Linux which process memory usage

How to check memory usage per process in Linux

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There are several metrics available to check memory usage per process in Linux. I will begin with the two that are easiest to obtain

• the virtual set size (vss)
• the resident memory size (rss)

both of which are available in most implementations of the ps and top commands.

Vss: called VSZ in the ps command and VIRT in top , is the total amount of memory mapped by a process. It is the sum of all the regions shown in /proc/

/map . This number is of limited interest, since only part of the virtual memory is committed to physical memory at any one time.

Rss: called RSS in ps and RES in top , is the sum of memory that is mapped to physical pages of memory. This gets closer to the actual memory budget of the process, but there is a problem, if you add up the Rss of all the processes, you will get an overestimate the memory in use because some pages will be shared.

Using top and ps to check memory usage per process (VSS and RSS)

The ps command shows Vss (VSZ) and Rss (RSS) with the options, -Aly , and a custom format which includes vsz and rss , as shown here

Likewise free and top also shows a summary of the free memory and memory usage per process:

Using smem to check memory usage per process

In 2009, Matt Mackall began looking at the problem of accounting for shared pages in process memory measurement and added two new metrics called the unique set size or Uss , and the proportional set size or Pss

• Uss: This is the amount of memory that is committed to physical memory and is unique to a process; it is not shared with any other. It is the amount of memory that would be freed if the process were to terminate.
• Pss: This splits the accounting of shared pages that are committed to physical memory between all the processes that have them mapped. For example, if an area of library code is 12 pages long and is shared by six processes, each will accumulate two pages in Pss . Thus, if you add the Pss numbers for all processes, you will get the actual amount of memory being used by those processes. In other words, Pss is the number we have been looking for.

The information is available in /proc/

/smaps , which contains additional information for each of the mappings shown in /proc/

/maps . Here is one section from such a file which provides information about the mapping for the libc code segment:

There is a tool named smem that collates the information from the smaps files and presents it in various ways, including as pie or bar charts. The project page for smem is https://www.selenic.com/smem.

There are various filters which you can apply with smem as shown below with the latest available release (1.4) at the time of writing this article

To check memory usage per process in total we can execute below command

This will give you memory usage detail of every process active on your system.

To get the memory usage of a single process we can grep the process from the list

Here as you see we get similar results as above with /proc/31768/smaps and with smem tool. So the actual memory usage of amsHelper is 56.4 MB

Lastly I hope the steps from the article to check memory usage per process on Linux was helpful. So, let me know your suggestions and feedback using the comment section.

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5 thoughts on “How to check memory usage per process in Linux”

There’s definately a lot to know about this
issue. I really like all of the points you’ve made.

I am happy that I noticed this site, precisely the right information that I was looking for! .

Thank you – excellent writeup!
But I would add this, from the smem man page: The USS and PSS only include physical memory usage. They do not include memory that has been swapped out to disk”
I’d also note that it would be faster and easier to choose the process via the -P option:
smem -k -P amsHelper

Thank you for sharing this additional information.

Cool! Thanks for the full ps flags to list the many kinds of memory options, as well as the tip about looking at the /proc/PID/smaps file for more information. I was trying to figure out how much memory one of my processes was consuming, but, alas, my Linux distro (running on an embedded system) has no way to install either smem or the other popular pmap tool. I’ve been just using good, old top for that, but your article gave me a vast array of many more suggestions! Thanks so much for that 🙂

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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.

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How to Check Memory Usage Per Process on Linux

Each of these programs runs as one or more processes. Every process allocates some amount of RAM or memory for itself. It is essential for the process to function correctly. If a process fails to allocate enough RAM or memory, then the process can’t be created and the program won’t be able to start.

So, one of the basic task you do on your computer is to check how much memory or RAM (Random Access Memory) each of the process is using. Because, RAM or memory of your computer is limited.

Imagine a case, where you want to run some program and it fails because you don’t have enough memory. May be some of the processes are using a lot of memory that you don’t need right now. You can kill or stop these processes to free up RAM or memory, so that you can start your important programs.

In this article, I will show you how to check memory usage of each of the processes running on your Linux machine. I will be using Debian 9 Stretch for all the demonstration in this article. But it should work on any modern Linux distributions. Let’s get started.

Checking Memory Usage Using ps Command:

You can use the ps command to check memory usage of all the processes on Linux. There is one problem with this procedure. ps don’t really show you how much memory a process uses in KB or MB format, but it will show you how much memory is being used in percentage.

You can check memory usage (in percentage) of all the process running on your Linux operating system with the following command:

As you can see, all the processes with memory usage in percentage is listed in descending order (The processes using most of the memory is listed first).

Checking Memory Usage of Processes with pmap:

You can check memory of a process or a set of processes in human readable format (in KB or kilobytes) with pmap command. All you need is the PID of the processes you want to check memory usage of.

Let’s say, you want to check how much memory the process with PID 917 is using. To do that, run pmap as follows:

As you can see, the total memory used by the process 917 is 516104 KB or kilobytes. You can also see how much memory the libraries and other files required to run the process with PID 917 is using as well here.

If you don’t care about how much memory the libraries or other dependent files are using, then run pmap as follows:

As you can see, only the total memory used by the process with PID 917 is printed on the screen.

If you want, you can further filter this with awk and get only the size in KB or kilobytes. To do that, run pmap as follows:

As you can see, only the memory usage in KB or kilobytes is printed.

Now you can also list how much memory is used by multiple processes using their PIDs with pmap as follows:

NOTE: Here 917 and 531 are process IDs or PIDs. You can put as many PIDs as you want this way.

Using pmap to List Memory Usage of All the Processes in Kilobytes:

In this section, I will show you how to write your own shell script to list memory usage of all the processes running on your Linux operating system in human readable format (kilobytes or KB).

First make a new file sysmon in your current working directory with the following command:

Now make the file executable with the following command:

sysmon is the shell script that will display all the running processes PID, OWNER, MEMORY (in KB in descending order) and COMMAND. Let’s start.

Open the sysmon script with your favorite text editor, I am going to use Kate.

Now, the first command I am going to run will give me the PID, OWNER and COMMAND of all the running processes separated by colon (:) symbol and store it in the RAWIN variable. Then loop through the output and print it on the screen.

As you can see, I am getting the correct output.

Now it’s time to process each line, store the colon delimited information in separate variables. That’s what I did on line 7, 8 and 9.

As you can see, I can print PID, OWNER and COMMAND in my own format now.

Now it’s time to fetch memory usage of each PID. Line 10 does just that.

As you can see, everything is working perfectly. Now I can print memory usage of each process in kilobytes (KB) as well.

Now all that is left to do is format the output to look nice. I prefer table format. Line 5 prints the header of each column of the table.

Finally, I printed PID, OWNER, MEMORY (in KB) and COMMAND of each processes in a tabular format using line 14.

As you can see, it’s working kinda well. There is a little bit of problem though, the processes are not correctly sorted in descending order by memory usage.

To fix that, I removed sort -bnr -k3 from line 3 and wrapped everything in a shell function sysmon_main(). Then left the job of sorting to the sort command.

The final shell script looks something like this:

As you can see, it works great.

Now you can move it to somewhere like /usr/bin and execute it just like other commands as follows:

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