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.

All Inits

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

Command Table

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/

All Inits Run Levels

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 (init)

Sysv init details not contained in All Inits section.

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

Defualt run level

Set in file: /etc/inittab

Example with run level 5 as default:

id:5:initdefault

Master Copy of Startup Scripts

/etc/rc.d/init.d/

rc#.d directories

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

Manage Services

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

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

Systemd details not contained in All Inits section.

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

Location of Unit Scripts

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

Laptop: Disable Suspend

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

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