cache is a component that stores data so future requests for that data can be served faster; the data stored in a cache might be the results of an earlier computation, or the duplicates of data stored elsewhere.

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0
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2answers
3k views

How to reduce buffers\cache

A monitoring system keeps alerting that my machine is reaching\breaking through it's RAM utilization threshold which is 15 GBs. I've done some reading and understood that the apparent RAM utilization ...
3
votes
1answer
12 views

How to enable package caching in dnf?

I started using fedora 22 and started learning dnf only to find out about two annoying facts: Almost every time I install or upgrade anything it has to rebuild the whole repository metadata cache ...
1
vote
0answers
41 views

Opcache and shared memory issue

I installed zend_opcache on my server box , but I can not increase opcache.memory_consumption over 1600 . (example : 2048) . after increase following error occur in server : Fatal Error Fatal Error ...
0
votes
1answer
24 views

why does my Ubuntu Virtual Machine slow down after a number of searches, and builds?

I recently learned that my Ubuntu Linux file system may cache the result of some commands such as searches, sorts, and perhaps build commands such as make. I run Ubuntu in a VM, and although I have ...
1
vote
0answers
6 views

CVMFS file access slow, although file is in cache

I have a directory in which there is a symlink to a file on CVMFS. When I first boot up, and do ls, it takes a long time (~a minute). The reason is that ls does fstat on each file to determine what ...
1
vote
1answer
115 views

Booting from an lvm-cached volume

I created a cache pool following this article. The process seems to be successful. After doing an upgrade-grub and rebooting, Grub complains that it can not find the root volume (showing a UUID). - ...
2
votes
1answer
45 views

How run free command by crontab

I want to run this command: free && sync && echo 3 > /proc/sys/vm/drop_caches && free -m by cron that why I'm able to free my RAM and cache in ubuntu system. I'm using ...
3
votes
0answers
25 views

What could cause dropping cache to be extremely slow on a large cluster?

I'm attempting to time file I/O on my disks. In order to make sure all the I/O is happening off the hard drives and not from ram, before I time any read, I run a drop cache command. Specifically, I ...
0
votes
0answers
14 views

Will btrfs snapshots ever share page cache?

It's common to run multiple container images based on the same parent. In theory you should be able to share page cache between these containers automatically. E.g. some of the code in shared ...
8
votes
1answer
588 views

Cleanup of temporary file ~/.cache/duplicity/temp failed

Often when I run Duplicity I see an error message like this at the end of the run: Cleanup of temporary file ...
2
votes
1answer
25 views

Directory traversal cache eviction despite having plenty of memory?

I have a huge Mercurial repository (take a guess how many directories it has -- it's gonna be more than you guessed). The time taken to do basic repository operations is heavily dependent on whether ...
101
votes
4answers
22k views

How do I clear Bash's cache of paths to executables?

When I execute a program without specifying the full path to the executable, and Bash must search the directories in $PATH to find the binary, it seems that Bash remembers the path in some sort of ...
8
votes
5answers
19k views

DNS queries not using nscd for caching

I'm trying to use nscd (Nameservices Cache Daemon) to cache DNS locally so I can stop using Bind to do it. I've gotten it started and ntpd seems to attempt to use it. But everything else for hosts ...
2
votes
2answers
263 views

Keeping disk caches when hibernating

Is there a way to keep disk caches when hibernating Linux? I understand and agree that dropping them is the best option all-around. But my system is unresponsive after resume and I would like to give ...
-1
votes
1answer
55 views

What is ~/.cache/weather.xml?

I use a clock-date-weather conky and I noticed that it is related to the file ~/.cache/weather.xml. I am curious: was this file created by conky or by what other program? Is it present on the system ...
6
votes
4answers
30k views

How to clear memory cache in Linux

Is there any command that by using I can clean the cache in RHEL? I used this command: sync; echo 3 > /proc/sys/vm/drop_caches but it didn't work.
1
vote
1answer
47 views

Change Linux Bcache device type

I have accidentally configured my SSD as a backing device instead of a caching device. Simply trying either one of the following: sudo make-bcache -C /dev/sdb1 sudo make-bcache -C /dev/sdb Gives ...
8
votes
2answers
23k views

How to read the local DNS cache contents?

