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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How to programmatically read until a certain character in a file? [migrated]

My C program writes a .json file. Few of the values in the schema of the .json file is string and has variable length. I am using jansson library. I will have to read a complete .json object ...
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1answer
23 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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38 views
+50

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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14 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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2answers
43 views

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 ...
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4answers
822 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
58 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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1answer
49 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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32 views

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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4answers
529 views

Utility to buffer an unbounded amount of data in a pipeline?

Is there a utility that I can stick in a pipeline to decouple read and write speeds? $ producer | buf | consumer Basically, I want a utility buf that reads its input as fast as possible, storing it ...
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74 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 ...
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2answers
852 views

What keeps one side of an rsync so busy?

I've got a Debian machine on my LAN serving as a backup server for the others. It has four HDDs combined into a software RAID 5 md device, on that an LVM, and on that btrfs. Backups are made using ...
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1answer
55 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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2answers
501 views

iotop but for particular disk?

Is there a tool like iotop but for monitoring IO on specific volumes? (Or perhaps I missed a way to filter iotop?) If not is there any way to get at this information via (say)/proc? (dstat etc. ...
2
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1answer
320 views

jdb2 keeps Hard Disk busy all the time

My system became too slow last few days. The hard disk indicator is on all the time. To discover which process is keeping the disk busy i run this command: # while true; do date; ps auxf | awk ...
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3answers
55 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 ...
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1answer
118 views

Unable to delete a directory even as root

I am unable to delete a directory even as root. The command rm -rf kdyiyv.pif returns nothing. Then I tried the command, touch kdyiyv.pif for which there was an error: touch: setting times of ...
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2answers
205 views

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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5answers
3k views

Why is iterating over a file twice faster than reading it into memory and computing twice?

I'm comparing the following tail -n 1000000 stdout.log | grep -c '"success": true' tail -n 1000000 stdout.log | grep -c '"success": false' with the following log=$(tail -n 1000000 stdout.log) echo ...
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3answers
82 views

Is it possible to generate a separate file list when creating a tarball?

When using tar for backups I'd like to create a separate list of the files that is included in the archive for storing alongside the backup tarball. I also want to be able to store the error messages ...
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5answers
405 views

performance monitoring

Is there some performace monitoring tool which would run in background gathering info about all system activity? Somethimes my system (Arch linux, 32 bit) slows down terribly and the top utility ...
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2answers
64 views

Monitor when read/write on metadata or mmaped files hit the disk

On a server hosting a wide range of websites, I often see IO becoming a bottleneck without being able to identify the processes responsible of IO operations with tools such as iotop, iostat or sar. I ...
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18 views

I2c with 16 bit addresses

So, i'm trying to interface with a device that has 16-bit addresses, and the master I'm using also supports this mode. However since this isn't standard I2C (should be 8-bit addresses) I haven't been ...
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2answers
25 views

How to know if io stream should stay open or close each time

I have a program that need to write in a file every second. I thought there is a too much overhead if I open and close the file each time. So I decided to keep open the file io stream. But I don't ...
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68 views

dd command: Finding read/write throughput of a flash/SD?

I am running petalinux from sd card. And trying to find data copying rate from Sd card and from QSPI flash that is there on the Xilinx Zynq board. As suggested here , I am doing like this: ...
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2answers
99 views

Tool to show PID and file I/O in realtime

I need to watch a program which modifies some files. I don't know which files the process is modifying_. So I'm looking for a tool that basically outputs a PID, and lista the files being ...
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274 views

Harddrive I/O per Pid

is there any way to see the disk I/O per pid/process ? Monitorix shows me the following and correct me if I´m wrong, but it looks like that the harddrive is slowing down the whole system: UPDATE #1 ...
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5answers
523 views

copy consumed output to stdout when stdout is redirected to a file

Given a command the output of which is being processed by, for example, grep I also want the actual output to be included in the log file for debugging purposes. For example if I have the following ...
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1answer
119 views

What is the recommended way of setting a default IO scheduler on Linux?

I would like deadline to be the default IO scheduler for my system, and I don't want to lose that config when I reboot. What is the proper way of doing that? (I'm using Debian) Some hints: have a ...
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96 views

Unable to close a Luks partition

For backup purposes, I have "snapshotted" a LVM partition. This partition was crypted so I have opened this Luks partition (snapshot) in order to do my backup. The problem is that I have forgotten to ...
2
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1answer
52 views

How to customize or reprogram function of specific keys on my keyboard and the LED on my laptop

When I disable bluetooth on my laptop, the light does not go off and the blinking of the Wi-Fi LED is starting to bother me. Since I sometimes use my laptop in a poor lighting condition an illuminated ...
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1answer
42 views

Copy a file that is in the middle of being written

I have a program that writes to the standard output. It does not write all info at once, it does computation and then writes new bits. The output of the program is being stored in a file. $ ...
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219 views

Poor IO due to LUKS/Software RAID/LVM ordering?

