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Old 05-12-2016, 12:09 PM   #1
paperbagperson
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Registered: Mar 2016
Posts: 10

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Why Can't I Fork ssh Command into Background?


So a bit of background, I'm having issues with my port forwarding scripts as they do not actually kill themselves after the time I set.

Here's what I currently have:
Code:
ssh -f -g -L 8080:host:80 user@host sleep 3600
I've been testing out the command timeout:
Code:
timeout 10 ssh -f -g -L 8080:host1:80 user@host1
but when I try to run the command I get the following:
Code:
Cannot fork into background without a command to execute.


I've also been looking into creating a config file just for these types of commands, but I don't see any values I can set to always kill the tunnel (TCPKeepAlive, ServerAliveInterval, are all based on data transfer)

Basically my main question is why am I unable execute the timeout command when I force it to the background?


A few other questions:
1) can you think of a way to get the connection to kill itself after an hour no matter what?
2) What data is being transferred when you're connected to a host but not running any commands (basically why is ServerAliveInterval not terminating if I ssh and do nothing)?
 
Old 05-12-2016, 01:06 PM   #2
AlucardZero
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Registered: May 2006
Location: USA
Distribution: Debian
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Code:
     -N      Do not execute a remote command.  This is useful for just forwarding ports
             (protocol version 2 only).
 
1 members found this post helpful.
Old 05-12-2016, 01:28 PM   #3
paperbagperson
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Registered: Mar 2016
Posts: 10

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Quote:
Originally Posted by AlucardZero View Post
Code:
     -N      Do not execute a remote command.  This is useful for just forwarding ports
             (protocol version 2 only).
Not sure if this is what you intended, but you pointing this out made me realize this is why my sleep command isn't working, some of my commands involved -N!

Thanks

... It's what I get for copying a command from the internet

Last edited by paperbagperson; 05-12-2016 at 01:41 PM.
 
Old 05-12-2016, 08:25 PM   #4
frankbell
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Registered: Jan 2006
Location: Virginia, USA
Distribution: Slackware, Debian, Mageia, and whatever VMs I happen to be playing with
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It sounds as if you might want to look at screen or tmux.

Both of them allow you to detach from terminals and reconnect to them later.
 
Old 05-12-2016, 09:37 PM   #5
Turbocapitalist
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Registered: Apr 2005
Distribution: Ubuntu, Devuan, OpenBSD
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Quote:
Originally Posted by paperbagperson View Post
... It's what I get for copying a command from the internet
In that case you might want to re-evaluate the -g option as well, which you seem to have included above.
 
  


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