How to Check Memory Usage on Linux CentOS/RHEL

Linux comes with many commands to check memory usage. The “free” command usually displays the total amount of free and used physical and swap memory in the system, as well as the buffers used by the kernel. The “top” command provides a dynamic real-time view of a running system. The top command can display system summary information as well as a list of the process currently being managed by the Linux kernel.

In this article I will describe lots of way to check the memory usage on Linux.

Check Memory Usage on Linux

Follow the below command to check memory usage on Linux machine.

/proc/meminfo

You can check memory usage is to read the /proc/meminfo file. The same file is used to know the free and other utilities report of free and used memory (both physical and swap) on the system.

# cat /proc/meminfo
or
# egrep --color 'Mem|Cache|Swap' /proc/meminfo

You will get some output like below:

MemTotal:        7996284 kB
MemFree:         5415608 kB
Cached:            92416 kB
SwapCached:        35924 kB
SwapTotal:       8187836 kB
SwapFree:        8059332 kB

free command

You can check the total free and used physical and swap memory as well as the buffer used using free command.

# free -m

You will get some output like below:

             total       used       free     shared    buffers     cached
Mem:          1006        317        689          0         36        190
-/+ buffers/cache:         90        916
Swap:         2015          0       2015

Where;

-b,-k,-m,-g: show output in bytes, KB, MB, or GB
–l: show detailed low and high memory statistics
–o: use old format (no -/+buffers/cache line)
–t: display total for RAM + swap
–s: update every [delay] seconds
–c: update [count] times

vmstat command

vmstat reports information about processes, memory, paging, block IO, traps, and cpu activity.

# vmstat

You will some output like below:

procs -----------memory---------- ---swap-- -----io---- --system-- -----cpu-----
 r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa st
 0  0      0 701072  38236 198804    0    0    18    23   88   97  1  3 96  1  0

The vmstat command with the s option, lays out the memory usage statistics much like the proc command.

# vmstat -s

You will some output like below:

      7996284  total memory
      3028732  used memory
      2587708  active memory
       253600  inactive memory
      4967552  free memory
        32212  buffer memory
        97732  swap cache
      8187836  total swap
       127572  used swap
      8060264  free swap
      2629730 non-nice user cpu ticks
          890 nice user cpu ticks
       335618 system cpu ticks
     80671997 idle cpu ticks
     14269700 IO-wait cpu ticks
            8 IRQ cpu ticks
        12963 softirq cpu ticks
            0 stolen cpu ticks
    320259348 pages paged in
    496267028 pages paged out
        40038 pages swapped in
        85154 pages swapped out
    151875583 interrupts
    278983792 CPU context switches
   1438090342 boot time
       300883 forks

atop command

The program atop is an interactive monitor to view the load on a Linux system. This program can display the amount of used and free memory, i.e. cpu, memory, disk and network.

# atop

You will get some output like below:

htop command

It is similar to top, also allows you to see all the processes running on the system, with their full command lines.

# htop

You will some output like below:

top command

The Linux top command is used to show all the running processes within your Linux environment.

# top 

You will some output like below:

Tasks:  84 total,   1 running,  83 sleeping,   0 stopped,   0 zombie
Cpu(s):  0.5%us,  2.4%sy,  0.0%ni, 96.0%id,  0.8%wa,  0.0%hi,  0.2%si,  0.0%st
Mem:   1030888k total,   324996k used,   705892k free,    37324k buffers
Swap:  2064376k total,        0k used,  2064376k free,   194916k cached