Daemons and Services: what changed

Revision 3 to 4. Removed lines have a minus sign; added lines have a plus sign.

Old	New		Line
1	1		## What are daemons, services and agents?
2	2
3	3		Unix daemons and Windows services are system-wide programs running without user interaction; macOS agents are per user programs (cf system-wide daemons) that may or may not run without user interaction. Although the nomenclature differs, their function is similar: for example www or ftp servers are called daemons under Linux and services under Windows. Because they do not interact with the user directly, they close their stdin, stdout, stderr descriptors at start.
4	4
5	5		With Free Pascal and Lazarus it is possible to write these daemons/services in a platform-independent manner using the Lazarus lazdaemon package. To avoid name conflicts with the Delphi components these classes are called 'daemons'.
6	6
7	7		> Note: This page focuses on Windows and Linux. To read about Lazarus and macOS "Agents", please refer to [[macOS daemons and agents]].
8	8
9	9		## Creating a Service/Daemon (using Lazarus and visual Components)
10	10
11	11		> Note: The complete sample source code for this wiki page is available via the link at the end of this wiki page.
12	12
13	13		### Prerequisite: Install the LazDaemon package
14	14
15	15		Before you can start creating a daemon using the Lazarus IDE, you must install the LazDaemon package either via "Components" - "Configure installed packages" or by installing the lpk file directly from .../lazarus/components/daemon/lazdaemon.lpk. The package installs some new components and menu items in the IDE.
16	16
17	17		![](/wiki-images/3/31/2022-02-21_14_34_28-LINDER-LAZW7_-_VMware_Workstation.png)
18	18
19	19		Due to the way packages work in Lazarus, you need to "Save and rebuild the IDE" to install the LazDaemon package.
20	20
21	21		### Creating and using scaffolded Daemon Project Files
22	22
23	23		After having installed the LazDaemon package, from the "Project" - "New Project" Menu, pick "Daemon (service) application)".
24	24
25	25		![](/wiki-images/e/ec/2022-02-17_16_31_12-Create_a_new_project.png)
26	26
27	27		This will automatically create two units, one for a TDaemon descendant ("DaemonUnit"), and one for a TDaemonMapper descendant ("DaemonMapperUnit"), and a main project file ("TestDaemon.lpr"). This file needs a little change to work:
28	28
29	29		``` pascal
30	30		Program TestDaemon;
31	31
32	32		Uses
33	33
34	34		// This is the scaffolded code, needs modification like shown below,
35	35		// since UseCThreads is usually not definied, and is not needed here
36	36		// {$IFDEF UNIX}{$IFDEF UseCThreads}
37	37		// CThreads,
38	38		// {$ENDIF}{$ENDIF}
39	39
40	40		{$IFDEF UNIX}
41	41		CThreads,
42	42		{$ENDIF}
43	43		DaemonApp, lazdaemonapp, daemonmapperunit, DaemonUnit
44	44		{ add your units here };
45	45
46	46		{$R *.res}
47	47
48	48		begin
49	49		Application.Initialize;
50	50		Application.Run;
51	51		end.
52	52		```
53	53
54	54		> Warning: The scaffolded .lpr file contains an additional {\$IFDEF UseCThreads} ... {\$ENDIF} clause (commented out in the sample above), which has been observed not to work, unless additional measures are taken to define UseCThreads. You can remove the conditional entirely or comment it out, like shown in the above .lpr sample, or add a -dUseCThreads option when you compile your daemon on Linux. Windows services are not affected.
55	55
56	56		Despite that daemons don't have a GUI, both the DaemonApp and the DaemonMapper unit have support for the Lazarus Form Editor. This way you get a familiar GUI to populate the various properties of the daemon and the mapper class. Of course, if you prefer, you can initialize all properties in code as well like shown below.
57	57
58	58		Both the scaffolded DaemonApp and the DaemonMapper unit contain a superfluous "var" definition (var DaemonMapper1: TDaemonMapper1; var Daemon1: TDaemon1;). Those are actually never used by the running daemon, they remain uninitialized, trying to access them results in an access violation fatal error. If you have a closer look at how daemon applications work internally you'll see that the code relies solely on the types (TDaemonMapper1, TDaemon), the vars can be ignored or removed entirely.
59	59
60	60		The code provided by the TDaemon class does mainly respond to the various service control messages sent by the OS. The TDaemonMapper contains data structures describing the service. Both classes need to be registered with the daemon application framework, they will be used internally to configure the daemon when it starts. In this code sample registration is done in the "Initialization" section of each unit.
61	61
62	62		The main "Application" object for a service-style application is introduced by putting a reference to DaemonApp into the uses section of each unit. In a daemon application, "Application" provides the complete service framework including advanced features like install and uninstall support, and logging. For the "worker" part of the daemon you are supposed to create a thread of its own, see sample code below, don't try to use the "Execute" method provided by the TDaemon class.
63	63
64	64		### Populating the DaemonMapper Class
65	65
66	66		For the moment let's just fill some basic properties to get things going. Note that the DaemonClassName must exactly match with what you have defined in the DaemonClass unit.
67	67
68	68		![](/wiki-images/1/19/2022-01-31_23_32_52-Settings.png)
69	69
70	70		> Note: For cross-platform programmers: In Unix everything is case-sensitive, using lowercase is common use, so you may cause some confusion if you define a mixed-case service name like shown in the above sample.
71	71
72	72		Maybe have a short look into the WinBindings property, which lets you configure various service properties for use by the Windows Service Manager, like service start type and service user account. While not used for this basic demo daemon, setting those options properly is important for a real life daemon application. WinBindings doesn't have any effect on Linux, see the section about install and uninstall support for Linux on how to achieve the same for Linux by setting options in the systemd "unit" (.service) file.
