StartUnixWorker(): don't exit() on fork() failure

[Al2Klimov]

... but let the caller handle the failure.

Not to stop working completely just because of fork() failure during a reload.

[julianbrost]

When this case happend, what's the state of the old worker process? Won't this already have ceased operation then and leave the umbrella process in a running state, but nothing is happening anymore? Will the fork be retried automatically?

[Al2Klimov]

1. Still running.
2. No.
3. No.

[julianbrost]

So now that I understand more of the code around this, this PR makes more sense to me.

This changes the meaning of the return value -1, so this should be adjusted as well:

icinga2/lib/cli/daemoncommand.cpp

Line 414 in 96ee6f1

* @return The worker's PID on success, -1 on failure (if the worker couldn't load its config)

icinga2/lib/cli/daemoncommand.cpp

Lines 736 to 739 in 96ee6f1

	pid_t nextWorker = StartUnixWorker(configs);
	if (nextWorker == -1) {
	Log(LogCritical, "Application", "Found error in config: reloading aborted");

[Al2Klimov]

➜  icinga2 git:(bugfix/fork-exit) prefix/sbin/icinga2 daemon -c tz.cpp
[2021-01-14 14:17:24 +0100] information/cli: Icinga application loader (version: v2.12.0-427-g931b9307a)
[2021-01-14 14:17:24 +0100] information/cli: Loading configuration file(s).
[2021-01-14 14:17:24 +0100] critical/config: Error: syntax error, unexpected T_IDENTIFIER
Location: in tz.cpp: 4:5-4:8
tz.cpp(2): #include <iostream>
tz.cpp(3):
tz.cpp(4): int main() {
               ^^^^
tz.cpp(5):  std::cout << boost::locale::time_zone::global() << std::endl;
tz.cpp(6): }
[2021-01-14 14:17:24 +0100] critical/cli: Config validation failed. Re-run with 'icinga2 daemon -C' after fixing the config.
➜  icinga2 git:(bugfix/fork-exit) touch 8427.conf; (sleep 10; rm 8427.conf; kill -HUP `cat prefix/var/run/icinga2/*.pid`) & prefix/sbin/icinga2 daemon -c 8427.conf
[2] 39212
[2021-01-14 14:19:45 +0100] information/cli: Icinga application loader (version: v2.12.0-427-g931b9307a)
[2021-01-14 14:19:45 +0100] information/cli: Loading configuration file(s).
[2021-01-14 14:19:45 +0100] information/ConfigItem: Committing config item(s).
[2021-01-14 14:19:45 +0100] information/ConfigItem: Instantiated 1 IcingaApplication.
[2021-01-14 14:19:45 +0100] information/ScriptGlobal: Dumping variables to file '/Users/aklimov/NET/WS/icinga2/prefix/var/cache/icinga2/icinga2.vars'
[2021-01-14 14:19:45 +0100] information/ConfigObject: Restoring program state from file '/Users/aklimov/NET/WS/icinga2/prefix/var/lib/icinga2/icinga2.state'
[2021-01-14 14:19:45 +0100] information/ConfigObject: Restored 281 objects. Loaded 0 new objects without state.
[2021-01-14 14:19:45 +0100] information/ConfigItem: Triggering Start signal for config items
[2021-01-14 14:19:45 +0100] information/ConfigItem: Activated all objects.
[2021-01-14 14:19:50 +0100] information/Application: Got reload command: Starting new instance.
[2]  - 39212 done       ( sleep 10; rm 8427.conf; kill -HUP `cat prefix/var/run/icinga2/*.pid`; )
[2021-01-14 14:19:50 +0100] information/cli: Loading configuration file(s).
[2021-01-14 14:19:50 +0100] critical/cli: Could not compile config files: Error: Function call 'std::ifstream::open' for file '8427.conf' failed with error code 2, 'No such file or directory'

