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.
Questions tagged [io]
620 questions
175
votes
7 answers
Can I watch the progress of a `sync` operation?
I've copied a large file to a USB disk mounted on a Linux system with async. This returns to a command prompt relatively quickly, but when I type sync, of course, it all has to go to disk, and that takes a long time.
I understand that it's going to…
mattdm
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137
votes
7 answers
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 denied: /tmp/foo
Sudoing doesn't help, because it runs the command as…
Michael Mrozek
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87
votes
7 answers
How can I read line by line from a variable in bash?
I have a variable which contains multiline output of a command. What's the most effecient way to read the output line by line from the variable?
For example:
jobs="$(jobs)"
if [ "$jobs" ]; then
# read lines from $jobs
fi
Eugene Yarmash
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83
votes
2 answers
When is dd suitable for copying data? (or, when are read() and write() partial)
Short version: In what circumstances is dd safe to use for copying data, safe meaning that there is no risk of corruption due to a partial read or write?
Long version — preamble: dd is often used to copy data, especially from or to a device…
Gilles 'SO- stop being evil'
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75
votes
5 answers
How portable are /dev/stdin, /dev/stdout and /dev/stderr?
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., and this "seems to do the right thing". But, for…
kjo
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72
votes
12 answers
What's the philosophy behind delaying writing data to disk?
In Linux, a finished execution of a command such as cp or dd doesn't mean that the data has been written to the device. One has to, for example, call sync, or invoke the "Safely Remove" or "Eject" function on the drive.
What's the philosophy behind…
marmistrz
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52
votes
1 answer
Why is most the of disk IO attributed to jbd2 and not to the process that is actually using the IO?
When monitoring disk IO, most of the IO is attributed to jbd2, while the original process that caused the high IO is attributed a much lower IO percentage. Why?
Here's iotop's example output (other processes with IO<1% omitted):
Sparkler
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51
votes
5 answers
Determining Specific File Responsible for High I/O
This is a simple problem but the first time I've ever had to actually fix it: finding which specific files/inodes are the targets of the most I/O. I'd like to be able to get a general system overview, but if I have to give a PID or TID I'm alright…
Bratchley
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50
votes
5 answers
Find out what processes are writing to hard drive
On my Lenovo T400 and Ubuntu, the light for hard drive writing keeps flashing. I was wondering if in Linux it is possible to find out what processes are doing I/O to the hard drive? Just like by top, you can find out what processes are using most…
Tim
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43
votes
1 answer
How to get total read and total write IOPS in Linux?
How do I get read and write IOPS separately in Linux, using command line or in a programmatic way? I have installed sysstat package.
Please tell me how do I calculate these separately using sysstat package commands.
Or, is it possible to calculate…
shas
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41
votes
5 answers
Measure pipe throughput in the shell
There is a shell command that allows you to measure how fast the data goes through it, so you can measure the speed of output of commands in a pipe. So instead of:
$ somecommand | anothercommand
you can do something like:
$ somecommand | ??? |…
Alex B
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40
votes
4 answers
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 per second hard drive writing speed.
Sepero
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40
votes
2 answers
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
mount my home directory from server to my laptop.
If I…
ungalnanban
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34
votes
5 answers
How to redirect stdout to a file, and stdout+stderr to another one?
How can I achieve
cmd >> file1 2>&1 1>>file2
That is, the stdout and stderr should redirect to one file (file1) and only stdout (file2) should redirect to another (both in append mode)?
Swarna Gowri
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34
votes
4 answers
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?
Will it speed up bulk reads and writes?
Where…
Matan
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