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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10
votes
3answers
27k 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 ...
0
votes
0answers
10 views

Is the iSCSI block device having client side-read cache (if yes how to disable)?

I have a remote block device with the test ext4 filesystem image. On the iSCSI initiator side, I have this device detected as let's say /dev/sdb. I am not mounting this filesystem but instead I use ...
1
vote
1answer
26 views

Using terminal to reset icon cache - which method?

I've been trying to find out how to reset the icon cache on my MacBook, and two methods seem to always be suggested. However, the two approaches differ slightly in the third line. Method 1 sudo find ...
8
votes
1answer
779 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 ...
0
votes
0answers
31 views

SSD + HDD performance from power on

I'm planing to buy a new laptop with a 128GB SSD and a 1TB HDD. And I would like to have reliability, performance and storage space from power up and during the whole runing time. During the running ...
3
votes
0answers
52 views

How to cache block devices (for device mapper)?

problem / observed effect It seems that the page cache ignores block devices which are not opened. And worse: Reads from device mapper (DM) devices which use a cached device are not cached at all ...
5
votes
4answers
660 views

Does bash have a built in caching command available (sort of like mktemp or sponge)?

I'm using the amazon ec2 command line tools, and the ec2-describe-instances tool is a little painful because of the 2-5 seconds it requires to make the request and display the output. I'm looking ...
3
votes
0answers
50 views

LVM cache and TRIM

I have set up LVM to cache a logical volume (located on an HDD) on a partition of an SSD (in writeback mode if this matters). As far as I can tell, this works correctly and the cache uses all ...
1
vote
1answer
528 views

flashcache tuning

I installed flashcache version 3.1.1 and created a write-back cache. The performance is good as long as the percentage of dirty blocks is not too high. My application does heavy I/O at the ...
17
votes
5answers
8k views

How to cache or otherwise speed up `du` summaries?

We have a large file system on which a full du (disk usage) summary takes over two minutes. I'd like to find a way to speed up a disk usage summary for arbitrary directories on that file system. For ...
13
votes
2answers
1k 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 ...
7
votes
1answer
891 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 ...
4
votes
0answers
120 views

Why are slab objects not reclaimed automatically

Everyday after a full system backup, various programs are failing with read errors until I run echo 2 > /proc/sys/vm/drop_caches to free reclaimable slab objects. For example, here's the output of ...
1
vote
0answers
30 views

One SSD cache for two partitions on two separate disks?

I have two hard drives: one for my operating system and the other for other data. I recently bought an SSD drive that I would like to use an LVM cache for those two devices. The problem is that I ...
8
votes
2answers
47k 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
2answers
56 views

how does o_sync trigger pdflush?

When I write using o_sync, the write call returns once the data has been written to the disk. But how does o_sync force Linux to write the data to disk? Normally you would have to wait a maximum of ...
0
votes
0answers
66 views

OpenLDAP as a Proxy cache only, no local database

I am trying to get a local LDAP proxy cache running. The idea is this: Currently a computer (A) is sending all ldap requests to a remote ldap server (L) Instead of that, there should be a proxy ...
0
votes
0answers
24 views

SSD as write target during reads

I have a real-time application which always writes data to a RAID 10 HDD configuration in a sequential manner at around ~50 MB/s. It uses mmap and writing should never be blocked due to waiting I/O. ...
0
votes
1answer
77 views

how to increase cache memory in centos

I have been facing a insuffient space in "/var/cache/yum" directory. due to this my gui of centos crashes.i want to increase the size of cache directory. also want to know the actual size of cache ...
2
votes
0answers
22 views

Which subsystem caches file reads?

I am trying to understand how exactly file reads are served from Page Cache. This will be useful when I will be implementing my own filesystem in the kernel. Is file content cached by VFS or ...
1
vote
1answer
76 views

Linux top -n 1 Command doesn't get update

I'm calling the Linux top -n 1 -b command from a Qt application to get the free CPU percentage. This application calls this command every 3 seconds, but the CPU usage seems to be updated only the ...
3
votes
1answer
124 views

How to 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 way I can free my RAM and cache in an Ubuntu system. I'm using ...
1
vote
1answer
27 views

Reset Bash's memory used for auto-complete

After renaming a file to a similar name, I noticed TAB was still completing the old filename (if it matched the letters so far) and not showing the new one. No matter how many letters I typed, it ...
2
votes
1answer
26 views

Is partition created by dd (and cached) instantly available for writing

I'm creating a partition (from backup) with dd and need to know if there is a need of some sort of sync/timeout before I can access it. As I know data may be cached in dirty pages. But what if I ...
0
votes
0answers
40 views

How to configure some proxy like Squid to download specific URL only once?

I have read article about Windows 10 spying my activity and blocked all mentioned addresses on my router's firewall. This included addresses az361816.vo.msecnd.net and az512334.vo.msecnd.net ...
1
vote
0answers
26 views

what is left inside the cache even after clearing the page cache data?

I was trying to clear the cache using echo 3 > /proc/sys/vm/drop_caches Even after performing the above operation there remain some space inside the cache? When I check with free -m around it ...
1
vote
1answer
141 views

Using readahead in Debian Jessie

The article BootProcessSpeedup on the Debian Wiki lists a tip to speed up boot time. It says to install readahead and then #touch /etc/readahead/profile-once. It seems like an outdated article, ...
1
vote
1answer
45 views

Linux Gateway as Download Accelerator like IPCop's

We're running dnsmasq on a linux box inside our network for DHCP and DNS. I would like to add a download accelerator like IPCop's (http://blockouttraffic.de/ua_index.php) but without having IPCop as ...
4
votes
1answer
226 views

How does Linux handle block devices?

Today I learned that FreeBSD removed support for block devices entirely. While reading their rational for the decision I came across this: Block devices are disk devices for which the kernel ...
1
vote
2answers
146 views

Force dig to forget records

I would like to let dig always forget a DNS record. I mean if I do dig yahoo.com then I have a record back in with ttl for 1790 seconds. Even if I have no cache service installed, next time i do the ...
37
votes
5answers
43k views

Can I safely remove /var/cache?

I am running out of disk space and noted that I have a large /var/cache directory. Can I safely remove this? (using Arch Linux, BTW).
0
votes
2answers
5k 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 ...
5
votes
1answer
102 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
108 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
64 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
17 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
224 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). - ...
3
votes
0answers
40 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
62 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 ...
2
votes
1answer
40 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 ...
123
votes
4answers
27k 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
22k 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
310 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
152 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 ...
1
vote
1answer
126 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 ...
1
vote
0answers
334 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 ...
15
votes
3answers
1k 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
53 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 ...
8
votes
2answers
15k 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
131 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 ...