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Ubuntu has been crashing on me recently. I think its because it runs out of memory so I ran the free -m command and found that my memory usage was really high. So then, i ran top to find the culprit, but the displayed processes were using less than 1.5% of m. how do i know which program is making ubuntu crash/run out of memory? Below is the output:

shafee@shafee-pc:~$ free -m
             total       used       free     shared    buffers     cached
Mem:          3824       3714        110          0        978       1954
-/+ buffers/cache:        780       3044
Swap:           99          0         99

shafee@shafee-pc:~$ top
top - 02:12:14 up  1:24,  2 users,  load average: 0.16, 0.42, 1.49
Tasks: 182 total,   1 running, 181 sleeping,   0 stopped,   0 zombie
Cpu(s):  2.9%us,  1.9%sy,  0.3%ni, 79.3%id, 15.5%wa,  0.0%hi,  0.2%si,  0.0%st
Mem:   3916708k total,  3803848k used,   112860k free,  1002308k buffers
Swap:   102396k total,        0k used,   102396k free,  2001852k cached

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND            
 4200 root      20   0  289m  53m  38m S    2  1.4   1:06.45 Xorg               
 5590 shafee    20   0 19348 1368  956 R    2  0.0   0:00.01 top                
    1 root      20   0 24124 2136 1264 S    0  0.1   0:02.05 init               
    2 root      20   0     0    0    0 S    0  0.0   0:00.00 kthreadd           
    3 root      20   0     0    0    0 S    0  0.0   0:24.23 ksoftirqd/0        
    6 root      RT   0     0    0    0 S    0  0.0   0:00.00 migration/0        
    7 root      RT   0     0    0    0 S    0  0.0   0:00.00 migration/1        
    9 root      20   0     0    0    0 S    0  0.0   0:00.11 ksoftirqd/1        
   11 root      RT   0     0    0    0 S    0  0.0   0:00.00 migration/2        
   13 root      20   0     0    0    0 S    0  0.0   0:03.89 ksoftirqd/2        
       14 root      RT   0     0    0    0 S    0  0.0   0:00.00 migration/3        
   16 root      20   0     0    0    0 S    0  0.0   0:00.16 ksoftirqd/3        
   17 root       0 -20     0    0    0 S    0  0.0   0:00.00 cpuset             
   18 root       0 -20     0    0    0 S    0  0.0   0:00.00 khelper            
   19 root       0 -20     0    0    0 S    0  0.0   0:00.00 netns              
   21 root      20   0     0    0    0 S    0  0.0   0:00.01 sync_supers        
shafee@shafee-pc:~$

or is it normal to have 110mb of free memory and is my issue related to something else?

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It looks like you also don't have enough swap. Recommended is around twice the size of your RAM –  Marco Ceppi Jul 15 '11 at 21:08
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2 Answers

up vote 20 down vote accepted

You're reading the output of free incorrectly. The Linux Kernel does a lot of it's own memory management, in turn allocating more than it actually needs - so you're true amount of "Free Memory" is 3044 located in the "Free" column of the +/- Buffers/cache line, making only 780 MB actually being consumed.

By default top will sort based on CPU consumption. You can press Shift+M to sort by percentage of memory consumed - giving you a better grasp of what software is using the memory allotted to the kernel.


free -m
             total       used       free     shared    buffers     cached
Mem:          7873       3916       3956          0        231       1117
-/+ buffers/cache:       2567       5305
Swap:        12401          0      12401

And in top with memory sorted:

top - 17:05:18 up 2 days,  1:40,  4 users,  load average: 0.21, 0.14, 0.11
Tasks: 237 total,   1 running, 234 sleeping,   0 stopped,   2 zombie
Cpu(s):  1.6%us,  0.8%sy,  0.1%ni, 96.7%id,  0.8%wa,  0.0%hi,  0.0%si,  0.0%st
Mem:   8062420k total,  4013632k used,  4048788k free,   237204k buffers
Swap: 12699644k total,      292k used, 12699352k free,  1144752k cached

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND                                                                                                                                                                          
 1632 root      20   0  884m 240m 6532 S    0  3.1   1:20.17 java                                                                                                                                                                             
 3911 marco     20   0 1011m 165m  22m S    0  2.1   9:20.62 chrome                                                                                                                                                                           
 3852 marco     20   0  770m 162m  45m S    0  2.1  14:59.59 chrome                                                                                                                                                                           
 1091 root      20   0  491m 160m 118m S    3  2.0  29:19.44 Xorg                                                                                                                                                                             
 1747 marco     20   0  659m 108m  34m S    1  1.4  18:43.92 compiz                                                                                                                                                                           
 3964 marco     20   0 1113m  99m  21m S    0  1.3  18:51.88 chrome                                                                                                                                                                           
 1759 marco     20   0  668m  94m  21m S    0  1.2   2:27.42 nautilus                                                                                                                                                                         
 3046 marco     20   0  788m  86m  26m S    0  1.1   1:22.96 evolution                                                                                                                                                                        
 1793 marco     20   0  647m  85m  18m S    0  1.1   0:12.74 shutter                                                                                                                                                                          
 1791 marco     20   0  404m  85m  13m S    0  1.1   5:19.51 bitcoin                                                                                                                                                                          
 2938 marco     20   0  809m  78m  31m S    0  1.0   1:01.07 empathy                                                                                                                                                                          
 9630 marco     20   0  265m  73m  19m S    1  0.9  12:41.52 skype                                                                                                                                                                            
 9618 marco     20   0  914m  64m  21m S    0  0.8   1:14.04 chrome                                                                                                                                                                           
 1777 marco     20   0  432m  64m  14m S    0  0.8   1:45.96 pastie

Finally to help you diagnose what the actual software is, try passing the -c flag to top: top -c as that will give you the full path, name, and parameters of the command running.

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thanks :/ seems my crashes are related to something else then. –  Shafee Jul 15 '11 at 21:05
    
@Shafee You might want to open a new question then, outlining what is crashing and providing any relevant log files or details to see if we can assist you with resolving those crashes. –  Marco Ceppi Jul 15 '11 at 21:11
    
Wow. learnt yet something new again....cheers marco yet again! –  andybleaden Jul 15 '11 at 21:15
4  
See also linuxatemyram.com –  Lekensteyn Jul 15 '11 at 21:56
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You can start the application gnome-system-monitor It's the best to find out how much ram is used by what apps, also how much cpu is used also. You can change the priority of a process to run even faster , for example if you want to convert video etc etc.

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ec2 does not have gnome-system-monitor on cmd line, is there a alternative ? –  Siddharth Jul 13 '12 at 5:56
2  
@Siddharth you can use htop which is a nicer version of top. Hit F6 to sort by e.g. CPU or RAM usage. –  rosch Nov 4 '12 at 12:46
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