Init for Mastodon Linux

Init is the mother of all processes – it is the first process a UNIX® system starts up and it manages all runlevel changes and essential programs (getty, and, on some systems xdm.) It reads the file /etc/inittab to find out what processes to run and when to run them.

The Mastodon init setup is a service based one, where each init script starts a particular system service and refers to the other services by name. init maintains an incore registry of active services – each init script queries this database to see if its prerequisites are running and starts them if they aren’t.

Init puts the system into one of 4 different runlevels:

=(S)ingle-user= This conventionally is just a single shell, with all filesystems except the root filesystem unmounted. =(M)ultiuser= This is the system as it normally functions, with all services running and accessable to users. =(R)ebooting= init goes into this runlevel when it’s stopping all services and preparing to do a software reboot of the computer. =(H)alting= init goes into this runlevel when it’s stopping all services and preparing to halt the computer. It’s much like the r runlevel, except that it will go back into multiuser mode if you press a key at the **system halted** prompt.

The init package comes with the following programs:

• init
• shutdown halts or reboots the system by either telling init to change to the appropriate runlevel or by just blindly taking the machine down.
• wall writes a message to everyone on the system.
• mesg sets your terminal to allow or deny messages.
• showreg shows all the processes currently registered.
• halt (and reboot) halt (and reboot) the system, either by telling init to go to runlevel h (r) or by bringing down the system by themselves.
• need queries the init service registry for a process, and if not found, starts that process and registers it. Need assumes that your system has the init scripts in the directories /etc/rc.d/rc.* and /etc/rc.d/init.d.
• runlevel displays the current runlevel.
• telinit tells init what runlevel you wish to change to. It is also used to tell init to reread /etc/inittab after it’s been changed.
• check checks /etc/inittab for validity.

Source Code

=version 1.1= With manpages! It also changes shutdown to not ask for a message unless you give the -m flag and checks in a fix to stop it from getting confused about how long to wait before entering OhMyGodProcessesWon'tStopTimeToPanicNow! mode during shutdown. =version 1.0= The first release of init. It uses a fifo to pass commands into the init process, except for runlevel changes which are passed by signal. A few manpages were written for this release, but not very many.