4 ways to check size of physical memory (RAM) in Linux

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

Without much delay lets dive into commands –

1. Using free command

First command is free. This is simplest command to check your physical memory. This command is mainly used for checking RAM and SWAP on system. Using different switch you can change the byte-format of output. Like -b for bytes, -k for kilobytes, -m for megabytes and -g for gigabytes.

Check row with Mem: and number against it. Thats the physical RAM of your server.

Shell

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root@kerneltalks # free -b              total       used       free     shared    buffers     cached Mem:    135208493056 1247084544 133961408512          0  175325184  191807488 -/+ buffers/cache:  879951872 134328541184 Swap:   17174347776          0 17174347776   root@kerneltalks # free -k              total       used       free     shared    buffers     cached Mem:     132039544    1218368  130821176          0     171216     187316 -/+ buffers/cache:     859836  131179708 Swap:     16771824          0   16771824   root@kerneltalks # free -m              total       used       free     shared    buffers     cached Mem:        128944       1189     127754          0        167        182 -/+ buffers/cache:        839     128105 Swap:        16378          0      16378   root@kerneltalks # free -g              total       used       free     shared    buffers     cached Mem:           125          1        124          0          0          0 -/+ buffers/cache:          0        125 Swap:           15          0         15

In above output you can see system is installed with 125GB of physical RAM (observe highlighted rows). By using different switch -b, -k, -m and -g output changed numbers according to selected byte-format.

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2. Using /proc/meminfo file

Another way is to read memory info from proc filesystem. /proc/meminfo is the file you should read to get detailed information about memory. The very first line or line starts with MemTotal is your total physical memory on server.

Shell

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root@kerneltalks # cat /proc/meminfo |grep MemTotal MemTotal:       132039544 kB

As you can see from output, memory is displayed in kilobytes.

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3. Using top command

Famous top command also lists physical memory information in very clear way. In upper section of top command output lies the CPU, Memory and SWAP information.

Shell

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root@kerneltalks # top top - 16:03:41 up 89 days,  3:43,  1 user,  load average: 0.00, 0.01, 0.05 Tasks: 141 total,   1 running, 140 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:  132039544k total,  1218336k used, 130821208k free,   171224k buffers Swap: 16771824k total,        0k used, 16771824k free,   187420k cached

I clipped above section of top command output in above example. Check second last line saying Mem:(highlighted row). This shows physical memory in kilobytes. You can see total, used and free portions of it. Total is your actual RAM installed on server.

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4. Using vmstat

Another way is to use vmstat (virtual memory stats) command with -s switch. This will list memory in details with first line being total memory on server.

Shell

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# vmstat -s     132039544  total memory       1218692  used memory        181732  active memory ----output trimmed----

Memory is displayed in kilobytes by default. Very first line shows you total memory on server.

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sangeethakumar

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