single option is used, or if the file /etc/singleboot exists, then single user mode will be entered, by starting /bin/sh. If the file /etc/securesingle exists, then the root password will be required to start single user mode. If the root password does not exist, or if /etc/passwd does not exist, the checking of the password will be skipped. If the file /etc/TZ exists, then the contents of that file will be read, and used to set the TZ environment variable for each process started by simpleinit. This "feature" is only available if it's configured at compile-time. It's not normally needed. After single user mode is terminated, the /etc/rc file is executed, and the information in /etc/inittab will be used to start processes. While init is running, several signals are trapped, with special action taken. Since init has PID 1, sending signals to the init process is easy with the kill(1) command. If init catches a SIGHUP (hangup) signal, the /etc/inittab will be read again. If init catches a SIGTSTP (terminal stop) signal, no more processes will be spawned. This is a toggle, which is reset is init catches another SIGTSTP signal. If init catches a SIGINT (interrupt) signal, init will sync a few times, and try to start reboot. Failing this, init will execute the system reboot(2) call. Under Linux, it is possible to configure the Ctrl-Alt-Del sequence to send a signal to init instead of rebooting the system.

THE INITTAB FILE
Because of the number of init programs which are appearing in the Linux community, the documentation for the /etc/inittab file, which is usually found with the inittab(5) man page, is presented here: The format is
    ttyline:termcap-entry:getty-command
An example is as follows:
    tty1:linux:/sbin/getty 9600 tty1
    tty2:linux:/sbin/getty 9600 tty2
    tty3:linux:/sbin/getty 9600 tty3
    tty4:linux:/sbin/getty 9600 tty4
    # tty5:linux:/sbin/getty 9600 tty5
    # ttyS1:dumb:/sbin/getty 9600 ttyS1
    # ttyS2:dumb:/sbin/getty -m -t60 2400 ttyS2
Lines beginning with the # character are treated as comments. Please see documentation for the getty (8) command that you are using, since there are several of these in the Linux community at this time.

FILES
/etc/inittab
/etc/singleboot
/etc/securesingle
/etc/TZ
/etc/passwd
/etc/rc

SEE ALSO
inittab(5), ctrlaltdel(8) reboot(8), termcap(5), getty(8), agetty(8), shutdown(8)

BUGS
This program is called simpleinit to distinguish it from the System V compatible versions of init which are starting to appear in the Linux community. simpleinit should be linked to, or made identical with, init for correct functionality.

AUTHOR
Peter Orbaek (poe@daimi.aau.dk)
Version 1.20, with patches for singleuser mode by Werner Almesberger