What is systemd in Linux and How Do You Use It?

We all want reliable operating systems, and Linux is just that. Linux is stable, efficient, and capable of operational uptimes countable in years, not just days! 

The average Linux server has much going on behind the scenes. Today we look at a management system that controls this ordered chaos, called systemd – but it’s more than just a glorified service manager. We will look at how systemd works with Linux to provide enhanced performance, convenient logging, and many other useful features. 

What is systemd?

Systemd is a tool that controls several systems in Linux. From systemd, you complete basic administrator and maintenance tasks, such as:

• Controlling startup options: Systemd can start target units, which are groups of services that start-up together, sometimes in a specific order, so they work correctly.

• Managing system resources: Systemd uses something called cgroups to manage many different clusters or groups of processes. This ensures that they are managed more efficiently, and it lets systemd keep a watchful eye on services and processes so they don’t consume too many system resources and slow down our business-critical servers.

• Logging and journaling: Another function that systemd offers is a combined logging system that gives you a single location to view log files. This has advantages over traditional system log organization, which we will look at towards the end of the article. 

• Mounting devices: Removable storage, hard drives, and optical devices are all controlled from here in addition to other devices.

Systemd is one of the most important parts of the Linux OS because it is both an initialization system and a system/service manager rolled into one. Below are some of the different areas where systemd is very useful for general administrative tasks:

Systemd Services 

Think of these as scripts that systemd executes to start or stop various system services, such as networking, firewalls, or databases. They are usually stored in /etc/systemd/system or /usr/lib/systemd/system directories on your Linux system. They are accessible to users with the right permissions to make changes when necessary.

Systemd Targets 

These are synchronization points that the Linux system uses during the boot process to help orchestrate the starting up sequence. They define what services should be started or stopped at certain times during the boot process, which is what moves the booting up process to finish, launches the Linux OS, and starts the system. 

Systemd Units 

The best way to visualize systemd units is to think of them as an object that controls a specific function and performs a particular action. Units are the objects used to start, stop and manage system services and perform other functions, such as managing the boot process and system task management. They also help with socket creation for networking, mounting file systems, and initializing hardware.

The parts that comprise a systemd unit are the name, type, and config file. There are many different unit types, and if you would like to see them for yourself, then all you need to do is type in “systemctl -t help” and you will get them all listed in your terminal.  

Basic Troubleshooting With systemd 

Things break when we least expect it, and while Linux is indeed one of the most stable platforms in use today, there are times when things don’t work as expected. Problems you can run into with systemd can range from services failing to start to problems with events logging. Some common issues that you could come across and potential fixes include:

Services Won’t Start 

Unfortunately, Linux is not immune to the problems that Windows systems have, such as an important service failing to start, even when you try to fire it up manually. This can happen for various reasons, such as missing dependencies, incorrect file or execution permissions, or even simple configuration errors. For you to be able to diagnose the problem properly, you can use the systemctl status command to check the service status and see if we are getting any error messages. Another avenue is to try and use the journalctl command to view the relevant service logs and look for clues as to what is causing the issue.

A Service Won’t Stop 

A service may not stop even after you issue the systemctl stop command. This can occur if the service has a child process that runs even after being told to terminate or the process is waiting for an event to finish before taking additional requests. To force the service to stop, use the systemctl kill command. This sends a signal and terminates the offending service and its associated processes. Be careful, as killing the wrong process can cause big issues with your running machine, including unscheduled downtime.

Issues with systemd’s Logging System

Systemd stores log files somewhere called “the journal.” The journal saves log files in /var/log/journal. Access these log files by using journalctl, which lets you access your log files and search them for specific words. If you do a good bit of remote work on Linux systems, for example, using text files for logging saves bandwidth and will make your connection faster. A handy tool that you can use for this is called rsyslog, a logging system that works with systemd and is easy to use.

Final Thoughts About systemd

Systemd is much more than just a simple service manager because it touches so many different areas of the Linux system, and it is quite simple to use. If you want to get Linux certified, then you must start using systemd and other system tools. An easy way to do this is to start practicing on your Linux-based PC or Virtual Machine. 

You will need to know how to engage with different run levels, services, and devices when you are responsible for maintaining systems that run Linux. But why learn Linux? Linux is one of the preferred operating systems in the cloud and open source arenas, making a Linux certification more relevant than ever!   

Having knowledge of systemd is one of the best ways to learn how to administer basic services on any Linux computer that runs it. We highly recommend that you start with the basics of Linux if you want to start working with cloud technologies, containerization, and other modern scalable technologies, having control of your Linux operating system starts with systemd. 

Ready to take your Linux skills to the next level? Take our Everything Linux Online Training online training course. Or take one to build your bash scripting skills. 

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