close dead ssh connections

nuliknol · 04-03-2012, 09:15 PM

I have a DSL modem internet connection at home and when I am logged in to my dedicated internet server using ssh, the modem times out my connections when they are idle. The result is, I am accumulating dead ssh connections being idle for days (wasting system resources) that I have to kill with -9 periodically. This is how they look like when I ps:

Code:

....
root     13610  0.0  0.1   5084  1160 ?        S    Apr02   0:00 su -c /usr/bin/xterm
root     13612  0.0  0.2   8104  2364 ?        S    Apr02   0:00  \_ /usr/bin/xterm
root     13616  0.0  0.1   4772  1388 pts/29   Ss+  Apr02   0:00      \_ bash
root     14091  0.0  0.1   5084  1156 ?        S    Apr02   0:00 su -c /usr/bin/xterm
root     14093  0.0  0.2   8100  2488 ?        S    Apr02   0:00  \_ /usr/bin/xterm
root     14095  0.0  0.1   4768  1448 pts/30   Ss+  Apr02   0:00      \_ bash
root     22160  0.0  0.1   5084  1164 ?        S    Apr02   0:00 su -c /usr/bin/xterm
root     22162  0.0  0.2   8100  2480 ?        S    Apr02   0:00  \_ /usr/bin/xterm
root     22164  0.0  0.1   4768  1384 pts/32   Ss+  Apr02   0:00      \_ bash
root      6946  0.0  0.1   5084  1156 ?        S    Apr03   0:00 su -c /usr/bin/xterm
root      6948  0.0  0.2   8100  2360 ?        S    Apr03   0:00  \_ /usr/bin/xterm
root      6950  0.0  0.1   4768  1388 pts/25   Ss+  Apr03   0:00      \_ bash
root     16522  0.0  0.1   5084  1160 ?        S    Apr03   0:00 su -c /usr/bin/xterm
root     16524  0.0  0.2   8100  2484 ?        S    Apr03   0:00  \_ /usr/bin/xterm
root     16526  0.0  0.1   4772  1392 pts/36   Ss+  Apr03   0:00      \_ bash
root     22133  0.0  0.1   5088  1156 ?        S    Apr03   0:00 su -c /usr/bin/xterm
root     22135  0.0  0.2   8100  2364 ?        S    Apr03   0:00  \_ /usr/bin/xterm
root     22137  0.0  0.1   4768  1388 pts/40   Ss+  Apr03   0:00      \_ bash
root     28787  0.0  0.1   5084  1156 ?        S    Apr03   0:00 su -c /usr/bin/xterm
root     28789  0.0  0.2   8100  2488 ?        S    Apr03   0:00  \_ /usr/bin/xterm
root     28791  0.0  0.1   4768  1388 pts/43   Ss+  Apr03   0:00      \_ bash
[root@newze ~]#

I know I can setup ssh client with keep-alive and it will send some data to avoid the connection being expired by the firewall of the modem, but I don't want this (since it is not a clean solution). I want the ssh daemon to kill idle connections and the resulting child processes automatically after some inactivity period (which I can configure somewhere). Is this possible?

My OS is a bit old: centos-release-5-2.el5.centos , hope this is not an issue, I just can't upgrade this server right now, its a productive environment.

Will appreciate any comments very much on this case.
Thanks

anomie · 04-03-2012, 11:48 PM

Actually, setting ServerAliveInterval 30 (or some such) in your client-side ~/.ssh/config is a clean solution, IMO.

If that's still a no-go, then just let bash(1) time out your session. In your server-side ~/.bash_profile, set TMOUT=600 (or similar).

nuliknol · 04-04-2012, 09:45 AM

Quote:

Originally Posted by anomie

Actually, setting ServerAliveInterval 30 (or some such) in your client-side ~/.ssh/config is a clean solution, IMO.

it is not clean because if the modem is reset and new ip is assigned, the connections will remain on the server side.

Quote:

If that's still a no-go, then just let bash(1) time out your session. In your server-side ~/.bash_profile, set TMOUT=600 (or similar).

this one looks good. thanks!

nuliknol · 04-04-2012, 10:00 AM

I found it, ClientAliveInterval configured on the server in sshd_conf should do what I need. Testing...

anomie · 04-04-2012, 06:42 PM

Quote:

Originally Posted by nuliknol

it is not clean because if the modem is reset and new ip is assigned, the connections will remain on the server side.

If that's a regular concern, then consider using GNU screen or tmux.

I often work during my bus ride in to work. (The connection quality is terrible, and is dropped at least once during the ride.) With tmux, I simply re-attach session when the connection is active again.

unSpawn · 04-04-2012, 07:25 PM

Also see Autossh to re-establish connections automagically.