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qwkbrnfox
Apprentice
Joined: 05 Nov 2002
Posts: 231
Location: Vancouver, BC, Canada
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 Posted: Tue Jul 06, 2004 12:47 am Post subject: Keeping jobs going after closing ssh shell? |
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OK, let's say I'm away from home, and I've decided that this is the perfect time to emerge a couple of giant packages on my home machine. I ssh to the machine, then emerge blah-blah >& dump & which seems to be working fine. However, when I Ctl-d to leave the shell - hoping to leave the emerge running after I log out - the shell just hangs. It won't logout properly until I open another shell, log in via ssh again, and kill the supposedly background process.
How can I start a job via ssh that is fully independent of the shell, so I can leave?
Thanks - and sorry about the newbie question  |
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Lajasha
Veteran
Joined: 17 Mar 2004
Posts: 1040
Location: Vibe Central
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| Posted: Tue Jul 06, 2004 12:52 am Post subject: |
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Well you have 2 options the first I will give is simply how to make things run in the background the second is the way that I prefer an application called screen.
To run an application in the background simply append an "&" to the end of it ex. | Code: | | emerge -Duv world & |
This would run the update world in the background and should survive the shell being shutdown, however you will not have a way to bring it back to the foreground when you reconnect.
Enter Screen:
I honestly can not say enough about this app. I absolutly love it. It will allow you to run what ever you want then Detatch from it and close your shell and then open the shell again later and re-attach to the session and it is like you never left. The applications that you had running stay running and you can even have multiple screens going at once. If you want to give this one a go just "emerge screen" I believe will get it for ya.
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qwkbrnfox
Apprentice
Joined: 05 Nov 2002
Posts: 231
Location: Vancouver, BC, Canada
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| Posted: Tue Jul 06, 2004 1:02 am Post subject: |
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| maletek wrote: |
To run an application in the background simply append an "&" to the end of it ex. | Code: | | emerge -Duv world & |
This would run the update world in the background and should survive the shell being shutdown, however you will not have a way to bring it back to the foreground when you reconnect.
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Sorry, it didn't work. Weird. I'm using ssh here, so something funny seems to be going on. I can put it into the background locally, and close the shell no problem.
I'll take a look at screen, too. I'm looking for something quick here, but that looks like a pretty useful app. |
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apeitheo
Apprentice
Joined: 09 Jan 2004
Posts: 222
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| Posted: Tue Jul 06, 2004 1:13 am Post subject: |
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Would using nohup work? Maybe? (Not sure if it would work through an ssh session)
| Code: | | # nohup emerge world |
As for screen (wonderful program btw), that should work.
Last edited by apeitheo on Tue Jul 06, 2004 1:15 am; edited 1 time in total |
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qwkbrnfox
Apprentice
Joined: 05 Nov 2002
Posts: 231
Location: Vancouver, BC, Canada
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| Posted: Tue Jul 06, 2004 1:14 am Post subject: |
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Got it - why do I always find these things just after I post? I have to use: | Code: | | emerge blah-blah < /dev/null >& outfile & |
Note the input redirection. This is a quirk of ssh. And *ahem* it's in the FAQ for ssh  |
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Angrybob
Guru
Joined: 19 Apr 2003
Posts: 575
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| Posted: Tue Jul 06, 2004 5:18 pm Post subject: |
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you need to use a clever little program called screen. run screen then type in your command, you can now kill your ssh session and the command will carry on running in the background. if you want to see how it's doing then log back in with ssh and do "screen -r" to resume your last session.
here's a better description: http://www.kuro5hin.org/story/2004/3/9/16838/14935
[edit] oops, only skimmed the posts didn't notice that screen was already mentioned... but anyway, it is the answer |
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Digital Storm
Tux's lil' helper
Joined: 07 Mar 2003
Posts: 116
Location: Toronto, Canada
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| Posted: Tue Jul 06, 2004 7:22 pm Post subject: |
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You should also be able to use
| Code: | | nohup emerge world & |
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carlosalvatore
n00b
Joined: 22 Nov 2011
Posts: 13
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| Posted: Tue May 05, 2015 8:25 am Post subject: |
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| qwkbrnfox wrote: | Got it - why do I always find these things just after I post? I have to use: | Code: | | emerge blah-blah < /dev/null >& outfile & |
Note the input redirection. This is a quirk of ssh. And *ahem* it's in the FAQ for ssh |
You are my personal hero! 
