Fix server systemd detection

* Use SYSTEMD_EXEC_PID to detect execution under systemd, since as of a9b5a19 NOTIFY_SOCKET is now cleared by the server code.
* Set the unit type to notify by default for both server and agent, which is what Rancher-managed installs have done for a while.

Signed-off-by: Brad Davidson <brad.davidson@rancher.com>

install.sh

@@ -217,11 +217,7 @@ setup_env() {
     if [ -n "${INSTALL_K3S_TYPE}" ]; then
         SYSTEMD_TYPE=${INSTALL_K3S_TYPE}
     else
-        if [ "${CMD_K3S}" = server ]; then
-            SYSTEMD_TYPE=notify
-        else
-            SYSTEMD_TYPE=exec
-        fi
+        SYSTEMD_TYPE=notify
     fi
 
     # --- use binary install directory if defined or create default ---

pkg/agent/containerd/config_linux.go

@@ -52,7 +52,7 @@ func setupContainerdConfig(ctx context.Context, cfg *config.Node) error {
 	if disableCgroup {
 		logrus.Warn("cgroup v2 controllers are not delegated for rootless. Disabling cgroup.")
 	} else {
-		cfg.AgentConfig.Systemd = controllers["cpuset"] && os.Getenv("NOTIFY_SOCKET") != ""
+		cfg.AgentConfig.Systemd = controllers["cpuset"] && os.Getenv("SYSTEMD_EXEC_PID") != ""
 	}
 
 	var containerdTemplate string