73	73
74	74		### Writing the Daemon Methods
75	75
76	76		TDaemons support the following methods:
77	77
78	78		\| Method/Event \| Description \|
79	79		\|----\|----\|
80	80		\| `OnStart` \| Called when daemon should start. This method must return immediately with OK:=True. \|
81	81		\| `OnStop` \| Called when daemon should stop. This method must return immediately with OK:=True. \|
82	82		\| `OnShutDown` \| Called when daemon should be killed, because the system shuts down. This method must stop the daemon immediately and return with OK:=True. This is not triggered under Linux. Linux simply kills the daemon process. \|
83	83		\| `OnPause` \| Called when daemon should pause. This method must return immediately with OK:=True. Under Linux this is not triggered, instead the kernel stops the whole daemon on STOP. \|
84	84		\| `OnContinue` \| Called when daemon should continue after a pause. This method must return immediately with OK:=True. Under Linux this is not triggered. \|
85	85		\| `OnExecute` \| Do not use this property to implement the working code, use a worker task like shown in the code sample. \|
86	86		\| `BeforeInstall` \| Called before service installation. \|
87	87		\| `AfterInstall` \| Called after (successful) service installation. \|
88	88		\| `BeforeUninstall` \| Called before service de-installation. \|
89	89		\| `AfterUninstall` \| Called after successful service de-installation. \|
90	90		\| \| \|
91	91
92	92		The following code snippets show all the major event handlers necessary to successfully implement a simple daemon. They have been tested on Windows 7/10/11 and several Linux distros (Debian 10.8 and Ubuntu 20.04.3).
93	93
94	94		Some handy helper functions have been offloaded into separate units, so they do not obfuscate the daemon core code:
95	95
96	96		- FileLoggerUnit: a thread safe log to file helper. It is required because the control signal receiver included in the TDaemon application and the service's working code need to be implemented as separate threads, otherwise the daemon will not respond to control signals while the service worker code runs. So in any daemon there are at least two tasks involved, which could create a clash when accessing the log file simultaneously. See the Lazarus wiki [[Multithreaded Application Tutorial]] for details about how to serialize accesses to a single resource by using a TRTLCriticalSection to make the code thread-safe. The FileLoggerUnit code does always write the log into the program directory, please make sure the daemon has write access permissions. The code writes one file per day, the filename contains the creation date. If you need a more sophisticated logger, consider using the [[LazLogger]] unit.
97	97		- [DaemonWorkerThread](https://gitlab.com/freepascal.org/lazarus/lazarus/-/tree/main/examples/TDaemon): a TThread descendant class to hold the daemon "worker" code. See the Lazarus wiki [[Multithreaded Application Tutorial]] for details about the TThread.Execute method containing the inevitable "while not terminated" loop. There is nothing special with a worker thread initiated by a TDaemon, it's just a simple thread like any other.
98	98		- [DaemonSystemdInstallerUnit](https://gitlab.com/freepascal.org/lazarus/lazarus/-/tree/main/examples/TDaemon): a unit which tries to provide support for the -install and -uninstall command line parameters for Linux. Adds systemd/systemctl support by writing an appropriate control file to /lib/systemd/system.
99	99
100	100		### Daemon Start/Stop Signal Handler
101	101
102	102		``` Pascal
103	103		// ---------------------
104	104		// Start and Stop signal
105	105		// ---------------------
106	106
107	107		procedure TDaemon1.DataModuleStart(Sender: TCustomDaemon; var OK: Boolean);
108	108		begin
109	109		LogToFile(Format('Daemon received start signal, PID:%d', [GetProcessID]));
110	110		// Create a suspended worker thread - see DaemonWorkerThread unit
111	111		FDaemonWorkerThread := TDaemonWorkerThread.Create;
112	112		// Parametrize it
113	113		FDaemonWorkerThread.FreeOnTerminate := False;
114	114		// Start the worker
115	115		FDaemonWorkerThread.Start;
116	116		OK := True;
117	117		end;
118	118
119	119		procedure TDaemon1.DataModuleStop(Sender: TCustomDaemon; var OK: Boolean);
120	120		begin
121	121		LogToFile('Daemon received stop signal');
122	122		// stop and terminate the worker
123	123		if assigned(FDaemonWorkerThread) then
124	124		begin
125	125		FDaemonWorkerThread.Terminate;
126	126		// Wait for the thread to terminate.
127	127		FDaemonWorkerThread.WaitFor;
128	128		FreeAndNil(FDaemonWorkerThread);
129	129		end;
130	130		LogToFile('Daemon stopped');
131	131		OK := True;
132	132		end;
133	133		```
134	134
135	135		These handlers deal with the start and stop signals issued by the operating system. If the daemon starts, DataModuleStart fires and we spawn the "worker" thread found in the DaemonWorkerThread unit, see the TDeamonWorkerThread.Execute method to find the actual working code of our daemon. To understand the thread code, refer to the [[Multithreaded Application Tutorial]] wiki page and to the documentation of TThread.
136	136
137	137		> Warning: To implement the daemon worker code, one might consider to implement a handler for the "execute" method found in TDaemon. This does not work well, especially not on WIndows. Execute does not run as a separate thread, while it executes the daemon stops handling control messages. The daemon will start and run fine, but if you try to stop/pause/resume it using the Windows Service Manager or the sc command, the daemon will not respond and appear to hang.
138	138
139	139		### Daemon Shutdown Handler
140	140
141	141		This Windows-only handler is called when the daemon is to be stopped because of an operating system shutdown. If we do not handle the event, Windows will simply forcefully kill the daemon process, potentially corrupting open files. For this simple demo service one can simply call the DataModuleStop event handler, executing the same code like a normal service stop. On Linux this handler is not supported, Linux will instead directly call the stop handler.
142	142
143	143		``` Pascal
144	144		procedure TDaemon1.DataModuleShutDown(Sender: TCustomDaemon);
145	145		// Supported on Windows systems only
146	146		begin
147	147		self.Stop; // On shutdown, we trigger the stop handler. This will do nicely for this demo
148	148		LogToFile('Daemon received shutdown signal');
149	149		end;
150	150		```
151	151
152	152		### Install and Uninstall for Linux (systemd)
153	153
154	154		The built-in install and uninstall support (-install and -uninstall command line parameters) is implemented in LazDaemon applications for Windows only. Here is a simple code sample showing how to make custom handlers for install and uninstall events to add a similiar functionality for Linux.
