On June 4, I upgraded Debian on one of my servers from "Lenny" to "Squeeze". Before the upgrade, system load of this server was generally low, mostly below 0.1, except for a daily spike every morning when several backup jobs run. Once Debian Squeeze was running I quickly observed that the server load was significantly higher. Watching top I figured that the new version 1.4 of Munin – running on this server, too – was the main culprit.
On June 5, I decided that the high load might very well affect my electricity bill and the environment. Since the Munin graphs of this server are not much accessed, I configured Munin to run on CGI. Afterwards, the load was down at 0.2.
Clearly, that was still higher than before the Debian upgrade. But
top didn't show anything (you know that feeling that the load always decreases once you start
top?) I almost set the findings aside as some artifact.
Early June 7, I replaced the UPS supporting this server. The old UPS was monitored by the
nut package, the new one was connected to
apcupsd. I did not expect this to have any influence on the load. Thus, I didn't even check.
In the morning of June 9, I received a message from the server letting me know that the attached GSM-USB-modem was apparently out of order. Actually, the message said that there was no log file from the previous day. Generally, this happened when the modem was not attached at all. But it was.
Looking at the Munin load graph, I assumed that for some unknown reason the modem was not detected when I rebooted the server on June 7. At least the log files said so. Strangely enough, during the 2 days without the modem the server's load was back down close to 0. After I made sure the modem was working, the load was up again (BTW, without showing any running processes in
On June 10, just to prove the point, I re-scheduled the job which was querying the modem. Until then, I had a Cron job running
gammu backupsms every 5 minutes asking the modem whether SMS arrived. To see how it affects the load I changed the interval to 10 minutes. And, indeed, the load was reduced by about 50%.
Late June 10, I gave
gammu-smsd a try, hoping that the high load of a repeated
gammu backupsms was caused mainly by the initialization of the modem (which took longer since Debian Squeeze was running), and that the
gammu-smsd daemon might cut that down by constantly monitoring the modem.
Apparently, this is the case. Since I switched Munin to run on Fast-CGI, and since I use
gammu-smsd instead of
gammu, the load after the Debian upgrade is in fact lower than before. As it should be.