Stub script to emulate systemd in WSL

systemd-stub

#!/bin/bash

# NOTE: replace the root user shell by placing this script at /usr/local/bin/systemd-stub

# login user
user=ed

if [[ -p /dev/stdin ]] || [[ "$BASH_ARGC" -gt 0 ]]; then
    shell=/bin/bash
else
    shell=$(getent passwd $user | cut -d : -f 7)
fi

if [[ "$PWD" =~ ^/root ]]; then
    cd $(eval 'echo ~$user')
fi


systemd_is_running() {
    systemd_pid=$(pgrep -xo systemd)

    if [[ $? -eq 0 ]]; then
        export SYSTEMD_PID=$systemd_pid
        return 0
    fi

    return 1
}

# if systemd is already running as PID 1, we just start a shell
if systemd_is_running && [[ $SYSTEMD_PID -eq 1 ]]; then
    exec "$shell" "$@"
fi

if ! systemd_is_running; then
    # start systemd as a daemon process
    /usr/sbin/daemonize -l "$HOME/.systemd.lock" /usr/bin/unshare --fork --pid --mount-proc /lib/systemd/systemd

    if [[ $? -ne 0 ]]; then
        echo 'Error: systemd failed to start.' 1>&2
        exit 1
    fi

    # wait for systemd to start
    max_retries=60
    while ! systemd_is_running && [[ "$retries" -le "$max_retries" ]]; do
        sleep 1
        (( retries++ ))
    done

    if [[ "$retries" -gt "$max_retries" ]]; then
        echo 'Error: systemd timed out; aborting.' 1>&2
        exit 1
    fi
fi


# save WSL mountpoints in PATH
if [[ ! -z $PATH ]]; then
    export WINPATH=$(echo "$PATH" | grep -oP ':/mnt/c/[^:]+' | tr -d '\n' | cut -c 2-)
fi


runopts=""
runopts="$runopts --login"
runopts="$runopts --whitelist-environment=WINPATH"
runopts="$runopts --shell=$shell"

# enter systemd namespaces and execute a login shell
exec /usr/bin/nsenter --all --target $SYSTEMD_PID --wd="$PWD" /sbin/runuser $runopts $user -- $@