155	155
156	156		``` Pascal
157	157		// --------------------------------
158	158		// Installation and De-Installation
159	159		// --------------------------------
160	160
161	161		procedure TDaemon1.DataModuleAfterInstall(Sender: TCustomDaemon);
162	162
163	163		var
164	164		isInstalled: boolean = True;
165	165		FilePath: string;
166	166
167	167		begin
168	168		LogToFile('Daemon installing');
169	169		{$IFDEF UNIX}
170	170		FilePath := GetSystemdControlFilePath(Self.Definition.Name);
171	171		isInstalled := CreateSystemdControlFile(self, FilePath);
172	172		if not isInstalled then
173	173		LogToFile('Error creating systemd control file: ' + FilePath);
174	174		{$ENDIF}
175	175		if isInstalled then
176	176		LogToFile('Daemon installed');
177	177		end;
178	178
179	179		procedure TDaemon1.DataModuleBeforeUnInstall(Sender: TCustomDaemon);
180	180		var
181	181		isUnInstalled: boolean = True;
182	182		FilePath: string;
183	183
184	184		begin
185	185		LogToFile('Daemon uninstalling');
186	186		{$IFDEF UNIX}
187	187		FilePath := GetSystemdControlFilePath(Self.Definition.Name);
188	188		isUnInstalled := RemoveSystemdControlFile(FilePath);
189	189		if not isUninstalled then
190	190		LogToFile('Error removing systemd control file: ' + FilePath);
191	191		{$ENDIF}
192	192		if isUninstalled then
193	193		LogToFile('Daemon uninstalled');
194	194		end;
195	195		```
196	196
197	197		These Unix/Linux-only handlers utilize the routines in DaemonSystemdInstallerUnit to write a systemd control file (.service file) for our service to /lib/systemd/system, so the daemon can be controlled using the systemctl command. On uninstall, the .service file ist deleted.
198	198
199	199		If you don't specify a user account in the .service file, systemd will run the daemon as root. Running a daemon as "root" (Linux) or "LocalSystem" (Windows) is, for security reasons, considered bad practice, and can, amongst many other obstacles, hamper debugging the running daemon. Consider to add a line
200	200
201	201		``` Pascal
202	202		[...]
203	203		f.WriteString('Service', 'Type', 'simple');
204	204		f.WriteString('Service', 'User', '...'); // insert a service account here, otherwise the daemon will run as root
205	205		f.WriteString('Service', 'ExecStart', Application.ExeName + ' -r');
206	206		[...]
207	207		```
208	208
209	209		in the DaemonSystemdInstallerUnit.CreateSystemdControlFile code.
210	210
211	211		> Note: At runtime you'll find all the TDaemonMapper and especially the TDaemonMapper.WinBindings settings in the "self.Definition" and "self.Definition.WinBindings" structures. If you prefer, you may consider using some of them to populate settings in the .service file.
212	212
213	213		For a comprehensive guide on all settings available in a systemd .service file (sometimes called a systemd "unit file") please see the documentation of your Linux distribution.
214	214
215	215		### Daemon Worker Thread
216	216
217	217		At the core of every daemon there is a piece of code which does the actual work, I named it the "worker" thread. It needs to be a separate thread, because in the background the daemon is supposed to continue to listen for control messages and process them. Creation and destruction of the thread can be seen in the above samples for TDaemon.DataModuleStart and TDaemon.DataModuleStop handlers.
218	218
219	219		``` Pascal
220	220		procedure TDaemonWorkerThread.Execute;
221	221
222	222		var
223	223		i: integer;
224	224
225	225		begin
226	226		LogToFile('Daemon worker thread executing');
227	227		while not Terminated do
228	228		begin
229	229		// placeholder, put your actual service code here
230	230		// ...
231	231		LogToFile('Daemon worker thread running');
232	232		// Thread- and CPUload friendly 5s delay loop
233	233		for i := 1 to 50 do
234	234		begin
235	235		if Terminated then break;
236	236		Sleep(100);
237	237		end;
238	238		// ...
239	239		// ----------------------------------------
240	240		end;
241	241		LogToFile('Daemon worker thread terminated');
242	242		end;
243	243		```
244	244
245	245		This "worker" doesn't do much, it loops until terminated and writes a message into the log every 5 seconds.
246	246
247	247		For your own daemon functionality, replace the code between "..." and "..." with your own.
248	248
249	249		The inner loop of a TThread.Execute method must be layed out in a way so it checks the "Terminated" flag frequently. The flag is set by the TThread.Terminate method which is called to gracefully end a thread execution, like it can be seen in the above TDaemon.DataModuleStop sample. There is more info about TThreads available in the [[Multithreaded Application Tutorial]] wiki.
250	250
251	251		To keep the sample demo code simple, it does not handle runtime errors in any way. Errors in the logging unit will be dropped silently, all other runtime errors in the daemon will crash the daemon. Please refer to the wiki page about [[Exceptions]] to read more about catching and handling exceptions in general, and see the documentation on TThread.HandleException to read more about how to properly catch and forward an exception within the execute method of a worker thread.
252	252
253	253		### Initializing TDaemon Properties in Code
254	254
255	255		If you prefer not to use the Lazarus IDE and its Forms Editor to populate your TDaemon and TDeamonMapper properties, you can do it all in code as well. If you want to go this route, note that your project must not be based on the LCL/Forms like other applications, but on DaemonApp. Failing this will make the code fail with numerous stream loading errors.
256	256
257	257		Working with TDaemon (The event driven approach to program a daemon) has already been described in the above sections, the only real difference is that you will assign the event handlers in the application code like so:
258	258
259	259		``` Pascal
260	260		TDaemon1 = class(TDaemon)
261	261		{...}
262	262		procedure DataModuleStart(Sender: TCustomDaemon; var OK: Boolean); // sample event handler event
263	263		{...}
264	264		public
265	265		constructor Create(AOwner: TComponent); override; // overwrite the constructor to initialize the event handlers
266	266		end;
267	267
268	268		{...}
269	269
270	270		constructor TDaemon1.Create(AOwner: TComponent);
271	271		begin
272	272		inherited Create(AOwner);
273	273		{...}
274	274		onStart := @DataModuleStart; // assign the sample event handler code
275	275		{...}
276	276		end;
277	277		```
278	278
279	279		Follow the same strategy with TDaemonMapper to populate the Mapper.
280	280
281	281		> Note: If you prefer an OOP based approach using inheritance to customize the daemon- and the mapper class you can do this as well, inherit your own daemon from TCustomDaemon and your own mapper from TCustomDaemonMapper, and overwrite the various virtual functions in the "Protected" section as needed
282	282
283	283		Here is an excerpt from the DaemonApp unit showing the available properties:
284	284
285	285		``` Pascal
286	286		TCustomDaemon = Class(TDataModule)
287	287		private
288	288
289	289		[...]
