4

I can run this command:

$ play mylist.m3u

And music plays.

I can then press Ctrl-Z to suspend the job, and issue bg to have it run in the background.

However, if I then run disown and exit, the music stops playing, even though the play command still shows up in ps.

I would expect the music to keep playing.

Also interesting

I run the command

$ play mylist.m3u &

Music does not play. The job shows as the stopped status.

I can also run the command

$ nohup play mylist.m3u &

And no music plays - the job immediately stops.

However,

$ nohup play mylist.m3u

Does have music play, but I can't disown it, as before.

It seems like all these are related.

Most programs behave well when disowned or run through nohup, but not SoX.

Does anyone know why?

Lesmana
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jwd
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  • If you want to play music as server, use mpd and ncmpc/mpc... – jirib May 31 '12 at 09:02
  • @JiriXichtkniha: Thanks - I already run xmms2, so it's no problem. I am more just curious why this fails. I want to know what is special about SoX that causes this odd behavior. – jwd May 31 '12 at 14:17

3 Answers3

8

For the rare person who, like me, both had this problem and finally managed to google for something that wasn't about baseball* and want an actual solution:

$ play whatever.wav &>/dev/null </dev/null &

That runs in the background without stopping.

* The Red Sox of Boston play baseball, and apparently some players prefer the limelight to the background. Grumble.

jw013
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tex
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  • Cool! I am curious - why are there two `&`? I'm unfamiliar with that syntax. – jwd Oct 10 '12 at 16:38
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    "&>/dev/null" means "Redirect both stdout and stderr to /dev/null." It's analogous to ">/dev/null 2>&1". The second ampersand just puts the job in the background in the usual way. – tex Oct 18 '12 at 14:00
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SoX wants/needs input & output... by typing 'play xxxx' in the console, you're running it normally, with stdin & stdout (& stderr) all connected.

When you background the job (with &), it starts, then is paused since it's waiting for access to stdin & stdout.

Same thing occurs when you 'nohup' a job. If it needs keyboard input, it'll "block", and get paused by the system until it receives access to stdin.

disown'ing a process effectively cuts it off from stdin & stdout which were connected to the console which started the process.

It's still "running", but is blocked (paused) by the system since it's waiting for access to stdin & stdout.

lornix
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  • Do you know why it successfully runs in 'bg' mode, while the controlling terminal still exists? Is stdin still active in that mode, just nothing sent to it? – jwd Jul 06 '12 at 14:50
  • That'd be my best guess. Depends on the program and how it handles its input & output too. – lornix Jul 06 '12 at 14:58
0

It's also possible to use the -q option to make sure SoX doesn't write to std-whatever, without redirecting to /dev/null.

$ play filename -q &
uyjulian
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