Super User is a question and answer site for computer enthusiasts and power users. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I have a linux server that keeps using up all its memory and I can't see what is using it. Running top gives the following response:

Tasks: 103 total,   1 running, 102 sleeping,   0 stopped,   0 zombie
Cpu(s):  0.0%us,  0.0%sy,  0.0%ni,100.0%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st
Mem:   8000452k total,  6336612k used,  1663840k free,   298784k buffers
Swap:  2187256k total,        0k used,  2187256k free,  4850536k cached

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND                                                                                                                                                                         
 1847 mwl       20   0 1604m 688m  10m S    0  8.8   1:18.02 java                                                                                                                                                                            
  767 mysql     20   0  301m 101m 7424 S    0  1.3   0:33.11 mysqld                                                                                                                                                                          
  970 www-data  20   0  216m  28m 3548 S    0  0.4   0:00.33 apache2                                                                                                                                                                         
  817 root      20   0 2216m  25m 8556 S    0  0.3   0:00.29 java                                                                                                                                                                            
  944 root      20   0  196m  10m 5320 S    0  0.1   0:00.07 apache2                                                                                                                                                                         
  969 www-data  20   0  196m 6888 1452 S    0  0.1   0:00.01 apache2                                                                                                                                                                         
 1681 www-data  20   0  196m 6884 1432 S    0  0.1   0:00.00 apache2                                                                                                                                                                         
  968 www-data  20   0  196m 6872 1432 S    0  0.1   0:00.00 apache2                                                                                                                                                                         
 1696 www-data  20   0  196m 6868 1432 S    0  0.1   0:00.00 apache2                                                                                                                                                                         
 1682 www-data  20   0  196m 6656 1332 S    0  0.1   0:00.00 apache2                                                                                                                                                                         
  971 www-data  20   0  196m 6636 1360 S    0  0.1   0:00.00 apache2                                                                                                                                                                         
 1703 www-data  20   0  196m 6488 1232 S    0  0.1   0:00.00 apache2                                                                                                                                                                         
 1683 www-data  20   0  196m 6132  896 S    0  0.1   0:00.00 apache2                                                                                                                                                                         
 1702 www-data  20   0  196m 5964  744 S    0  0.1   0:00.00 apache2                                                                                                                                                                         
 1014 root      20   0  117m 3576 2304 S    0  0.0   0:00.00 console-kit-dae                                                                                                                                                                 
 2049 root      20   0 81164 3520 2736 S    0  0.0   0:00.02 sshd                                                                                                                                                                            
 1010 root      20   0 81164 3504 2724 S    0  0.0   0:00.01 sshd                                                                                                                                                                            
  706 syslog    20   0  187m 2388 1100 S    0  0.0   0:00.03 rsyslogd                                                                                                                                                                        
 2073 root      20   0 19564 2344 1624 S    0  0.0   0:00.03 bash                                                                                                                                                                            
 2065 bob       20   0 19564 2316 1600 S    0  0.0   0:00.00 bash                                                                                                                                                                            
  924 root      20   0 37196 2284 1784 S    0  0.0   0:00.01 master                                                                                                                                                                          
 1741 mwl       20   0 19452 2256 1640 S    0  0.0   0:00.00 bash                                                                                                                                                                            
  937 postfix   20   0 39420 2228 1752 S    0  0.0   0:00.00 qmgr                                                                                                                                                                            
 1092 mwl       20   0 19432 2228 1636 S    0  0.0   0:00.01 bash                                                                                                                                                                            
  936 postfix   20   0 39260 2180 1720 S    0  0.0   0:00.01 pickup                                                                                                                                                                          
    1 root      20   0 23692 1828 1240 S    0  0.0   0:01.05 init                                                                                                                                                                            
 1091 mwl       20   0 81164 1696  856 S    0  0.0   0:00.01 sshd                                                                                                                                                                            
 2064 bob       20   0 81164 1660  856 S    0  0.0   0:00.00 sshd                                                                                                                                                                            
  739 avahi     20   0 34052 1620 1300 S    0  0.0   0:00.01 avahi-daemon                                                                                                                                                                    
 2100 root      20   0 19220 1400 1064 R    0  0.0   0:00.10 top                                                                                                                                                                             
  713 root      20   0 49256 1112  564 S    0  0.0   0:00.00 sshd                                                                                                                                                                            
  801 root      20   0 21072 1016  780 S    0  0.0   0:00.00 cron                                                                                                                                                                            
  341 root      20   0 17032  984  604 S    0  0.0   0:00.05 upstart-udev-br                                                                                                                                                                 
  477 root      18  -2 17344  984  204 S    0  0.0   0:00.00 udevd                                                                                                                                                                           
  478 root      18  -2 17344  984  204 S    0  0.0   0:00.00 udevd                                                                                                                                                                           
  728 messageb  20   0 23420  912  608 S    0  0.0   0:00.01 dbus-daemon                                                                                                                                                                     
  343 root      16  -4 17048  908  320 S    0  0.0   0:00.04 udevd                                                                                                                                                                           
 1861 mwl       20   0  9752  868  704 S    0  0.0   0:00.00 tail                                                                                                                                                                            
  745 root      20   0  6076  652  544 S    0  0.0   0:00.00 getty                                                                                                                                                                           
  749 root      20   0  6076  652  544 S    0  0.0   0:00.00 getty                                                                                                                                                                           
  756 root      20   0  6076  652  544 S    0  0.0   0:00.00 getty                                                                                                                                                                           
  967 root      20   0  6076  652  544 S    0  0.0   0:00.00 getty                                                                                                                                                                           
  746 root      20   0  6076  648  544 S    0  0.0   0:00.00 getty                                                                                                                                                                           
  750 root      20   0  6076  648  544 S    0  0.0   0:00.00 getty     

As you can see over 6GB of memory is being used but the processes (which are ordered by memory usage) only add up to about 10%.

share|improve this question

migrated from stackoverflow.com Nov 16 '11 at 12:07

This question came from our site for professional and enthusiast programmers.

    
Disk cache? Corroborated by swap used = 0. – Didier Trosset Nov 16 '11 at 11:56
up vote 7 down vote accepted

The memory usage as reported by top and free is divided into:

  • The "free" memory that isn't used by the kernel at all.
  • "cached" memory, that is contents of files that the kernel remembered for fast access.
  • "buffers" memory, AFAIK cached filesystem metadata

The kernel can give memory that was used for "buffers" and "cached" to applications as well, so in a slightly incorrect way you can say that really_free = free + cached + buffers.

See also: Help! Linux ate all my RAM!

share|improve this answer

This memory is summarized as 4850536k cached: Files that were cached in memory.

share|improve this answer

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .