Dear server fault community, This is my first question on server fault, i'm new to server (mis)configuration so please forgive me for asking something stupid :)

I'm running Directadmin on a CentOS 6.4 64b with 4GB memory and over 10000Gh virtual machine. I migrated my websites because my former vps couldn't keep up anymore. Only half of the websites from this 1GB machine were migrated jet. So the migration is still in progress and already my server crashes every day. The server performance up until that moment is perfect.

The directadmin log files show nothing out of the ordinary. Yesterday only the mysql server crashed but it also crashed the entire machine before.

The memory usage in DA seems to be normal:

directadmin directadmin (pid 3923 22158 22159 22160 22161 22162 )8.75 MB    
dovecot dovecot (pid 3851 ) 47.8 MB 
exim    exim (pid 1350 )    1.29 MB 
httpd (pid 21525 21528 21529 21530 21531 21532 21546 21571 21742 21743 21744 )490.4 MB  
mysqld  mysqld (pid 1299 )  287.8 MB        
named   named (pid 3807 )   16.3 MB 
proftpd proftpd (pid 1481 ) 1.91 MB 
sshd    sshd (pid 1173 21494 )  5.16 MB 

Restarting services immediately frees up memory, but slowly over time the memory usage increases(about 24 hours to crash).

The commands:

# sync
# echo 3 > /proc/sys/vm/drop_caches

Will free al memory correct. I could just create a cronjob but it seems the wrong way around to me. I can't seem to pinpoint the cause. Any advices, references or tips are highly appreciated!

Greetings, Coen

edit: free -m : after drop_caches:

                 total       used       free     shared    buffers     cached
Mem:          3830        735       3095          0          0         21
-/+ buffers/cache:        712       3117
Swap:          991          0        991

I'll post another one this evening.