290	290
291	291		Protected
292	292		Function Start : Boolean; virtual;
293	293		Function Stop : Boolean; virtual;
294	294		Function Pause : Boolean; virtual;
295	295		Function Continue : Boolean; virtual;
296	296		Function Execute : Boolean; virtual;
297	297		Function ShutDown : Boolean; virtual;
298	298		Function Install : Boolean; virtual;
299	299		Function UnInstall: boolean; virtual;
300	300
301	301		[...]
302	302		```
303	303
304	304		## Creating a Service/Daemon (in Code only)
305	305
306	306		> Note: The complete sample source code for this wiki page is available via the link at the end of this wiki page.
307	307
308	308		TestDaemonCodeOnly is a demo project utilizing the TCustomDaemon and TCustomDaemonMapper classes, and it works without the Lazarus IDE. It does therefore not need any Lazarus specific helper files like .lpr or .lfm, and can be maintained using any plain text editor. The programming paradigm used is not event-driven like in GUI centric code, but works based on OOP and inheritance. The helper units providing file logging, a daemon worker thread and support for systemd -install and -uninstall for Linux are the same as in the above GUI sample.
309	309
310	310		Support for -install and -uninstall for Linux is provided by the same DaemonSystemdInstallerUnit as used above. Windows service installation and uninstallation is already built-in in the DaemonApp unit. The TDaemonMapper class provides the WinBindings property to configure the service for Windows, on Linux this property is not used and has no effect. The code provided in the DeamonSystemdInstallerUnit provides similar functionality for Linux/systemd/systemctl.
311	311
312	312		The -run parameter is not supported on Windows, Windows has its own facilities (the Windows Service Control Manager or the "sc" command line tool) to control services.
313	313
314	314		The daemon code needs to be implemented in multiple threads, one for handling the daemon control messages and a separate thread for the daemon "worker" code. Just overwriting the TCustomDaemon.Execute method won't work well, since while the daemon loops in the "TDaemon.Execute" method it will not handle control messages. It will therefore appear to hang in the Service Control Manager and refuse to respond to sc commands. The "worker" thread code is identical with what's required in the above GUI sample, and implemented in the DaemonWorkerThread unit.
315	315
316	316		The absence of a GUI and console requires the use of a logging facility. The TCustomDaemon object provides a logging facility (through the EventLog property), but that is not thread-safe. The FileLoggerUnit provides a simple thread-safe log to file facility. For more sophisticated logging, consider to use the [[LazLogger]] unit.
317	317
318	318		> Warning: The logfile created by the FileLoggerUnit is written to the program directory, please ensure that the dameon has write access to it.
319	319
320	320		For more detailed informations about multithreading and how to make code thread-safe through the use of CriticalSections see the [[Multithreaded Application Tutorial]].
321	321
322	322		``` Pascal
323	323		program TestDaemonCodeOnly;
324	324
325	325		{$mode objfpc}{$H+}
326	326
327	327		uses
328	328		{$IFDEF UNIX}
329	329		cthreads,
330	330		{$ENDIF}
331	331		Classes,
332	332		SysUtils,
333	333		{ you can add units after this }
334	334		DaemonApp,
335	335		FileLoggerUnit, // Thread safe file logger
336	336		DaemonWorkerThread, // a TThread descendant to do the daemon's work
337	337		DaemonSystemdInstallerUnit; // -install and -uninstall support for Linux/systemd
338	338
339	339		// ------------------------------------------------------------------
340	340		// TDaemonMapper: This class type defines the settings for the daemon
341	341		// ------------------------------------------------------------------
342	342
343	343		type
344	344		TDaemonMapper1 = class(TCustomDaemonMapper)
345	345		public
346	346		constructor Create(AOwner: TComponent); override;
347	347		end;
348	348
349	349		constructor TDaemonMapper1.Create(AOwner: TComponent);
350	350
351	351		begin
352	352		inherited Create(AOwner);
353	353		with TDaemonDef(self.DaemonDefs.Add) do
354	354		begin
355	355		DaemonClassName := 'TDaemon1'; // This must exactly match the daemon class
356	356		Name := 'TestDaemonCodeOnly'; // Service name
357	357		DisplayName := 'Test Daemon (CodeOnly)'; // Service display name
358	358		Description := 'Lazarus Daemons and Services Wiki Demo Service (Created in Code only)';
359	359		Options := [doAllowStop, doAllowPause];
360	360		WinBindings.StartType := stManual; // stBoot, stSystem, stAuto, stManual, stDisabled
361	361		WinBindings.ServiceType := stWin32;
362	362		end;
363	363		end;
364	364
365	365		// -------------------------------------------------------------------
366	366		// TDaemon: This class type definies the daemon task and handles the
367	367		// events triggered by the Windows/Linux Service Manager
368	368		// -------------------------------------------------------------------
369	369
370	370		type
371	371
372	372		{ TDaemon1 }
373	373
374	374		TDaemon1 = class(TCustomDaemon)
375	375		private
376	376		FDaemonWorkerThread: TDaemonWorkerThread;
377	377		public
378	378		function Start: boolean; override; // start the daemon worker thread
379	379		function Stop: boolean; override; // stop the daemon worker thread
380	380		function Pause: boolean; override; // pause the daemon worker thread (Windows only)
381	381		function Continue: boolean; override; // resume the daemon worker thread (Windows only)
382	382		function ShutDown: boolean; override; // stop the daemon worker thread because of OS shutdown
383	383		function Install: boolean; override; // added -install suppport for Linux
384	384		function UnInstall: boolean; override; // added -uninstall suppport for Linux
385	385		end;
386	386
387	387		{ TDaemon1 }
388	388
389	389		// ------------------------------------------------
390	390		// Daemon start and stop signal
391	391		// ------------------------------------------------
392	392
393	393		function TDaemon1.Start: boolean;
394	394		begin
395	395		// Create a suspended worker thread - see DaemonWorkerThread unit
396	396		FDaemonWorkerThread := TDaemonWorkerThread.Create;
397	397		// Parametrize it
398	398		FDaemonWorkerThread.FreeOnTerminate := False;
399	399		// Start the worker
400	400		FDaemonWorkerThread.Start;
401	401		LogToFile(Format('TDaemon1: service %s started, PID=%d', [self.Definition.Name, GetProcessID]));
402	402		Result := True;
403	403		end;
404	404
405	405		function TDaemon1.Stop: boolean;
406	406		begin
407	407		// stop and terminate the worker
408	408		if assigned(FDaemonWorkerThread) then
409	409		begin
410	410		FDaemonWorkerThread.Terminate;
411	411		// Wait for the thread to terminate.
