I/O is an acronym for Input/Output, which refers to the mechanism or process for the transfer of information between one system or component and another.

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If an I/O function cannot fail with EINTR, does that mean it never blocks? [migrated]

For example, consider fdopen. I have been wondering whether it's possible for this to block, if, say, the file descriptor argument refers to a pipe or socket. A Google search hasn't turned up anything ...
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How is a process state updated to blocked state (TASK_INTERRUPTABLE)? [migrated]

When a process is waiting for IO, how is the task state updated to TASK_INTERRUPTABLE (that is, blocked)? Imagine this case, a process issues an IO request to a block device. According to my ...
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32 views

Relationship between IO scheduler and cpu/process scheduler?

The concepts of IO scheduler and CPU scheduler confuse me. Below are my understanding: Linux uses CFS scheduler + nice values by default to schedule processes. Each process has an IO queue. There ...
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39 views

How to track down the source of I/O spikes?

I am using Linux as a desktop, and keep getting seemingly random I/O Spikes. The machine becomes unusably slow. At first I thought it was just that I don't have enough memory. But looking at the ...
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1answer
18 views

Set ionice for a multi-threaded application

I have a program that spawns multiple threads, all of which do fairly intensive IO, running on the background. I want to set the scheduling class to idle so that it doesn't clog up the system; ...
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30 views

stdin read notification

I want to detect when/if an application issues read(stdin, ...). Is it possible to use unbuffered I/O so that I could wait on write in external process? The problem: Some commands require user input ...
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50 views

How does one determine when a process or machine is IO bound?

I have a node.js process which writes to many different sqlite databases. Sqlite can handle only one concurrent write per database, which is fine since there will be only one write per database at a ...
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39 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. ...
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27 views

NAS: 100% system (kernel) cpu usage

I have a single core NAS My Live Duo. It runs Debian lenny release. I found via htop utility that it constantly use 100% of red cpu without any noticeable process to eat it. Than I checked via iostat ...
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51 views

Very slow file operation

I recently rebuild a machine with Centos 5.8 with a brand new disk. This machine is old and has been running 5.8 for a long period with no issues so the only thing which changed recently is the new ...
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33 views

Selecting IO scheduler on external drives

I'm running linux on the beaglebone black. My system is running directly from the sdcard. To change the IO scheduler I need to configure /sys/block/xxx/queue/scheduler where xxx is the mounted ...
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1answer
97 views

Set bash script output to the line that called bash script

I've looked for the greater part of two hours trying to see if I could find a way to redirect the output of a bash script to the line that called the bash script. The best example I can use to ...
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1answer
33 views

pipe speed benchmark with machine readable output

I'm looking for a tool similar to pv which is producing machine readable output. And i cant believe that nobody did it bevore... I looked at the manpages of pv, pipemeter, dd and cpipe but all these ...
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454 views

tar to pipe but keep -v verbose output separate from STDERR

A normal tar command tar cvf foo.tar ./foo >foo.out 2>foo.err has three output IO streams archive data to foo.tar list of filenames to STDOUT (redirected into foo.out) error messages to ...
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1answer
123 views

Does dm-multipath schedule I/O?

I have a multipath device I'm interested in: [root@xxx dm-7]# multipath -ll mpathf mpathf (3600601609f013300227e5b5b3790e411) dm-7 DGC,VRAID size=3.0T features='1 queue_if_no_path' hwhandler='1 alua' ...
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1answer
42 views

Running command on server, but have the server read/write local files [duplicate]

Is it possible to have a remote machine run a command, but redirect all reads and writes to a local machine. Example: I have a bunch of scripts in folder 'project'. When 'make simulate' is run in ...
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48 views

View syscalls/kernel activity for I/O from a running process

I'd like to be able to view syscalls or kernel activity for a process...I'm not actually sure of the terminology I need here! Specifically I'm looking for the difference between I/O going to local ...
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23 views

