golang exec a command on a running binary / process

Question

If you look at Nginx it calls "nginx reload" to reload itself. Is there any　way to send a signal from the command line to a running process? Even if the main process starts child processes how can I send commands to the main to notify its children?

ex:

myapp start -debug // starts a server
myapp reload -gracefull // stops the app gracefully

Now i need to send os signals to notify my server to perform a graceful shutdown

kill -QUIT pid
kill -USR2 pid

I hope my question is clear enough Thnx

Emil Davtyan · Accepted Answer · 2014-09-17 17:26:35Z

7

Receive signals

Take a look at the os/signal package.

Package signal implements access to incoming signals.

There is even an example in the documentation :

// Set up channel on which to send signal notifications.
// We must use a buffered channel or risk missing the signal
// if we're not ready to receive when the signal is sent.
c := make(chan os.Signal, 1)
signal.Notify(c, os.Interrupt, os.Kill)

// Block until a signal is received.
s := <-c
fmt.Println("Got signal:", s)

Send signals

To see how to send signals take a look at signal_test.go, it uses syscall. For example :

// Send this process a SIGHUP
t.Logf("sighup...")
syscall.Kill(syscall.Getpid(), syscall.SIGHUP)
waitSig(t, c, syscall.SIGHUP)

edited Sep 17, 2014 at 17:26

answered Sep 17, 2014 at 17:15

Emil Davtyan

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6 Comments

Anthony De Meulemeester Over a year ago

I know this and i use this in my program. But i want it to send a signal to its own process from the commandline

Anthony De Meulemeester Over a year ago

and if my program is already running and i want to send it a sig from its own cli? app -quit. its a different pid right?

Emil Davtyan Over a year ago

@AnthonyDeMeulemeester I guess you can store the pid in a local file or in an environment variable.

Anthony De Meulemeester Over a year ago

I call the same binairy with its cli but they dont share os.Env

Emil Davtyan Over a year ago

@AnthonyDeMeulemeester Do they share the same file system? When binary starts write PID number to a PID file, then when you want to reload read PID file for PID number.

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Anthony De Meulemeester · Accepted Answer · 2014-09-18 21:32:36Z

0

I figured out that in go i we can pass the environment to syscall.Exec

err := syscall.Exec(argv0. os.Args. os.Environ())

simply copies the current env to the child process.

answered Sep 18, 2014 at 21:32

Anthony De Meulemeester

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