Linux measure memory consumption

5 commands to check memory usage on Linux

Memory Usage

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

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.

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

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

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.

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] .

66 thoughts on “ 5 commands to check memory usage on Linux ”

You have explained the topic very well. Thanks for sharing a nice article.

Thanks for these commands. It saved a lots of time.

How about explaining what we are looking for? Most people would know these commands. Waste of time.

Please correct the typo in “RAM Information” section. The command for viewing hardware info about RAM is “dmidecode” and not “demidecode”.
And it also requires root privileges.

Источник

Linux Check Memory Usage Using the CLI and GUI

H ow do I check used and free RAM memory usage under Linux operating systems using command line and GUI tools?

Linux comes with different set of commands to check memory usage. The free command 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 vmstat command reports information about processes, memory, paging, block IO, traps, and cpu activity. Finally, you can use the top or atop/htop commands which provides a dynamic real-time view of a running system. top and friends can display system summary information as well as a list of tasks currently being managed by the Linux kernel. Let us see various commands for Linux to check memory usage.

Tutorial details
Difficulty level	Easy
Root privileges	Yes/NO
Requirements	Linux/free command top/atop/htop
Est. reading time	N/A

Linux check memory usage using /proc/meminfo file

The /proc/meminfo file stores statistics about memory usage on the Linux based system. The same file is used by free and other utilities to report the amount of free and used memory (both physical and swap) on the system as well as the shared memory and buffers used by the kernel.

Examples

Use the cat command or grep command to see /proc/meminfo file:
$ cat /proc/meminfo
$ less /proc/meminfo
$ more /proc/meminfo
$ egrep —color ‘Mem|Cache|Swap’ /proc/meminfo

free command

To display free memory size in MB (megabytes):
$ free -m

Displays a line containing the totals memory in MB:
$ free -t -m

Understanding the free command outputs

The Mem columns contain the following information:

1. Total : The total amount of RAM installed in my system. In this case 30Gi.
2. Used : The total amount of RAM used. It is calculated as: Total – (free + buffers + cache)
3. Free : The amount of unused or free memory for your apps.
4. Shared : Amount of memory mostly used by the tmpfs file systems. In other words, Shmem in /proc/meminfo.
5. Buff/cache : It is sum of buffers and cach. Buff is amount of memory used by Linux kernel for buffers. Cache is memory used by the page cache and slabs.
6. Available : This is an estimation of how much memory is available for starting new applications on Linux system, without swapping.

The Swap columns contain the following information:

1. Total : The total amount of the swap partition or file installed in my system. For example, 119Gi is the size of my swap space on Linux.
2. Used : The total amount of swap sapced used.
3. Free : The amount of unused or free swap space for Linux systems.

So how much free ram I have?

Type the following command:
$ free -m

Understanding Free Command Output

A list of free command options

• -h : Human readable output. In other words, show all output fields automatically scaled to shortest three digit unit and display the units of print out. For example, B used for bytes, Ki means kibibyte, Mi is mebibyte, Gi is gibibyte, Ti means tebibyte, and Pi for pebibyte.
• -b,-k,-m,-g : display output in bytes, KB, MB, or GB.
• -l : show detailed low and high memory statistics.
• -o : use old format (no -/+buffers/cache line).
• -t : see total for RAM + swap usage on Linux.
• -s : update every [delay] seconds.
• -c : update [count] times.

vmstat command

Type the vmstat command at shell prompt:
$ vmstat

top command

Type top command at the shell prompt:
$ top

Fig.01: top command displaying used memory

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. It is similar to top command but comes with additional advanced options. By default, the atop command is not installed on most Linux distributions.
$ atop

Fig.02: Linux Check Amount Of Memory With atop Command (click to enlarge)

htop command

The program htop is an interactive process viewer. It is similar to top, but allows to scroll the list vertically and horizontally to see all processes and their full command lines.
By default, the htop command is not installed on most Linux distributions.
$ htop

Fig.03: Linux Check Amount Of Physical Memory With htop Command (click to enlarge)

GNOME Desktop: GUI tool to see memory usage

The “Gnome System Monitor” application enables you to display basic system information and monitor system processes, usage of system resources, and file systems. You can also use System Monitor to modify the behavior of your system. You can start System Monitor by visiting System menu > Choose Administration > System Monitor option. Or type the following command at the shell prompt:
$ gnome-system-monitor

