Inactivity timeout for SSH sessions

anon091 · 01-16-2013, 01:51 PM

I did some googling, and everything seems to say to
add the following two things into /etc/ssh/sshd_config

ClientAliveInterval 600
ClientAliveCountMax 3

But when I look at an existing server we have that disconnects a putty session if left idle, those two settings are commented out in the file. Maybe I'm searching for the wrong thing, or there's another way to do it?

Kustom42 · 01-16-2013, 01:55 PM

/etc/ssh/sshrc can also contain these directives. did you check there and the other files under /etc/ssh/?

Habitual · 01-16-2013, 02:02 PM

Quote:

an existing server we have that disconnects a putty session...

putty on Windows?
A.7.10 My PuTTY sessions unexpectedly close after they are idle for a while. points to
4.13.1 Using keepalives to prevent disconnection

anon091 · 01-16-2013, 02:37 PM

they both appear to be commented out in every file that has them in /etc/ssh

chrism01 · 01-16-2013, 05:21 PM

Check the header of /etc/ssh/sshd_config

Code:

# The strategy used for options in the default sshd_config shipped with
# OpenSSH is to specify options with their default value where
# possible, but leave them commented.  Uncommented options change a
# default value.

Samba does something similar ie lines beginning with '#' are doc comments, lines beginning with ';' are like ssh; default values commented out.

HTH

anon091 · 01-17-2013, 02:34 AM

OK, on the server i'm looking at that disconnects, and the new one that doesn't appear to (or maybe it's just set to some much great value perhaps), the two settings mentioned above both have # in front of them and both have the same number. So I'm thinking there has to be another spot to set this, maybe?

chrism01 · 01-17-2013, 05:54 AM

Here's the full manpage http://www.openbsd.org/cgi-bin/man.c...penBSD+Current which describes the options in detail.
It may even come down to tweaking the client settings as mentioned there.

anon091 · 01-17-2013, 06:11 AM

I guess I'm not understanding how if it's commented out on a server that does timeout a session after a period just like it is on this server, how it is this setting even. unless i'm just totally missing something here.

chrism01 · 01-17-2013, 07:05 PM

If(?) I understand your qn (& it is a bit confusing I agree), here is the situation.

At install time, sshd_config is pre-created for you, with the most-likely-to-be-required options already specified in the file.
The default values are used/set, BUT the line in the cfg file marks them as commented out (nonetheless, they ARE active).
This enables you to easily see which options are in the default setting and what those values are.
It also saves you having to guess/research a reasonable value for it.
If a setting is NOT commented out, it has likely been amended by a human being.

In Samba they use '#' & ';' to distinguish between doc comments ( # ) and default settings values ( ; ).

HTH

anon091 · 01-18-2013, 07:58 AM

Yeah, I gotcha now. Kinda odd in my mind that is uses default settings, but it leaves them commented out, you'd think it just have them in there uncommented set to the default value, then still have the note in the comments. Or at least that's how i'd do it haha.

I'm going to open up a session to that server and just let it sit for a few hours, see if it disconnects me or not. Maybe I really didn't have to do anything in the first place, other than not work so much on the server haha.

Thanks for the help Chris, you are always extremely helpful, and can break it down into something I can understand.