Ubuntu For Free

Occasionally I forget to use the nicecommand. Linux is kind enough to allow us to change the nice level of a process that’s already running, by using the snice command. It’s very easy to use and much quicker than stopping and restarting the process.

Let’s say I have mpeg2enc encoding a video, and after 10 minutes, I realize I forgot the nice command. It’s going to take another hour or two, but I don’t want to waste the 10 minutes I’ve already spent working on the video. No fear!

The command below will save me:

sudo snice -5 mpeg2enc

You’ll notice that I prefixed the line with the sudo command. snice requires sudo privilege for a nice level of anything below zero.

Exploiting the shell’s capabilities can be fun and very helpful. Using the shell, I’ll often want to chain commands together. While you may already be familiar with using the semicolon to call commands in the order they were typed on the command line, the shell provides two “constructs” that permit some related, yet very specific behaviors. These constructs are more powerful than simply running commands in a sequence. They allow us to perform a command based on the success or failure of the prior command, and they’re both very easy to use.

The first construct is the double ampersand, &&. When combined with commands on both sides of the double ampersand, the second command will only be executed if the first command was successful. For example, I’ll often execute something like this:

nice unrar e mymoviebackup.rar && rm mymoviebackup.rar

This will delete the original archive, but only if the extraction was successful. On the converse, I may want a command to execute, but only if the first previous command failed. Using the double pipe to separate two commands allows me to do just that.For example,

cp mysysbackup.tar /media/usbdisk1/mytapebackup.tar || touch ~/Desktop/BackupFailed

The above commands works like this : If the copying of mysysbackup.tar to my external drive fails, create or update a file on my desktop that advises me of the failure.