The free Utility

The free utility can determine the amount of free RAM on your system. The output is easier to understand than vmstat's. Here's a sample:

     [root@bigboy tmp]# vmstat
     procs-memory -swap -io
      r  b  swpd    free    buff   cache   si   so   bi   bo
      0  0    80  158196  276272  357236    0    0    1    0
     [root@bigboy tmp]#

You should generally try to make your system run with at least 20% free memory on average, which should allow it to handle moderate spikes in usage caused by running memory-intensive cron batch jobs or tape backups. If you cannot achieve this, consider running more efficient versions of programs, offloading some applications to servers with less load, and, of course, upgrading the capacity of your RAM.