[[linux_wiki:init_systems]]

Init Systems

General Information

Down and dirty quick info about three different init systems that Linux uses; SysV init, upstart, and systemd.

Checklist

  • Distro(s): Varies, depending upon init system.

This section will compare three init systems; sysv, upstart, and systemd.

  • The service name “foo” will be used in all examples.
  • systemctl assumes “.service” appended to unit name if left off
Command Sysv Upstart Systemd
Status of Service service foo status initctl status foo systemctl status foo
Start Service service foo start initctl start foo systemctl start foo
Stop Service service foo stop initctl stop foo systemctl stop foo
Restart Service service foo restart initctl restart foo systemctl restart foo
Reload config file service foo reload initctl reload foo systemctl reload foo
List services ls /etc/init.d/ initctl list systemctl (or)
systemctl list-unit-files (or)
systemctl list-unit-files –type=service
Enable Service At Boot chkconfig foo on Edit /etc/init/<jobname>.conf “start on” field systemctl enable foo
Disable Service At Boot chkconfig foo off Edit /etc/init/<jobname>.conf “start on” field systemctl disable foo
List services and enabled run levels chkconfig –list initctl show-config systemctl list-unit-files –type=service (or)
ls /etc/systemd/system/*.wants/

Description Sysv Upstart Systemd
Halt system 0 runlevel [0] poweroff.target
Single user mode 1,s,single runlevel [1] rescue.target
User defined. Same as 3 by default. 2,4 runlevel [24] multi-user.target
Multi-user, non-graphical 3 runlevel [3] multi-user.target
Multi-user, graphical 5 runlevel [5] graphical.target
Reboot 6 runlevel [6] reboot.target
Emergency shell emergency ? emergency.target
  • Note: Upstart has many different “events” besides runlevels that can trigger jobs to start, such as “start on file-system” or “start on startup”

Sysv init details not contained in All Inits section.

Distributions: RHEL/CentOS ⇐ 6 (RHEL 6 uses an init/upstart combination), Debian ⇐ 7

  • Set in file: /etc/inittab

Example with run level 5 as default:

id:5:initdefault

/etc/rc.d/init.d/

The rc#.d directories contain symbolic links to the scripts in /etc/rc.d/init.d.

# = the run level, ie rc0.d, rc1.d, rc2.d, rc3.d, rc4.d, rc5.d, rc6.d

Locations

  • /etc/rc.d/rc#.d or
  • /etc/rc#.d

Script Names

  • Scripts are named for if they are going to Start(S) or Kill(K) the script, a sequence number, and then the name of the script.
  • /etc/rc2.d/S80cups = This would Start(S) cups after any scripts numbered S01 to S79
  • /etc/rc0.d/K80cups = This would Stop/Kill (K) cups after any scripts numbered K01 to K79
  • service command: RedHat and Debian (service status/stop/start/restart)
  • chkconfig: Red Hat based systems (enable/disable services)
  • update-rc.d: Debian/Ubuntu (enable/disable services)

Upstart details not contained in All Inits section.

Distributions: Ubuntu 9.10 - Current (migrating to systemd), RHEL/CentOS 6 (some scripts)

Upstart uses event driven jobs, instead of run levels to executes scripts. It does have events for rc0-6 to maintain compatibility with init.

  • Job Definition Files Location: /etc/init/
  • Job control: initctl

Systemd details not contained in All Inits section.

Distributions: RHEL/CentOS 7, Debian 8, Ubuntu 15.4?

  • All of systemd unit scripts are located here (and sub folders): /usr/lib/systemd/
  • Systemd uses this directory of symlinks to run those scripts: /etc/systemd/system/
  • Other systemd configuration: /etc/systemd/
  • Unit control: systemctl

On systemd based systems, the laptop suspend on lid closed can be disabled by changing the logind config.

1) Edit /etc/systemd/logind.conf

2) Uncomment “HandleLidSwitch” and set to ignore

HandleLidSwitch=ignore
  • linux_wiki/init_systems.txt
  • Last modified: 2019/05/26 03:50
  • (external edit)