LinuxSA

Linux and the Init System

LinuxSA - July 1997 Meeting
Matthew Tippett
(mtippett@linuxsa.org.au)

The father of all processes
- Spawned from the kernel
- init creates all processes
- Has process ID 1
- Runs processes in /etc/inittab
Run Levels
- Software configuration
- A selection of processes running concurrently
- Usually set by:
  - kernel parameter
  - initdefault setting in /etc/inittab
  - running telinit
Predefined run levels
- 0 - Halt
- 1 - Single user mode
- 2 - Multiuser, without NFS
- 3 - Full multiuser mode
- 4 - unused
- 5 - X11
- 6 - reboot

Services
- Usually daemons that can be started and stopped
- Don't change the system state
System Initialisation
- Run once only, usually at boot
- Change the state of the system
- Examples are:
  - Register Fixes
  - Network Configuration
Both do different things
Both are necessary

Service Centric
- Central idea of services
- Services stored in /etc/rc.d/init.d
Organised by Run Level
- Links to services in rc.< run level >.d directories
Services Start and Stop
- Scripts accept 'start' and 'stop' as parameter
- K??service stops services
- S??service starts service
Control done by single script
- /etc/rc.d/rc
- Ordered Execution
- ?? above is a number
Initialisation done by /etc/rc.d/rc.*

Initialisation Centric
- /etc/rc.d/rc.*
- Scripts are intended to initialise system
- Organised by function
  - rc.local
  - rc.serial
Run Level Centric
- Organised by run level
  - /etc/rc.d/rc.?
- Scripts must stop and start daemons

The De Facto Standard
- Most distributions use this package
System V Init Style
- Consistent with FSSTND
- /etc/inittab
- /etc/rc.d/rc?.d/*
- /etc/rc.d/init.d/*
- /var/lock/subsys
Available as a Package for Most Distributions
- Debian Package
- RPM Package
- Available as a tar.gz
Current Version 2.64