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This question already has an answer here:

When I cat /proc/meminfo I see:

MemTotal:      1048576 kB
MemFree:         11136 kB
Buffers:             0 kB
Cached:              0 kB
SwapCached:          0 kB
Active:              0 kB
Inactive:            0 kB
HighTotal:           0 kB
HighFree:            0 kB
LowTotal:      1048576 kB
LowFree:         11136 kB
SwapTotal:           0 kB
SwapFree:            0 kB
Dirty:              88 kB
Writeback:           0 kB
AnonPages:           0 kB
Mapped:              0 kB
Slab:                0 kB
PageTables:          0 kB
NFS_Unstable:        0 kB
Bounce:              0 kB
CommitLimit:         0 kB
Committed_AS:        0 kB
VmallocTotal:        0 kB
VmallocUsed:         0 kB
VmallocChunk:        0 kB
HugePages_Total:     0
HugePages_Free:      0
HugePages_Rsvd:      0
Hugepagesize:     2048 kB

when I do top and sort by memory I see:

%MEM    TIME+  COMMAND
%22.9   0:44.11 java
% 0.1   0:04.57 init
% 2.9   0:02.52 /usr/local/cpan
% 0.3   0:00.50 sshd
% 1.5   0:00.14 mysqld
% 0.5   0:00.13 leechprotect
% 0.1   0:00.12 bash
% 0.4   0:00.11 httpd
% 0.3   0:00.07 queueprocd - wa
% 0.4   0:00.06 tailwatchd
% 0.8   0:00.02 cpsrvd-ssl
% 0.1   0:00.02 top
% 0.1   0:00.01 syslogd
% 0.4   0:00.01 named
% 0.1   0:00.00 udevd
% 0.0   0:00.00 klogd
% 0.0   0:00.00 courierlogger
% 0.1   0:00.00 authdaemond
% 0.0   0:00.00 authdaemond
% 0.0   0:00.00 authdaemond
% 0.1   0:00.00 sshd
% 0.1   0:00.00 xinetd
% 0.1   0:00.00 mysqld_safe
% 0.0   0:00.00 courierlogger
% 0.1   0:00.00 couriertcpd
% 0.1   0:00.00 exim
% 0.1   0:00.00 pure-ftpd
% 0.1   0:00.00 pure-authd
% 0.1   0:00.00 crond
% 0.0   0:00.00 atd
% 0.2   0:00.00 cPhulkd - proce
% 2.8   0:00.00 spamd child
% 0.8   0:00.00 cpdavd - accept
% 0.4   0:00.00 httpd
% 0.4   0:00.00 httpd
% 0.4   0:00.00 httpd
% 0.4   0:00.00 httpd
% 0.4   0:00.00 httpd
% 0.2   0:00.00 cpanellogd - sl
% 0.1   0:00.00 saslauthd
% 0.0   0:00.00 saslauthd
% 0.1   0:00.00 ssh-agent

Why does top show ~38% used when in reality it used 900mb out of 1000mb? How i know how much memory each process uses?

marked as duplicate by slm, Hauke Laging, Anthon, jasonwryan, Chris Down May 22 '13 at 3:52

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

  • If I search for "memory usage" on this site I get 224 results. Don't you think you should have searched for the answer before you ask that question one more time? – Hauke Laging May 22 '13 at 2:18
1

Memory usage can be quite confusing when first starting out with Linux. In general Linux takes the perspective that all of RAM should be put to use instead of conserving it just for processes.

So RAM is used for both processes and as a cache for files as they get loaded from the hard drive. You can see this better with the free command:

# free output in MBs
$ free -m
             total       used       free     shared    buffers     cached
Mem:          7800       6724       1075          0        397       1952
-/+ buffers/cache:       4374       3425
Swap:         5823         27       5796

This is showing you that I have ~7.8GB of RAM, of which ~6.7GB is in use, leaving ~1GB free, in this line:

Mem:          7800       6724       1075          0        397       1952

The next line is the one that enlightens you to what's actually going on:

-/+ buffers/cache:       4374       3425

This line shows that of the ~6.7GB being reported as "used" by the first line, if you take the buffers and cache out of the mix we're really only using ~4.4GB. So in actuality I really have ~3.4GB of RAM free.

The buffers and cache are files that have been loaded by the Kernel from the HDD to RAM to improve performance.

excerpt from linfo.org

The second line of data, which begins with -/+ buffers/cache, shows the amount of physical memory currently devoted to system buffer cache. This is particularly meaningful with regard to application programs, as all data accessed from files on the system that are performed through the use of read() and write() system calls pass through this cache. This cache can greatly speed up access to data by reducing or eliminating the need to read from or write to the HDD or other disk.

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