Linux Init

LINUX INIT
--------------
This is the mother of all other userspace's processes.

Where to find it?
In the util-linux package (to be found at ftp.*.kernel.org) for simpleinit or in the sysvinit package for SysV init.

Probably also in [sunsite|metalab].unc.edu or ftp.debian.org


Title: sysvinit and utilities
Version: 2.78
Entered-Date: 11FEB2000
Description: This is the Linux System V init.
                The source package has the debian build files included.
                This version can be compiled with glibc 2.0.6 and up.
Author: miquels@cistron.nl (Miquel van Smoorenburg)
Primary-Site: sunsite.unc.edu /pub/Linux/system/daemons/init
                109K sysvinit-2.78.tar.gz
Alternate-Site: ftp.cistron.nl /pub/people/miquels/software
                109K sysvinit-2.78.tar.gz
Alternate-Site: ftp.debian.org /debian/dists/potato/main/source/base
                108K sysvinit_2.78-X.tar.gz
Copying-Policy: GPL
Keywords: init shutdown halt reboot
End


ftp.debian.org:/debian/dists/potato/main/source/base/sysvinit_2.78-2.tar.gz

https://build.opensuse.org/package/files?package=sysvinit&project=YaST%3AWeb

Some properties:

#define VT_MASTER "/dev/tty0"         /* Virtual console master */
#define CONSOLE "/dev/console"     /* Logical system console */
#define SECURETTY "/etc/securetty"     /* List of root terminals */
#define SDALLOW "/etc/shutdown.allow" /* Users allowed to shutdown */
#define INITTAB "/etc/inittab"     /* Location of inittab */
#define INIT "/sbin/init"     /* Location of init itself. */
#define NOLOGIN "/etc/nologin"     /* Stop user logging in. */
#define FASTBOOT "/fastboot"         /* Enable fast boot. */
#define FORCEFSCK "/forcefsck"     /* Force fsck on boot */
#define SDPID "/var/run/shutdown.pid" /* PID of shutdown program */
#define SHELL "/bin/sh"         /* Default shell */
#define SULOGIN "/sbin/sulogin"     /* Sulogin */
#define INITSCRIPT "/etc/initscript"     /* Initscript. */
#define PWRSTAT_OLD "/etc/powerstatus"     /* COMPAT: SIGPWR reason (OK/BAD) */
#define PWRSTAT "/var/run/powerstatus" /* COMPAT: SIGPWR reason (OK/BAD) */

#if 0
#define INITLVL "/etc/initrunlvl"     /* COMPAT: New runlevel */
#define INITLVL2 "/var/log/initrunlvl" /* COMPAT: New runlevel */
                            /* Note: INITLVL2 definition needs INITLVL */
#define HALTSCRIPT1 "/etc/init.d/halt"     /* Called by "fast" shutdown */
#define HALTSCRIPT2 "/etc/rc.d/rc.0"     /* Called by "fast" shutdown */
#define REBOOTSCRIPT1 "/etc/init.d/reboot" /* Ditto. */
#define REBOOTSCRIPT2 "/etc/rc.d/rc.6" /* Ditto. */



- It exits if UID is != 0 (root)
- It exits if PID != 1 (the first process in Kernel's userspace)
- It check command-line args:
    "single", "-s"      : dfl_level is set to 'S'
    "-a", "auto"        : set environment "AUTOBOOT=YES"
    "-b", "emergency"   : emerg_shell = 1
    "-z"                : ignore -z xxxx
    any of [0-9],[sS]   : dfl_level is set accordingly to that level

- set default environment PATH to "/sbin:/usr/sbin:/bin:/usr/bin"
- say "@(#) init version 2.89  DATE 26-Mar-2010  miquels@cistron.nl booting" into syslog
- spawn/fork to emergency shell if emerg_shell == 1
- read inittab and configure setting based on the settings stored in INITTAB

init.c: main() ---> setproctitle()
    |
    |
    V
init_main() ----------------------------> read_inittab()
 |  |   |
 |  |   |
 |  |   V
 |  |   init_reboot(BMAGIC_SOFT)
 |  |
 |  |
 |  V
 | ioctl(f, KDSIGACCEPT, SIGWINCH): tell kernel SIGACCEPT
 |
 +---> set a bunch of signals' flags
 |
 +----> console_init(), open /dev/CONSOLE (or otherwise if specified in env "CONSOLE") for O_RDONLY
 |
 +----> console_stty() : Set terminal settings to reasonable defaults
 |
 +----> set default environment PATH to "/sbin:/usr/sbin:/bin:/usr/bin"
 |
 loop forever by doing this stuf:
    1) boot transitions
    2) Read from the init FIFO by calling check_init_fifo():
        2.1) try to create /dev/initctl if not present.
        2.2) If /dev/initctl is open, stat the file to see if it is still the _same_ inode
        2.3) try to open /dev/initctl
        2.4) Read data from the pipe, return on EINTR
        2.5) console_init
        2.6) process requests (e.g., runlevel change request, power fail request, set env)

    3) check the 'failing' flags
    4) process any signal:
        4.1) SIGPWR event/signal
        4.2) SIGINT
        4.3) SIGWINCH
        4.4) SIGALRM
        4.5) SIGCHLD
        4.6) SIGHUP
    5) See whether we need to start up (again)




BOOT TRANSITION FSM
--------------------



        '#' (SYSINIT) --+-----> '*' (BOOT) ------> (NORMAL)
                        |              ^
                        |              |
           newlevel=='S'|              | !did_boot && newlevel != 'S'
                        |              |
                        +-----> 'S' (INIT)
                                       ^
                                       |
                                       |
                                   start here