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6
votes
1answer
5k views

How can I tell which version of Varnish I'm running?

How can I get the installed Varnish cache version string from the command line?
2
votes
1answer
150 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 ...
8
votes
1answer
299 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 ...
4
votes
3answers
33k views

How to flush local DNS cache in CentOS

(I am aware that googling this question gives me tons of stuff, but literally none worked) I'm looking for a way to flush the local DNS cache on a Centos 6 system, it is not running any DNS server or ...
2
votes
1answer
416 views

DNS cache for wget

I want wget to use a global DNS cache, not just in memory for the current instance. The wget manual mentions --no-dns-cache Turn off caching of DNS lookups. Normally, Wget remembers the IP ...
3
votes
2answers
487 views

Memory management, bias to swapping

I was having 768 MB RAM. In a general day MySQL was using 100-180 mb of RAM and MySQL was swapping 80-120 mb. I was having 50-60 mb free RAM. So I thought I should upgrade. Then I upgraded my RAM ...
1
vote
2answers
249 views

TLB cache flusing when a page is swapped out

I recently heard that Linux simply flushes the TLB cache when the corresponding data in that physical address is swapped out, resulting in underutilization of the TLB. I don't know whether all OSes do ...
3
votes
1answer
698 views

Measure hard-disk read(), write() speed without caching in QNX 6.5

I am working on QNX 6.5 Operating system. QNX 6.5 supports POSIX APIs. I am trying to build an application which is used to evaluate performance of hard-disks. My application will read/write/read ...
1
vote
0answers
1k views

How to set up ZFS with ZIL and L2ARC SSD?

I have been considering bcache and flashcache. However my friend suggested me something called ZFS. In fact it says that formating disk with ZFS can actually do the exact same thing without kernel ...
-1
votes
2answers
2k views

Where can I find a good tutorial for installing bcache? [closed]

Question is updated. Now bcache is part of the standard OS compilation. So it should be easy to install that now. I'll just order some SSD and some big HDD. Where can I found it? I found on the net ...
0
votes
1answer
364 views

Does linux have something like supercache?

I installed http://www.superspeed.com/desktop/supercache.php for windows and the result is awesome. Every program I run is faster. Basically it uses the memory to cache data. Simple idea. I also use ...
4
votes
4answers
468 views

If I have an SSD and a hard disk in a system, can the SSD act as cache for the hard disk?

Say I have some partitions; one on a SATA drive and one on an SSD. I want to create a "virtual" hybrid disk. Is this possible?
4
votes
1answer
294 views

Limit disk buffer usage in SLES 11SP2 to allow more efficient memory overcommit on esxi host

When running VMs on an ESXi host, you can overcommit the memory. Example: host == 20GB physical RAM The amount of RAM allocated to each VM is VM1 == 10gb VM2 == 10gb VM3 == 10gb VM4 == 10gb The ...
4
votes
2answers
377 views

Does sysctl kern.bufcachepercent not work in OpenBSD 5.2 above 1.7GB?

I run OpenBSD/amd64 5.2 on a system with 12GB of RAM, and I want to use about 6GB to 8GB for filesystem caching. By default, 5.2 amd64 comes with sysctl kern.bufcachepercent set to 20 (20%); I've ...
3
votes
2answers
454 views

iptables routing marked packets from router to PC and routing them back to router

I'm trying to do deep packet inspection on HTTP packets. The purpose of this is to collect HTTP payload data and then create some proxy/cache-independent reports. Following this, the idea is to ...
3
votes
3answers
7k 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
257 views

How to debug/audit which devices cache writes?

I store documents on btrfs partition built upon sparse dm-crypt device located on ext4 main partition on physical harddrive. When kernel panics (and this happens on daily basis on my ASUS P53E with ...
13
votes
2answers
800 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 ...
3
votes
2answers
335 views

linux disk caching affects access times reported by stat?

On Ubuntu 12.04 I did the following stat a file cat the same file stat the file again cat the file again after 5 min stat the file The access time reported at 3. reflects the point at which 2. was ...
2
votes
2answers
900 views

Can readahead-services be safely disabled?

I am just going through the service-list of a server (CentOS 5) - the question will probably apply to other RedHat, Fedora, ... versions, too. Note that my servers normally run in runlevel 3 (no GUI ...
3
votes
2answers
142 views

RAID Lag-Behind Burst Write

I would like to setup RAID1 so that a ramdisk in the RAID configuration has occasional synchronisation with a physical disk (that is very battery intensive to run, so I hope to let it spinout). Is ...
2
votes
1answer
601 views

How to cache all internet downloads

I am currently running Ubuntu 12.04. How would I go about caching all downloads? And if Linux does not have this built in, then what are good tools for this? Please note that this isn't a browser ...
3
votes
1answer
1k views

AIX 6.1 JFS2 Oracle files system, not using much files system cache

I am running Oracle database on AIX 6.1, Oracle using JFS2 file systems. Maxperm is set to 90%. This is busy database server, but it is not using the file system cache (less then 2%). The system has ...
3
votes
2answers
79 views

How to get size of data that haven't been written to disk yet?

