In computing, memory refers to the state information of a computing system, as it is kept active in some physical structure.

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89
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11answers
45k views

How to fill 90% of the free memory?

I want to do some low-resources testing and for that I need to have 90% of the free memory full. How can I do this on a *nix system?
82
votes
3answers
47k views

How do I read from /proc/$pid/mem under Linux?

The Linux proc(5) man page tells me that /proc/$pid/mem “can be used to access the pages of a process's memory”. But a straightforward attempt to use it only gives me $ cat /proc/$$/mem ...
60
votes
9answers
12k views

Why can't Vim open a 100 MB text file when I have 16 GB RAM?

I have a 100MB MySQL database backup file and I have trouble to open it in Vim on my Linux box that has 16G of RAM. Vim just hangs (at least unusable). This is something I don't understand. I have 16 ...
60
votes
5answers
36k views

What are high memory and low memory on Linux?

I'm interested in the difference between Highmem and Lowmem: Why is there such a differentiation? What do we gain by doing so? What features does each have?
57
votes
12answers
10k views

Do I need swap space if I have more than enough amount of RAM?

From what I understand, the purpose of a swap partition in Linux is to free up some "not as frequently accessed" information from RAM and move it to a specific partition on your harddrive (at the cost ...
54
votes
4answers
61k views

How to display `top` results sorted by memory usage in real time?

How can I display the top results in my terminal in real time so that the list is sorted by memory usage?
50
votes
5answers
63k views

Limit memory usage for a single Linux process

I'm running pdftoppm to convert a user-provided PDF into a 300DPI image. This works great, except if the user provides an PDF with a very large page size. pdftoppm will allocate enough memory to ...
37
votes
4answers
32k views

How to display meminfo in megabytes in top?

Sometimes it is not comfortable to see meminfo in kilobytes while you have several gigs of RAM. In Linux it looks like that: And here is how it looks in Mac OS X: Is there a way to display ...
36
votes
6answers
83k views

How to find which processes are taking all the memory?

I'm looking for somthing like top is to CPU usage. Is there a command line argument for top that does this? Currently, my memory is so full that even 'man top' fails with out of memory :)
31
votes
5answers
10k views

Measuring RAM usage of a program

time is a brilliant command if you want to figure out how much CPU time a given command takes. I am looking for something similar that can measure the max RAM usage of the program and any children. ...
30
votes
7answers
41k views

Correctly determining memory usage in Linux

I'm a bit confused on some of the results I am seeing from "ps" and "free". On my server, this is the result of "free -m" [root@server ~]# free -m total used free shared ...
29
votes
2answers
5k views

Will Linux start killing my processes without asking me if memory gets short?

I was running a shell script with commands to run several memory-intensive programs (2-5 GB) back-to-back. When I went back to check on the progress of my script I was surprised to discover that some ...
25
votes
3answers
7k views

grep: memory exhausted

I was doing a very simple search: grep -R Milledgeville ~/Documents And after some time this error appeared: grep: memory exhausted How can I avoid this? I have 10GB of RAM on my system and few ...
24
votes
3answers
16k views

How to Determine the Amount of RAM Slots In Use?

I forgot how many RAM modules are installed on my laptop. I do not want to unscrew it but want to look it up on the console using bash. How do I gather this information?
24
votes
1answer
20k views

Getting information about a process' memory usage from /proc/pid/smaps

For a given process in /proc/<pid>/smaps, for a given mapping entry what are: Shared_Clean Shared_Dirty Private_Clean Private_Dirty Is Shared_Clean + Shared_Dirty the amount of memory that ...
24
votes
3answers
5k views

What does the vm.swappiness parameter really control?

Per the kernel documentation: This control is used to define how aggressive the kernel will swap memory pages. Higher values will increase aggressiveness, lower values decrease the amount of swap. ...
21
votes
4answers
871 views

Making Linux read swap back into memory

The Linux kernel swaps out most pages from memory when I run an application that uses most of the 16GB of physical memory. After the application finishes every action (typing commands, switching ...
18
votes
7answers
8k views

Is there a way to limit the amount of memory a particular process can use in Unix?

