Prevent daemon sudden termination (SIGKILL only) upon restart/shutdown

Question

I'm running daemon service under macOS Sierra and High-Sierra, and get unexpected behavior upon shutdown.

according to the manual of daemon life cycle (https://developer.apple.com/library/content/documentation/MacOSX/Conceptual/BPSystemStartup/Chapters/Lifecycle.html),

"If the system is being shut down or restarted, it sends a SIGTERM signal to all daemons, followed a few seconds later by SIGKILL signal"

However, in my case I see that my daemon only gets SIGKILL from `launchd` (my signal handler callback function for SIGTERM isn't being called)

I've verified that I doesn't allow sudden termination by setting the following fields in plist :

<key>NSSupportsSuddenTermination</key>

<key>EnableTransactions</key>

Any idea what am I missing here ?

XPC

2.0k

Posted by

rrr1981

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Answer 1

This is working for me. Here’s what I did:

I created a small Swift daemon that logs when it gets a
```
SIGTERM
```
. The code is pasted in at the end. Note that this logs by creating a file in
```
/var/log/DaemonTermination/
```
, to avoid any complications with the system’s logging subsystem. Also, I use a dispatch event source for my signal handling because that allows me to doing things that are not async signal safe (most notably, write in Swift!).
I created a matching launchd property list, also pasted in below.
IMPORTANT I did not include
```
EnableTransactions
```
because that defaults to false. Also,
```
NSSupportsSuddenTermination
```
is not a launchd job key (it’s for Cocoa apps) and thus doesn’t belong in a launchd property list.
On a victim (virtual) machine running 10.13, I created the destination log directory:
```
$ sudo mkdir /var/log/DaemonTermination
```
.

I then installed the daemon and its property list:

$ sudo cp DaemonTermination /Library/PrivilegedHelperTools/
$ sudo cp com.example.apple-samplecode.DaemonTermination.plist /Library/LaunchDaemons/

.

And then loaded and started the daemon:

$ sudo launchctl load -w /Library/LaunchDaemons/com.example.apple-samplecode.DaemonTermination.plist
$ sudo launchctl start com.example.apple-samplecode.DaemonTermination

.

I then restarted the machine using the Finder.

After the restart I looked in

/var/log/DaemonTermination/

and, lo!, there is one of my log files:

$ ls -lh /var/log/DaemonTermination/
total 8
-rw-r--r--@ 1 root  wheel    25B Dec  6 01:52 DFEE5FCC-4DE0-49C2-9D85-51F4151BCA3E.txt
$ cat /var/log/DaemonTermination/DFEE5FCC-4DE0-49C2-9D85-51F4151BCA3E.txt 
2017-12-06 09:52:46 +0000

.

I’m not sure what’s going on with your setup but this should give a good starting point for your investigations.

Share and Enjoy
—
Quinn “The Eskimo!”
Apple Developer Relations, Developer Technical Support, Core OS/Hardware

let myEmail = "eskimo" + "1" + "@apple.com"

import Foundation

func main() {
    let tempDir = URL(fileURLWithPath: "/var/log/DaemonTermination")
    let termFile = tempDir.appendingPathComponent("\(UUID().uuidString).txt")
    NSLog("termFile: %@", termFile.path)

    signal(SIGTERM, SIG_IGN)

    let termSource = DispatchSource.makeSignalSource(signal: SIGTERM)
    termSource.setEventHandler {
        try? Date().description.write(to: termFile, atomically: false, encoding: .utf8)
        NSLog("SIGTERM")
        exit(123)
    }
    termSource.resume()

    dispatchMain()
}

main()
exit(EXIT_FAILURE)

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>Label</key>
    <string>com.example.apple-samplecode.DaemonTermination</string>
    <key>ProgramArguments</key>
    <array>
        <string>/Library/PrivilegedHelperTools/DaemonTermination</string>
    </array>
</dict>
</plist>

Posted by

eskimo

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Prevent daemon sudden termination (SIGKILL only) upon restart/shutdown

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