Init

Init is top level process of a WSL distribution. For WSL1 distributions, it is launched by wslservice (see src/windows/service/LxssInstance.cpp) and for WSL2 distributions, it is launched by mini_init.

WSL2 specific distributions startup

Each WSL2 distributions runs in a separate mount, pid and UTS namespace. This allows distributions to run in parallel, without "seeing" each other.

When a WSL2 distribution starts, mini_init:

Mounts the distribution VHD
Clones into a child namespace
Chroots in the VHD mountpoint
Executes init (see the LxMiniInitMessageLaunchInit message).

While each distribution runs in its own mount namespace, the /mnt/wsl mountpoint is shared between all distributions.

Distribution initialization

Once started, the init process performs various initialization tasks such as:

Mounting /proc, /sys and /dev
Configuring cgroups
Registering the binfmt interpreter (see interop)
Parsing /etc/wsl.conf
Starting systemd (see systemd)
Mounting drvfs drives (See drvfs)
Configuring wslg (see wslg)

Running the distribution

Once ready, init establishes either an lxbus (WSL1) or an hvsocket (WSL2) connection to wslservice. This channel is used to transmit various commands to init (see src/shared/inc/lxinitshared.h), such as:

LxInitMessageInitialize: Configure the distribution
LxInitMessageCreateSession: Create a new session leader. See session leader
LxInitMessageTerminateInstance: Terminate the distribution