How to get I/O usage by process in Unix?

Question

Possible Duplicate:
Linux: Is there something similar to "top" for I/O?

I am trying to do some CPU intensive operation on a Linux machine and it is showing very high load.

I want to figure out if this load is due to I/O or CPU usage. How could I get the percentage of I/O usage by process?

Solution

Try program called "iotop". It shows usage of local disk drives in similar way than "top" for CPU usage. For network traffic there's a tool called "iftop".

Also, if you are uncertain about why the load is high, look at the "IO Wait" column on "top" view. If the CPU time mainly goes to "user" or "system" work, then it's CPU that's the bottleneck, if "IO wait", then disk. Also worth looking are swap numbers - if the physical memory has less than 5% free and/or lot of swap file is used, you might be limited by physical memory.

For example:

top - 17:18:37 up 1 day,  5:20, 19 users,  load average: 0.18, 0.26, 0.35
Tasks: 249 total,   2 running, 246 sleeping,   0 stopped,   1 zombie
Cpu(s):  8.5%us,  2.1%sy,  0.3%ni, 85.4%id,  3.7%wa,  0.0%hi,  0.1%si,  0.0%st
Mem:   8183668k total,  8082464k used,   101204k free,    11148k buffers
Swap: 11847900k total,   248528k used, 11599372k free,  3361444k cached

"us" stands for userspace code, "sy" for system, "id" for idle, "wa" for IO wait.

Comments

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also related: How do I find out what processes are accessing the hard disk in a GNU/Linux-based system?, Good software to monitor disk io, memory and cpu use?, How can I record what process or kernel activity is using the disk in GNU/Linux?

[slhck]

aand: Ubuntu: tool for displaying disk activity in general and by process, What is an XPerf alternative for Linux and Mac OS X?, et cetera.