Find out what processes are writing to hard drive

Question

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 CPU and memory.

Solution 1

iotop (simple top-like I/O monitor) is a good tool for what you want. It also allows one to display the accumulated amount of I/O on any of the DISK READ, DISK WRITE, SWAPIN, and IO (overall percentage). This is through a nifty interface:

• You just press a on the keyboard, and it will sort the hungriest processes on top.
• Reversing the order, you just press r.
• If you want to sort by other colums, you just press the left/right key.

Like top, the presentation is rather busy. Another thing is that it doesn't have the myriad options that top has (e.g. I can't chose to hide any of the columns I'm uninterested in), but the tool is more than good enough for its specific purpose.

Solution 2

You can use lsof (man lsof). The following will return a list of all files that are open for writing:

lsof | grep -e "[[:digit:]]\+w"

Solution 3

Especially for low disk activity, it is necessary to use iotop in batch mode, to prevent short access lines from disappearing quickly. The answer by How do I log file system read/writes by filename in Linux? shows how to do this.

So far iotop is the best overall solution. The following command gives you a real-time output of all the processes using the disk.

iotop -bktoqqq -d .5

where: -b     is batch mode
       -k     is kilobytes/s
       -t     adds timestamp
       -o     only show processes or threads actually doing I/O
       -qqq   removes output headers
       -d .5  updates every .5 seconds

Once you have the process id, you can also find the files with

 lsof -p $PID

Solution 4

Use strace.

View more solutions

Comments

[Gilles 'SO- stop being evil']

That's going to tell you what a particular process is doing, it won't help to find which process is doing something.

[Gilles 'SO- stop being evil']

Powertop is also useful to find what's using up the battery on a laptop; iotop is still the first place to look for disk accesses.

[psusi]

What files are open, and what files are actually being accessed are two different things.

[James Sumners]

@psusi An open file for writing is very likely being "accessed." Also, more information can be retrieved by learning lsof via its manpage.

[psusi]

Files open for writing may be written to at some point, but not necessarily right now. Many files are kept open but are rarely written to. On the other hand, the files being written to may be opened and closed quickly and so won't show up in lsof. Either way, it is of little help figuring out what process is actually writing to the disk at the moment.

[Martijn]

The w from the command above make you grep for files that are open for writing only. Files open for writing and reading (u) will not be displayed, but they can also be written to. If you'd like to see files open for write and for read+write, I believe this is what you're looking for: lsof | grep -e "[[:digit:]]\+[wu]\{1\}"

[Admin]

@Martijn You'll want to use grep -e**w** to avoid matching [0-9]\+[wu] inside another columns

[voices]

@user84010 What's the whole command that you're suggesting?

[Stephen Rauch]

How does this answer differ from the above (very old) answers? It is good when answering an old question to explain how your answer differs from previous answers. This helps reader sort among the answers.

[Frank Breitling]

Thanks for pointing this out. I have edited this answer taking your comment into account.

[Marcin Orlowski]

one can pass -o (--only) to actually filter out all the tasks not doing any I/O. This makes the list less crowded

[codenoob]

Is there a way to show activity only on a particular mount/disk? I can't find such.