Our server has a memory leak and I am trying to find out what is causing it. Its a Debian Sarge system with the following services.

mysql, apache2, named, sshd, saslauthd, imapd, couriertls, authdaemon.plain

The server has a gig of RAM which fills up in about 72 hours of uptime.

Running htop, I added the memory persentages of all processes that showed up but the result accounted for a 48% load. The memory however is full. I can only conclude that some process doesn't release the memory properly.

I would be glad with any suggestions on how to carry the investigation further. Or someone already knows the answer?

Are you getting out of memory errors? Or heavy swap usage that stays at high levels? Your htop (and ps) outputs might be useful as I run most of those but don't have any problems with memory.

Memory is often full on a Linux system.

The reason is, memory is not cleared. This allows applications to re-access memory later that includes application themselves without having to make expensive calls to the harddrive.

Now, if you are experiencing excessive swapping then something odd might be happening.

Your next question might be how can I tell what is being kept for later usage and what is currently being used and therefore has higher priority in not being booted out of memory.

It is called the cache - and this is the reason apps like firefox seem a little slow on first invoke but subsequently seem a bit faster.

free -m -s 4

have a look at the cache details.

It is a common misconception, and as I don't use htop you might actually be seeing real system memory usage in which case a memory leak is possible but if it is like top you are actually seeing total memory usage.

sar is another good sysstat tool, and yeah I looked at htop (very pretty) but it is top like and really only use those as front line analysis.

You are not the first to come across this and I am sure not the last.

It makes perfect sence to release memory on demand rather than load programs from hd all the time. The server is using only 340k of swap space, so I guess this is not so bad.

Thank you both for your informative responces.