Systemd

Systemd support for a WSL distribution can be enabled by setting the following in /etc/wsl.conf:

[boot]
systemd=true

When enabled, init will take launch /sbin/init (which points to systemd's init) when the distribution starts. One key difference when this setting is enabled is that init won't be pid 1 in the given distribution, since systemd's init requires running as pid 1, so init will fork(), and launch systemd in the parent while continuing WSL configuration in the child process.

After launching /sbin/init, init waits for systemd to be ready by waiting for systemctl is-system-running to return either running, or degraded. After a given amount of time, WSL will time out and allow the distribution to continue starting, even if systemd isn't ready.

User sessions

When systemd is enabled, WSL tries synchronizes launching processes with systemd user sessions. This is currently done by launching login -f <user> to start the associated systemd user session.

Additional systemd configuration

To improve compatibility with systemd, WSL creates various systemd configuration files during boot (under /run). These configurations files are used to:

• Protect the WSL binfmt interpret from being deleted by systemd-binfmt.service
• Protect the X11 socket from being deleted by `systemd-tmpfiles.serviceè