After upgrading to a new CentOS 5.3 server three months ago we have
been experiencing timeouts now and then with both Squirrelmail and
Thunderbird.
Sympotoms are:
* a user cannot access her Sent folder with Thunderbird (user receives
an error about a timeout)
* a user cannot login with Squirrelmail (error saying about timeout)
At the same time I can access my own mailbox ok with Mac Mail
(Squirrelmail doesn't work for me either at these times). This usually
happens at busy times (noon), almost never in the evenings, so it
could be related to number of users and maybe to some limits the
system have? Stopping and starting the qmail service resolves the
problem for a while, but recently I've had to do this almost every
day.
I have about 100 domains having 5 users each. The system is a Xen
virtual server with a dedicated Xeon 2.5 GHz CPU and 4 gigs of memory
(of which there over 2 gigs free). Sar reports some iowait, but that
shouldn't be crucial:
12:00:02 AM CPU %user %nice %system %iowait %steal %idle
11:00:01 AM all 1.63 0.00 0.36 3.70
0.02 94.30
11:10:01 AM all 2.00 0.00 0.40 3.47
0.01 94.11
11:20:01 AM all 1.58 0.00 0.35 3.63
0.01 94.43
11:30:01 AM all 1.03 0.00 0.34 3.25
0.01 95.36
11:40:01 AM all 1.04 0.00 0.42 3.09
0.02 95.43
11:50:01 AM all 1.45 0.00 0.33 2.90
0.01 95.31
12:00:01 PM all 1.15 0.00 0.31 3.28
0.01 95.25
Average: all 0.56 0.00 0.15 1.19
0.01 98.09
Here are some settings related to limits:
/var/qmail/supervise/imap4*/run
/usr/bin/softlimit -m 9000000 \
/var/qmail/supervise/smtp/run
exec /usr/bin/softlimit -m 20000000 \
/var/qmail/control/concurrencyincoming
500
/var/qmail/control/concurrencyremote
500
/etc/courier/imapd
MAXDAEMONS=40
MAXPERIP=4
Any ideas how to debug this more? I haven't seen anything special in
the logs while this happens?
Regards,
Peter
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