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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Force dirty pages limit in kernel sources

First of all, I'm not sure if that's a solution to my problem. My problem is that during I/O embedded linux is allocating too much memory in cache causing OOM if I run anything else. I/O operations ...
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How to stop xargs from badly merging output from multiple processes?

I'm using xargs with the option --max-args=0 (alternatively -P 0). However, the output of the processes is merged into the stdout stream without regard for proper line separation. So I'll often end ...
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43 views

How can I differentiate disk I/O occured explicitly by a user and OS prefetching?

I am monitoring disk I/O usages of an application program (running on CentOS 7) It uses lots of sequential disk I/Os where I expect that OS prefetching is something! dstat shows how many disk I/Os ...
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High Idle CPU / Low CPU Load average

After removing APC (alternative php cache), I noticed that there are less pagination access and less dirty pages but in the same time: High idle CPU Very low CPU load (relatively to the time before ...
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427 views

How to tell if a character special file would block if read from

I would like to be able to tell if a character special file would block if a character were read from it without actually reading a character from it. Can this be done?
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151 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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1answer
64 views

How to tell whether a process is network I/O intensive or not in user mode in Linux?

I am currently writing a program in Linux which needs to tell whether a specific process is network I/O intensive or not at runtime. I have tried some tools such as iotop and iftop, but none of them ...
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89 views

What does the symbol '-' mean in Linux? [duplicate]

I see this symbol all the time and my book has yet to clarify what it means. None of the man pages or web searches clarify this either. At first I believed it to be a I/O symbol, but that never works ...
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1answer
20 views

Very low disk performance on Samba

I'm using Samba on Debian 8.4 (Jessie) to share files with a small number of Windows & Mac users (~20 total, ~5 at a time at most) and I'm seeing abysmal performance on read and write: tested by ...
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73 views

Slow USB 3 write speed

Writing to my USB 3 thumb drive (SanDisk Extreme SDCZ80-064G-FFP) is very slow on Linux: 1 GB takes longer than 200s. Using Windows (dual-boot on the same computer), the same 1 GB file can be copied ...
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Samba performance tuning

Hi I'm using Samba to share a folder from linux to a Windows client(Windows Server 2012 R2). The disk backing the linux share is pretty fast (NAS of 500+ MB/s). However, when I benchmark the IO ...
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iozone read test slower than fio

I'm currently using both iozone and fio to test my disk performance. However, iozone show much much poor speed than what is shown from fio. (about 1/3) Now the question for me is which number should ...
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1answer
44 views

Persistent process substitutions? [duplicate]

Is there a way to take a process substitution like <(grep foo some/file), and save it to a "file-like entity" on disk (reminiscent of a fifo), so that, every time this thing was opened for reading ...
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1answer
33 views

How does iotop calculate the relative I/O activity?

I am running some heavy I/O processes on my workstation and recently installed iotop to monitor them. Here's a recent screenshot: I'm a bit confused about the readings in the IO> column. It ...
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1answer
31 views

Sometimes syncing gets stuck with dd

Sometimes when I use dd then sync or use dd with conv=fsync, the syncing process gets stuck, but sometimes not, with exactly the same input and output targets and configuration. dd if=2016-03-18-...
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88 views

Arch Linux: blk_update_request: I/O error, dev sr0, sector 1452024: unrelated to user input

I just left my Arch Linux installation running in a virtual machine. When I came back to it, I found the following error: [14554.169929] blk_update_request: I/O error, dev sr0, sector 1452024 [14554....
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5answers
4k views

Special File that causes I/O error

I want to automatically test if a piece of software reacts as expected if an essential SQLite DB file fails to be read (causing an I/O error). Exactly that happened some days ago at a client. We ...
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1answer
68 views

Monitor temperature/IO of NVMe drive

Is there a way to monitor temperature or reads/writes of and NVMe drive (in this case Intel 750). hdparm, udisksctl, smartctl, and hddtemp all seem to lack this capability, google searches have been ...
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Determine affected file given logical block number [duplicate]

Given the logical block number from these log lines in /var/log/messages, is there a way to determine what file was affected? ...Buffer I/O error on device sdd1, logical block 203953715 ...lost page ...
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2k views

CentOS 7 Live - Read-only file system error

I have loaded a CentOS 7 Gnome Live USB. I wanted to do some operations on it without touching the installed system on the computer, because I only want to try some things. I installed openssh-server ...
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1answer
1k views

-bash: /usr/sbin/useradd: Input/output error — What does this mean?

Today, on my Centos server I tried to add a user but got the following error: -bash: /usr/sbin/useradd: Input/output error How do I fix it?
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Input/output error, cannot install anything

I have done something strange to my debian server and now I cannot install anything. It says, that locale is broken. I tried to fix it by reconfiguring dpkg, cleaning apt-get and and many other ...
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Portability of “> /dev/stdout”

Occasionally I need to specify a "path-equivalent" of one of the standard IO streams (stdin, stdout, stderr). Since 99% of the time I work with Linux, I just prepend /dev/ to get /dev/stdin, etc., ...
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1answer
24 views

How to clear data from all files present in a directory?

I have a folder which has some text files and other folders in it which in turn have more text files in them. I need a command which will recursively loop over the folder and clear all the contents ...
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When a process will go to 'D' state?

