This command summarizes the disk usage across the files and folders in a given directory, including hidden files and folders beginning with ".", but excluding the directories "." and ".." It produces a sorted list with the largest files and folders at the bottom of the list Show Sample Output

This command is useful for finding out which directories below the current location use the most space. It is summarised by directory and excludes mounted filesystems. Finally it is sorted by size. Show Sample Output

This command finds all the files whose status has changed between the ctime of the older and newer . Very useful if you can see from an ls listing a block of consecutive files you want to move or delete, but can't figure out exactly the time range by date.

On systems where your home directory is shared across different machines, your bash history will be global, rather than being a separate history per machine. This setting in your .bashrc file will ensure that each machine has its own history file.

Write 200 blocks of 512k to a dummy file with dd, timing the result. The is useful as a quick test to compare the performance of different file systems. Show Sample Output

Instead of deleting an existing symlink and then re-creating it pointing at the new location, it is possible to perform the same action with this one command. Interesting discussion on whether this is possible to do atomically here: http://answers.google.com/answers/threadview?id=526119

On a machine behind a firewall, it's possible to pass the proxy server address in as a prefix to wget to avoid having to set it as an environment variable first.