What init scripts in linux

init

Warning: Arch Linux only has official support for systemd. [1] When using a different init system, please mention so in support requests.

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)

• anopa — Init system built around the s6 supervision suite.

• GNU Shepherd — Init system written in Guile.

• OpenRC — Dependency-based init system.

• 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.

Inits

• BusyBox — Utilities for rescue and embedded systems.

• sinit — Simple init initially based on Rich Felker’s minimal init.

• SysVinit — Traditional System V init.

Init scripts

• initscripts-fork — Maintained fork of SysVinit scripts in Arch Linux.

• minirc — Minimal init script designed for BusyBox.

• kisslinux-init — Init framework of KISS Linux.

Service managers

• 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.

• perp — Persistent process (service) supervisor and management framework for UNIX.

• 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.

• Supervisor — A system that allows its users to monitor and control processes on UNIX-like operating systems.

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 [2].

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 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 

Rootless X

As Xorg.wrap does not check if logind is active [5], root rights for Xorg need be enabled manually.

Power management

Scheduled tasks

Arch uses timer files instead of cron by default. See archlinux-cronjobs for basic cron jobs.

Dbus

This article or section needs expansion.

User instances of dbus-daemon are launched by systemd/User [6]. When requiring IPC between desktop applications, restore 30-dbus.sh :

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

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

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.[7] [8]. 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

Warning: Replacing udev is not required as systemd-udev is functional without systemd as PID 1. Some replacements such as eudev can also not coexist with systemd —ensure an alternative init is booted prior to their installation.

• eudev — eudev is a fork of udev started by the Gentoo project. It is primarily designed and tested with OpenRC.

• mdev — Device manager for usage in embedded systems.

• smdev — smdev is a simple program to manage device nodes. It is mostly compatible with mdev but does not have all of its features.

See also

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What is ‘init’ Process and Command in Linux?

In this article, you will learn about the short description of the init process, the runlevels of init, and the init command in a Linux system.

What is Init Process?

In layman’s terms, when you press the power button, your system will first look for the bootloader (basically, your Linux grub), and then it will try to launch the kernel.

But the kernel itself cannot launch all of the processes, so it will start the first (or parent) process, known as init (sort for “initialization“), with PID “1” (process identifiers are assigned in sequential order).

The “/etc/inittab” script is used by the “init” process. It has entries for processes that do basic things when the system starts up and shuts down, like showing the user a login screen with gettys, mounting and unmounting file systems, and managing daemons.

As a result, it should be kept running until the system terminates. If the kernel is unable to start it, the system will reach a stage called “Kernel Panic“.

Run Levels

Run Levels is a system software configuration (by init) that defines a set of processes to start when the system boots. The processes spawned by the init for each of these run levels are defined in the file “/etc/inittab“.

Run Levels are numbered from zero to six and define the state of the machine after boot, as listed below.

Run Levels	Mode	Functions
0	Halt	Halt the system.
1	Single-User Mode	Get the system into single user mode.
2	Multi-User Mode	Get the system into multiuser mode without networking.
3	Multi-User Mode with Networking	Get the system into multiuser mode with networking.
4	Undefined	Not used
5	X11	Get the system into multiuser mode with networking and X windows.
6	Reboot	Reboot the system.

The majority of Linux systems is based on runlevel 3 or 5. Although, users can modify these runlevels or create new ones based on their requirements.

The 0, 1, and 6 are reserved runlevels used for halting, getting into single user mode, and rebooting the system.

Init Command in Linux

In most Linux systems, the init command is used to send control commands to the init daemons that run as background processes.

$ init [OPTION]

The following is a list of all known options, along with their descriptions.

Commands	Description
0	Shutdown the system.
6	Reboot the system.
2, 3, 4, 5	Start runlevelX.target unit.
1, s, S	Enter rescue mode.
q, Q	Reload the init daemon configuration.
u, U	Re-execute the init daemon.

Conclusion

There are numerous items that should be included, but the goal of this article is not to provide a detailed description of the init process or command; rather, it is to walk you through them.

If you are more interested in knowing the init process, then check this article, as this method of booting the system is deprecated with systemd, so there is no future plan to have a major update in this article.

If you are interested in learning about them from our site or want this article to be more concise, then do let me know in the comment section.

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