How to Check Linux Memory Usage
If your Linux server or workstation seems to be suffering from a dip in performance then a good starting point when troubleshooting is to check the current memory usage. With that in mind, this article will explore some of the ways you can check RAM usage on Linux to help you diagnose what may be causing your Linux system to slow down.
Many of the commands used to check Linux free memory shown here will already be present on your Linux system, which is convenient!
View Memory Usage with /proc/meminfo
Proc is a virtual filesystem on Linux which contains runtime system information. Many Linux system utilities are calls to files in this directory in order to retrieve and display information about the system. The meminfo file contains details about the memory usage of the Linux system:
$ cat /proc/meminfo MemTotal: 1992964 kB MemFree: 93032 kB MemAvailable: 1137284 kB Buffers: 52144 kB Cached: 1113000 kB SwapCached: 0 kB Active: 505572 kB Inactive: 1202796 kB Active(anon): 1172 kB Inactive(anon): 562036 kB Active(file): 504400 kB Inactive(file): 640760 kB Unevictable: 23008 kB Mlocked: 18472 kB SwapTotal: 0 kB SwapFree: 0 kBThis is a quick and simple way to check memory usage and should work on any distribution. Rather than list the whole file contents you can use grep to filter the output. For example, to view only the total memory on the system, run the following:
$ cat /proc/meminfo | grep MemTotal MemTotal: 1992964 kBAs this is text output there are many ways in which this data can be retrieved using scripts:
In the example above, awk has been used to parse the output of /proc/meminfo and convert the memtotal value into Gb.
Check Linux Memory Usage using Free
The free command is another convenient way to view Linux memory usage details. Running it without any arguments will output the following:
$ free total used free shared buff/cache available Mem: 1992964 666712 179912 9628 1146340 1147644 Swap: 0 0 0Running it again, but with the -h option produces a more readable result, with the memory unit displayed:
$ free -h total used free shared buff/cache available Mem: 1.9Gi 651Mi 175Mi 9.0Mi 1.1Gi 1.1Gi Swap: 0B 0B 0BThe following information is displayed:
| total | Total installed memory (Physical Memory installed on the system) |
| used | Memory currently in use |
| free | Unused memory on the system |
| shared | Memory shared by multiple processes on the system |
| buffers | Memory reserved by the OS to allocate as buffers when process need them |
| cached | Recently used files cached in RAM |
| buff/cache | Buffers + Cache |
| available | How much memory is available, without swapping. |
A great thing about the free command is that it can output memory usage statistics using different memory units. The help option shows the numerous memory units available:
Options: -b, --bytes show output in bytes --kilo show output in kilobytes --mega show output in megabytes --giga show output in gigabytes --tera show output in terabytes --peta show output in petabytes -k, --kibi show output in kibibytes -m, --mebi show output in mebibytes -g, --gibi show output in gibibytes --tebi show output in tebibytes --pebi show output in pebibytes -h, --human show human-readable output --si use powers of 1000 not 1024 -l, --lohi show detailed low and high memory statistics -t, --total show total for RAM + swap -s N, --seconds N repeat printing every N seconds -c N, --count N repeat printing N times, then exit -w, --wide wide output --help display this help and exit -V, --version output version information and exitTo output Linux memory usage in gigabytes the following can be used:
$ free --giga total used free shared buff/cache available Mem: 2 0 0 0 0 1 Swap: 0 0 0Now, lets take a look at how to use the top command to look at memory usage.
View Memory usage using the Top Command
The top command is a well known Linux command for viewing real time Linux system information, including memory usage. To run top :
The output should look similar to the following:
top - 13:31:56 up 40 min, 1 user, load average: 0.00, 0.00, 0.00 Tasks: 200 total, 1 running, 199 sleeping, 0 stopped, 0 zombie %Cpu(s): 0.3 us, 0.2 sy, 0.0 ni, 99.5 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st MiB Mem : 1946.3 total, 396.6 free, 644.6 used, 905.1 buff/cache MiB Swap: 0.0 total, 0.0 free, 0.0 used. 1124.2 avail Mem PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 1 root 20 0 103420 13200 8512 S 0.0 0.7 0:06.29 systemd 2 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kthreadd 3 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 rcu_gp 4 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 rcu_par_gpThe section at the top of the output displays overall system memory usage:
MiB Mem : 1946.3 total, 396.6 free, 644.6 used, 905.1 buff/cache MiB Swap: 0.0 total, 0.0 free, 0.0 used. 1124.2 avail MemYou can also see the memory usage of individual processes by checking out the %MEM column. If you have worked with VMware ESXi hosts you will notice this is similar to esxtop.
Summary
In this article you have learned a number of ways to check memory usage on Linux, including how to use the top and free commands which tend to be present on all Linux distributions, and how to list the contents of the /proc/meminfo file to get detailed memory usage statistics.
5 commands to check memory usage on Linux
On linux, there are commands for almost everything, because the gui might not be always available. When working on servers only shell access is available and everything has to be done from these commands. So today we shall be checking the commands that can be used to check memory usage on a linux system. Memory include RAM and swap.
It is often important to check memory usage and memory used per process on servers so that resources do not fall short and users are able to access the server. For example a website. If you are running a webserver, then the server must have enough memory to serve the visitors to the site. If not, the site would become very slow or even go down when there is a traffic spike, simply because memory would fall short. Its just like what happens on your desktop PC.
1. free command
The free command is the most simple and easy to use command to check memory usage on linux. Here is 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 MBs. The total os 7976 MB is the total amount of RAM installed on the system, that is 8GB. The used column shows the amount of RAM that has been used by linux, in this case around 6.4 GB. The output is pretty self explanatory. The catch over here is the cached and buffers column. The second line tells that 4.6 GB is free. This is the free memory in first line added with the buffers and cached amount of memory.
Linux has the habit of caching lots of things for faster performance, so that memory can be freed and used if needed.
The last line is the swap memory, which in this case is lying entirely free.
2. /proc/meminfo
The next way to check memory usage is to read the /proc/meminfo file. Know that the /proc file system does not contain real files. They are rather virtual files that contain dynamic information about the kernel and the 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 of MemTotal, MemFree, Buffers, Cached, SwapTotal, SwapFree.
They indicate same values of memory usage as the free command.
3. vmstat
The vmstat command with the s option, lays out the memory usage statistics much like the proc command. Here is 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 generally used to check memory and cpu usage per process. However it also reports total memory usage and can be used to monitor the total RAM usage. The header on output has the required 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 the KiB Mem and KiB Swap lines on the header. They indicate total, used and free amounts of the memory. The buffer and cache information is present here too, like the free command.
5. htop
Similar to the top command, the htop command also shows memory usage along with various other details.
The header on top shows cpu usage along with RAM and swap usage with the corresponding figures.
RAM Information
To find out hardware information about the installed RAM, use the demidecode command. It reports lots of information about the installed RAM memory.
$ 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
Provided information includes the size (2048MB), type (DDR2) , speed(667 Mhz) etc.
Summary
All the above mentioned commands work from the terminal and do not have a gui. When working on a desktop with a gui, it is much easier to use a GUI tool with graphical output. The most common tools are gnome-system-monitor on gnome and
ksysguard on KDE. Both provide resource usage information about cpu, ram, swap and network bandwidth in a graphical and easy to understand visual output.
A Tech Enthusiast, Blogger, Linux Fan and a Software Developer. Writes about Computer hardware, Linux and Open Source software and coding in Python, Php and Javascript. He can be reached at [email protected] .