Red Hat

hi
i've notice a huge problem on my newly installed centOS server and i have no idea how to solve it and where to start..
memory on server 3 GB and it goes down, down, down..
after reboot it shows 71mb used
after a hour its 76mb
and after 24h it's around 200
later = more

i have NO idea where goes this mem..
i've checked ps -AF (no info in SZ column about where so much memory is hiding)
i did shutdown all services (atm there only: crond, haldaemon, messagebus, network, rawdevices, sshd, syslog and some dm-raid45 which i have no idea how to shut down (i have no raid but it just loading on startup even blacklisted in /etc/modprobe.d/blacklist))
still! system loosing memory in nowhere

wtf & what to do?

Linux 2.6.18-194.32.1.el5 #1 SMP Wed Jan 5 17:53:09 EST 2011 i686 i686 i386 GNU/Linux

How do you check the memory usage? Can you post the output of the command used?

free or top

Code:

# free
             total       used       free     shared    buffers     cached
Mem:       3114464      78028    3036436          0      13680      28328
-/+ buffers/cache:      36020    3078444
Swap:      5245212          0    5245212

that's 1 hour 7 minutes uptime
after reboot was 71536 and i did absolutely nothing on server for that hour

The "used" number includes the values for buffers and caches, and isn't limited to memory used by applications alone. Buffers are primarily used for communication between processes (using pipes) and network buffers, while the cache is used to keep file contents in the fast-access RAM, instead of reading the much slower disk all the time. Linux tries to use as much memory as possible for buffers and cache in order to speed up processing and making the most of the expensive memory.

To check this, run echo 3 > /proc/sys/vm/drop_caches, which should drop the numbers back to near zero.

allright, thanks for explanation
now there's 44mb only used ^^

2 questions:
is number '3' means something or i can use any number/symbol ?
if linux marks this memory as 'used' - means other programs can't use it and i should use cron all the time to 'drop near zero' these numbers ?

P.S. freebsd not does this btw - that's why i'm kinda surprised
also didn't saw these on mandriva

---------- Post updated at 04:26 PM ---------- Previous update was at 02:18 PM ----------

this is the link about 'linux ate my ram' for newbies
Help! Linux ate my RAM!

Linux says it's used (meaning it's allocated), but it has a lower priority than application memory. Should applications require more space, the buffer and cache sizes are gradually reduced, and the free space is made available.

The '3' tells the kernel (to which /proc is the interface) to drop all file buffers and filesystem caches that aren't "dirty" (modified in memory only; not yet written to disk). There's a description here. But again, it's not really required to clear that memory, since it's re-allocated to applications should they need it.

You really, really don't want to do that. Caches are good. Caches make things faster. Linux doesn't have to do the same disk accesses over and over. And the memory is still 'free', Linux will give up caches and buffers as readily as 'free' RAM. Any ram sitting around doing nothing is wasted, after all!

In short, don't panic, do a little research, and always find out what you're doing before you punch in someone else's advice.

Yes, the '3' means something. Different numbers refer to different VM modes, it won't take just anything. It also goes away on reboot, so if you forget what it was before, a reboot will undo what you did.