Useful OS stuff

Change FS scheduler

echo <scheduler> > /sys/block/$disk/queue/scheduler
(http://stackoverflow.com/questions/1009577/selecting-a-linux-i-o-scheduler)

Change hostname

CentOS:
sudo vim /etc/sysconfig/network
reboot

Change window action buttons placement

Ubuntu: bash> gconf-editor 
Then: /apps -> metacity -> general -> button_layout = :minimize,maximize,close

Create service on Ubuntu

1.Run: sudo vi /etc/init/<service-name>.conf

2.Then edit the file with follows:
description "service description goes here"
exec <service-command>

3. Then try it:
sudo service <service-name> start
sudo status <service-name>

Determine OS version

cat /etc/issue /proc/version

Enable or disable CPUs

$start=0
$end=1
$isenabled=0
for i in {$start..$end}; do echo $isenabled > /sys/devices/system/cpu/cpu$i/online; done

Get number of CPUs

grep processor /proc/cpuinfo | wc -l

Remote machine monitoring

In order to watch cpu usage on multiple machines one may use:
watch mussh -h host1 host2 -c vmstat

Or a faster version (runs in parallel):
watch "parallel -- 'ssh host1 vmstat' 'ssh host2 vmstat'"

Remove non ASCII characters from file

tr -cd '[:print:]\n' < infile > outfile

Ubuntu Sources List Generator

In order to generate /etc/apt/sources.list for ubuntu you may use:
http://repogen.simplylinux.ch/