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steveL
Watchman
Joined: 13 Sep 2006
Posts: 5153
Location: The Peanut Gallery
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| Posted: Tue May 05, 2015 11:55 am Post subject: |
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What Digital Storm said.
Yeah screen/tmux, but if nohup does the job, it's less hassle. |
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miket
Guru
Joined: 28 Apr 2007
Posts: 488
Location: Gainesville, FL, USA
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| Posted: Wed May 06, 2015 6:48 pm Post subject: |
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| qwkbrnfox wrote: | Got it - why do I always find these things just after I post? I have to use: | Code: | | emerge blah-blah < /dev/null >& outfile & |
Note the input redirection. This is a quirk of ssh. And *ahem* it's in the FAQ for ssh :oops: |
Actually, I wouldn't call this a quirk. Simply backgrounding a process makes it so that the new process inherits fd's from its parent; those fd's become unusable when the ssh process exits.
One way to avoid this problem in spawning background processes (and a typical way to spawn processes to run as daemons) is to close the child's fd's before executing the daemon. Most software, though, does badly if started with fd's 0, 1, and 2 closed. The typical thing, then, is instead of just closing those fd's is to reopen them to /dev/null. You're command line is doing almost that; the difference is that it opens stdout and stderr to a file. That's good too.
I'm a big fan of the screen approach. If the merge goes off the rails, you can see what went wrong and can make needed corrections while you have your command history still easily available (command history around the emerge is likely to drift away in the noise of other commands issued under the same user in other sessions). You can detach the screen and go away and even reopen it later at a different computer. I use a build host separate from my main machine. I usually have the screen session that contains the build chroot alive for months at a time. I connect back to it when I need to build a new package or do an update. |
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luismw
Tux's lil' helper
Joined: 04 Jan 2010
Posts: 91
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| Posted: Thu May 07, 2015 5:52 pm Post subject: |
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| Wouldn't "disown" work in this situation? |
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toralf
Developer
Joined: 01 Feb 2004
Posts: 3922
Location: Hamburg
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| Posted: Thu May 07, 2015 6:08 pm Post subject: Re: Keeping jobs going after closing ssh shell? |
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| qwkbrnfox wrote: | | How can I start a job via ssh that is fully independent of the shell, so I can leave? |
| Code: | | nohup ./my_very_long_lasting_script.sh & |
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szatox
Advocate
Joined: 27 Aug 2013
Posts: 3135
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| Posted: Fri May 08, 2015 9:21 pm Post subject: |
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Nohup is nice but it can only run programs. However there is also a way that works even with shell's runtime defined functions... and it is to be used on already running processes:
$ stuff_i_want_to_run & disown $!
which means: run some command in the background, and call disown with it's PID |
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toralf
Developer
Joined: 01 Feb 2004
Posts: 3922
Location: Hamburg
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| Posted: Sun May 10, 2015 3:44 pm Post subject: |
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| szatox wrote: | | Nohup is nice but it can only run programs |
erm, | Code: | | nohup emerge blah-blah >& dump & |
should work fine |
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szatox
Advocate
Joined: 27 Aug 2013
Posts: 3135
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| Posted: Sun May 10, 2015 10:11 pm Post subject: |
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Emerge is a named program accessible with some path. A function defined in shell during runtime is not.
: () { sleep 60; echo "something illustrative and harmless"; }
nohup :
won't work, but
: & disown $?
will do just fine
Rendered harmless to the unwary. -- desultory |
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Naib
Watchman
Joined: 21 May 2004
Posts: 6051
Location: Removed by Neddy
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| Posted: Sun May 10, 2015 10:18 pm Post subject: |
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| szatox wrote: | Emerge is a named program accessible with some path. A function defined in shell during runtime is not.
: () { :&:;}
nohup :
won't work, but
: & disown $?
will do just fine |
bad form recommending a forkbomb!
I would recommend tmux, fantastic terminal multiplexer. It essentially does what screen does but I have had less issues with it than with screen. This is viable if you need to reconnect to see the output or carry on.
If you just want to launch and forget then nohup or at
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Malaki
n00b
Joined: 14 Nov 2011
Posts: 19
Location: Montreal, Québec, Canada.
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| Posted: Thu May 14, 2015 6:28 am Post subject: |
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| I also recommend tmux over screen. |
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