In some programs percentage of copying large files get to 100% very fast and then I'm waiting much more before it goes next step. It's caused by buffer. How to I see amount of data that are going to ...
1
vote
2answers
2k views

How to bypass youtube's local cache?

Youtube performance here in Brazil has been terrible lately. Checking my browser's activity I can see that my ISP has a local Youtube cache and serves videos in 1.7 MB chunks. Talking to some friends ...
1
vote
4answers
7k views

How to clean up the RAM memory that is being used as cache memory?

My processor is using a big part of my RAM memory as cache and I want to clean it up because of that; will it prejudice something?
2
votes
1answer
235 views

How to utilize extended attributes for image preview?

Is there any file browsers for Linux that cache image previews, just like Windows Explorer cache them to a file named Thumbs.db? As in the latest ext3/4 filesystems, an inode can hold extended ...
0
votes
0answers
104 views

Real copy to Android device

When i copy files to the Android phone, they are copied to some cache, but they aren't written. I don't like it, because i don't know what is done. I've tried these methods: copying via thunar file ...
2
votes
1answer
445 views

Running a query without the OS cache

I want to emulate a client site who doesn't have much caching because they have so much I/O all the time. I want to run a SQL query on my machine (on my VM to be precise) with the same limitations ...
4
votes
3answers
405 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 ...
13
votes
1answer
2k views

Is disabling barriers for ext4 safe on a laptop with battery?

The manual page says about the barrier option for ext4: Write barriers enforce proper on-disk ordering of journal commits, making volatile disk write caches safe to use, at some performance ...
4
votes
1answer
605 views

Drop a specific file from the Linux filesystem cache?

I know I can drop everything from the Linux filesystem cache, but is there a way to drop just one specific file? Or prevent a file from being cached? Or tell a process not to cache any files it ...
2
votes
2answers
569 views

mbcache documentation

I want to experiment with mbcache kernel module, but I'm having trouble finding the documentation for it. If I understood correctly, mbcache allows the use of a fast SSD disk to act as a transparent ...
8
votes
2answers
1k views

lshw and lscpu disagree on caches - which is right?

I am trying to find out specifics about caches (in particular which caches are shared between cores and which are not) and have stumpled onto a inconsistency. sudo lshw says *-cache:0 ...
3
votes
1answer
2k views

What is the buffers column in the output from free?

These questions briefly list the format of the free command, noting that buffers is kernel memory that must be written out to disk and cache is file data that does not need to be written disk. On my ...
3
votes
2answers
420 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 ...
2
votes
3answers
944 views

delayed write in operating file system

I read in some papers about NFS and Sprite that a system can use delayed writes when a client writes something to the server. I would like to know what is the purpose of this technique?
1
vote
2answers
454 views

Embedded device: How to do raw reads and write to flash (emmc/movinand) bypassing file system cache

I have an embedded device with a flash memory running linux. I want to do raw read writes on the flash part but I also want to avoid any file system cache. How can I do this? Any pointers?
2
votes
1answer
427 views

dav2fs caching problem on Debian Squeeze

I have apache/mod_dav and davfs2 all on the same host. davfs2 is used to mount what Apache is serving to the local filesystem - a sort of loopback. The purpose is that the content of the files served ...
2
votes
3answers
524 views

Is there a way to tell the system to keep a folder to reside in memory?

I'm developing a Java EE web application and I'm trying to speed up the testing process. To do so I was wondering if there is a way to tell the system to keep my build folder in system memory?
9
votes
4answers
1k views

Is there a way to sync only one partition?

Is there a way to sync only one partition instead of all partitions? Something like "sync /dev/sdc1".
6
votes
1answer
16k 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 ...
3
votes
3answers
2k views

/proc/cpuinfo “cache” category: L1, L2 or total?

When I look in /proc/cpuinfo, one of the lines tells me I have 6144 KB of cache. Is this L1 cache, L2 cache, or the sum of both of them? In any case, how do I find out how much L1 and L2 cache my ...
6
votes
1answer
9k 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 ...
20
votes
4answers
22k 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).
1
vote
3answers
1k 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 ...
5
votes
2answers
5k views

Cleancache vs zram?

I have an old laptop here with only 512 MB of RAM. Since a few kernel releases, I am using zram to convert 256 MB of it to a compressed ramdisk which is then used as swap. This has proved to be very ...
1
vote
0answers
958 views

What is meant by cache aliasing? [closed]

What is the meant by cache aliasing? I searched around some, but wasn't satisfied with the answers I found. I also saw two associated terms, instruction cache aliasing & data cache aliasing. ...
2
votes
0answers
619 views

Linux kernel slab usage growing on embedded system

I'm in the process of QA/debugging a project on a custom embedded linux system. The problem we're VERY tight on memory, and even a couple megs can cause issues with our software. What I'm seeing ...
4
votes
1answer
2k views

What options are there for tuning Linux file system caching?

What various types of caching are possible in the ext3 file system and how can their values be changed using system calls or other methods? I don't want to use commands or tools.