412	412		FDaemonWorkerThread.WaitFor;
413	413		FreeAndNil(FDaemonWorkerThread);
414	414		end;
415	415		Result := True;
416	416		LogToFile(Format('TDaemon1: service %s stopped', [self.Definition.Name]));
417	417		end;
418	418
419	419		// ------------------------------------------------
420	420		// Daemon pause and continue signal (Windows only)
421	421		// ------------------------------------------------
422	422
423	423		function TDaemon1.Pause: boolean;
424	424		begin
425	425		FDaemonWorkerThread.Suspend; // deprecated, yet still working
426	426		LogToFile(Format('TDaemon1: service %s paused', [self.Definition.Name]));
427	427		Result := True;
428	428		end;
429	429
430	430		function TDaemon1.Continue: boolean;
431	431
432	432		begin
433	433		LogToFile(Format('TDaemon1: service %s continuing', [self.Definition.Name]));
434	434		FDaemonWorkerThread.Resume; // deprecated, yet still working
435	435		Result := True;
436	436		end;
437	437
438	438		// --------------------------------------------------------------
439	439		// Daemon stop on operating system shutdown signal (Windows only)
440	440		// --------------------------------------------------------------
441	441
442	442		function TDaemon1.ShutDown: boolean;
443	443		begin
444	444		Result := self.Stop; // On shutdown, we trigger the stop handler. This will do nicely for this demo
445	445		LogToFile(Format('TDaemon1: service %s shutdown', [self.Definition.Name]));
446	446		end;
447	447
448	448		// -----------------------------------------------------------------------------------------
449	449		// Daemon install and uninstall helpers for Linux, Windows is already built in TCustomDaemon
450	450		// -----------------------------------------------------------------------------------------
451	451
452	452		function TDaemon1.Install: boolean;
453	453
454	454		var
455	455		FilePath: string;
456	456
457	457		begin
458	458		Result := False;
459	459		{$IFDEF WINDOWS}
460	460		Result := inherited Install;
461	461		{$ELSE}
462	462		{$IFDEF UNIX}
463	463		FilePath := GetSystemdControlFilePath(Self.Definition.Name);
464	464		LogToFile(Format('TDaemon1: installing control file: %s',[FilePath]));
465	465		Result := CreateSystemdControlFile(self, FilePath);
466	466		if not Result then
467	467		LogToFile('TDaemon1: Error creating systemd control file: ' + FilePath);
468	468		{$ENDIF}
469	469		{$ENDIF}
470	470		LogToFile(Format('TDaemon1: service %s installed: %s', [self.Definition.Name, BoolToStr(Result, 'ok', 'failure')]));
471	471		end;
472	472
473	473		function TDaemon1.UnInstall: boolean;
474	474
475	475		var
476	476		FilePath: string;
477	477
478	478		begin
479	479		Result := False;
480	480		{$IFDEF WINDOWS}
481	481		Result := inherited UnInstall;
482	482		{$ELSE}
483	483		{$IFDEF UNIX}
484	484		FilePath := GetSystemdControlFilePath(Self.Definition.Name);
485	485		Result := RemoveSystemdControlFile(FilePath);
486	486		if not Result then
487	487		LogToFile('TDaemon1: Error removing systemd control file: ' + FilePath);
488	488		{$ENDIF}
489	489		{$ENDIF}
490	490		LogToFile(Format('TDaemon1: service %s uninstalled: %s', [self.Definition.Name, BoolToStr(Result, 'ok', 'failure')]));
491	491		end;
492	492
493	493		// ---------------------
494	494		// Daemon main init code
495	495		// ---------------------
496	496
497	497		begin
498	498		RegisterDaemonClass(TDaemon1);
499	499		RegisterDaemonMapper(TDaemonMapper1);
500	500		Application.Run;
501	501		end.
502	502		```
503	503
504	504		## Daemon/Service Installation
505	505
506	506		### Windows
507	507
508	508		You can install the service from any elevated command prompt by starting the executable with the -install parameter.
509	509
510	510		Open a terminal with elevated privileges (run as administrator), navigate to the directory where you compiled your test application into, and try the following commands:
511	511
512		-	~~<thead>~~
513		-
514		-	~~</thead>~~
515		-	~~<tbody>~~
516		-
517		-	~~when the machine boots</td>~~
518		-
519		-	~~</tbody>~~
	512	+	\| Command \| Description \|
	513	+	\|---\|---\|
	514	+	\| `TestDaemon -install` \| install the daemon \|
	515	+	\| `sc query TestDaemon` \| check the service status \|
	516	+	\| `sc config TestDaemon start=auto` \| configure the service to be started · when the machine boots \|
	517	+	\| `sc config TestDaemon start=manual` \| configure the service to be started manually \|
	518	+	\| `sc config TestDaemon start=disabled` \| disable the service (cannot be started manually) \|
	519	+	\| `TestDaemon -uninstall` \| remove the daemon \|
520	520
521	521		![](/wiki-images/a/a4/2022-01-31_23_50_28-Lazarus_IDE_v2.2.0RC2_-_Daemon_application.png)
522	522
523	523		After successful installation you can control the service either via the sc command line, or by GUI using the "Services" management console. Recent Windows Versions do also have a basic service control facility on the "Services" tab of the Task Manager.
524	524
525	525		The most important sc commands to control a service after installation are:
526	526
527	527		\| Command \| Description \|
528	528		\|-----------------------\|-------------------------\|
529	529		\| `sc start TestDaemon` \| start the service \|
530	530		\| `sc query TestDaemon` \| query the service state \|
531	531		\| `sc stop TestDaemon` \| stop the service \|
532	532
533	533		You may also use the Windows service control manager console.
