Questions tagged [cache]

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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Reposync default temp-cache location

I'm trying to change the temp-cache directory (can do it using the flag "-t"), but I want to know what is the default location of this temp directory. How can I know that? Thanks!
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redis startup on boot via systemd

while preparing two redis server instances and getting them work as systemd services i'm running into problems. Its the first time creating own services. The systemd service file was copied from the ...
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How to get cache used per process on *nix systems

I would like to know, what is cache usage per process. Is there a way to do it? I'm currently on Ubuntu. The problem is, that my PC fills up whole cache, and then when I need RAM just starts swapping ...
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How do I undo copying a file that is ended up in cache?

I have copied a large file to USB drive. The file appeared to be copied almost instantly, but copying operation stalled at the very end. /proc/meminfo is showing large, gigabyte Dirty: entry which is ...
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Explanation about free, available and buff/cache and how to find what process is buff/cache saved for in a server in the command "free -mh "

I see explanation for free -mh as: free displays the total amount of free and used physical and swap memory in the system, as well as the buffers and caches used by the kernel. The information is ...
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Remove temporary files in chrome, without losing access to websites

My chrome (PortableApps) profile takes above 1Gb. I found no way of cleaning the cache (to the point of freeing a large fraction of the space taken), without losing access to websites, e.g. Is that ...
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Why flatpak cannot continue downloading file?

I'm new to flatpak and get confused about it. Before downloading any package I need to install flathub first. It requires a package called org.freedesktop.Sdk which is about 500M. My internet ...
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how to sudoers drop_caches w/o proxy script?

not echo 3 |sudo -k tee /proc/sys/vm/drop_caches as we cant ensure if it will be "3" the value passed. So, from where could I grantedly get the "3" text and how to write it at ...
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Is it reasonable to have a network-mounted home dir but a local ~/.cache?

I want to free up some space in my network-mounted home directory. I'm noticing that my .cache directory is very big. I was wondering whether I should replace it with a symlink, ~/.cache -> /...
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Is there a way to restrict use of swap to cases when otherwise the OOM-Killer would kick in? [duplicate]

Is there a way to completely restrict using swap if there are buffers/cache in use? And use swap only to prevent Out-Of-Memory Killer. Is there a way to forbid using swap if are there still buffers/...
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Is it possible to avoid cached data duplication in bcache and Btrfs RAID1?

There is a possibility to attach single bcache cache drive to multiple backing devices. Since bcache is not aware about filesystem which lies on top, this means it is not aware about any software RAID ...
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Execute single command with write caching disabled

Whenever I write a large file to a USB drive, write caching makes it very difficult to track process. I can disable it in various ways like echo 1000000 > /proc/sys/vm/dirty_bytes which solves the ...
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Which kernel functions are called upon page cache accesses?

I have an application and I'd like to measure its page cache hit/miss numbers. I found this tool called cachestat by Brendan Gregg, which uses the ftrace tool to count the number of 4 specific ...
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Creating an SSD partition with a different block size

I am trying to put together a complex setup (Debian) that uses LUKS+LVM+LVM cache in a mixed SSD+HD environment. To use a partition on the SSD (partition size for lvmcache volumes: 20 GB) as the LVM ...
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Fdisk showing wrong SD card size

So I've been formatting and reformatting a couple SD cards as I'm running some tests and I need to reformat pretty often however every time I plug a different card in fdisk reports the old cards ...
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Can I use virtual memory for ARC ZFS write cache?

I want to use virtual memory for ARC ZFS write cache, because it is troublesome for me to increase physical memory but I want fast writing to a DB in a ZFS. $ free -h total used ...
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"Credentials cache" (temporary cache password) for rsync/ssh?

