Thursday, September 24, 2009

I/O usage per process on Linux

Linux kernel 2.6.20 and later supports per process I/O accounting. You can access every process/thread's I/O read/write values by using /proc filesystem.

You can check if your kernel has built with I/O account by just simply checking /proc/self/io file. If it exists then you have I/O accounting built-in.

$ cat /proc/self/io
rchar: 3809
wchar: 0
syscr: 10
syscw: 0
read_bytes: 0
write_bytes: 0
cancelled_write_bytes: 0

Field Descriptions:

rchar  - bytes read
wchar  - byres written
syscr  - number of read syscalls
syscw  - number of write syscalls
read_bytes  - number of bytes caused by this process to  read
            from underlying storage
write_bytes - number of bytes caused by this process to written from
            underlying storage

As you know, ever process is presented by it's pid number under /proc directory. You can access any process's I/O accounting values by just looking /proc/#pid/io file.

There is a utility called iotop which collects these values and shows you in like top utility. You see your processes I/O activity with iotop utility.

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