How to clear Linux buffer and cache space

If you ever want to empty it you can use this chain of commands.

[root@test ~]# free -m && sync && echo 3 > /proc/sys/vm/drop_caches && free -m
             total       used       free     shared    buffers     cached
Mem:          5855       4469       1385          0         21        952
-/+ buffers/cache:       3495       2360
Swap:         4095         50       4045
             total       used       free     shared    buffers     cached
Mem:          5855       4412       1442          0          0        917
-/+ buffers/cache:       3493       2361
Swap:         4095         50       4045  

You can signal the Linux Kernel to drop various aspects of cached items by changing the numeric argument to the above command.

• 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  

Non root users run with Sudo:

$ sudo sh -c 'echo 1 >/proc/sys/vm/drop_caches'  $ sudo sh -c 'echo 2 >/proc/sys/vm/drop_caches'  $ sudo sh -c 'echo 3 >/proc/sys/vm/drop_caches'  

NOTE: There's a more esoteric version of the above command if you're into that:

$ echo "echo 1 > /proc/sys/vm/drop_caches" | sudo sh  

Why the change in syntax? The /bin/echo program is running as root, because of sudo, but the shell that's redirecting echo's output to the root-only file is still running as you. Your current shell does the redirection before sudo starts.