What is the systemd in CentOS/RHEL 7/8?

In this article, you will learn about what is the systemd in Linux?

In CentOS/RHEL 7/8, there is a new systemd introduced to manage the services and the system. Thesystemd is the first process that starts after the system boots, and it is the final process that is running when the system shuts down.

Systemd is designed to have backward compatibility with SysV that is init scripts. Maximum it supports backward compatibility.

Features of systemd

It has many different features, some of them you can find as follows.

  • Parallel start. It means multiple services can be started once. This feature makes the booting process faster.
  • It supports the on-demand activation of the daemon.
  • The systemd supports the system state snapshot.
  • It also supports the dependency-based service control logic.

The systemd configuration files location

You can find the below information useful to get the location of systemd configuration files. These are essential details and must be aware of it.

The unit configuration files are located

/usr/lib/systemd/system/

The run time created directory located

/run/systemd/system/

The files can be created and managed by the system administrator are located

/etc/systemd/system

Getting an overview of the system state

You can use the systemd to pull the information of the system state, and it will tell you the active service status. So, use the below command for it.

systemctl list-units

Also, you can see all the inactive and active services status using the below command.

systemctl list-units --all

If you want to list all of the units installed on the system, including those that systemd has not tried to load into memory so you can use the following command.

systemctl list-unit-files

Viewing basic log information

A systemd component called journald collects and manages journal entries from all parts of the system. It gets this logs information from applications and the kernel. Also, you can use the below command to get the general logs.

journalctl

These logs do not stay after system boot. If you want to make it persistent then you have to create a directory. Use the below command to create it.

sudo mkdir -p /var/log/journal

You can get the arguments for journalctl using the below command.

journalctl --help

Conclusion

In this article, we learn about systemd in Linux. It is important in the latest Linux versions like CentOS 7 and 8 or Red Hat Enterprise Linux 7 and 8 and also in Fedora. I hope, you understand but if you have any questions, you can ask in the comment section.

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