Why does a Daemon randomly stop?

Question

Hello,

This is sort of related to a previous, yet so far unsuccessful question of mine. I have a daemon that is placed in the LaunchAgents folder (on Mac) and it should run perpetually in the background, but after a couple of days it just stops for no apparent reason. I have no idea why and thus my question:

What are the reasons that a daemon might randomly stop?

Thanks for the help!

Answer 1

A Daemon is just a long lasting (forked) process. The reason a Daemon crashes is the same any other program crashes:

• attempting to read or write memory that is not allocated for reading or writing by that application (segmentation fault) or x86 specific (general protection fault)
• attempting to execute privileged or invalid instructions
• attempting to perform I/O operations on hardware devices to which it does not have permission to access
• passing invalid arguments to system calls
• attempting to access other system resources to which the application does not have permission to access (bus error)
• attempting to execute machine instructions with bad arguments (depending on CPU architecture): divide by zero, operations on denorms or NaN values, memory access to unaligned addresses, etc.

Answer 2

Since it's a LaunchAgent, it runs as part of your login session, and hence will be killed if you log out.

On the other hand, if it's dying before you log out, and you can't find/fix whatever is causing it to crash/exit, or you can tell launchd to automatically restart it by adding

<key>KeepAlive</key>
</true>

to its .plist