emandret · June 27, 2023 17:34 · Jun 27, 2023
diff --git a/systemd-stub b/systemd-stub
@@ -0,0 +1,70 @@
+#!/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 -- $@