What is "systemd" in CentOS 7

Question

Can anyone tell me what is systemd and why CentOS 7 has systemd but CentOS 6 doesn't have it?

Related question : Which ubuntu versions have systemd?

Solution 1

What is systemd?

systemd is a system and service manager for Linux, compatible with SysV and LSB init scripts. systemd provides aggressive parallelization capabilities, uses socket and D-Bus activation for starting services, offers on-demand starting of daemons, keeps track of processes using Linux control groups, supports snapshotting and restoring of the system state, maintains mount and automount points and implements an elaborate transactional dependency-based service control logic.

Systemd replace SysVinit on CentOS 7 , it makes a server boot quicker because it uses fewer scripts and tries to run more tasks in parallel, Systemd calls them units,

The global Systemd configuration is stored in the /etc/systemd directory.Service configuration files are located in the /usr/lib/systemd/system directory and custom service configuration files are stored in the /etc/systemd/system directory.

Why CentOS 7 have systemd but CentOS 6 doesn't have ?

Red Hat-based distributions are migrating to systemd, it has been the default system and services manager in Red Hat 7 , CentOs7 and Fedora since the release of Fedora 15.

Which ubuntu version have systemd ?

Ubuntu 15.04 is the first version (of Ubuntu) that uses systemd , You can read the blog post of Mark_Shuttleworth

Solution 2

When your kernel finishes booting, it starts a special process which possesses the following properties^[1]:

• it runs until the system shuts down
• it is the parent (or indirect parent) of all processes
• it automatically adopts all orphaned processes ^{(see comment below)}

This process is usually assigned a PID of 1 and is referred to as the "init" process.

Systemd is a replacement for the traditional init implementation that many distributions were using. Upstart is another alternative implementation and the one that CentOS 6 was using.

One of the reasons that CentOS 6 did not ship with systemd is because the first release of systemd was in March 2010 and CentOS 6 was released in July 2011. Put simply, it hadn't been around long enough. It took a couple years before Ubuntu added systemd to its repositories and another couple of years before it was enabled by default.

To answer your second question, Ubuntu 15.04 (Vivid Vervet) and all subsequent releases have systemd enabled by default.

Solution 3

Systemctl - System and Service manager for linux systems

Basics about systemd: Features:

1. Parallel startup of system service at boot time
2. On demand activation of daemons

3. Dependecy based service control logic

   • limited support at runlevel
   • panic is not support panic command(systemctl no custom commands)
   • systemctl can only communicate with services which are started by systemd
   • sysd stop only running services
   • system services don't inherit any context like HOME or PATH variable
   • All services subject to default timeout of 5 minutes can be configured.These prevents from system to freeze in case of some application stop to respond.

unit file's Filelocation: /etc/systemd/system

Conf file: /etc/systemd/system.conf

Systemd provides a lot of functionallity basically you can control all the resouces of linux system that gives you give a lot of functionality.We are focussing on managing system service in this article.

for more details: https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/7/html/system_administrators_guide/chap-managing_services_with_systemd

Comments

[JdeBP]

The third bullet point is wrong. Ironically, it is for systemd's benefit that it became wrong, years ago.

[dbush]

@JdeBP someone should update Wikipedia then :D

[Арсений Черенков]

wellcome to U&L, I tried to reformat your text, this look like a copy/paste and tabular version was somehow lost. You can reformat data in tabular form. thank for answering this two year old question.

[frostcs]

Actually i was reading about this topic made some notes for me and pasted this for plain vanilla understanding of systemd