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Keeping SSH Sessions Alive February 3, 2006

Posted by Carthik in administration, snippets, ubuntu.
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Scott Merrill writes in to say:

I noticed recently that ssh connections from my Ubuntu laptop to my
Debian server would time out and disconnect if I left the connection
idle for a long-ish period of time. This really annoyed me, because my
Debian desktop does not exhibit this behavior when connecting to the server.

I added the following line to /etc/ssh/ssh_config :
ServerAliveInterval 5

That seems to have fixed the problem, and my laptop can now remain
connected, though idle, to my server. Maybe this will help someone
else, too.

What this does, essentially is every 5 seconds, the client sends a small keep-alive packet to the server to make it look like the ssh connection is being actively used. The reason for Scott’s timeout could be a NAT firewall that seeks to minimize the nember of active connections to reduce its memory footprint, or to improve performance for other clients. Most firewalls and networks let you keep your connections alive for as long as you wish, but some may act up, and that’s when you can use Scott’s trick.

Tip: Change 5 to 240 or 300, so that instead of every 5 seconds, the keep-alive signal is sent only once in 4 or 5 minutes :)

Sorry it took me so long to post this useful tip, Scott.

Comments»

1. BEG - February 3, 2006

The point of dropping the connection is a security one, though. I let mine time out after idling for that reason. Just sayin’.

2. fred - February 3, 2006

I’m using gnu screen with a status line that displays the time, and as this is refreshed every minute, its enough.

3. Samokk is a Geek » Keeping SSH sessions alive - February 4, 2006

[...] This post from Scott Merril explains how to keep SSH sessions alive. [...]

4. krampo - February 8, 2006

On the Ubuntu SSH server side (sshd_config) I inserted these lines:
ClientAliveInterval 60
ClientAliveCountMax 60

and got pretty much the same result, although it says 60min, it doesn’t disconnect (time out) ssh clients. It really annoyed me before…

5. airtonix - February 12, 2006

hey, great stuff……any idea how i can resume a ssh session…
im no expert, so i’d thought you’d be able to harness your contacts and resevoir of knowledge.

ie i start a ssh session to my exclusive torrent box, and start some torrents via bitttorrent-ncurses, then either leave the sessions, or maybe my ssh client machine dies.
how do i resume a ssh session.

6. airtonix - February 12, 2006

woops. how do i resume the session, and keep an eye on the progress of the torrents.

or are programs that are executed by a remote ssh client always killed upon client exiting the session?

7. elixxir - February 15, 2006

airtonix: apt-get install screen
(then lookup the man page for it on how to detach and re-attach sessions)

8. bvankuik - March 6, 2006

That man page is really for looking up known information. I’d suggest taking a look at McPherson’s tutorial (originally from kuro5hin): http://jmcpherson.org/screen.html

9. diego sevilla’s weblog » Conexiones SSH que se cortan - March 8, 2006

[...] El caso es que se me ha ocurrido que esto deberÝa estar ya pensado en SSH, por ejemplo enviando un źKeep-Alive╗, y efectivamente es asÝ. En źKeeping SSH connections alive╗ lo he encontrado. Y parece que funciona. Related posts in t8i References in t8i [...]

10. Little Fucking Ray of Sunshine » Blog Archive » links for 2007-02-08 - February 10, 2007

[...] Keeping SSH Sessions Alive ┬ź Ubuntu Blog (tags: linux ubuntu howto) [...]

11. Jack Suzuki - June 1, 2007

You can also make this change in your home directories .ssh folder.

In the file, replace “username” with your name, create a text file if it doesn’t exist:

/home/username/.ssh/config

make the following entries:

serveraliveinterval 60
serveralivecountmax 10

Adjust as you see fit.

12. Dean - December 4, 2007

Is there any way to specify a idle/timeout setting when initiating the ssh client session to the remote server? I would like to not modify the default behavior of SSH, just a single instance from time to time. If possible, please post here would be a nice addition.

13. Tony McCrae - I’m a Tourist - Get me out of Here! » Blog Archive » Review: Three’s wireless broadband thing-a-ma-gig - December 16, 2007

[...] Technical Cons. – Initial connections and DNS lookups are rubbish. It takes several seconds for DNS queries to complete. New ssh connections take about 5 seconds to come up. – It’s NATed. You don’t seem to get a real IP number and you can’t make inbound connections. – It dropped ssh connections like nobodie’s business. This was becoming a real issue until I realised why it was happening; you just need to set an ssh keep alive. [...]

14. Linux T&T : Keeping SSH Sessions Alive - April 8, 2008

[...] Keeping SSH Sessions Alive ┬ź Ubuntu Blog [...]

15. I’m a Tourist - Get me out of Here! » Blog Archive » Review: Three’s wireless broadband thing-a-ma-gig - May 26, 2008

[...] agressive NAT gateway which is timing out your connections as fast as it can. You just need to set an ssh keep alive. – There seems to be a transparent http proxy involved. You can’t access an http svn [...]

16. Christoph H├╝ffelmann, der Blog » Blog Archive » SSH keep alive time - July 10, 2008

[...] Quelle: ubuntu.wordpress.com [...]

