3 files changed, 19 insertions, 4 deletions
diff --git a/util/prosodyctl.lua b/util/prosodyctl.lua
index 9cb4b4dd..c6856526 100644
--- a/util/prosodyctl.lua
+++ b/util/prosodyctl.lua
@@ -40,6 +40,7 @@ local error_messages = setmetatable({
 		["unable-to-save-data"] = "Unable to store, perhaps you don't have permission?";
 		["no-pidfile"] = "There is no 'pidfile' option in the configuration file, see https://prosody.im/doc/prosodyctl#pidfile for help";
 		["invalid-pidfile"] = "The 'pidfile' option in the configuration file is not a string, see https://prosody.im/doc/prosodyctl#pidfile for help";
+		["pidfile-not-locked"] = "Stale pidfile found. Prosody is probably not running.";
 		["no-posix"] = "The mod_posix module is not enabled in the Prosody config file, see https://prosody.im/doc/prosodyctl for more info";
 		["no-such-method"] = "This module has no commands";
 		["not-running"] = "Prosody is not running";
@@ -143,8 +144,14 @@ local function getpid()
 		return false, "pidfile-read-failed", err;
 	end
 
+	-- Check for a lock on the file
 	local locked, err = lfs.lock(file, "w"); -- luacheck: ignore 211/err
 	if locked then
+		-- Prosody keeps the pidfile locked while it is running.
+		-- We successfully locked the file, which means Prosody is not
+		-- running and the pidfile is stale (somehow it was not
+		-- cleaned up). We'll abort here, to avoid sending signals to
+		-- a non-Prosody PID.
 		file:close();
 		return false, "pidfile-not-locked";
 	end
diff --git a/util/prosodyctl/shell.lua b/util/prosodyctl/shell.lua
index d6d885d8..a0fbb09c 100644
--- a/util/prosodyctl/shell.lua
+++ b/util/prosodyctl/shell.lua
@@ -64,6 +64,13 @@ local function printbanner()
 	print("https://prosody.im/doc/console\n");
 end
 
+local function check()
+	local lfs = require "lfs";
+	local socket_path = path.resolve_relative_path(prosody.paths.data, config.get("*", "admin_socket") or "prosody.sock");
+	local state = lfs.attributes(socket_path, "mode");
+	return state == "socket";
+end
+
 local function start(arg) --luacheck: ignore 212/arg
 	local client = adminstream.client();
 	local opts, err, where = parse_args(arg);
@@ -180,4 +187,5 @@ end
 
 return {
 	shell = start;
+	available = check;
 };
diff --git a/util/startup.lua b/util/startup.lua
index c54fa56d..2fa2d0b2 100644
--- a/util/startup.lua
+++ b/util/startup.lua
@@ -814,12 +814,12 @@ function startup.hook_posix_signals()
 	end);
 end
 
-function startup.systemd_notify()
+function startup.notification_socket()
 	local notify_socket_name = os.getenv("NOTIFY_SOCKET");
 	if not notify_socket_name then return end
 	local have_unix, unix = pcall(require, "socket.unix");
 	if not have_unix or type(unix) ~= "table" then
-		log("error", "LuaSocket without UNIX socket support, can't notify systemd.")
+		log("error", "LuaSocket without UNIX socket support, can't notify process manager.")
 		return os.exit(1);
 	end
 	log("debug", "Will notify on socket %q", notify_socket_name);
@@ -827,7 +827,7 @@ function startup.systemd_notify()
 	local notify_socket = unix.dgram();
 	local ok, err = notify_socket:setpeername(notify_socket_name);
 	if not ok then
-		log("error", "Could not connect to systemd notification socket %q: %q", notify_socket_name, err);
+		log("error", "Could not connect to notification socket %q: %q", notify_socket_name, err);
 		return os.exit(1);
 	end
 	local time = require "prosody.util.time";
@@ -928,7 +928,7 @@ function startup.prosody()
 	startup.posix_daemonize();
 	startup.write_pidfile();
 	startup.hook_posix_signals();
-	startup.systemd_notify();
+	startup.notification_socket();
 	startup.prepare_to_start();
 	startup.notify_started();
 end