# sigquit: sigint and sigquit are handy signals to handle specially

if you have a terminal application in linux, you can easily send it the following two signals from your keyboard:

• sigint: ctrl-c
• sigquit: ctrl-\

in go binaries the default behavior for sigint is to simply exit the application. for sigquit it also exits but with a full stacktrace of all the goroutines.

i started to use the same pattern in multiple tools i wrote in the recent times so i thought i share it. it's for daemon-like or long running tools where the tools don't require any input, and they just keep running and logging what they are doing. for such tools i occasionally want it to do a specific action on demand. this can be something like dumping stats and/or reinitialization.

in such case i set up sigint to do my one-off action and sigquit to quit without the stacktrace dump (those stacktraces can be quite spammy).

for example my server that serves this page doesn't touch disk to serve the pages. it reads everything to memory and serves from there. when i change or write a new post, or when i update the ssl certificates, i simply hit ctrl-c in the terminal where the server is running to reload all the data.

or i'm working on a little backup daemon that periodically wakes up to upload changed files from my homedir to google drive as a backup. in there i interpret ctrl-c as a triggering mechanism to start a backup cycle sooner.

now all this could be implemented with raw keyboard input or with other signals (sighup, sigusr1). it's just that sigint is very convenient to use out of box thanks to go's signal package that uses channels for them.

one caveat: you have to handle sigquit in a background goroutine:

  go func() {
    sigquitch := make(chan os.Signal, 1)
    signal.Notify(sigquitch, syscall.SIGQUIT)
    <-sigquitch
    log.Print("sigquit received, quitting.")
    os.Exit(3)
  }()

this is needed so that sigquit is immediately handled. but sigint you can handle on your main loop. e.g. when there are no requests in flight or when there's no backup cycle ongoing.

also note that such artistic reinterpretation of sigint can be surprising to the users. make sure to print a reminder to use ctrl-\ to quit whenever the user presses ctrl-c.

published on 2022-01-14

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