• No ads and tracking
• In-depth guides for developers and sysadmins at Opensourceflare✨
• Join my Patreon to support independent content creators and start reading latest guides:
  • How to set up Redis sentinel cluster on Ubuntu or Debian Linux
  • How To Set Up SSH Keys With YubiKey as two-factor authentication (U2F/FIDO2)
  • How to set up Mariadb Galera cluster on Ubuntu or Debian Linux
  • A podman tutorial for beginners – part I (run Linux containers without Docker and in daemonless mode)
  • How to protect Linux against rogue USB devices using USBGuard

Join Patreon ➔

Fig.04: Linux See Memory Usage With GNOME GUI System Monitor Tool

Check out related media

A note about the performance

1. RAM – An occupation percentage of 90% is considered as critical.
2. SWAP – An occupation percentage of 80% is considered as critical.
3. To solve performance related problems, add more RAM and increase the swap space (or move swap space to another disk controller).

Conclusion

In this quick tutorial, you learned about various Linux commands that you can use to check the server or desk memory usage. Read man pages of free, vmstat, top, atop, and htop commands for more information by typing the following man command:
$ man free
$ man top
$ man vmstat

🐧 Get the latest tutorials on Linux, Open Source & DevOps via

Category	List of Unix and Linux commands
Documentation	help • mandb • man • pinfo
Disk space analyzers	df • duf • ncdu • pydf
File Management	cat • cp • less • mkdir • more • tree
Firewall	Alpine Awall • CentOS 8 • OpenSUSE • RHEL 8 • Ubuntu 16.04 • Ubuntu 18.04 • Ubuntu 20.04
Linux Desktop Apps	Skype • Spotify • VLC 3
Modern utilities	bat • exa
Network Utilities	NetHogs • dig • host • ip • nmap
OpenVPN	CentOS 7 • CentOS 8 • Debian 10 • Debian 8/9 • Ubuntu 18.04 • Ubuntu 20.04
Package Manager	apk • apt
Processes Management	bg • chroot • cron • disown • fg • glances • gtop • jobs • killall • kill • pidof • pstree • pwdx • time • vtop
Searching	ag • grep • whereis • which
Shell builtins	compgen • echo • printf
Text processing	cut • rev
User Information	groups • id • lastcomm • last • lid/libuser-lid • logname • members • users • whoami • who • w
WireGuard VPN	Alpine • CentOS 8 • Debian 10 • Firewall • Ubuntu 20.04

Comments on this entry are closed.

I need a unix command to get the total memory usage percentage.so that i can call this command from java.The output of the command should only be the percentage of memory utilization.

Using the command free, vmstat, top all shows it uses almost 100% of the memory. But if I use the system monitor, it will show only less than 10%.

I am using CentOS 5. can anyone explain why the free, vmstat, top all displaying wrong information? Thanks.

$ free -m
total used free shared buffers cached
Mem: 3792 3638 154 0 128 3231
-/+ buffers/cache: 277 3515
Swap: 1983 0 1983
$ vmstat
procs ———–memory———- —swap– —–io—- –system– —–cpu——
r b swpd free buff cache si so bi bo in cs us sy id wa st
0 0 108 158380 131948 3309388 0 0 106 75 203 180 0 0 98 1 0

Cached memory is a kind of free memory.

Actualy memory is not used by application, but it is used for disk caching.
If memory is not fully utilized by kernel than it is wasted, by keeping data in cache when an application needs data again it can be provided faster.
If you want to see the memory from the perspective of application you should look at +- buffers/cache line, the free column of this line shows you the memory that can be used for applications.

In the case below my application using 2GB of memory.

# free -m
total used free shared buffers cached
Mem: 7973 7323 650 0 128 5152
-/+ buffers/cache: 2042 5931
Swap: 8189 40 8149

I take care 2000 PCs that using Redhat 7.3. I’m finding the command to create script file to check RAMBus of the PCs. Could you please help to recommend the appropriate one ?

is there any way/script to find out physcial memory usage exclusive of buffer/cache usage??

very good
thanks
Regard,

You can also check memroy by using command “cat /proc/meminfo” it will give you detail info.

the memory information is also stored in /proc/meminfo… so just in case you don’t have any tools installed… cat /proc/meminfo

i am expecting a command to see memory information. you said cat /proc/meminfo ,it is for seeing the configuration file right… is there any possibility to get the details of memory directly..

Yes. All other tools read info from /proc/meminfo.

I use sun servers and solaris os and memory load has been increased to 90%

I need to know which command can i use to check on its memory and how i know the abnormal increase

Did you get the answer amm? I am also seeking answer for the same question? If you got the answer please mail me.

