I have a program, where I am starting a program called mpv. I want to use the shell to start mpv with a video, and then exit my ruby program. My problem is that currently, the mpv instance is killed the the ruby program ends. How can I fix this?
# do some stuff
system 'mpv \"#{video_url}" & disown'
# end of program
I have also tried using
pid = Process.spawn "mpv \"#{video_url}\""
Process.detach pid
The program is that both of these will make the mpv process be killed immediately. If I do not exit, or if I sleep at the end of the program, the video plays until the program ends. How can I make spawning of mpv last longer than my ruby program?
You can just use exec(). It will terminate your ruby program and execute the given command
exec('mpv \"#{video_url}\"')
or you can use spawn too
spawn exec "mpv \"#{video_url}\" &"
Related
I have two scenarios:
#!/usr/bin/env bash
sleep infinity
# When I type Ctrl-C here, "sleep" command and script are stopped so I didn't see "End"
echo End
#!/usr/bin/env bash
docker exec container-id sleep infinity
# When I type Ctrl-C here, "docker exec" command is stopped but script continued so I saw "End"
echo End
Why the difference in behaviour?
That's how bash behaves when its process group receives a SIGINT but the program currently running on the foreground terminates normally.
The rationale for this behavior is given here as follows:
The basic idea is that the user intends a keyboard-generated SIGINT to go
to the foreground process; that process gets to decide how to handle it;
and bash reacts accordingly. If the process dies to due SIGINT, bash acts
as if it received the SIGINT; if it does not, bash assumes the process
handled it and effectively ignores it.
Consider a process (emacs is the usual example) that uses SIGINT for its
own purposes as a normal part of operation. If you run that program in a
script, you don't want the shell aborting the script unexpectedly as a
result.
I have a bash script server.sh which is maintained by an external source and ideally should not be modified. This script writes to stdout and stderr.
In fact, this server.sh itself is doing an exec tclsh immediately:
#!/bin/sh
# \
exec tclsh "$0" ${1+"$#"}
so in fact, it is just a wrapper around a Tcl script. I just mention this in case you think that this matters.
I need a Tcl script setup.tcl which is supposed to do some preparatory work, then invoke server.sh (in the background), then do some cleanup work (and display the PID of the background process), and terminate.
server.sh is supposed to continue running until explicitly killed.
setup.tcl is usually invoked manually, either from a Cygwin bash shell or from a Windows cmd shell. In the latter case, it is ensured that Cygwin's bash.exe is in the PATH.
The environment is Windows 7 and Cygwin. The Tcl is either Cygwin's (8.5) or ActiveState 8.4.
The first version (omitting error handling) went like this:
# setup.tcl:
# .... preparatory work goes here
set childpid [exec bash.exe server.sh &]
# .... clean up work goes here
puts $childpid
exit 0
While this works when started as ActiveState Tcl from a Windows CMD shell, it does not work in a pure Cygwin setup. The reason is that as soon as setup.tcl ends, a signal is sent to the child process and this is killed too.
Using nohup would not help here, because I want to see the output of server.sh as soon as it occurs.
My next idea would be to created an intermediate bash script, mediator.sh, which uses disown -h to detach the child process and keep it from being killed:
#!/usr/bin/bash
# mediator.sh
server.sh &
child=$!
disown -h $child
and invoke mediator.sh from setup.tcl. But aside from the fact that I don't see an easy way to pass the child PID up to setup.tcl, the main problem is that it doesn't work either: While mediator.sh indeed keeps the child alive when called from the Cygwin command line directly, we have the same behaviour again (server.sh being killed when setup.tcl exits), when I call it via setup.tcl.
Anybody knowing a solution for this?
You'll want to set a trap handler in your server script so you can handle/ignore certain signals.
For example, to ignore HUP signals, you can do something like the following:
#!/bin/bash
handle_signal() {
echo "Ignoring HUP signal"
}
trap handle_signal SIGHUP
# Rest of code goes here
In the example case, if the script receives a HUP signal it will print a message and continue as normal. It will still die to Ctrl-C as that's the INT signal which is unhandled.
I'm trying to write a ruby script that:
Run a command/script
Stores the command's process pid in a file so I can check if it's still running later, and
the command should keep running after the ruby code exits.
I'm successful in steps 1 and 2, but it looks like the started script (i.e, the child process) terminates once the ruby code is finished.
This is the last version of what I could think about (super simplified):
pid = fork do
exec "/my/fancy/daemon/style/script"
end
File.open('tmp/process.pid', 'w') { |file| file.write(pid.to_s) }
Can you please tell me what am I doing wrong? The ultimate goal is to keep the other script (i.e, the child process) running after the ruby code exits.
You can "detach" your child process:
Process.detach(pid)
See Process#detach for more info.
If you're running your script on a shell, and if your script is the last interactive process, your virtual terminal may exit and cause your child process to hangup as well. If you consider not sending output to the terminal, you can use Process.daemon before running exec.
See Process#daemon.
In Ruby, I'm running a system("command here") that is constantly watching changes for files, similar to tail. I'd like my program to continue to run and not halt at the system() call. Is there a way in Ruby to create another process so both can run independently, output results to the terminal, and then when you exit the program all processes the application created are removed?
Just combine spawn and waitall:
spawn 'sleep 6'
spawn 'sleep 8'
Process.waitall
You don't want to use system as that waits for the process to complete. You could use spawn instead and then wait for the processes (to avoid zombies). Then, when you want to exit, send a SIGTERM to your spawned processes. You could also use fork to launch your child processes but spawn is probably easier if you're using external programs.
You could also use process groups instead of tracking all the process IDs, then a single Process.kill('TERM', -process_group_id) call would take care of things. Your child processes should end up in the same process group but there is Process.setpgid if you need it.
Here's an example that uses fork (easier to get it all wrapped in one package that way).
def launch(id, sleep_for)
pid = Process.fork do
while(true)
puts "#{id}, pgid = #{Process.getpgid(Process.pid())}, pid = #{Process.pid()}"
sleep(sleep_for)
end
end
# No zombie processes please.
Process.wait(pid, Process::WNOHANG)
pid
end
# These just forward the signals to the whole process group and
# then immediately exit.
pgid = Process.getpgid(Process.pid())
Signal.trap('TERM') { Process.kill('TERM', -pgid); exit }
Signal.trap('INT' ) { Process.kill('INT', -pgid); exit }
launch('a', 5)
launch('b', 3)
while(true)
puts "p, pgid = #{Process.getpgid(Process.pid())}, pid = #{Process.pid()}"
sleep 2
end
If you run that in one terminal and then kill it from another (using the shell's kill command)you'll see that the children are also killed. If you remove the "forward this signal to the whole process group" Signal.trap stuff, then a simple SIGTERM will leave the children still running.
All of this assumes that you're working on some sort of Unixy system (such as Linux or OSX), YMMV anywhere else.
One more vote for using Spawn. We use it in Production a lot and it's very stable.
I would like to write a Ruby script that runs a daemon Ruby process, so that I can do something like the following:
$ task start
Started...
# start a daemon to do useful work; don't block
# Some time later:
$ task end
Finished.
What's the best way to go about this?
Use the Process.daemon method when you want your process to detach from the terminal and stop being able to send output. To end the process, you will have to send it a signal. Most programs handle this by using a file that contains the PID.