CentOS - Jun 2006 - ssh session output stalls

Hello,

Is anyone else having problems with the ssh session output stalling
when ssh'd to another system and the command is running via sudo and a
pager is being used (e.g., more)?

Too highly reproducible :(  to date, all known occurrences have
involved Centos 4.3 servers;  makes no difference whether client is
RHEL WS 4.3, Centos 4.3 or FC 5 or WinDoze.  Makes no difference if
terminal emulator is Gnome's stock issue or Konsole or Putty.  Not
sure about SecureCRT.

Sometimes one can break loose the logjam;  if so:
. terminal prompts are stacked left to right vs. vertically
. keyboard input is not echo'd
. in this event, terminal clear/reset doesn't
end if so.

Any thoughts?

rgds/ldv

[vaden at mx1 ~]$ ps auxw | grep -i pts/0
vaden     2475  0.0  0.1 37444 3064 ?        S    04:53   0:00 sshd: vaden at
pts/0
vaden     2476  0.0  0.0 53964 1480 pts/0    Ss   04:53   0:00 -bash
root      2511  0.0  0.0 71284 1312 pts/0    S    04:53   0:00 su -
root      2512  0.0  0.0 53968 1492 pts/0    S    04:53   0:00 -bash
root      3426  0.0  0.0  2376  288 pts/0    S+   13:57   0:00 sesh
/bin/grep -i unknown /var/log/maillog
root      3427  0.1  0.0 51128  784 pts/0    S+   13:57   0:00
/bin/grep -i unknown /var/log/maillog
vaden     3434  0.0  0.0 51072  540 pts/1    R+   13:58   0:00 grep -i pts/0

> Is anyone else having problems with the ssh session output stalling
> when ssh'd to another system and the command is running via sudo and a
> pager is being used (e.g., more)?
Are you sure you aren't accidentally hitting ctrl-s or scroll lock?  Try 
hitting ctrl-q next time it happens.
> Too highly reproducible
What are the steps to reproduce?

j


--
Jason Bradley Nance                        What would you cry for?
aitrus at tresgeek.net                          Swallow your pride for?
            Tres Geek                       What would you go wild for?
http://tresgeek.net/
                                                           -Poe,
"Wild"
--

On Sun, 2006-06-25 at 14:20 -0500, Larry Vaden wrote:
> Hello,
> 
> Is anyone else having problems with the ssh session output stalling
> when ssh'd to another system and the command is running via sudo and a
> pager is being used (e.g., more)?
> 
> Too highly reproducible :(  to date, all known occurrences have
> involved Centos 4.3 servers;  makes no difference whether client is
> RHEL WS 4.3, Centos 4.3 or FC 5 or WinDoze.  Makes no difference if
> terminal emulator is Gnome's stock issue or Konsole or Putty.  Not
> sure about SecureCRT.
If sudo is removed from the mix, does it still happen?
> 
> Sometimes one can break loose the logjam;  if so:
> . terminal prompts are stacked left to right vs. vertically
> . keyboard input is not echo'd
These two tell us that end-of-line and other terminal settings (usually
NL on *IX systems, but I don't know about ssh) are getting lost before
the pager is seeing them. Possibly doing stty against the pseudo-terms
involved will give a clue?
> . in this event, terminal clear/reset doesn't
> end if so.
> 
> Any thoughts?
Generally, having a pager involved when there are interactive prompts
("terminal prompts are stacked...") is a bad idea. Commands often
issue
prompts with no EOL so that you see on one line something like

  Enter reply [Y/N/Q] -

and the cursor is after the dash. The pager usually works on *lines* not
*characters*, although some used to have timeouts that could be applied
to force output flushing (don't know if this applies anymore).

Wish I had more to offer than just a couple Qs that might get you going.

> 
> rgds/ldv
> 
> [vaden at mx1 ~]$ ps auxw | grep -i pts/0
> vaden     2475  0.0  0.1 37444 3064 ?        S    04:53   0:00 sshd: vaden
at pts/0
> vaden     2476  0.0  0.0 53964 1480 pts/0    Ss   04:53   0:00 -bash
> root      2511  0.0  0.0 71284 1312 pts/0    S    04:53   0:00 su -
> root      2512  0.0  0.0 53968 1492 pts/0    S    04:53   0:00 -bash
> root      3426  0.0  0.0  2376  288 pts/0    S+   13:57   0:00 sesh
> /bin/grep -i unknown /var/log/maillog
> root      3427  0.1  0.0 51128  784 pts/0    S+   13:57   0:00
> /bin/grep -i unknown /var/log/maillog
> vaden     3434  0.0  0.0 51072  540 pts/1    R+   13:58   0:00 grep -i
pts/0
> <snip sig stuff>
-- 
Bill
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On 6/26/06, William L. Maltby <BillsCentOS at triad.rr.com>
wrote:
>
> If sudo is removed from the mix, does it still happen?
Dunno, but I'll try removing sudo from the mix.
> Generally, having a pager involved when there are interactive prompts
> ("terminal prompts are stacked...") is a bad idea.
The original example published _inadvertently_ didn't have a pager in
the pipe.

To my knowledge, the hangs have all been while watching logs which
don't exhibit interactive prompts (other than paging more, and more is
not always involved);  examples are:

sudo grep -i unknown /var/log/maillog | more
sudo tail -F /var/log/maillog | grep -i "yada1 yada2"

rgds/ldv