I am trying to get the output of the command top in java using a processbuilder. But its not giving any output. Though a command such as ‘ps -all’ is giving the required output. Can anyone help please. Its urgent…

How can I find the memory used by each php script on the server?

hi this is kishore

with single command can we get information of version of linux , ram,and memory status informationa. And as well as with single command the total system information
can i know the comman of linux

[kishore] You need to write a script which excutes various commands and output as a single command.

ps aux | awk ‘; END ’. It works.
Thanks Matt…
Is there any way to do the same for SWAP also.

How can get the average memory usage of a perl script that I am running on a linux machine? Can anybody help?

Use this coomand to get all the required information

lsb_release -a && free -m

Believe that we have a memory leak on RHEL 4.5 with Java & Apache running.

ps -eo pid,ppid,rss,size,vsize,sz,pmem,comm | awk ‘ < rss += $3; size += $4; vsize += $5; sz += $6; pmem += $7>; END < print "rss = "rss" size = "size" vsize = "vsize" sz = "sz" pmem = "pmem >‘ ; free -m
rss = 4590060 size = 7302928 vsize = 11360544 pmem = 26.7
total used free shared buffers cached
Mem: 16028 15979 48 0 0 24
-/+ buffers/cache: 15954 73
Swap: 32767 4571 28196

Does anyone have a command, code, or program to identify where the memory is being utilized?
After a reboot the server is using 24.6% of memory or free shows 4869 MiB.

ps -auxf | sort -nr -k 4 | head -10

The above mentioned command will display top 10 memory usage in % by each process

T Sudhakarraj, This is a great answer in order to see the top 10 application based on the percent usage but I thought I could help improve it a little. As you probably know, most hard core/old school bash programmers often object to using more commands then you need to get the output you want. When you are performing this command, it’s important to realize that the percentage shown is a reflection of the RSS size of that application and it does not consider RAM allocated by shared objects / dynamically linked libraries (I hate using that term since most people associate it with Windows DLL files but dynamically linked library, while the proper term in Windows is also the generic term to refer to these types of libraries / objects on any OS).

Because the percentage of RAM shown in ps for any output that uses the %mem / pmem format specifier is in direct correlation with host much data that application has in RSS relative to how much physical ram the host has, you can sort the ouput in ps yourself by using the `–sort rss` option. The final command would look like:

ps -A —sort -rss -o comm,pmem | head -n 11

The output would look like:

This will give you the 10 processes using the most ram ( I only showed 3 in my example) as well as the ps header describing each field. If you want to remove the header then you can add the option “–no-headers” (without the qyuotes) to ps. If you remove the headers in ps, you will probably want to change the head command to use 10 instead of 11 since the extra line is for the headers Also this example only shows the “short” command name or basically it only shows the command but non of the arguments. It also doesn’t show the actual amount of RSS being used. If you want to show the “long” command or basically the command name with all the arguments, replace “comm” with “cmd” in the ps options. If you want to display the actual amount of RSS being used by each app in the top 10 list, replace “comm,pmem” with “comm,pmem,rss” and it will now have three columns for command, percent of memory and kilobytes of RSS used instead of just command and percent of memory.

Also, unfortunately ps doesn’t have the option to convert kilobytes to megabytes. This can still be displayed but it requires a bit more of a complex answer. In order to display the RSS usage in megabytes instead of kilobytes we run through a loop and do the math ourselves on each line.

while read command percent rss; do if [[ «$» != «COMMAND» ]]; then rss=»$(bc

The example below calculates the megabytes used by each applications RSS rounded to nearest 100th of a whole number. You can change this to show more or less places after the decimal by changing «scale=2» to whatever number you like.

Hope this helps some people.

P.S.: I saw that the term RSS was used by someone before me but I don’t see anywhere on this thread where anyone has defined it. RSS as it relates to RAM (on any OS as far as I know) is the portion of memory that a process is using that is held in RAM. Every process has RSS and RSS does not include any items in RAM which have been swapped to disk or are otherwise anywhere else then in the physical RAM. This means that the size of each programs RSS is the amount of data that program itself is storing in physical RAM.

Yes, yes it does. Bloody Apache. Thanks jetole.

Actualy memory is not used by application | swap file memory is 1534196 and uses 0
so pleas solution

how we can know status of the RAM through the JAVA Programming?
plz

Hi All,
We use a hospital Information system application. From 10:30 AM the performance becomes really slow and the application freezes. Not sure if it is due too many sessions open or number of client connections or cpu/memory issue.
We have the application installed on all client machines. The application server running on RHEL 5.2 version on IBM Balde work stations with 2 node cluster. App server is connected to Oracle 11g Db server.
Currently, we restart the the application server every 2 days after working hours and see that the performance back to normal. But if we do not restart the servers, the performance is bad again.
Please let me know what all things I need to check here so to know what is causing the performance issue.