534	534
535	535		![](/wiki-images/0/07/ServiceControlManager.png)
536	536
537	537		> Note: Most Windows service properties, like autostart on boot or usage of a specific service account, can be set via the TDaemonMapper1.WinBindings property in the DaemonMapperUnit1 file.
538	538
539	539		### Linux
540	540
541	541		Unlike for Windows, the TDaemonApp application does not have any support for an automated installation, since under Linux/Unix there is a wide variety of service control subsystems. You can implement your own installation scripts in the install and uninstall handlers of the TCustomDaemon object, like shown for systemd support in the above code sample. If you follow that route, installation and de-installation is essentially the same like on Windows.
542	542
543	543		You can install and uninstall the service from a terminal by starting the executable with sudo and the -install or -uninstall parameter:
544	544
545		-	~~<thead>~~
546		-
547		-	~~</thead>~~
548		-	~~<tbody>~~
549		-
550		-	~~when the machine boots</td>~~
551		-
552		-	~~when the machine boots</td>~~
553		-
554		-	~~</tbody>~~
	545	+	\| Command \| Description \|
	546	+	\|---\|---\|
	547	+	\| `sudo ./TestDaemon -install` \| install the service \|
	548	+	\| `sudo ./TestDaemon -uninstall` \| uninstall the service \|
	549	+	\| `systemctl enable TestDaemon` \| configure the service to be started · when the machine boots \|
	550	+	\| `systemctl disable TestDaemon` \| configure the service to not be started · when the machine boots \|
555	551
556	552		After successful installation you can control the service using the systemctl command
557	553
558	554		\| Command \| Description \|
559	555		\|-------------------------------\|-------------------------\|
560	556		\| `systemctl start TestDaemon` \| start the service \|
561	557		\| `systemctl status TestDaemon` \| query the service state \|
562	558		\| `systemctl stop TestDaemon` \| stop the service \|
563	559
564	560		![](/wiki-images/4/4f/OnLinuxWithSystemctl.png)
565	561
566	562		The code in DaemonSystemdInstallerUnit.CreateSystemdControlFile triggered by the -install command line parameter reads the most basic properties of the TDaemonMapper class and writes a simple systemd .service file into the /lib/systemd/system directory to put your daemon under control of systemd. If you prefer to do it manually, you may use any text editor to create your own file following this template:
567	563
568	564		``` ini
569	565		[Unit]
570	566		Description=Long description of your application
571	567		After=network.target
572	568
573	569		[Service]
574	570		Type=simple
575	571		User=name_of_a_service_user_account
576	572		ExecStart=complete_path_and_file_name -r
577	573		RemainAfterExit=yes
578	574		TimeoutSec=25
579	575
580	576		[Install]
581	577		WantedBy=multi-user.target
582	578		```
583	579
584	580		- Edit the following values
585	581		- Description - Long Description of your service application
586	582		- ExecStart - complete-path_and_file_name is the name of your compiled service application with its complete path
587	583		- User - specify an service user account here, if omitted the daemon will run as root, running a daemon as root is strongly discouraged
588	584
589	585		- Save the file
590	586		- Navigate to /lib/systemd/system/
591	587		- Name the file the name_of_your_service.service
592	588
593	589		Many more entries in the .service file created by DaemonSystemdInstallerUnit.CreateSystemdControlFile are available to customize how systemd controls your daemon, please see the the systemd "unit" file reference of your Linux distribution.
594	590
595	591		## Reading the Log File
596	592
597	593		This is a sample log file showing the daemon's internals while running, it was created on Windows, but will look exactly the same on Linux.
598	594
599	595		![](/wiki-images/d/d1/2022-02-01_12_17_27-TestDaemon.png)
600	596
601	597		> Warning: The FileLoggerUnit does always log into the program directory, please make sure the daemon has write access permissions to it.
602	598
603	599		## Debugging a Daemon/Service
604	600
605	601		Debugging a daemon is not as straightforward as debugging a normal application, since a running daemon does usually have neither a GUI nor a console, and its run/stop state is usually managed by the operating system. Windows and Linux require different approaches to debugging, especially to the way you initiate a debugging session. Once you have attached the debugger to the daemon and hit your first breakpoint, things work just with any other application, and you may control the debugger directly from your Lazarus GUI and the daemon source code.
606	602
607	603		As a prerequisite, you need to compile your service/daemon using a "debug" configuration, so debug code gets inserted and a matching debug symbol file (.dbg) file is created.
608	604
609	605		### Windows
610	606
611	607		The debugging strategy on Windows depends on what portion of the code you need to examine:
612	608
613	609		\- If you need to debug -install or -uninstall, set "Run" - "Run Parameters" in the Lazarus GUI to -install or -uninstall, set your breakpoints, and start the code \[F9\].
614	610
615	611		\- If you need to debug the service worker code, start the service via the operating system (sc command or Windows Service Manager), determine the Process ID (PID), and then choose "Run" - "Attach to Program". Once attached, the debugger will automatically halt at a predefined temporary breakpoint in ntdll.dll!DbgUserBreakPoint, and the service will be looping somewhere within the worker code. After setting your breakpoints and watches in the worker code, resume your debugging by running the code using \[F9\].
616	612
617	613		![](/wiki-images/d/da/2022-02-21_21_25_22-Lazarus_IDE_v2.2.0_-_Daemon_application_%28debugging_...).png "2022-02-21_21_25_22-Lazarus_IDE_v2.2.0_-_Daemon_application_(debugging_...).png")
618	614
619	615		> Warning: The "Pause" button in the Lazarus symbol bar does not seem to work when debugging a running process remotely, it will hang the debugger if pressed. Use "Run" \[F9\] to resume debugging after a breakpoint.
620	616
621	617		\- If you need to debug the create or start handlers, or any other piece in code which might have already been executed before you had a chance to "Attach to program" you can make your code wait until a debugger is attached by inserting the following line in your code:
622	618
623	619		``` Pascal
624	620		// This code will loop until a debugger is attached
625	621		While not IsDebuggerPresent do sleep(100); // will loop until a debugger is attached
626	622		// ... put a breakpoint somewhere after the loop to catch the code as soon as it leaves the loop
627	623		```
628	624
629	625		![](/wiki-images/c/c4/2022-02-21_21_36_38-Lazarus_IDE_v2.2.0_-_Daemon_application_%28debugging_...).png "2022-02-21_21_36_38-Lazarus_IDE_v2.2.0_-_Daemon_application_(debugging_...).png")
630	626
631	627		After attaching the debugger and pressing \[F9\] the daemon will stop right at the breakpoint.