I'm trying to determine if I should re-setup my RAID array due to poor IO performance. First off, the system: i7 920 4 4TB WD 5400 Green drives CentOS 6.3 host Secondly, the disk setup: ...
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3answers
481 views

Can I just disable updatedb?

Is updatedb necessary at all? I never use locate and my servers tend to have dozens of millions of files which usually makes updatedb to run for a long time and consume I/O needed by MySQL and/or ...
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2answers
166 views

why does blktrace only write blocks of 8?

I want to understand the I/O pattern a database is writing to disk to decide how many disks to use for best performance. To analyse the I/O pattern I want to use blktrace and I have to grok it first. ...
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253 views

Why is I/O uninterruptible?

What is the rationale behind making I/O uninterruptible? What would be the negative consequences if a process handling I/O were allowed to handle a signal?
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106 views

jbd2 journal constant i/o

iotop reports a constant i/o about 3% of [jbd2/vda1-8], I think this is the journal manager for ext4. my fstab is: UUID=X / ext4 defaults,noatime,nodiratime 1 1 tmpfs /dev/shm ...
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1answer
561 views

how can I retrieve disk IO utilization in percents on HP-UX

I need to collect data about disk utilization for selected disks. I can use glance-plus monitoring tool to display the current data in percents (it looks similar to top), but I need to collect these ...
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445 views

Is setting a higher nice level for a process an effective way to reduce its impact on system load/CPU time?

I have an rsync cron job which is pushing the server load and triggering monitor alerts. If I set the job to be run with a high nice level, would that effectively reduce the impact it has on system ...
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144 views

IOMMU causing freezes, disabling causes USB to not work

I'm somewhat new to linux, but I'm running a Xubuntu machine that I recently built. Since I started it up, I had noticed frequent freezes, where both the screen (if plugged in) and any SSH session ...
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80 views

Is swapping the cause of high IO on my box?

I'm running a LAMP stack on an Amazon EC2 micro instance with 616 MB of memory. This seems sufficient to be able to run a few small websites with Apache, MySQL and PHP. I have one Wordpress site ...
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3answers
297 views

Amazon EC2 micro instance large number of IO requests

I'm trying to understand why I have a huge number of EBS IO request on my Amazon EC2 micro instance. I launched the instance roughly 6 days ago and has racked up over 4 million IO requests so far. ...
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1answer
3k views

iostat: await vs. svctm

In the iostat manpage I have found these two similar columns: await The average time (in milliseconds) for I/O requests issued to the device to be served. This includes the time spent by ...
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1answer
154 views

Moving a file to a file that is being read

When a file is moved and the destination file already exists and is currently being read, will the operation succeed? Will it depend on how long the reading operation on the destination file lasts?
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2answers
5k views

How to Throttle per process I/O to a max limit?

I'm looking for a way to limit a processes disk io to a set speed limit. Ideally the program would work similar to this: $ limitio --pid 32423 --write-limit 1M Limiting process 32423 to 1 megabyte ...
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332 views

How I/O channels are implemented in Linux kernel?

stdin, stdout, stderr are some integers that index into a data structure which 'knows' which I/O channels are to be used for the process. I understand this data structure is unique to every process. ...
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3k views

Redirecting stdout to a file you don't have write permission on

When you attempt to modify a file without having write permissions on it, you get an error: > touch /tmp/foo && sudo chown root /tmp/foo > echo test > /tmp/foo zsh: permission ...
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1answer
62 views

I/O brings a machine to its knees [closed]

Why, on every Linux I've used, when a program is really I/O bound, it bogs the machine down? It just happened when I (accidentally) tried to make gcc compile a (valid!) 50Mb C file. GCC was so I/O ...
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3answers
76 views

Disallow File IO for a process except for FIFOs

How do you start a process that cannot do any file IO (opening / closing files, creating / deleting files, reading / writing files, etc.), except to read and write to pre-created FIFOs? (chroot will ...
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1answer
101 views

best programming language for I/O intensive tasks [closed]

I need to process "big data" (nearly 1TB which can be partitioned into smaller chunks). Consider several programming languages (Java, Python, C++, Perl) and other scripting options (Perl, awk, sed, ...