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?
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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.
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
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
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 ?
When your kernel finishes booting, it starts a special process which possesses the following properties:
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.
Systemctl - System and Service manager for linux systems
Basics about systemd: Features:
Dependecy based service control logic
unit file's Filelocation:
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.
Systemd is a system and service manager for Linux operating systems. It is designed to be backwards compatible with SysV init scripts, and provides a number of features such as parallel startup of system services at boot time, on-demand activation of daemons, support for system state snapshots, or dependency-based service control logic. In Red Hat Enterprise Linux 7, systemd replaces Upstart as the default init system.
If you need more detail information about systemd you have to read this page: https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/7/html/System_Administrators_Guide/chap-Managing_Services_with_systemd.html