I need to test a process for memory management. I do not have the source, so I need to do all the testing from the OS side. I want to be able to say something like limitmemory 400k -p <pid> ...
18
votes
2answers
7k views

How to blacklist a correct bad RAM sector according to MemTest86+ error indication?

MemTest86+ (the version included with Ubuntu 13.04) says Failing address: 002f796c48 - 759.5 MB What should I specify in the memmap kernel parameter to bypass this area? I've tried running ...
17
votes
2answers
21k views

How to create a user with limited RAM usage?

So I have 4 GB RAM + 4GB swap. I want to create a user with limited ram and swap: 3 GB RAM and 1 GB swap. Is such thing possible? Is it possible to start applications with limited RAM and swap ...
17
votes
1answer
8k views

What is maximum RAM supportable by Linux?

What is the maximum supportable RAM by Linux? Assume that hardware is/supports 64-bit. Among all Linux distros. Does it go up to 16 exabytes, or is it limited like with Windows which I believe is 192 ...
16
votes
1answer
5k views

Loading of shared libraries and RAM usage

I'm wondering about the way Linux manages shared libraries. (actually I'm talking about Maemo Fremantle, a Debian-based distro released in 2009 running on 256MB RAM). Let's assume we have two ...
15
votes
3answers
12k views

How can I reserve a block of memory from the Linux kernel?

I have a device that needs a block of memory that is reserved solely for it, without the OS intervening. Is there any way to tell BIOS or the OS that a block of memory is reserved, and it must not ...
15
votes
4answers
7k views

How to re-load all running applications from swap space into RAM?

If my desktop run out of memory and swaps a lot then I free or kill the application wasting my RAM. But, after that, all my desktop/applications have been swapped and are horribly slow, do you know a ...
15
votes
1answer
19k views

Need explanation on Resident Set Size/Virtual Size

I found that pidstat would be a good tool to monitor processes. I want to calculate the average memory usage of a particular process. Here is an example output: 02:34:36 PM PID minflt/s ...
15
votes
2answers
3k views

Linux: Total swap used = swap used by processes +?

So, I'm trying to do some investigation on where does swap use come from in a system with high swap usage: # free total used free shared buffers cached Mem: ...
15
votes
3answers
476 views

How to force Linux kernel to “freeze” (or nearly freeze) for a few hundred milliseconds

We are running a real-time process on a non real-time kernel (CentOS 6), and this is probably not going to change. We have a streaming video application that requires about 500 MB/s of PCIe traffic ...
14
votes
3answers
5k views

How to detect memory type under Linux?

Which Linux utility can tell me if I have registered or unbuffered ECC memory in my server? Lshw and dmidecode do not work for me; dmidecode provides no information about registered vs. unbuffered: ...
13
votes
8answers
3k views

Memory problems when compressing and transferring a large number of small files (1TB in total)

I have 5 million files which take up about 1TB of storage space. I need to transfer these files to a third party. What's the best way to do this? I have tried reducing the size using .tar.gz, but ...
13
votes
2answers
932 views

Why does Linux purge the memory cache when it is nearly full?

Here's what the memory graph looks like on a VPS running CentOS with 512MB of RAM and nginx/php-fpm/mysqld serving (mostly static) content to a couple thousand visitors per day. (those are days on ...
13
votes
3answers
3k views

Increasing kernel memory size

I have an embedded board with 512MB of RAM running Linux 2.6.29 and UBoot bootloader. But the kernel is able to utilize only 128MB of RAM. I tried changing the value of XCODE_MEMSIZE, which I think ...
12
votes
3answers
2k views

On system memory… specifically the difference between `tmpfs,` `shm,` and `hugepages…`

I've been curious lately about the various Linux kernel memory based filesystems. Note: As far as I'm concerned, the questions below should be considered more or less optional when compared with a ...
12
votes
1answer
6k views

What does the Virtual kernel Memory Layout in dmesg imply?

