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systemd and WSL

WSL's motto used to be "Just because you can, doesn't mean you should", but a lot has changed
Posted April 5, 2023 Updated Apr 10, 2023 Linux

Microsoft have done a pretty good job with WSL, and while it still has a lot to do - for the basics, it’s pretty reliable and sure as hell beats spinning up VM’s every time you need to run a quick command.

But can it run systemd, and if so… should you?

The quick answer is yes, you can. In fact the Debian\Ubuntu images shipped with WSL and maintained by Microsoft include systemd as standard. But how does a not-quite-virtual yet not-quite-real Linux system even handle the low level functions of an init system?

Enabling systemd

I think it’s safe to say we’ve all now accepted systemd as the defacto init (for those of you still clinging on, feel free to send hate mail to the usual address), so it’s natural to assume systemd would be part of WSL. Until recently, it wasn’t, and was noticeably absent. This caused many issues for packages expecting to install\manage services using unit files that while should be backwards-compatible, typically were not.

This continued until about September 2022, when Microsoft dropped this bombshell of a post.

We know that WSL actually rolls its own init system, but what you may not know is that systemd still isn’t the default. You’ll need to instruct WSL to use it. You can confirm this by checking on PID1, and attempting to query the system using systemctl.

xor@deathstar:~$ sudo systemctl list-units --type=service
System has not been booted with systemd as init system (PID 1). Can't operate.
Failed to connect to bus: Host is down

What is PID 1 you ask?

xor@DeathStar:~$ sudo ps -x
    1 ?        Sl     0:00 /init

This is the actual WSL init. While WSL supports systemd, it’s not enabled as the primary init by default. To fix that, create the file /etc/wsl.conf and add the following:


Shutdown WSL using wsl.exe --shutdown and restart your WSL instance, you’ll now see WSL is booting systemd just like any other Linux distro:

xor@deathstar:/sbin$ systemctl list-units --type=service
  UNIT                               LOAD   ACTIVE SUB     DESCRIPTION
  console-getty.service              loaded active running Console Getty
  cron.service                       loaded active running Regular background program processing daemon
  dbus.service                       loaded active running D-Bus System Message Bus
  getty@tty1.service                 loaded active running Getty on tty1
  ifupdown-pre.service               loaded active exited  Helper to synchronize boot up for ifupdown
  networking.service                 loaded active exited  Raise network interfaces
  rsyslog.service                    loaded active running System Logging Service
  ssh.service                        loaded active running OpenBSD Secure Shell server
  systemd-journal-flush.service      loaded active exited  Flush Journal to Persistent Storage
  systemd-journald.service           loaded active running Journal Service

What’s interesting is that WSL init is still active and managing the system, but has shifted itself into the background:

xor@deathstar:/sbin$ sudo ps x
      1 ?        Ss     0:00 /sbin/init
      2 ?        Sl     0:00 /init

You’re now running a system that’s as close to a systemd deployment as you can get in WSL. Note that you’ll also get journalctl and other systemd support tools to manage the system.

systemd and WSL
Posted April 5, 2023
Updated Apr 10, 2023
Written by John Payne