When you run a memory intensive application (VirtualBox, large java application, etc) swap area is used as soon as memory becomes insufficient. After you close the program, the data in swap is not put back on memory and that decreases the responsiveness. Swapoff disables the swap area and forces system to put swap data be placed in memory. Since running without a swap area might be detrimental, swapon should be used to activate swap again.

Both swapoff and swapon require root privileges.

helps you keep watch on the load of a system, without having to stare constantly at the terminal. The -d argument to watch highlights the difference from the last run, making it easier to note how the load is fluctuating. The sed command just strips off the information about how long the box has been up, and how many users are logged in.

Mount an smb share with this command. other options -ousername=$USERr,gid=$groupname,scope=rw

The arguments of "seq" indicate the starting value, step size, and the end value of the x-range. "awk" outputs (x, f(x)) pairs and pipes them to "graph", which is part of the "plotutils" package.

Displays six rows and five columns of random numbers between 0 and 1. If you need only one column, you can dispense with the "for" loop.

This example calculates the averages of column one and column two of "file.dat". It can be easily modified if other columns are to be averaged.

I use this to convert mp3 files to m4a files that can be used as ringtones on the iPhone. I've documented the process here: http://www.control-d.com/?p=60

Takes filenames and directory names and replace space to '_'.

The queryformat option can be used in a number of ways to find things like duplicate packages, wrong arch, or the exact package to pass to rpm -e, yum remove, etc.

Another combination of seq and awk. Not very efficient, but sufficiently quick.

"seq 100" outputs 1,2,..,100, separated by newlines. awk adds them up and displays the sum.

"seq 1 2 11" outputs 1,3,..,11.

Variations:

1+3+...+(2n-1) = n^2

1/2 + 1/4 + ... = 1

Leading zeros might help correct sorting and they can be removed by sed after sorting

Does not necessarily require a file to process, it can be used in a pipe as well:

I don't remember where I copy/pasted this from, I wish I credited the original author

Replace < pw-length > with the desired password-length.

The password-length is not always correct, but wayne...

verifry if link detected or no and speed of network.

-N removes header

-s removes separator chars

-r raw output

After using these options, the MySQL ouptut can be used with pipes very easily