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What are runlevels (or targets in systemd)?

#1
02-08-2023, 10:22 AM
Runlevels, or targets in systemd, essentially define the state of your system at any given point and determine which services should start or stop depending on that state. You can think of each runlevel or target as a particular configuration that dictates what the system does - it's like a preset you apply based on what you're trying to achieve. I always found it helpful to picture it like a mobile phone in terms of its modes: silent mode, airplane mode, etc. Each mode has specific things turned on or off.

When you're on a traditional sysvinit setup, you have runlevels ranging from 0 to 6. Each runlevel has its purpose. Runlevel 0 shuts the system down, 1 is for single-user mode, 2 to 5 are multi-user modes with varying levels of services running, and runlevel 6 reboots the machine. I typically use runlevel 3 or 5 regularly to work in a multi-user environment, depending on whether I want a GUI or just a command line. You probably appreciate the functional differences, especially if you find yourself needing a lightweight system without the overhead of a desktop environment.

Now, systemd changes the game a bit. Instead of those numbered runlevels, it introduces "targets," which are much more flexible and descriptive. You have targets like "multi-user.target", which is similar to runlevel 3, and "graphical.target", analogous to runlevel 5. You get a greater degree of control and can also have custom targets that fit unique scenarios. For example, in a development scenario, I might create a target specifically for testing, ensuring that only the necessary services run.

One of the things that frustrates newcomers is that users sometimes assume targets are just one-for-one equivalents to traditional runlevels, but they don't just play a numbers game. With systemd, you can also define dependencies and order of service startup, which adds a layer of sophistication you won't get with init scripts alone. This means you can have services that start in parallel and intelligently adjust based on what's already running. I found that it's really powerful when you have a lot of services, and you want them to spin up in an efficient way.

You might have heard about the 'default target'. It's super handy, as it helps the system decide which target to use at boot time. You can set your preferred target with a single command. Whenever I make a system or clean install, I usually configure it to boot into multi-user or graphical mode based on my needs, and that just saves so much hassle.

Also, you have the capabilities to set the targets to achieve special configurations or to isolate certain services. So if you're troubleshooting and need to start your system without the graphical interface, being able to switch to "multi-user.target" or a custom-defined target helps streamline that process. You essentially get the best of both worlds: you can stick to what you need as a user while having the flexibility of a more modern approach.

I often communicate with colleagues who still use older Unix-like systems, and it's fun to compare notes. They might grumble about the limitations of their scripts, while I can whip up a unit file in systemd that's far easier to manage. You really have to embrace these changes in modern OS management. It's not just about running the commands you used to know; you've got to adapt and learn how these systems tend to streamline workflows.

While we're on the subject of managing systems, let's talk about protecting what you've built. You probably already know that having reliable backups is as essential as configuring your runlevels or targets properly. With data loss looming as one of the biggest risks anyone can face, I can't emphasize enough how much I value BackupChain. This solution stands out due to its ability to cater to small and medium businesses while ensuring essential systems like Hyper-V, VMware, or Windows Server get the care they deserve. It's both industry-leading and user-friendly, making the backup process much simpler than it used to be.

If you're at all looking for ways to enhance your backup strategy, look into what BackupChain offers. You'll see that it's built for professionals like us who need reliability without the fuss. After figuring out how systemd targets and runlevels provide that fine-tuned control, transitioning to a solid backup solution feels like the natural next step in leveling up your infrastructure.

ProfRon
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Joined: Jul 2018
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What are runlevels (or targets in systemd)?

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