Linux sound lags while copying from USB key

Why did I experienced sound skipping while copying a big file from my USB key onto my computer's drive? I monitored the system during this I/O operation: music was playing from Internet on the ...
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458 views

Optimizing logical sector size for physical sector size 4096 HDD

With many new hard drive disks the physical sector size is 4096. Would it be possible to make the system use a logical sector size of the same size, rather than the default logical sector size of 512? ...
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2answers
33 views

Current disk load

I'm using iostat to get the current disk load each second with iostat -dx 1 (specially, %util column). However, I'd like to put this in a bash script and control the interval with the watch command ...
2
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1answer
181 views

how to read any process' /proc/pid/io

I'm trying to monitor disk activity of each process. One way that I found how to do this is to read /proc/pid/io file and compare fields with previous read. That works fine except my monitoring ...
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1answer
39 views

How to collect disk read/write activity over a given period of time?

Sometimes, especially upon login, I have a lot of disk activity. I can use iotop to see what's doing that at a given moment, but I would like to have an integral table over a given time, say the first ...
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278 views

Disk busy is close to 100% and iowait is 0,0% on SunOS, how can it be possible?

During monitoring of SunOS5.10 machine I noticed strange behavior: Disk busy is close to 100% Disk waiting time is 0,0% Primary purpose of this machine is running application server on jvm. This ...
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1answer
476 views

Alternative to iotop for non-root user without sudo privileges

I'm looking for an alternative to iotop. Here's my situation: I want to find out if a program is accessing the hard drive a lot while running. iotop requires root/sudo privileges. My account is on ...
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117 views

Can you throttle the bandwidth to a tmpfs based ramdisk?

I created a ramdisk using tmpfs as follows: sudo mount -t tmpfs -o size=1024m tmpfs /myramdisk I was looking into cgroup blkio subsystem bandwidth limits "read_bps_device" and "write_bps_device" ...
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IO throughput lower when only a single process using the disk?

I am running a busy cacti server on centos and sometimes the rrdtool process is painfully slow when writing to disk, in HTOP the IO Column would display something between 100-300. I a polling cycle ...
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295 views

How can I prevent disk I/O from taking over my CPU?

I run Debian Jessie on a quad-core i7 processor, which results in 8 cores being shown thanks to hyperthreading. On disk-heavy loads, all eight cores are maxed out with io-wait, as shown by htop. This ...
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78 views

How to calculate blkio shares in cgroups?

Currently I'm trying to setup a test scenario with the use of Debian Wheezy with its default kernel 3.2.60-1+deb7u3 and the cgroups blkio controller. The calculation of blkio.weight is not working for ...
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456 views

External Hard disk Input/Output error

One of WD external harddrives is not working when I try to access some folder. I am able to access the rest of the folders on the disk. I am getting Input/Output error as show in the attached Image. ...
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2k views

ERROR: init: ttyS0 (/dev/ttyS0) main process (1612) terminated with status 1

I'm getting the following errors every 10-30 seconds on a virtual Red Hat Enterprise Linux 6.5 2 Server on Amazons EC2. Sep 23 09:57:05 ServerName init: ttyS0 (/dev/ttyS0) main process (1612) ...
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1answer
262 views

Dirty in /proc/meminfo for dd

I read from here that the below command gives me the amount of data that needs to be written to the disk. grep ^Dirty /proc/meminfo It particularly says Ever ask yourself "How much data would be ...
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mkfifo - Does disk I/O actually occur?

I have 2 applications: Producer (N instances) Consumer (1 instance) I currently write out intermediate results from the producers, and then the consumer reads these files from disk and produces a ...
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Journal commit I/O error for Seagate Expansion external USB hard drive

I am using Debian 7.6 (amd64) and for some reason when I am trying to read or write to my Seagate Expansion 1TB external USB drive, I am getting input/output errors ... Here is what the output of ...
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211 views

blktrace - differentiating between sequential to random io

I'm looking for a way to determine whether an app is doing sequential or random I/O. Is it possible to look at a blktrace capture and say if I/O is sequential or random? If yes, any examples of what ...
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1answer
236 views

How to test Disk IO on VMs with iozone?

