High RAM usage on Ubuntu Linux

When you have 16 gigabyte RAM and you run top you might be surprised:

Tasks: 167 total,   2 running, 164 sleeping,   0 stopped,   1 zombie
Cpu(s):  0.9%us,  0.5%sy,  0.0%ni, 98.6%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st
Mem:  16333884k total,  1722432k used, 14611452k free,   163984k buffers
Swap: 16675836k total,        0k used, 16675836k free,   697196k cached

 PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
1198 root      20   0  143m  16m 7836 S    5  0.1   0:21.80 Xorg
2150 maurits   20   0 1039m 324m  44m S    3  2.0   0:54.05 firefox

Just booted and already 1.7 gigabyte of RAM used. Oh no, Linux ate my ram!

maurits@nuc:~$ free -m
             total       used       free     shared    buffers     cached
Mem:         15951       1657      14293          0        160        655
-/+ buffers/cache:        841      15109
Swap:        16284          0      16284
maurits@nuc:~$

But is is actually not so bad. Using the “free” command we see that only 841 megabytes are used. Others are used for buffers. Fortunately “htop” also shows the correct RAM usage number:

htop

So, just remember that free RAM may actually be used for buffers to optimize operating system I/O. These buffers are immediately discarded when more RAM is needed by applications and they should therefore be considered free.

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