632	628
633	629		> Note: The -run parameter supported by Linux is not available on Windows. You must use the Windows Service Control Manager to start and stop the service. To attach the debugger to the then running process you need to run the Lazarus IDE with Administrative Prvilege (elevated), otherwise you will get Error 5 (access denied) when trying to attach to the service. If you are running Lazarus elevated, and nevertheless have difficulties attaching to your service ("Access denied" or "Run" - "Attach to program" is grayed out) make sure you have set the debugger in "Project" - "Project Settings" - "Debugger" properly, most likely you will need "Gdb (Gnu Debugger)".
634	630
635	631		### Linux
636	632
637	633		Linux is propably somewhat easier to debug, since you can execute your daemon like every other program from within the Lazarus IDE, if you enter -run into "Command line parameters" in the "Run" - "Run Parameters" menu. Keep in mind though, that many problems originate from security restrictions enforced by the operating system. Many of those restrictions are not applied when the daemon is run in user context.
638	634
639	635		![](/wiki-images/f/fd/2022-02-22_12_18_20-Debian_10.8_Buster_-_VMware_Workstation.png)
640	636
641	637		Now you can start the daemon using \[F9\] like any normal application and debug it.
642	638
643	639		![](/wiki-images/e/e9/2022-02-22_12_19_41-Debian_10.8_Buster_-_VMware_Workstation.png)
644	640
645	641		If you do, for instance because you suspect a problem with service specific restrictions, need to attach the debugger to the already running daemon, you can do so using "Run" - "Attach to Program", if you have configured the daemon to run under a specific user account instead of root. See the chapter above about Linux install and uninstall support on how to add an appropriate option to the .service file.
646	642
647	643		Unfortunately there isn't such a handy "IsDebuggerPresent" call available like under Windows, but the following trick works nicely.
648	644
649	645		``` Pascal
650	646		procedure WaitForDebugger;
651	647
652	648		var
653	649		SetMeValue:boolean=false;
654	650
655	651		begin
656	652		// Linux trick: attach the debugger, and change SetMeValue to true
657	653		while not SetMeValue do
658	654		sleep(100); // put a breakpoint here
659	655		end;
660	656		```
661	657
662	658		Put a breakpoint into the line with the "sleep" command. Once the daemon is started using systemctl, execution it will be halted at your breakpoint in the while loop. Now you can attach the debugger to the PID you got from systemctl status, put a watch (\[Ctrl-F5\]) on the "SetMeValue" variable and then use the Evaluate/Modify context menu to change the value of the "SetMeValue" variable from "false" to "true", and resume program execution (\[F9\]). The execution will immedately leave the while loop and run to the next breakpoint.
663	659
664	660		## Known problems
665	661
666	662		### Permission related Problems
667	663
668	664		While you can do most of the development of the core daemon code under a user account and from within an IDE (Lazarus), the live daemon will most likely run "in the background" under a different context. Nowadays operating systems do, for security reasons, run daemons in more or less restricted environments. Because a daemon does have neither a terminal nor a GUI to show any messages, debugging such issues can be hard. Unfortunately there is no common recipe which resolves all service related problems in all operating systems supported by FPC/Lazarus, as the strategy behind restricting service code is vastly different between Windows, Linux and macOS, and it is even changing between different versions of the same operating system, with the more recent versions trending to be more restrictive than their predecessors.
669	665
670	666		If you make the transition from running the daemon code under your developer account to "go live" and test the daemon running under a service user account oder under "Localsystem" or "root" (which, btw, is considered bad security practice since many years), take the time to study the security related documentations of your operating system and find out which restrictions and other specialities apply if code runs in the background.
671	667
672	668		> Note: See the section above about debugging daemons running in the background by attaching the debugger to the running code. Make your daemon, once the daemon is started by the operating system, wait until the debugger is attached. From there you can then observe the execution and detect restrictions related exceptions and other security/background operation related nastinesses.
673	669
674	670		### Exception EStreamError: "no streaming method available"
675	671
676	672		```text
677	673		Exception at 0041A30E: EStreamError:
678	674		Failed to initialize component class "TDaemon1": No streaming method available.
679	675		```
680	676
681	677		You have included visual components (which require initalization by a built-in resource stream created by the .lfm file in GUI applications) in a code-only daemon project. If you decide to create the daemon in code, you may neither include the LazDaemon package, nor add the "LazDaemonApp" to the uses section. If you do, your project will compile fine, but if you start the exe you get the above error.
682	678
683	679		### Several "Stream Read" and "Unkown Properties" errors ...
684	680
685	681		... when loading a daemon project through the Lazarus IDE.
686	682
687	683		Most likely you try to open a TDaemon (GUI component) based project, but you haven't yet installed the LazDaemon package.
688	684
689	685		Abort all loading errors, and install the LazDaemon package using the Lazarus Package Manager like described above. After Lazarus has re-compiled, the daemon project should re-load and compile without problems.
690	686
691	687		![](/wiki-images/f/fb/Image_9.png)
692	688
693	689		![](/wiki-images/b/b3/Image_10.png)
694	690
695	691		### Lazarus IDE suggests to clear invalid properties from the .lpm file
696	692
697	693		This is another issue which was observed when you try to open a TDaemon (GUI) based project, but you haven't yet installed the LazDaemon package.
698	694
699	695		![](/wiki-images/1/13/Image_11.png)
700	696
701	697		Abort all loading errors, and install the LazDaemon package using the Lazarus Package Manager like described above. After Lazarus has re-compiled itself, the daemon project should re-load and compile without problems.
702	698
703	699		### The Daemon won't start on Unix because of missing threading support
704	700
705	701		The code compiles fine, but if you try to run the daemon using a console and the -run parameter, you get a message saying something like "no thread support compiled in". If you try to start the dameon through systemctl, you won't see any message, it simply won't seem to run. You can use "systemctl status" to see the last error caused by the daemon, this will reveal the same crash infos like starting it using -run.