I know that on Windows I can issue ipconfig /displaydns and I see the local DNS's cache content. How can I list the DNS's cache content in Linux? I would like to get as much as cross-distro solution ...
1
vote
0answers
115 views

ssd caching in loop device on btrfs

I have an ssd and 2TB hard disk. The ssd is used for the root filesystem which uses only around 20G of the 120G available. Is there a way to use an image/loop on the root filesystem (btrfs) as a cache ...
13
votes
3answers
823 views

Is it safe to remove ~/.cache?

When I scanned my $HOME directory with baobab (Disk Usage Analyzer), I found that ~/.cache is consuming about half a GB. I also tried to restart and again check size but no difference. So, I am ...
3
votes
0answers
24 views

Is posix_fadvice / POSIX_FADV_DONTNEED functional in Linux?

If I am doing once only scanning across big files then do I need to worry about impact on the page cache or does the OS take care to avoid my scan causing pointless churn in the page cache. I want to ...
7
votes
2answers
13k views

Is there a command which will force Linux to flush cache of one file on an NFS share?

Related to this question on StackOverflow, I am wondering if there is a way for me to flush the NFS cache / force Linux to see the most up-to-date copy of a file that's on an NFS share. I have a ...
3
votes
1answer
59 views

Linux doesn't drop FS Caches. Instead Memory starts Swapping

I'm quite confused about this behaviour of linux memory caching. total used free shared buffers cached Mem: 15953 14188 1765 64 ...
3
votes
0answers
60 views

Limit the inode cache used by a command

I want to run a task with limits on the kernel objects that they will indirectly trigger. Note that this is not about the memory, threads, etc. used by the application, but about memory used by the ...
81
votes
3answers
157k views

How do you empty the buffers and cache on a Linux system?

Prior to doing some benchmarking work how would one free up the memory (RAM) that the Linux Kernel is consuming for its buffers and cache?
0
votes
2answers
50 views

Precaching the list of files of the filesystem

I was wondering where and in what form a list of files and directories is stored on the ext4 filesystem. The problem is that whenever I try to access a certain directory for the first time since boot ...
2
votes
1answer
97 views

how to check default cache mode for disk in kvm

KVM/qemu support various types of cache - none, writethrough, writeback. How to check which one is default and is used on system when no cache= is specified? For RHEL6 i found that it's writethrough ...
1
vote
1answer
33 views

Reading ELF file after dropping caches

I have an eMMC backed Linux 3.10 development device (Android) and I am trying to better understand when Linux is actually reading from the eMMC as opposed to the page cache. Specifically, I am ...
5
votes
1answer
45 views

What memory is not used by processes and freed by `echo 3 > /proc/sys/vm/drop_caches`?

Without programs open, my computer uses about 512M of memory. Yesterday, I had nothing open, yet 2 GB of mem use (used - cache = 2153): total used free shared buffers ...
1
vote
0answers
76 views

how to clear NFS client side cache and server side cache?

I would like to know what is the cache size NFS is using at client side and server side. How to clear it.? Is there a difference between system cache and network cache ?
4
votes
1answer
82 views

Avoid -dbg_version packages on apt-cacher-ng server

Intro: We have created a apt-cacher-ng server to provide cached packages to our users that have Ubuntu 14.04 installed. Combined with the cached packages, we are doing a weekly "mirror" of some Ubuntu ...
3
votes
2answers
98 views

How and where is file system meta data cached in Linux

My earlier question apparently had a wrong premise. I thought file system meta data was cached in the inode and dentry cache, but apparently not. When I do: # time find . > /dev/null real ...
3
votes
0answers
73 views

How to generate graphs from lmbench results?

