es:Init hu:Init ja:Init pt:Init zh-hans:Init

Init is the first process started during system boot. It is 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 explicitly depend on each other.

Inits (integrated)

Inits

Init scripts

Service managers

Configuration

Migrate running services

To run daemons under the new init, save a list of running daemons:

$ systemctl list-units --state=running "*.service" > daemons.list

and configure the #Init scripts accordingly. See also https://unix.stackexchange.com/questions/175380/how-to-list-all-running-daemons.

logind

logind requires systemd to be the init process. https://systemd.io/PORTABILITY_AND_STABILITY/ As such, local sessions and other functionality is not available.

Device permissions

Add users to respective user groups for device access and reboot. Current group membership should first be checked with id user.

# usermod -a -G video,audio,power,disk,storage,optical,lp,scanner,input user

See also Users and groups#Pre-systemd groups. To create group rules for use with Polkit, see Polkit#Bypass password prompt.

Rootless X

As Xorg.wrap does not check if logind is active https://bugs.freedesktop.org/show_bug.cgi?id=86975#c5, root rights for Xorg need be enabled manually.

Power management

See pm-utils and acpid to replace Power management with systemd.

Scheduled tasks

Arch uses timer files instead of cron by default.

Dbus

User instances of dbus-daemon are launched by systemd/User https://archlinux.org/news/d-bus-now-launches-user-buses/. When requiring IPC between desktop applications, restore 30-dbus.sh:

#!/bin/bash

# launches a session dbus instance
if [ -z "${DBUS_SESSION_BUS_ADDRESS-}" ] && type dbus-launch >/dev/null; then
  eval $(dbus-launch --sh-syntax --exit-with-session)
fi

/etc/X11/xinit/xinitrc.d/30-dbus.sh

Tips and tricks

systemd-nspawn

systemd-nspawn is a tool for systemd systems. Since Linux 2.6.19, it is possible, however, 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.https://vincent.bernat.im/en/blog/2011-jchroot-isolation.html https://github.com/vincentbernat/jchroot. 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 udev

See also

• Debian:Debate/initsystem

• How to run s6-svscan as process 1

• Replace systemd with busybox + minirc

• Init vs. runsv

• Demystifying the init system

• A history of modern init systems (1992-2015)

• Gentoo:Comparison of init systems

• InitWare: Contributors' Study Guide

• The nosh package