On Mon, 2006-06-26 at 09:30 -0500, Larry Vaden wrote:
> On 6/26/06, William L. Maltby <BillsCentOS@xxxxxxxxxxxx> wrote:
> >
> > If sudo is removed from the mix, does it still happen?
>
> Dunno, but I'll try removing sudo from the mix.
> <snip>
> 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"
Sounds like isolation of the problem source is in order. Since a pager
is not always involved, maybe a monitor of the involved processes to see
which one becomes blocked and what it is waiting for. Ah! Some things
just came to mind.
Don't know if it is related, but we recently had a discussion of
swapping here. One of the symptoms when it got excessive was almost non-
existent response (in some cases). Have you run a top or other process
to see if swap usage has jumped up when the problems occur? If "less" is
one of the potential culprits, the -B option might help. Seems unlikely
since you said a pager is not always involved.
From rom "man more"
-l more usually treats ^L (form feed) as a special character, and
will pause after any line that contains a form feed. The -l
option will prevent this behavior.
Again, seems unlikely.
Regardless, with the right field displays enabled in top (or other
monitoring processes), maybe a blocked process will appear.
Another possibility. Whenever there is a "pipe", there is (by default?)
some buffering, IIRC. Someone correct me if I'm wrong here! Further,
more and tail normally operate on lines. Your mention of "stacked
prompts" made me think of CR/LF problems. Even if there are no stacked
prompts, could it be there are missing or deferred CR/LF characters?
This would be common if a response to an error message was expected by
one of the applications or waiting for some input, like more or less. If
the physical connection losing characters? E.g. dial-up modem without
flow control on one or both ends? Ssh connection vi UDP, which is
"connectionless", advertised as "unreliable" and not the usual mode?
If you put the outputs into a log file and then tail or more them, what
are the results? Have you tried running the commands without SSH
involvement?
>
> rgds/ldv
> <snip sig stuff>
HTH
--
Bill
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