I need to use the lmbench benchmarking tool to get the system performance statistics. I am able to execute and run the results. In the results folder this is a MakeFile with this information # ...
1
vote
0answers
63 views

Out of Memory with unused memory and swap

I have a strange error on my Raspberry Pi2. System is archlinuxarm. Short after boot (about 30 secs), the system states that it is out of memory, resulting in closing many applications, most time ...
0
votes
0answers
49 views

Linux - is it possible to limit VFS cache usage on a per-process basis

I'm trying to investigate performance degradations while running background copy operations (using dd to write or read large disk-images). Is it possible to limit VFS cache usage for a single ...
3
votes
2answers
822 views

SSD as a read cache for FREQUENTLY read data

I'm looking for ways to make use of an SSD to speed up my system. In “Linux equivalent to ReadyBoost?” (and the research that triggered for me) I've learned about bcache, dm-cache and EnhanceIO. All ...
4
votes
2answers
76 views

How to determine whether the data is written to disk or cached?

I'm learning file operation calls under Linux. The read() and write() and many other functions use cache to increase performance, and I know fsync() can transfer data from cache to disk device. ...
2
votes
1answer
58 views

How to get all CPU cache information without SU access

I am trying to find out the cache mapping scheme for all the levels of class of a linux server, however I do not have root access. I would just use DMIdecode for this but you need root access. Is ...
0
votes
0answers
91 views

Using Varnish + Nginx Forcing SSL

i'm using Varnish and i would like to force communication only with SSL. My server is Nginx. What's the best way to do so? Or the easiest? I read about Pound proxy and installed it but guides were too ...
2
votes
3answers
2k views

Increasing the size limit for /var/cache/apt/archives

I have 2 systems running Debian at home and I am trying to minimize the bandwidth use while upgrading the packages. How can I increase the size limit of the cache, so that I could just copy the ...
6
votes
1answer
677 views

How to use an SSD for caching, so my hard disks can spin down?

I've got a file server with a bunch of disks running together in a BTRFS pool and want to add an SSD for caching. I'm not mainly after speeding up things, but want to catch the regular small accesses ...
0
votes
2answers
108 views

Memcached on a webserver

We host a Magento webshop hosted by Amazon EC2, and we have speed issues. We're currently looking at moving to another provider. We found one hosting provider where we have a test account now. Speed ...
3
votes
0answers
81 views

Discover what is cached by dm-cache

I am using dm-cache successfully for quite a while now. Now I would like to know which files are being currently in the cache. I understand that dm-cache works with blocks, not files, but since there ...
1
vote
2answers
161 views

Random application crashes in Linux

Sometimes after booting my computer, some applications fail to start: they crash. They're usually the largest ones, such as firefox, thunderbird or virtualbox. Rebooting or cleaning the cache usually ...
1
vote
1answer
1k views

Clear Memory Cache on Amazon EC2

In our project we have a few tests which run for about 3-4 hours continuously. In due course, the tests fail as they couldn't find enough memory. On googling, I found that running the following ...
2
votes
0answers
93 views

Restore /var/cache files

I've accidentally deleted all contents of /var/cache files. I managed to reinstall most by doing dpkg -S /var/cache and apt-get --reinstall install PACKAGE_NAME (see here) on every package that I've ...
2
votes
3answers
100 views

Buffering (named) pipe in GNU OS

In the GNU OS a process can only write data to a pipe if another process reads the same data (from the same pipe) at the same time. Is there something like a pipe which lets the 1st process write and ...
3
votes
1answer
72 views

Cache directory and file list to prevent hard drive access when browsing contents

I have 7 hard drives that are in a virtual pool (mhddfs) so they appear as one directory. I put them to sleep after 5 minutes of inactivity to save a significant chunk of power. The problem with this ...
0
votes
1answer
254 views

How to enable a non-root user to empty the linux buffer cache

I'm required to empty the linux buffer cache in a python script, that runs on a Debian wheezy VM. As root I run sync; echo 3 | sudo tee /proc/sys/vm/drop_caches, but the script is run by a user, ...
8
votes
2answers
524 views

Linux cache evictions

Looking at how the VFS cache on my Linux machine behaves, I can see that even when effectively idle (crond and most other daemons stopped, interfaces down) the amount of free memory gradually ...