4 ways to check size of physical memory in Linux

Introduction

In this article we will see basic commands to check the physical memory on the server under Linux. Many beginners struggle to know their system well in the context of resources such as CPU, Memory, Disks, etc. So I decided to write this small item pointing command to check the RAM on the Linux server. These commands will work in different flavors of Linux like Red Hat, CentOS, Suse, Ubuntu, Fedora, Debian etc.

1) Using free command

This command is mainly used to check the RAM and SWAP on the system. Using a different change, you can change the output byte format. Like -b for bytes, -k for kilobytes, -m for megabytes, and -g for gigabytes.

# free -b
              total        used        free      shared  buff/cache   available
Mem:     3976634368  3096838144   187990016    51572736   691806208   540106752
Swap:    4001361920     8826880  3992535040
# free -k
              total        used        free      shared  buff/cache   available
Mem:        3883432     3024204      183600       50364      675628      527488
Swap:       3907580        8620     3898960
# free -m
              total        used        free      shared  buff/cache   available
Mem:           3792        2953         179          49         659         515
Swap:          3815           8        3807
# free -g
              total        used        free      shared  buff/cache   available
Mem:              3           2           0           0           0           0
Swap:             3           0           3

2) Using /proc/meminfo file

# cat /proc/meminfo |grep Mem
MemTotal:        3883432 kB
MemFree:          183268 kB
MemAvailable:     527276 kB

3) Using top command

# top
top - 12:36:36 up 8 days,  2:58,  2 users,  load average: 0.14, 0.14, 0.08
Tasks: 213 total,   1 running, 212 sleeping,   0 stopped,   0 zombie
%Cpu(s):  0.2 us,  0.7 sy,  0.0 ni, 99.0 id,  0.2 wa,  0.0 hi,  0.0 si,  0.0 st
KiB Mem :  3883432 total,   182356 free,  3025080 used,   675996 buff/cache
KiB Swap:  3907580 total,  3898960 free,     8620 used.   526608 avail Mem 

  PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND                                                                                            
 2303 root      20   0 2378464 541076   7692 S   1.0 13.9 417:16.56 OpsCenterDBd   

4) Using vmstat

[root@opscenter ~]# vmstat -s
      3883432 K total memory
      3025552 K used memory
      2439780 K active memory
       870348 K inactive memory
       181812 K free memory
       138712 K buffer memory
       537356 K swap cache
      3907580 K total swap
         8620 K used swap
      3898960 K free swap
      2323674 non-nice user cpu ticks
         2978 nice user cpu ticks
       944914 system cpu ticks
    135133743 idle cpu ticks
       692582 IO-wait cpu ticks
          121 IRQ cpu ticks
        49623 softirq cpu ticks
            0 stolen cpu ticks
      1931906 pages paged in
     23034525 pages paged out
          377 pages swapped in
         2353 pages swapped out
    956323695 interrupts
   2040196891 CPU context switches
   1505191059 boot time
       849343 forks