I'm using "Linux hostname 2.6.28-15-generic #49-Ubuntu SMP Tue Aug 18 18:40:08 UTC 2009 i686 GNU/Linux" All the client machines will use Thin-client ,I will use my laptop for working and I will ...
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Massive, unpredictable I/O performance drop in Linux

I'm using Debian testing without any problems for ~6 years (I'm just regularly updating it), but recently it started to show a random behaviour that can be summarized as "Low I/O performance which ...
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53 views

Why does hdparm and dd show two completely different results?

I have an external hard drive (/dev/sdc1) mounted at /mount1 When running hdparm -tT /dev/sdc1 I get: /dev/sdc1: Timing cached reads: 2246 MB in 2.00 seconds = 1123.75 MB/sec Timing buffered ...
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1answer
74 views

Create a file of fixed size with specific contents

I want to create a file of fixed size (1G, 10G, 100G etc) with a single random word of length within the specified limit on every line. I basically want this to run a benchmark which will sort the ...
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2answers
64 views

Defer *all* disk writes, keep them in memory

How to temporarily stop synchronizing of dirty data with disk, instead just keeping it in memory. Clarification: I want to sync it later.
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2answers
6k views

How can I specify that curl (via command line) overwrites a file if it already exists?

I'm using curl in this syntax: curl -o myfile.jpg http://mysite.com/myfile.jpg If I run this command twice, I get two files: myfile.jpg myfile-1.jpg How can I tell CURL that I want it to ...
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117 views

How to redirect STDIN of background process?

In my Ubuntu, i run java application in background. I use bash script to run it and now it looks like: nohup java -jar app.jar & exit 0 The problem that i want to be able to write an input ...
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Diagnose input/output errors on a Truecrypt container

I have been trying to get a local repository located on a usb drive working on an air-gapped machine. The repository was created with apt-mirror on the same kind of system (ubuntu i386). Currently I ...
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31 views

How do I give an input to an infinitely running program? [closed]

I have a python program that runs infinitely, takes an input and throws an output. I want to write a bash program that gives an input while the python script is running. So, how do I give an input to ...
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1answer
438 views

hdparm: SECURITY_SET_PASS: Input/output error

I'm trying to use hdparm to secure erase an SSD as suggested here. Following the directions in that guide has worked okay so far, but I can't seem to resolve this error: ~ $ sudo hdparm --user-...
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2answers
855 views

Why do systems become slow when doing massive writes to disk?

I want to know why systems become slow when writing mass data to disk. I think that for system to become slow, there should be some issue with CPU. But write is only I/O bound. Do hardware ...
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2k views

Intercept input and output from specific executable

I have a certain Linux executable that is called from a bigger application to perform some calculations. I want to modify the way the calculations are performed, for that I first need to understand ...
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89 views

command to list logical volume I/O statistics on AIX

I am looking for a command which displays the I/O statistics of logical volumes (like reads/sec , writes/sec, io utilization %, read kb per second, written kb per second) . I tried iostat, but its ...
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1answer
39 views

understanding lsof during long operation on big file

Background I'm running Musicbrainz Picard to update a ~11M ogg file on a 500GB NTFS disk (Transcend StoreJet) connected via USB and mounted using autofs. The connection is through docking station. ...
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117 views

The interrupt timeline for a single process doing output

I'm studying the book 'Operating System Concepts' 9th edition. In the first chapter, part 1.2.1 computer system operation, I can't understand the figure 1.3: Can any one make a quick interpretation ...
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1answer
56 views

Why is uninterruptible sleep indicated by 'D'?

From "man ps": R = Running or Runnable S = interruptable Sleep T = sTopped Z = Zombie D = uninterruptible sleep (usually IO) Where does this D come from?
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How do I hook an application and find out what files it writes while running? [duplicate]

I'm not sure how to exactly word this question, because my searching hasn't yielded anything that describes my situation what I'm looking for. Say my friend writes an application and sends it to me ...
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1answer
94 views

Desktop completely freezing on I/O operations

In my old system, I was already having desktop freezes on some heavy I/O operations like apt-get dist-upgrade and copying 4 GB video files. But now, it has become a lot worse: any apt-get install is ...
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1answer
193 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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1answer
27 views

Crash with input/out error and swap unmounting [duplicate]

I am looking for hints on this problem. I've searched around, but can't find something exactly similar. I am running Debian 8 stable, updated, very minimal install (i3wm, small number of apps running)...
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2k views

Construct a command by putting a string into a tty

I managed to do this echo -n "command" > /dev/tty1 The letters appear, and the cursor moves, but they are "ghosts" – if you hit Enter, nothing happens (they are not in stdin). Edit: In the ...
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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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What's the difference between ioremap and file operation mmap?

I'm currently working on a PCI device driver for Ubuntu. I have some example code about PCI driver, but I have difficult on understanding the ioremap and file_operation.mmap. The description of file ...
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How do I run a command in a different tty?

Suppose there are two terminals, pts/0 and pts/1. In pts/0, I have fired a command: ls>/dev/pts/1 Then, we only get the output of the ls command in pts/1, but I want to run a command as well as ...
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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
79 views

copy and symlink mysql to another disk partition

I'm using ubuntu 12.04 and have two disk partition named: /dev/sda and /dev/sdb. my home partition and other programs are in /dev/sda. therefor any work like database benchmark on my mysql databases ...