706	702
707	703		``` pascal
708	704		This binary has no thread support compiled in.
709	705		Recompile the application with a thread-driver in the program uses clause before other units using thread.
710	706		Runtime error 232 at ...
711	707
712	708		No heap dump by heaptrc unit
713	709		Exitcode = 232
714	710		```
715	711
716	712		Most likely you compiled your project without support for the CThreads library (not required on Windows). See the above project lpr file sample code and the notes about "UseCThreads". The short of it is to go to the .lpr file and remove the {\$IFDEF UseCThreads} ... {\$ENDIF} around the "uses CThreads" statement, so the CThreads library gets linked into your code on Linux. On Windows this library is not required.
717	713
718	714		### Debugging Issues observed on Windows
719	715
720	716		The "Pause" button in the Lazarus symbol bar activates, if a breakpoint is hit, but it does not seem to work when debugging a running process remotely, debugging will hang if the button is pressed. Use "Run" \[F9\] instead to resume debugging after a breakpoint.
721	717
722	718		To attach the debugger to the running daemon process you need to run the Lazarus IDE with Administrative Prvilege (elevated), otherwise you will get "Error 5 (access denied)" when trying to attach the debugger.
723	719
724	720		If all debugging selections in the "Run" menu are unavailable (grayed), navigate to "Project" - "Project Options" - "Debugger" and set the "Debugger Backend" to "Gdb \[GNU debugger (gdb)\]". It has been observed that this setting may get messed up if you copy the project source files from one computer / Lazarus installation over to a different one.
725	721
726	722		### Debugging Issues observed on Linux
727	723
728	724		Using "Attach to program" to debug a running daemon via process ID (PID) does not seem to work, you get an error "Debugger Error" ... "Attach failed". One reason may be that you haven't specified a user in the service control file, and thus the service runs as "root", which hampers debugging. Besides of running the service using a dedicated service user account, as a workaround, consider to start debugging by loading the daemon from within Lazarus using "Run" - "Run Parameters" and entering the -run command line parameter. This way debugging does work, but note that the code runs in a different context (user instead of system- or service user account), which may change it's behaviour because of permission related issues.
729	725
730	726		### Daemons have no Access to Network- and Cloud Drives (Onedrive, Dropbox)
731	727
732	728		When choosing the directory for storing the daemon executable (which is by default also used for logging), keep in mind that once the daemon runs in the background it does usually run under the context of a system- or service account. User-specific virtual drives created in one user's account are usually available neither to other user accounts nor to the system account. If you run the daemon from a networked/cloud drive, it is likely that the daemon won't start, since the OS will not be able to find the executable, and that write attempts to the log will fail, since by default the log file is written where the executable is. This may be confusing, since -install and -uninstall will likely work and log fine, because they are usually executed by hand and thus run in your user's context.
733	729
734	730		### Specifying a Service User Account does not work on Linux
735	731
736	732		If you start the daemon and check which account it runs under, it appears to run as root, despite you have specified a different account in your systemd .service file.
737	733
738	734		There are (unconfirmed) reports around that (on some versions of Linux?) in the .service file controlling the systemd the "User" entry must appear before the "ExecStart" entry to work properly, like shown in the code samples in the sections about Linux install and uninstall support.
739	735
740	736		### System Codepage / UTF-8
741	737
742	738		\[Old content, needs verfification 3/2022, may be obsolete\] A LazDeamon project is working with default, not UTF-8, codepage. The -dDisableUTF8RTL mode has to be activated with Project Options ... -\> Compiler Options -\> Additions and Overrides -\> Use system encoding.
743	739
744	740		## \[Some historical contents - needs to be verified and integrated or removed\]
745	741
746	742		\[Old content, needs verfification 3/2022, may be obsolete\]
747	743
748	744		### Linux (only for older Debian)
749	745
750	746		Download, configure, and "Save As" - the sample script located at Web Archive: [1](https://web.archive.org/web/20130209102726/http://aurawin.com/lazarus/debian-service.sh) (The original link is dead for a long time).
751	747
752	748		- SVC_ALIAS is the long description of your application
753	749		- SVC_FILENAME is the actual file name of your compiled service application
754	750		- SVC_DIR is the place your you copied the service application
755	751		- SVC_SERVICE_SCRIPT is the final name of the service.sh when you "Save As" the customized debian-service.sh script.
756	752
757	753		Place your script in the /etc/init.d/ folder
758	754
759	755		start the service by running "sudo service Name_Of_Your_Script start"
760	756
761	757		> Note: sudo has some variations, e.g.:
762	758		>
763	759		> ```text
764	760		> sudo -s #
765	761		> sudo -H #
766	762		> sudo -i #
767	763		> sudo su #
768	764		> ```
769	765		>
770	766		> \
771	767		> `sudo sh #`
772	768
773	769		In order to auto-run the service at startup you can try update-rc.d or else will need a third party tool that will do this.
774	770
775	771		Option 1
776	772
777	773		``` bash
778	774		sudo update-rc.d Name_Of_Your_Script defaults
779	775		```
780	776
781	777		Option 2
782	778
783	779		``` bash
784	780		sudo apt-get install chkconfig
785	781		sudo chkconfig --add Name_Of_Your_Script
786	782		sudo chkconfig --level 2345 Name_Of_Your_Script on
787	783		```
788	784
789	785		## See also
790	786
791	787		- [GitHub Repository](https://github.com/arminlinder/Lazarus-FPC-Wiki-Code-Samples/zipball/master/) Complete demo project sample code (.zip)
792	788		- [[macOS daemons and agents]] - macOS native agents using launchd
793	789		- [[ServiceManager]] Example for the Free Pascal unit for managing Windows services
794	790		- [Taming the daemon: PDF by Michaël Van Canneyt](https://www.freepascal.org/~michael/articles/daemons/daemons.pdf)
795	791		- [[Docker Containerization]] - Containerization as a means to create daemons / services
796	792		- [[UniqueInstance]]
797	793
798	794		---
799	795		From the Free Pascal wiki, page "Daemons and Services", as it stood on 2022-12-29 after a change by Alextp, out of the wiki's dump of 2024-05-26. Copyright stays with the author who wrote it, according to the old wiki's [[Licensing]] page. If you have concerns about this material, [message the admin](/wiki-contact).

Back to history