5 commands to check memory usage on Linux

Memory usage

In Linux, almost all commands are without a GUI. When running on access servers, only the shell. So today we are going to show you the commands that can be used to check the memory usage on a Linux system. Memory includes RAM and swap.

It is often important to check shared memory and process memory usage on servers, as well as unused resources. If you are running a web server, then the server must have enough memory to serve site visitors. If this does not happen, the site will become very slow or even become inaccessible when there is a surge in traffic, simply because memory is not enough. The same as what happens on a desktop computer.

1. The free command

The free command is the simplest and easiest to use command to check memory usage on Linux. Here’s a quick example

$ free -m
             total       used       free     shared    buffers     cached
Mem:          7976       6459       1517          0        865       2248
-/+ buffers/cache:       3344       4631
Swap:         1951          0       1951

The -m option displays all data in megabytes. The total total RAM of Linux is 7976 MB installed in the system, that is, 8 GB. The used column shows the amount of RAM that can be used on Linux, in our case it will be about 6.4 GB. The catch here is the cached and buffers columns. The second line says 4.6 GB is free. This is the free memory on the first line with the addition of buffers and the amount of cache memory.

Linux has a habit of caching to improve performance so that memory can be freed and used as needed. The last line is swap, which in this case is completely free.

2. / proc / meminfo

The next way to check memory usage is to read / proc / meminfo. Be aware that the / proc filesystem contains no real files. They are virtual files that contain dynamic information about the kernel and system.

$ cat /proc/meminfo
MemTotal:        8167848 kB
MemFree:         1409696 kB
Buffers:          961452 kB
Cached:          2347236 kB
SwapCached:            0 kB
Active:          3124752 kB
Inactive:        2781308 kB
Active(anon):    2603376 kB
Inactive(anon):   309056 kB
Active(file):     521376 kB
Inactive(file):  2472252 kB
Unevictable:        5864 kB
Mlocked:            5880 kB
SwapTotal:       1998844 kB
SwapFree:        1998844 kB
Dirty:              7180 kB
Writeback:             0 kB
AnonPages:       2603272 kB
Mapped:           788380 kB
Shmem:            311596 kB
Slab:             200468 kB
SReclaimable:     151760 kB
SUnreclaim:        48708 kB
KernelStack:        6488 kB
PageTables:        78592 kB
NFS_Unstable:          0 kB
Bounce:                0 kB
WritebackTmp:          0 kB
CommitLimit:     6082768 kB
Committed_AS:    9397536 kB
VmallocTotal:   34359738367 kB
VmallocUsed:      420204 kB
VmallocChunk:   34359311104 kB
HardwareCorrupted:     0 kB
AnonHugePages:         0 kB  
HugePages_Total:       0
HugePages_Free:        0
HugePages_Rsvd:        0
HugePages_Surp:        0
Hugepagesize:       2048 kB
DirectMap4k:       62464 kB
DirectMap2M:     8316928 kB

Check the values ​​MemTotal, MemFree, Buffers, Cached, SwapTotal and SwapFree. They point to the same memory usage values ​​in the free command.

3.vmstat

The vmstat command, with the -s option, shows memory statistics much like the Proc command. Here’s an example

$ vmstat -s
      8167848 K total memory
      7449376 K used memory
      3423872 K active memory
      3140312 K inactive memory
       718472 K free memory
      1154464 K buffer memory
      2422876 K swap cache
      1998844 K total swap
            0 K used swap
      1998844 K free swap
       392650 non-nice user cpu ticks
         8073 nice user cpu ticks
        83959 system cpu ticks
     10448341 idle cpu ticks
        91904 IO-wait cpu ticks
            0 IRQ cpu ticks
         2189 softirq cpu ticks
            0 stolen cpu ticks
      2042603 pages paged in
      2614057 pages paged out
            0 pages swapped in
            0 pages swapped out
     42301605 interrupts
     94581566 CPU context switches
   1382755972 boot time
         8567 forks

The top few lines indicate total memory, free memory, etc., and so on.

4.top command

The top command is commonly used to check memory and cpu for each process. However, it also reports total memory usage and can be used to monitor overall memory usage. The output of the result has the necessary information. Here is a sample output

top - 15:20:30 up  6:57,  5 users,  load average: 0.64, 0.44, 0.33
Tasks: 265 total,   1 running, 263 sleeping,   0 stopped,   1 zombie
%Cpu(s):  7.8 us,  2.4 sy,  0.0 ni, 88.9 id,  0.9 wa,  0.0 hi,  0.0 si,  0.0 st
KiB Mem:   8167848 total,  6642360 used,  1525488 free,  1026876 buffers
KiB Swap:  1998844 total,        0 used,  1998844 free,  2138148 cached

  PID USER      PR  NI  VIRT  RES  SHR S  %CPU %MEM    TIME+  COMMAND                                                                                 
 2986 enlighte  20   0  584m  42m  26m S  14.3  0.5   0:44.27 yakuake                                                                                 
 1305 root      20   0  448m  68m  39m S   5.0  0.9   3:33.98 Xorg                                                                                    
 7701 enlighte  20   0  424m  17m  10m S   4.0  0.2   0:00.12 kio_thumbnail

Check out KiB Mem and KiB Swap in the header. They indicate total, used and free memory space. Buffer and cache information is present here as well as the free commands.

5. The htop command

Like the free command, the htop command also shows memory usage along with other details.

The heading at the top shows the CPU usage with RAM and swap usage with corresponding numbers.

Memory information (RAM)

Use the dmidecode command to find out the hardware information about the installed RAM. The command displays detailed information about the installed RAM.

$ sudo dmidecode -t 17
# dmidecode 2.11
SMBIOS 2.4 present.

Handle 0x0015, DMI type 17, 27 bytes
Memory Device
        Array Handle: 0x0014
        Error Information Handle: Not Provided
        Total Width: 64 bits
        Data Width: 64 bits
        Size: 2048 MB
        Form Factor: DIMM
        Set: None
        Locator: J1MY
        Bank Locator: CHAN A DIMM 0
        Type: DDR2
        Type Detail: Synchronous
        Speed: 667 MHz
        Manufacturer: 0xFF00000000000000
        Serial Number: 0xFFFFFFFF
        Asset Tag: Unknown
        Part Number: 0x524D32474235383443412D36344643FFFFFF

Information includes size (2048MB), type (DDR2), speed (667 MHz), etc.

Summary

All of the above commands work from the terminal and do not have a graphical interface. When working on a desktop with a graphical interface, it is much easier to use a graphical tool with graphical output. The most common tools are gnome-system-monitor in gnome and KSysguard in KDE. Both provide information about resource usage about CPU, RAM, exchange and network bandwidth in graphical mode and easy-to-understand visual conclusions.

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