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Questions tagged [memory]

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

135
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4answers
112k 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 /proc/self/...
143
votes
5answers
204k 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 ...
14
votes
2answers
11k 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
2answers
5k views

How can I get the amount of available memory portably across distributions?

The standard files/tools that report memory seem to have different formats on different Linux distributions. For example, on Arch and Ubuntu. Arch $ free total used free ...
59
votes
9answers
126k 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 ...
45
votes
5answers
25k 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. ...
36
votes
3answers
61k 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 ...
79
votes
1answer
84k views

How does the OOM killer decide 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 ...
39
votes
4answers
31k 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 ...
5
votes
2answers
3k views

`free`: output format

I use free to get the amount of free space on some of my servers. Its output is something like: $ free -m total used free shared buffers cached Mem: 374 ...
26
votes
2answers
23k 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 ...
20
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4answers
14k 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 ...
14
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1answer
5k 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?
172
votes
7answers
211k views

How to display meminfo in megabytes in top?

Sometimes it is not comfortable to see meminfo in kilobytes when you have several gigs of RAM. In Linux, it looks like: And here is how it looks in Mac OS X: Is there a way to display meminfo in ...
89
votes
13answers
48k 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 ...
18
votes
3answers
102k views

Actual memory usage of a process

The following are the memory usage of mysql and apache respectively on my server. As per the output of pmap say, mysql is using about 379M and apache is using 277M. [root@server ~]# pmap 10436 | ...
10
votes
2answers
2k views

30% of RAM is “buffers”. What is it?

$ free -h total used free shared buff/cache available Mem: 501M 146M 19M 9.7M 335M 331M Swap: 1.0G ...
62
votes
2answers
29k 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 ...
34
votes
3answers
9k 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. ...
14
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3answers
8k 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 ...
17
votes
6answers
17k 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?
11
votes
1answer
9k views

Why does Linux show both more and less memory than I physically have installed?

I know about swap - this question isn't about that. In dmesg, the Linux (x86-64) kernel tells me this about how much memory I have: [ 0.000000] Memory: 3890880k/4915200k available (6073k kernel ...
46
votes
1answer
52k 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 is ...
55
votes
1answer
59k 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 some example output: 02:34:36 PM PID minflt/s ...
19
votes
1answer
13k 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 ...
24
votes
2answers
5k views

Is it possible to trigger OOM-killer on forced swapping?

Is it possible to have the system preemptively swap out inactive pages (vm.swappiness), but invoke the oom-killer when the system runs out of RAM (as opposed to running out of memory) and is forced to ...
34
votes
7answers
32k views

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

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> Is ...
23
votes
4answers
35k 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 ...
6
votes
2answers
8k views

MMU-less kernel?

I would like to try compile mmu-less kernel. From what I found in configuration there is no option for such a thing. Is it possible to be done?
8
votes
1answer
3k views

Shared library mappings in /proc/pid/maps

Why does /proc/pid/maps contain a few records for the same library ? Here is an example: 7fae7db9f000-7fae7dc8f000 r-xp 00000000 08:05 536861 /usr/lib/x86_64-linux-gnu/libstdc++....
6
votes
1answer
9k views

What happens after a page fault?

When a page fault occurs in a Linux system, the interrupt-handler has to figure out the reason why the page fault happened. But how ? Is there anywhere a special number for that !? If yes, where is ...
7
votes
1answer
7k views

Does kernel: EDAC MC0: UE page 0x0 point to bad memory, a driver, or something else?

kernel: EDAC MC0: UE page 0x0, offset 0x0, grain 0, row 7, labels ":": i3200 UE All of a sudden today, our CentOS release 6.4 (Final) system started throwing EDAC errors. I rebooted, and the errors ...
5
votes
1answer
2k views

Tracking huge buffer usage under Linux

I have a Linux server running under Debian Lenny with 4Go of RAM. It doesn't run much, just: Postfix/spamassassin (daemon mode) Bind9 KVM (one guest - 1Go of RAM for it) Every day at exactly 3:05 ...
1
vote
2answers
99 views

Can I see the amount of memory which is allocated as GEM buffers?

My /proc/meminfo shows about 500 MB is allocated as Shmem. I want to get more specific figures. I found an explanation here: https://lists.kernelnewbies.org/pipermail/kernelnewbies/2013-July/008628....
1
vote
2answers
6k views

free / top difference. Does free show virtual memory?

free -m shows me the following in my system: total used free shared buffers cached Mem: 3954 3842 111 0 248 2585 -/+ ...
173
votes
12answers
139k 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?
343
votes
9answers
502k 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?
89
votes
6answers
82k 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?
112
votes
5answers
116k views

How do I determine the number 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?
117
votes
7answers
328k views

Sorting down processes by memory usage

I am able to see the list of all the processes and the memory via ps aux and going through the VSZ and RSS Is there a way to sort down the output of this command by the descending order on RSS ...
37
votes
1answer
24k 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 ...
82
votes
7answers
289k 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 :)
38
votes
6answers
3k views

How do I use swap space for emergencies only?

I have a Debian (Buster) laptop with 8 GB RAM and 16GB swap. I'm running a very long running task. This means my laptop has been left on for the past six days while it churns through. While doing ...
25
votes
5answers
176k views

How to check which process is using most memory

When I check free in one of Prod server it showing 70% of memory is being used: total used free shared buffers cached Mem: 164923172 141171860 23751312 ...
38
votes
4answers
51k 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 ...
33
votes
4answers
19k views

System hanging when it runs out of memory

I've got an eeePC 900a: it has a 8GB flash as disk and only 1GB of RAM. The Linux distribution installed on it is ArchLinux. When the system runs out of memory it becomes extremely unresponsive: it ...
17
votes
2answers
8k 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: ...
10
votes
1answer
6k views

Which parts of an ELF executable get loaded into memory, and where?

What I already know: An ELF executable has a number of sections, obviously the .text and .data sections get loaded into memory as these are the main parts of the program. But for a program to work, ...
8
votes
1answer
10k views

Is the file table in the filesystem or in memory?

In the context of operating system control tables, does the term "file tables" refer to a data structure that is part of the filesystem, or that is in main memory (and in which case I assume it would ...
19
votes
1answer
22k 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 ...