In git (at least on Linux), there is a thing known as a credential-cache (see for instance https://stackoverflow.com/questions/5343068/is-there-a-way-to-cache-https-credentials-for-pushing-commits). ...
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Behaviour of nscd is undeterministic

I have a question regarding how nscd works. I ran this on Terminal #1 docker --version && docker pull ubuntu:20.04 && docker run --rm -it --name dns-cache ubuntu:20.04 apt-get update -...
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Linux gaslighting me by pretending to write to USB

When I boot my Linux and start writing to a USB-backed block device, everything goes fine for the first few times. Afterwards, if I write to it once more, dd reports absurdly huge transfer rates (2.9 ...
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IO Throttling After Reaching dirty_background_ratio

I am trying to understand the Linux IO throttling mechanism. This is what I got so far: By calling the write (fd, data, size) system call, the data will be written into the OS cache as dirty pages. ...
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Are direct writes to block devices buffered? How do I ensure it's written to disk before removing it?

Say I do something like dd if=file of=/dev/sdc (simplified for illustration), is this buffered? Can I sync it like I would any other filesystem write, or do I need to do something else to make sure ...
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Why does mouse and cursor movement become erratic when I copy an entire memory stick to another stick?

I copied a 16 GB USB memory stick to another 16 GB stick (cloned it), by using the following command: cp /dev/sdb /dev/sdd It took about 27 minutes, and the cloning works. But during the entire copy ...
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LVM writecache not fully emptying

I'm struggling with an LVM issue. I have a writecache attached to an existing LV. I've been polling the LV as well as the writecache with lvs -o+writecache_total_blocks,writecache_free_blocks but no ...
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How to purge in-memory disk cache

Linux uses free RAM to store pages of disk files to speed up overall disk access. However for the purposes of benchmarking, I want to test the disk read speed and I don't want that speed measurement ...
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How to configure cache memory to automatically sync on program close?

Currently I have an issue with programs not de-allocating their stack upon close. It appears to be a natural behaviour of Linux page caching. When I open my desktop, it runs at ~300-500MB. After ...
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Testing zfs scrubbing with sparse files

I want to play around with and test zfs a little, at the moment I want to test the scrubbing, live if possible. So I decided to create some sparse files in /zfs (similar to here): $ for i in {0..3}; ...
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The reason why buffers in "free -h" command output is increased

I did two experiments. The first experiment (Ubuntu 20.04, ext4 filesystem): Run command free -h -w: $ free -h -w total used free shared buffers cache ...
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2 votes
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LVMCache: Why use a cachepool instead of a cachevol?

I'm aware of the differences between a cachepool and cachevol. Cachepool separates the cache data and metadata into two separate volumes, whereas a Cachevol uses a single volume for both. My question ...
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How to use swap less often?

I use an SSD swap just to avoid full memory related crashes. There are limited erasures that can occure on SSDs. The memory related crashes have stopped, but my system uses swap constantly and vmstat ...
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Why I don't see any increase in "Dirty" memory when writing to a file?

I read a bunch of stuff about "Write-back" mechanism today and wanted to try an experiment. EDIT: file downloaded from the Internet shows up in Dirty stats Based on the comments, I tried to ...
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Can I limit the size of disk write cache on a per-device basis?

My main desktop has 64GB of RAM. This seems to cause the dirty write cache to often exceed 10GB during disk-intensive operations such as file copies or network transfers. (I gathered this by observing ...
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Using LVMCache or BCache for Hot-Warm-Cold Caching

I've recently reconfigured my current debian machine with three different drives: An SLC SSD, a QLC SSD, and a 4TB HDD. I've been toying around with lvmcache and other utilities, and I wanted to know ...
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LVM SSD cachepool how to trim (Debian 10)

I was playing with LVM and I was setting up a volume with ext4 on an HDD and I want to use an SSD as a cache. What I first done was lvcreate --type cache-pool -l 100%FREE -n datacache SSD /dev/sda3 ...
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Which caching mode does Stratis-storage use? writeback or writethrough?

