Compared to the /proc/meminfo file, the free command provides less information. However, it is easier to understand. The key figure being the available value as it displays how much memory is still available for running new applications.
Aside from providing you with essential memory information, the top command provides a limited interactive interface. It is possible to manipulate and configure operations by using command-line options.
This guide provided several options to check memory usage on your Linux system. We learned that a single command provides an abundance of valuable data for future analysis. Learning to interpret the information correctly is critical.
smem is a tool that can provide numerous reports of memory usage on Linux systems. Unlike existing tools, smem can report Proportional Set Size (PSS), Unique Set Size (USS) and Resident Set Size (RSS).
At times we will need to know precisely how our Linux systems use memory. This article will examine how to use the free command-line utility to view memory usage on a Linux system. In doing so, we will clearly define the difference between free vs. available memory on Linux systems.
Free memory is the amount of memory that is currently not used for anything. For this reason, especially on servers, I like to consider free memory as wasted memory. Once your applications/processes have launched and considerable uptime has passed, this number should almost always be small.
Available memory is the amount of memory that is available for allocation to new or existing processes. Available memory is then an estimation of how much memory is available for use without swapping.
The difference between free memory vs. available memory in Linux is, that free memory is not in use and sits there doing nothing. While available memory is used memory that includes but is not limited to caches and buffers, that can be freed without the performance penalty of using swap space.
For most monitoring tools, the free memory is what is being used without considering cache/buffers. For example a server configured with 64GB and having free memory to be 5GB and available to be 30GB will be flagged as being under memory pressure. How do you think this gap can be resolved ?
This will decrease the cache pressure [uses MORE memory for cache]. Since caching is good for performance, we want to keep cached data in memory longer. Since the cache will grow larger, we still want to reduce swapping to not cause increased swap I/O. [still promote opportunistic swapping]
We are being notified that multiple servers seeing high memory utilization on RHEL hosts and suspecting PAMSC agent could be the reason. I have uploaded support.tar' s from 2 servers which were notified. Pls review
The kernel.shmax parameter defines the maximum sizein bytes for a shared memory segment. The kernel.shmall parametersets the total amount of shared memory in pages that can be used at one timeon the system. Set the value of both of these parameters to the amount physicalmemory on the machine. Specify the value as a decimal number of bytes.
The kernel is restricted to allocating it's data structures in the Normal zone. This includes data structures used to manage the High memory zone. The more memory in the system, the more of the Normal zone must be dedicated to managing it. For example:
In this article, we will see How to Clear RAM Memory Cache, Buffer, and Swap Space on Linux. In every system we do come across caches that have unwanted files and can harm our system, the same thing happens in Linux cache and if you want to clear the cache and free some memory then Linux has many commands to do that.
I hope these Linux processor and memory commands have been helpful. When you have some spare time, take a look at the /proc filesystem on your Linux system for other system information you can find, including /proc/loadavg, /proc/vmstat, and much more.
In this article we will see basic commands to check physical memory on a 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 pinpointing commands to check RAM on the Linux server. These commands will work in different flavors of Linux like Red Hat, CentOS, Suse, Ubuntu, Fedora, Debian, etc.
The first command is free. This is the simplest command to check your physical memory. This command is mainly used for checking RAM and SWAP on the 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.
Another way is to read memory info from the 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 the server.
I clipped the above section of the top command output in the above example. Check second last line saying Mem: (highlighted row). This shows physical memory in kilobytes. You can see the total, used, and free portions of it. Total is your actual RAM installed on the server.
Some unexpected behaviour on the server side may at times be caused by system resource limitations. Linux by its design aims to use all of the available physical memory as efficiently as possible, in practice, the Linux kernel follows a basic rule that a page of free RAM is wasted RAM. The system holds a lot more in RAM than just application data, most importantly mirrored data from storage drives for faster access. This debugging guide aims to explain how to identify how much of the resources are actually being used, and how to recognise real resource outage issues.
Suddenly killed tasks are often the result of the system running out of memory, which is when the so-called Out-of-memory (OOM) killer steps in. If a task gets killed to save memory, it gets logged into various log files stored at /var/log/
If for example a process crucial to your web application was killed as a result of out of memory situation, you have a couple of options, reduce the amount of memory asked by the process, disallow processes to overcommit memory, or simply add more memory to your server configuration.
Here it is important to make the distinction between application used memory, buffers and caches. On the Mem line of the output it would appear nearly 75% of our RAM is in use, but then again over half of the used memory is occupied by cached data.
The difference is that while applications reserve memory for their own use, the cache is simply commonly used hard drive data that the kernel stores temporarily in RAM space for faster access, which on the application level is considered free memory.
The readout of this gives us a single numerical value for the chance of the process getting axed by the OOM killer. The higher the number the more likely the task is to be chosen if an out of memory situation should arise.
If your important process has a very high OOM score, it is possible the process is wasting memory and should be looked into. However just high OOM score, if the memory usage otherwise remains nominal, is no reason for concern. OOM killer can be disabled, but this is not recommended as it might cause unhandled exceptions in out of memory situations, possibly leading to a kernel panic or even a system halt.
In major Linux distributions, the kernel allows by default for processes to request more memory than is currently free in the system to improve the memory utilization. This is based on heuristics that the processes never truly use all the memory they request. However, if your system is at risk of running out of memory, and you wish to prevent losing tasks to OOM killer, it is possible to disallow memory overcommit.
The safest and most futureproof option for solving out of memory issues is adding more memory to your system. In a traditional server environment you would need to order new memory modules, wait for them to arrive, and install them to your system, but with cloud servers, all you have to do is increase the amount of RAM you wish to have available at your UpCloud control panel.
I have Mem issue in one of server after installing Solemon agent, before also we have high memory utilazation in the server but we didnt get any alerts but now after installing agent we got alerts . strange thing is that am not getting any process using more memory by using top nmon sar ,vmstat all mem comands shows no utilization on memory . its almost less than 10 % .
Thanks for the reply janne , and reg above issue , server has 32 GB RAM when am hitting free command its showing 31 GB used and even cache also more , i could see disk I/O is happening more in the server as servers has only one disk . i can also say that cache is filling so soon . , could you please help me how to get exact process using more memory (except top,sar,nmon ,vmstat etc as i tried all these none showing memory utilization high ) . please help
Hi , I need to display all process with command line of each process of cpu and memory usage in the top command or ps . I tried with multiple options in ps command but no luck Is any option we can get it in top command or ps , can you please advise.
What do you think with my case declared and what should I do to recover as well as to fix it up soon. Should be cleared RAM memory cache/buffer or better idea to take for adding space of memory in my VPS?
This is how you can increase or add SWAP memory in Linux 7 server easily. If you have any issue in performing this task, then please leave your comments below. We will be happy to help you. You can also drop email to us or leave your question in our Facebook page.
Virtual Memory is called as Swap space in Linux and is used when the physical memory (RAM) is full. When the system needs more memory and the RAM is full, inactive pages in the memory will be moved to the swap space. Swap is not a replacement to physical memory, it is just a small portion on hard drive; it must be created during the installation. It is better to have swap space equal to 2X RAM. 041b061a72