Try to kill unused running commands/applications.

I want to get the cat output in memory buffer. Can anybody please let me know how it is possible.

Hello…
Can you pleas tell me how can I check Guaranteed Ram and Burstable Ram from shell prompt?

cyberciti has been my partner since we had linux servers in the office, thank you and hope you will continue this site and more power to the webmaster and all its staff.

Seconded. Cyberciti is better than

i see my sites apache uses more memory around 4G, after restarting it release 3G.

The actual problem is Apache keeps increasing its memory usage.

Do you guys know how to overcome this issue.

Linux memory management is more flexible than windows

how to setup the IP address in running production server

thanks in advance
muthukumaran.g

hi guys.
The top 10 application are using 0% mem for ME …but top says..

Mem: 4145948k total, 2776936k used, 1369012k free, 146512k buffers
Swap: 1558296k total, 4k used, 1558292k free, 2467592k cached

out of 4G ram 2.6 is already used..WIll the kernel allocate if a process require more than the free memory. Wat process is actually using the used one .

kindly help me with this.

n 11id:/localdisk/lattice/lattice_36041# ps -A –sort -rss -o comm,pmem | head
COMMAND %MEM
ntpd 0.0
named 0.0
vim 0.0
bash 0.0
sshd 0.0
sshd 0.0
sshd 0.0
sshd 0.0
bash 0.0
sshd 0.0

I see your using the command I mentioned above but with one less item in the head command output but that’s alright 😉

You can show the same data, without limiting the input but also displaying the RSS usage (and the pid) for each process by running:

ps -A –sort -rss -o pid,comm,pmem,rss

The far right column will show you the RSS usage in kilobytes. The order is descending so the application with the highest allocated RSS (using the most) is at the top of the list. The application with the lowest allocated RSS (using the least) is at the bottom of the list. Remember that RSS is only referring to the memory you application is using that is actually in RAM and does not include anything swapped to disk so this is in fact the amount of RAM your application is using.

Something important though that you may not have realized is that Linux tends to use almost all available memory whenever it can by default. Linux will leave an percent free (I don’t know how to check what the percent is but it doesn’t matter) and then it will allocate the rest to buffers and cache. The general idea is this, buffers is the smaller segment it allocates for I/O usage of processes that are running. This mostly refers to items that programs need to write to a disk but that data is often cached in memory and then written. This causes programs not to have to wait for I/O to complete and the kernel is then able to write the data to disk as quickly as it’s capable of doing but at the same time without having to have a program and hence the user wait for the information to be written to disk. The buffers are also used for IPC or inter process communication. The cache is mostly used for reading files off disk. The algorithm is uses, while complex, basically stores a combination of files that are popular and recent in cache memory. This speeds up disk read times a lot too. You will notice that the cache is almost always significantly larger then the buffers. You can view both of these using free to see total, used and free memory. You can use free -m for megabytes and free -g for gigabytes.

This RAM, more quickly with cache then buffers, can be very quickly (on both) be released and therefor given to any process asking for RAM. This means that, although this RAM is used and it is used in way that speeds up your system, if any task needs the RAM, it will instantly be given to that process. One example would be if I start VLC movie player and VLC needs and therefor requests 50MB to run, then the kernel will free 50MB from cache and buffers and allocate it to VLC. This is why there is also a line when you run free which says “-/+ buffers/cache”. This line which shows numbers under used and free, isn’t the RAM you literally have used and literally have free because of ram allocated to cache and buffers, however it is the line you should refer to when you want to see how much free RAM you have because RAM allocated to buffers and cache will be instantly released and given to a process whenever it needs it.

When you view your free memory inside top, it shows you the literally used RAM and literally free RAM meaning cache and buffers are added to used and subtracted from free and their is nothing wrong with this but the RAM inside cache and buffers is still available to you when you need it. As I mentioned, the best way to really see how much used and free RAM you have is to look at the “-/+ buffers/cache” line inside free. That line is there for a reason.

Hope this helps.

Ah I forgot that the forum breaks double hyphens by default (poor mans attempt to stop SQL injections maybe?). The actual command I have up top is

ps -A —sort -rss -o pid,comm,pmem,rss

Notice the double hyphens in front of sort.

Источник