Having a large HDD and a small SSD makes me tempted to use Stratis for my /home because currently I can't recognize my manually LVM cached partition scheme anymore. According to Linuxsysadmins: Manage ...
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How to truly disable the write cache function(in dmesg) in Ubuntu for an external HDD?

I use sudo hdparm -W 0 /dev/sdb to disable the write cache for the HDD, and the information /dev/sdb: write-caching = 0 (off) shows that the write cache is truly off. But when I use the instruction ...
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Directory /var/cache/apt is not autocleaned?

I am trying to save some space from /var/cache/apt however the apt autoclean command does not have any impact. Why is that? root@server:/var/cache# du -sh * 4.7G apt 3.2M debconf 20K ldconfig 1....
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Cannot create /proc/sys/vm/drop_caches: Permission denied

I am using python because i try to run some queries from psql in cold state in a for loop.So before the execution of every query my cache must be clear.I imported os and then i did this: if state==&...
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Rsync progress waits a long time after finish

When I am running rsync to copy big file (within directory on local hard drive) + rsync -P bigfile1.img bigfile2.img bigfile1.img 6,512,705,536 100% 413.76MB/s 0:00:15 (xfr#1, to-chk=0/1) it ...
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How does the linux perf tool get the miss rate of the l2 cache?

I want to use perf tool to get the miss rate of l2 cache. I know how to get L1, and LLC. perf stat -e L1-dcache-loads,L1-dcache-load-misses,L1-dcache-stores command perf stat -e LLC-loads,LLC-load-...
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Unable to start a LVM-Volume after crash of cache-device

I'm running a radi6(HDD) setup on a debian 10.7 machine. I'm using this md-device for a LVM VG. I added a SSD as writethrough-Cache. Unfortunately my bash-history doesnt' contain the commands of the ...
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How to judge whether the cache is shared or private?

In general, l1 and l2 are private, and llc is shared. But I want to confirm if this is the case on my linux server. How can I know this information? The configuration of my server is as follows: Linux ...
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How does one clear at commands cache/queue?

Where/how can I clear the at commands log on my system, if one exists? job 102 at Wed Nov 25 09:37:00 2020 I imagine that after awhile these should be cleared somehow... How would one do this ...
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Has anybody heard of (a trick to make) a local hard drive based cache of NFS? (primarily in FreeBSD)

Problem: NFS can be slow, when starting binaries (e.g. /usr/bin) over NFS, such as in a network booted system. RAM buffer cache might not be sufficient to avoid slowness. Idea: it seems we should be ...
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Is it possible to create a cache directory that refuses unlink/delete?

I have a cache directory that stores files that should never change once downloaded. However, the program that uses this cache directory deletes the files from the cache. Is there any mechanism (like ...
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How do I know what replacement algorithm the linux server uses? [closed]

I am doing some experiments on the replacement algorithm. How do I know what replacement algorithm is used in the L1 cache on my Linux server? And how do I set up L1 Cache to use random replacement ...
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Why is free memory not used as disk cache?

My file server says: $ free total used free shared buff/cache available Mem: 8023836 5250252 2534480 668 239104 2515488 Swap: ...
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Is there a way to let me know all the data in the cache?

Is there any tool that can tell me which cache set the data is placed in when I run the C language? What data is placed in each Cache line? The reason for doing this is because I want to have a deeper ...
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Pre-Caching large files

I have a CPython routine which is time critical, it reads large binary files to generate dynamic spectrum, it's slower if the files are not cached previously. When I use vmtouch to pre-cache, it takes ...
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What are the benefits to using multiple LVM caches?

I strangely can't find any documentation on this, just how to use LVM cache for a device. If add another SSD as a second LVM cache to LVM volume, will I get better or worse performance? Or does it ...
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htcacheclean with "-A" flag only lists 64 cache entries, where are the rest?

I have a webserver running Apache. It has caching enabled via cache_disk_module. CacheRoot "/var/cache/httpd/mod_cache" CacheDirLevels 1 CacheDirLength 1 I would like to list ...
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