While going through the "Output of dmesg" I could see a list of values which i am not able to understand properly. Memory: 2047804k/2086248k available (3179k kernel code, 37232k reserved, 1935k ...
12
votes
1answer
622 views

Does window minimizing free memory usage?

Both the undisplayed maximized window and minimized window are invisible to the end user. By undisplayed I mean an inactive maximized window covered by the active window. There is a difference ...
12
votes
4answers
3k views

Read the stack of another process?

I'm trying to read a child process's stack but with no luck. I know it is possible using ptrace, but ptrace's interface allows you to read only one word at a time, and I'm trying to scan a larger ...
11
votes
1answer
9k views

How can I test the RAM for data corruption on an ARM-based system?

I have an embedded device. It is ARM based, with Linux 2.6.31 and has 256 MB RAM. I wanted to get some ideas/tips on what is the most effective way to test the device RAM for data corruptions. Is ...
11
votes
2answers
5k views

Why does my system show only 3.2 GiB of RAM when I definitely have 4.0 GiB

I have 2x2 GiB sticks of RAM installed. Running memtest86 from the grub boot menu confirms this.. memtest86 reports no errors. However every which way I check my available memory in a running ...
11
votes
1answer
515 views

What is the difference between shared memory in early unix systems vs modern unix systems?

How could processes share memory in early versions of UNIX version modern implementations of shared memory?
11
votes
4answers
6k views

Shell command to read device registers?

On a single-board computer running Linux, is there a way to read the contents of the device configuration registers that control hardware? I think it would be a wrapper for inw(), more or less. I'm ...
10
votes
6answers
4k views

Is there a tool that allows logging of memory usage?

I want to monitor memory usage of a process, and I want this data to be logged. Does such a tool exist?
10
votes
4answers
3k views

Suspend/resume single process to/from disk

On occasion, we would like to suspend memory-intensive processes on our Ubuntu and OS X servers to temporarily free up some RAM for other jobs. If all we were worried about was CPU usage, a simple ...
10
votes
2answers
4k views

real memory usage

if I understand correctly, in the following output produced by free, 3535m is the actual free memory available to applications, only 413m is used, is this correct? need some clarification on the ...
10
votes
1answer
6k views

How OOM killer decides which process to kill first?

This answer explains the actions taken by the kernel when an OOM situation is encountered based on the value of sysctl vm.overcommit_memory. When overcommit_memory is set to 0 or 1, overcommit is ...
10
votes
3answers
646 views

After researching, still confused about monitoring RAM usage

I went through this article, which explains various methods for checking your RAM usage. However, I can't reconcile the different methods and don't know which one is correct. When I first login, I'm ...
10
votes
2answers
742 views

Reserve fixed RAM memory region as a block device ( with a given start physical address)

There have been a lot of questions about RAM Disks and I am aware of ramfs and tmpfs which allow the use of ram as a block device. However my interest is in using a fixed memory address range as a ...
10
votes
1answer
122 views

Does anyone actually use and benefit from transparent huge pages?

I've been struggling with transparent huge pages performance issues of late, and noticed many database systems recommend turning it off. I am talking Oracle, Postgresql, MySQL, Cassandra, NuoDB, ...
9
votes
3answers
457 views

Physically break into box? (Memory & disk)

I have a VPS. I might be able to encrypt my partition but I havent tried. My VPS company I believe can reset my root password although the only SSH key I see is my own. With all my data I have it ...
9
votes
2answers
815 views

Memory management principle used by Linux

Is memory management in the Linux Kernel done using paging or segmentation or both?
9
votes
3answers
4k views

how is page size determined in virtual address space?

Linux uses a virtual memory system where all of the addresses are virtual addresses and not physical addresses. These virtual addresses are converted into physical addresses by the processor. To ...
9
votes
1answer
1k views

Turning off swapping for only one process with cgroups?

I would like to turn off swapping for only one process. Swap should work as usual for the other processes. How I can implement this with cgroups?