I want to test the disk IO performance like read, write, random read, random write and so on both in physical machine and VMs (with aufs file system). Also I want to test the throughput performance in ...
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146 views

why doesn't iozone generate output file?

I'm using iozone3 for tesing, on Xamin (an Debian-based OS). When I enter iozone command, for example iozone -Rab output.xls, the test runs successfully. But after running the test (after displaying ...
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219 views

wget internal buffer size

I'm constantly using wget to download many files over 1GB each. I'm getting concerned about how this may be straining my HDD. Can wget's internal buffer size be modified so that it writes to my HDD ...
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202 views

/dev/sda not appearing after secure erase

I decided to wipe my SSD with a secure erase before installing Arch Linux, since the Arch wiki said that it would improve performance. I followed the instructions listed on the wiki, but now when I ...
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1answer
50 views

prevent filesystem access while passing information to and from programs [closed]

I have written a main script that calls a system program tens of thousands of times. The main script creates and provides this program with an input file on each call. Upon completion, the program ...
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1answer
189 views

Spawn multiple dirty page flusher threads per device

In earlier 2.6.X kernels, pdflush was used and it would spawn more pdflush threads if all current pdflush threads were busy for a second (read from The Linux Page Cache and pdflush). Since the ...
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72 views

How to decrease the time the processes would wait (blocked) for disk reads (only to discover an error)?

Waiting too long when encountering an unreadable sector on a disk is really very annoying. (Especially if you are trying to read as much data as can be read from a disk with bad sectors, and do it ...
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41 views

Can ramdisk improve performance when stats show low wait and system cpu use?

I have jobs that do I/O of rates peaking around 200mb/s. On high load (over twice cpu cores) I tried to copy large file and got only few mb/s. Gathered dstat show single digits in wai and sys category ...
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How can I see i/o stats for a briefly running process?

For long running processes like init, I can do things like $ cat /proc/[pid]/io What can I do if I want to see stats for a briefly running process such as a command line utility like ls? I don't ...
3
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1answer
101 views

Artificially prime buffer cache?

Is it beneficial to artificially prime the buffer cache when dealing with larger files? Here's a scenario: A large file needs to be processed, line by line. Conceptually, it is easy to parallelize ...
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639 views

Reduce bad block retry / wait times in Ubuntu

How can I reduce the IO wait time and retry times so that the OS doesn't continually try to write to a failing drive? I have an system that I use to make copies of demo content that gets loaned out ...
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Calculate Total disk i/o by a single process [duplicate]

I am looking for some tool that will dump total disk I/O by a single process after it ends. So far my finding is :- iotop= It shows i/o per process in real time but does not give total after process ...
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100 views

Are writes to eventfd counted as io?

I am trying to reduce hard-disk activity on my system. Running iotop shows that Eclipse (the IDE, latest version (Luna)) is writing kilobytes of data every few seconds. So I ran strace on the eclipse ...
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565 views

`crontab -e` sometimes fails with “Creation of temporary crontab file failed”

From time to time crontab -e fails on me on a Ubuntu box. It is the same for all users including the root and crontab -eu <user> under the root. Goes like this on a regular basis, a success here ...
2
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1answer
125 views

I/O schedulers for normal harddisks

For me figuring out what is the best choice for I/O in kernel was a challenge. First I learned that it is subjective then it is depend upon the File-System you use. I know you should use No-op for ...
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3answers
144 views

Low level disk i/o on linux

Can a user level program do page level or block level I/O on SSDs? I've looked at disk devices, but am unsure if they provide this as they work only if the partition has a file system. UPDATE #1 I ...