SystemD Explained

Welcome back to the channel and in this video, we are going to talk about the topic a which has been really controversial for years - SystemD

For those who don't know SystemD is the lastest Linux startup process - the mother of all processes
It's controversial because many developers and sysadmins - including Linus Torvalds thought that it is trying to replace something that does not need replacement - the SysVinit system


http://0pointer.de/blog/projects/the-biggest-myths.html


But systemD is developed and promoted by RHEL which is one of the popular distributions across the industry so SystemD is here to stay.
So what does having systemD means
SystemD starts as many services as possible in parallel unlike SysVinit - that calls for faster boot time
- the /etc/inittab file is no more, instead a directory /etc/systemd/system is referred for init files, this directory has bunch of symlinks to a directory /usr/lib/systemd/system.
- service command is replaced by systemctl command but still, user can use the service command


- the bash scripts in /etc/rc.d directory are replaced by unit files
- to enable service at boot you need to enable service instead of chkconfig


and last run-levels are replaced by a thing called targets


SystemD is not only capable of managing system services but it can also interact with hardware, mount filesystem, etc.


/etc/systemd/system/default.target is like inittab file which tells systemD in which state is should boot the system, this is just a symlink to the actual target file. multi-user target is equivalent to run level 3 here


you can also get default target with systemctl get-default


You can also change the default target with systemctl set-default


Each target has its dependencies described in their config files like - thus systemD builds a dependency graph
systemctl list-dependencies multi-user.target


Sysinit.target can be considered as check-point in the startup process, it starts all the low-level services required for the system to be functional. https://www.patreon.com/awshandson https://amzn.to/2A9DVv1

https://amzn.to/3cEGVNf