I have a linux (slackware) system with 1 gig of physical memory and 2 gigs of swap space. The system hasn't been rebooted in over a month, and it's been pretty stable. However, last few days, I've noticed that there's less and less free physical memory available - I think there's a memory leak in some piece of software I'm running, but I don't know how to find out which application is eating up all my memory.

If I do a top, I see several instances of mysqld and httpd, but the mysqld instances are (according to top) using only 1.8% of memory or less each, and the httpd instances are using only 0.8% or less each. This doesn't add up to the 80% or so memory usage I'm seeing. There are various other services running, but according to top they're only using between 0.1% and 0.4% of memory each.

Output from `cat /proc/meminfo`

Last time I checked (a few days ago), my free physical memory was twice what it is now. There's something eating up my memory, but I don't know what.

The following software is used on this box:

• Apache 1.3.34
• PHP 4.4.2
• MySQL 5.0.18
• Courier IMAP 4.0.6
• Postfix 2.2.8

I also have a bunch of PHP scripts that I wrote myself that hit the db (MySQL) quite often, and I'm wondering if that could be responsible for my memory trouble. What I really need is a way to diagnose what's going on - is there a better way (other than top and meminfo) to find out which applications are using memory?

I'm worried that if this keeps up, eventually it's going to start hitting the swap (currently I'm not using any of the 2 gigs of swap space available), which will slow things down significantly.

This has to do with the fact that Linux automatically preallocates memory to buffers and cache so that processes can grab the memory more quickly. To see what is REALLY in use use the "free" command.

You should see something like:
total used free shared buffers cached
Mem: 8248768 7648536 600232 0 321644 6381176
-/+ buffers/cache: 945716 7303052
Swap: 5245096 216 5244880

The first line shows you essentially what you were seeing (except its in kb rather than bytes). The second line shows you what you're really using up for processes as it adds or subtracts the cache and buffers back. So long as the "free" column on the second line is fairly high you should be fine.

My output shows this:

So when it says "used" memory, it's actually referring to memory that has been reserved by the OS and is not actually in use by any application? Just trying to understand. If that's the case, great, no problem here. That would also explain why the top command isn't showing any memory-hogging applications - I guess there just aren't any.

Thanks for the insight.

Right. In your output it shows 862544 "Used" on first line but that includes the preallocation for cache and buffers. The "Used" you should be concered with the is the 162568 on the second line as that leaves out the cache and buffers. Based on what you displayed it appears you have no memory issue.

Of course you can do the calculation from the /proc/meminfo manually but since "free" does it for you its better to use.