![]() ![]() ![]() Htop is very similar in functionality to the top command, yet it’s slightly different. You can press Shift+M keys to sort top command on memory usage. It also gives you a real time visualization of the current running processes and the amount each one is consuming. In the header you will notice how it reports the total amount of memory, the amount used and the amount free, and this for both regular (RAM) memory and SWAP memory as well. Here is a screenshot of how it looks: top command running It gives the information about memory and CPU. This is probably one of the most common and the one that I use at first. You can see that the free command provides only the necessary info at a glance. RAM, the swap usage and the buffer used by the Linux kernel.Īll you have to do is to type free in the terminal and hit enter: You can see the free and used physical memory i.e. It shows the amount of free and used memory on your Linux system. The free command in Linux has the simplest output. In this article, we will cover how to check memory in different ways and explain a little bit how each of the command lines for this purpose works. 5 Commands to check memory usage in Linux If you want to check disk space in Linux, you use disk related commands. In other words, if you want to check RAM usage in Linux, you use the memory related commands. Note: Memory, physical memory terms are used for RAM (which is a more popular term). We have already showed you how to check CPU info in Linux, today, I am going to show how to check memory in Linux. PSS should therefore represent a more accurate (private) memory usage of a process, yet it still contains a (smaller) amount of some shared memory objects.When using any Linux distribution, it is important as a SysAdmin to know how to visualize your available and used resources, such as memory, CPU, disk space, etc. So if a process has 1000 pages all to itself, and 1000 shared with one other process, its PSS will be 1500. The proportional set size (PSS) of a process is the count of pages it has in memory, where each page is divided by the number of processes sharing it. Partitioned in this case means "amount of shared memory divided by number of processes". ![]() PSS is short for Proportional Set Size and shows the private memory of the process itself and a partitioned size of the shared memory. A more accurate way to show the process' "real" memory usage would therefore be a value without the shared memory. RSS is the total number of pages, shared or not, currently mapped into the process.Īlthough RSS represents a roughly correct memory usage of a process, it also contains memory resources used by other processes. A good explanation can be found on StackExchange: Such objects are in most cases shared (system) libraries. Shared memory means objects used in memory which are used by other processes. The value is a calculation of three different RSS values (which can also be found in /proc//status): The RSS value represents the process' memory usage including shared cat /proc/15201/status | grep '^VmRSS:' Does this mean the VmRSS/RES value is the real memory usage? Close, but still not 100% accurate. So the VmSize from /proc/PID/status and VIRT column in htop are far off. Comparing this data with htop shows the same values:įrom the htop output we can also see the total capacity of memory on this machine is 10 GB and the current overall usage is calculated at 6.78 GB. With a grep for the lines starting with "Vm." we can find the memory related cat /proc/15201/status | grep '^Vm'įrom this output, we can see the VMSize entry showing 17545436 kB (= 17134 MB = 16.73 GB) and the VmRSS entry showing 3899852 kB (= 3808.45 MB). This contains quite a lot of information. There are a couple of ways to do this as several files inside /proc// contain memory information of the process The preferred method, at least to the human eye, would be reading memory statistics from /proc//status. Using the discovered PID (15201) we can retrieve the memory statistics. A Java process for example usually runs as a single ps -C java -o pid,rss:8,cmdġ5201 3899912 /opt/atlassian/jira/jre//bin/java .file Pretty accurate memory usage calculations can therefore be made. Memory usage of a single processĪ single process has a single process ID (PID) and has all its statistics in one place: /proc//. Besides running into the everlasting question "how to see the real memory usage?" I also ran into unexpected permission problems caused by capabilities. While working on a Bash script, which should be used for per process memory monitoring, I came across a couple of hurdles. Published on January 26th 2023 - Listed in Linux Figuring out the real (and combined) memory usage of forked processes on Linux: Not the easiest thing
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