Init
Related articles
Init is the first process started during system boot. It is a a daemon process that continues running until the system is shut down. Init is the direct or indirect ancestor of all other processes, and automatically adopts all orphaned processes. It is started by the kernel using a hard-coded filename; if the kernel is unable to start it, panic will result. Init is typically assigned process identifier 1.
The init scripts (or rc) are launched by the init process to guarantee basic functionality on system start and shutdown. This includes (un)mounting of file systems and launching of daemons. A service manager takes this one step further by providing active control over launched processes, or process supervision. An example is to monitor for crashes and restart processes accordingly.
These components combine to the init system. Some inits include the service manager in the init process, or have init scripts in close relation to them. These inits are below referred to as integrated, though entries in different categories may explicitely depend on each other.
Contents
Inits (integrated)
- systemd — Dependency-based init system with aggressive parallelization, process supervision using cgroups, and the ability to depend on a given mount point or dbus service.
- uselessd — A fork of systemd v208.
- Upstart — Event-based init system which handles starting, stopping and supervising of tasks and services.
- initng — Dependency-based init system with parallelization and asynchronous start.
- Epoch — Single-threaded init system designed for minimal footprint, compatibility and unified configuration.
- finit — Fast and extensible init, originally based on EeePC fastinit.
Inits
- BusyBox — Utilities for rescue and embedded systems.
- SysVinit — Traditional System V init.
- ninit — Fork from minit
- sinit — Simple init initially based on Rich Felker’s minimal init.
Init scripts
- initscripts-fork — Maintained fork of SysVinit scripts in Arch Linux.
- minirc — Minimal init script designed for BusyBox.
- OpenRC Arch services — OpenRC service scripts compatible to Arch Linux.
- spark-rc — A simple rc script to kickstart your system.
- watchman-sm-services — Examples of services for watchman.
Service managers
- daemontools — Collection of tools for managing UNIX services.
- Monit — Monit is a process supervision tool for Unix and Linux. With monit, system status can be viewed directly from the command line, or via the native HTTP(S) web server.
- OpenRC — Dependency-based rc system that works with the system-provided init, normally SysVinit.
- perp — Persistent process (service) supervisor and managment framework for UNIX.
- http://b0llix.net/perp/ || perpAUR
- runit — UNIX init scheme with service supervision, a replacement for SysVinit, and other init schemes.
- s6 — Small suite of programs for UNIX, designed to allow service supervision in the line of daemontools and runit.
- watchman — A not-so-simple service manager for Linux.
Configuration
Migrate running daemons
To run daemons under the new init, save a list of running daemons:
$ systemctl list-units --state=running "*.service" > daemons.list
then configure the #Init scripts accordingly.
logind
logind requires systemd to be the init process. [3] As such, local sessions and other functionality is not available.
Device permissions
Add users to the correct groups for device access, and reboot. Current group membership should first be checked with id user
. For example:
# usermod -a -G video,audio,power,disk,storage,optical,lp,scanner user
See Policykit#Bypass password prompt to create group rules for use with Policykit.
Rootless X (1.16)
As Xorg.wrap
does not check if logind is active, root rights for Xorg need be enabled manually:
/etc/X11/Xwrapper.config
needs_root_rights = yes
This file is also available through xorg-xwrapperAUR from the AUR.
Scheduled tasks
Arch uses timer files instead of cron by default. Install archlinux-cronjobsAUR from the AUR for basic cron jobs.
System logging
rsyslog works with the default configuration.
Syslog-ng is configured for journalctl
by default. Edit /etc/syslog-ng/syslog-ng.conf
:
source src { unix-stream("/dev/log"); internal(); file("/proc/kmsg"); };
See Syslog-ng#Sources for details.
Tips and tricks
systemd-nspawn
systemd-nspawn is a tool for systemd systems. Since Linux 2.6.19 it is however possible to run systemd on a non-systemd system by using PID namespace. For it, the kernel needs to be configured with CONFIG_PID_NS
and CONFIG_NAMESPACES
).
The PID namespace creates a new hierarchy of processes starting with PID 1. In addition to this, systemd requires a chrooted root filesystem to be mounted. Hence, you have to at least make a bind mount, because otherwise some services will fail with
"Failed at step NAMESPACE spawning" due to "Invalid operation"
as systemd tries to remount the root with private
option.
To setup a chroot with a new PID namespace you can use jchroot.[4] [5].
Make sure not to mount /proc
inside the new root before chrooting, otherwise systemd will detect the chroot environment. You can mount it later once systemd is running.
Replacing the systemd package
See Eudev#Replacing the systemd package.