check memory usage:
free command displays amount of total, free and used physical memory (RAM) in the system, as well as shoing information on shared memory, buffers, cached memory and swap space used by the Linux kernel.
Syntax of free
Example usage of free
The command will display information about physical memory in MB.
free -m -s 5
The command will activate continuous polling delay at 5 seconds apart, and then display memory status in megabytes on terminal. Any floating point number for delay can be specified.
free -t -m
Same with “free -m”, but -t switch will display a line containing the totals of physical memory and swap space.
vmstat reports report virtual memory statistics, which has information about processes, swap, free, buffer and cache memory, paging space, disk IO activity, traps, interrupts, context switches and CPU activity. With vmstat command, administrators can has instantaneous reports on memory usage.
Syntax of vmstat
vmstat -[options] [delay count]
Example usage of vmstat
The command will display report based on averages since last reboot.
The command will pool average system resources usage level for a sampling period of 5 seconds at interval of 5 seconds, except the first result that is averages since the last reboot.
empty / free up memory caches
To free pagecache:
echo 1 > /proc/sys/vm/drop_caches
To free dentries and inodes:
echo 2 > /proc/sys/vm/drop_caches
To free pagecache, dentries and inodes:
echo 3 > /proc/sys/vm/drop_caches
As this is a non-destructive operation and dirty objects are not freeable, the user should run “sync” first!
This was originally found @ http://www.linuxinsight.com/proc_sys_vm_drop_caches.html