	(0) Compiling configuration file '8427.conf'
[2021-01-14 14:19:50 +0100] critical/Application: Found error in config: reloading aborted
^C[2021-01-14 14:20:02 +0100] information/Application: Received request to shut down.
[2021-01-14 14:20:03 +0100] information/Application: Shutting down...
[2021-01-14 14:20:03 +0100] information/ConfigObject: Dumping program state to file '/Users/aklimov/NET/WS/icinga2/prefix/var/lib/icinga2/icinga2.state'
[2021-01-14 14:20:03 +0100] information/IcingaApplication: Icinga has shut down.
➜  icinga2 git:(bugfix/fork-exit) touch 8427.conf; (sleep 10; kill -HUP `cat prefix/var/run/icinga2/*.pid`) & prefix/sbin/icinga2 daemon -c 8427.conf
[2] 39249
[2021-01-14 14:20:41 +0100] information/cli: Icinga application loader (version: v2.12.0-427-g931b9307a)
[2021-01-14 14:20:41 +0100] information/cli: Loading configuration file(s).
[2021-01-14 14:20:41 +0100] information/ConfigItem: Committing config item(s).
[2021-01-14 14:20:41 +0100] information/ConfigItem: Instantiated 1 IcingaApplication.
[2021-01-14 14:20:41 +0100] information/ScriptGlobal: Dumping variables to file '/Users/aklimov/NET/WS/icinga2/prefix/var/cache/icinga2/icinga2.vars'
[2021-01-14 14:20:41 +0100] information/ConfigObject: Restoring program state from file '/Users/aklimov/NET/WS/icinga2/prefix/var/lib/icinga2/icinga2.state'
[2021-01-14 14:20:41 +0100] information/ConfigObject: Restored 2 objects. Loaded 0 new objects without state.
[2021-01-14 14:20:41 +0100] information/ConfigItem: Triggering Start signal for config items
[2021-01-14 14:20:41 +0100] information/ConfigItem: Activated all objects.
[2021-01-14 14:20:46 +0100] information/Application: Got reload command: Starting new instance.
[2]  - 39249 done       ( sleep 10; kill -HUP `cat prefix/var/run/icinga2/*.pid`; )
[2021-01-14 14:20:46 +0100] information/cli: Loading configuration file(s).
[2021-01-14 14:20:46 +0100] information/ConfigItem: Committing config item(s).
[2021-01-14 14:20:46 +0100] information/ConfigItem: Instantiated 1 IcingaApplication.
[2021-01-14 14:20:46 +0100] information/ScriptGlobal: Dumping variables to file '/Users/aklimov/NET/WS/icinga2/prefix/var/cache/icinga2/icinga2.vars'
[2021-01-14 14:20:46 +0100] information/Application: Reload done, old process shutting down. Child process with PID '39271' is taking over.
[2021-01-14 14:20:46 +0100] information/Application: Received request to shut down.
[2021-01-14 14:20:46 +0100] information/Application: Shutting down...
[2021-01-14 14:20:46 +0100] information/ConfigObject: Dumping program state to file '/Users/aklimov/NET/WS/icinga2/prefix/var/lib/icinga2/icinga2.state'
[2021-01-14 14:20:46 +0100] information/IcingaApplication: Icinga has shut down.
[2021-01-14 14:20:46 +0100] information/ConfigObject: Restoring program state from file '/Users/aklimov/NET/WS/icinga2/prefix/var/lib/icinga2/icinga2.state'
[2021-01-14 14:20:46 +0100] information/ConfigObject: Restored 2 objects. Loaded 0 new objects without state.
[2021-01-14 14:20:46 +0100] information/ConfigItem: Triggering Start signal for config items
[2021-01-14 14:20:46 +0100] information/ConfigItem: Activated all objects.
^C[2021-01-14 14:20:58 +0100] information/Application: Received request to shut down.
[2021-01-14 14:20:59 +0100] information/Application: Shutting down...
[2021-01-14 14:20:59 +0100] information/ConfigObject: Dumping program state to file '/Users/aklimov/NET/WS/icinga2/prefix/var/lib/icinga2/icinga2.state'
[2021-01-14 14:20:59 +0100] information/IcingaApplication: Icinga has shut down.
➜  icinga2 git:(bugfix/fork-exit)