17. Stephan Wehner - July 28, 2008

Q. How to add a status line to “screen” that displays the time?

A. Add this to ~/.screenrc

hardstatus alwayslastline “%D-%M-%Y %c”

18. open sshd time out problem « My everyday fixes for linux and other networking troubles - July 29, 2008

[...] References:Keeping SSH Sessions Alive [...]

19. Fabio - September 2, 2008

Hey Scott, thanks for the tip. This was really annoying!!!!

20. triniboy - September 15, 2008

Hi guys I would like to have all ssh connections time out after 5 minutes of inactive connection

21. Dysprositos - December 17, 2008

Triniboy: see Jack’s comment (number 11).

Scott (and Carthik): thanks for the tip, this was exactly what I needed!

22. TEHEK - July 12, 2009

Hey, thx for info! I was scanning through manpage and dind’t notice the option right a way.

Here’s the commanline I use:

# ssh -o ServerAliveInterval=10

sets 10 sec keep-alive-ping interval for this particular connection.

23. Anthony Honstain - September 9, 2009

Awesome! Thanks for the tip.

24. Mauro Morales - September 18, 2009

very very usefull tip, thanks!

25. siki┼č - September 20, 2009

Is there any way to specify a idle/timeout setting when initiating the ssh client session to the remote server? I would like to not modify the default behavior of SSH, just a single instance from time to time. If possible, please post here would be a nice addition.

26. Jeremy - November 20, 2009

siki┼č,

Look into this command:
ssh -o TCPKeepAlive user@host

I’m not sure what the defaults are when using it but it’ll basically do the same thing as mentioned in this post.

27. Sa─čl─▒k Bilgilendirme - April 2, 2010

Thank you for the opportunity you gave

28. ChrisMar035 — Keep ssh sessions from timing out - May 20, 2010

[...] The Ubuntu Blog has a nice lil’ article about keeping SSH sessions alive. [...]

29. Mantener viva la sesi├│n ssh « El Blog de rubensa - June 14, 2010

[...] v├şa Posted by rubensa Filed in GNU/Linux, Recetas Leave a Comment » [...]

30. Anon - July 13, 2010

This works for sshfs and sftp and ssh port forwarding as well

31. SSH session timeout or Putty session timeout, Network error: Software caused connection abort | RafaelWolf.com - September 22, 2010

[...] this tip is for a Linux client (found here –> Link); from February of 2006 it’s still pertinent today and what tipped me off to where I might [...]

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Ron Jeremy - December 30, 2010

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33. porno siki┼č - September 27, 2010

The point of dropping the connection is a security one, though. I let mine time out after idling for that reason. Just sayinÔÇÖ.

34. sex siki┼č - September 28, 2010

airtonix: apt-get install screen

35. Prevent SSH Timeout on Remote Server via Client Configuration - October 6, 2010

[...] http://embraceubuntu.com/2006/02/03/keeping-ssh-sessions-alive/ This entry was posted in Linux. Bookmark the permalink. Post a comment or leave a trackback: [...]

36. ankara ke├ži├Âren nakliyat - December 4, 2010

evden eve But I believe that resolves a few questions for me personally. Anyone else agree?This works for sshfs and sftp and ssh port forwarding as well ankara

37. SSH port forwarding from VPS to home server - January 6, 2011

[...] used exactly as stated in ssh’s manpages. Last, I had a problem with the SSH session dying, possibly due to lack of activity as in this article. I used the ‘-o ServerAliveInterval=’ command line option and that seemed to make it [...]

38. Jessy de Bruyn - February 10, 2011

Tip: when the session does freeze, hit enter, followed by tilde (~), followed by a dot (.). That doesn’t resume the session though.

39. blogTrav » Keeping My SSH Connections Alive on Verizon 4G LTE - April 10, 2011

[...] workflow has a lot of 5 minute breaks from SSH, too. After some searching the ‘net, I found a reference to setup SSH so that it transmits a keepalive packet to keep my connection alive. That got me [...]

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41. piri reis - May 18, 2011

Do you publish anything witout first seeing what is written in it? :) Do not do it or there will be always kinds of ads here.

42. piri reis - May 18, 2011

By the way, I am thankful for the tip. It had been 11 minutes idle and I checked still the session is up. It should have gone so far without this fix (I used 180 secs).

43. neil - May 26, 2011

Put this in a script on the server then add the script to ~/.bashrc with & to run in background:

while true
do
echo -en “\x0″
sleep 60
done

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45. gabblet - July 18, 2011

nice informative tips for me thanks

46. ukrayna vizesi - July 30, 2011

─░Y─░

47. Leny - July 31, 2011

run ‘top’ when you are done with your window! Problem solved. You can keep an eye on the box too with that.

48. arkada┼č - August 5, 2011

te┼ček├╝rler bilgi i├žin elinize sa─čl─▒k

49. antalya b├Âcek ila├žlama - August 7, 2011

antalya ev ila├žlama

50. webchat - September 11, 2011

hello and thank you…

51. Master Ryan - October 16, 2011

fyi this works great for Krusader on Ubuntu Natty.

52. Keeping My SSH Connections Alive on Verizon 4G LTE | blogTrav - April 10, 2013

[...] workflow has a lot of 5 minute breaks from SSH, too. After some searching the ‘net, I found a reference to setup SSH so that it transmits a keepalive packet to keep my connection alive. That got me [...]

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