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Friday, December 30, 2011

How effectively use Linux system tools to find out the default Linux kernel I/O scheduler

In many troubleshooting situation we overview and check large numbers of logs generated by one or another application. Kernel is nothing special here. The kernel log files can  usually be found under /var/log/kern.log.

How to find out and confirm all names of the used io kernel scheduler in the last several reboots.

$ zcat kern.log.3.gz  | egrep 'io scheduler.*\(default\)' 
Oct  8 22:20:16 udesktop kernel: [    0.888090] io scheduler cfq registered (default)
Oct 10 20:30:33 udesktop kernel: [    0.688367] io scheduler cfq registered (default)
Nov  3 23:31:05 udesktop kernel: [    0.872053] io scheduler cfq registered (default)

$ zcat kern.log.1.gz  | egrep 'io scheduler.*\(default\)' | sed -r 's/ +/ /g' | cut -d' ' -f10 | sort | uniq

We first grep for the names of the configured io scheduler. Next we pars it trought sed to repalce all multi space string with a single space and at the end we cut of the scheduler name.

Choosing an I/O Scheduler for Red Hat® Enterprise Linux® 4 and the 2.6 Kernel

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