All students are allocated a certain amount of disk space on the file system for their personal files, usually about 5 Megabytes (equivalent to 4 floppy disks worth). If you go over your quota, you are given 7 days to remove excess files. [Ignore the numbers; they're out-of-date. The flavor is correct, though.]
To check your current quota and how much of it you have used, type
% quota -v
The df command reports on the space left on the file system. For example, to find out how much space is left on the fileserver, type
% df .
The du command outputs the number of kilobytes used by each subdirectory. Useful if you have gone over quota and you want to find out which directory has the most files. In your home-directory, type
% du
This compresses a file. For example, to zip science.txt, type
% gzip science.txt
This will zip the file and place it in a file called science.txt.gz
To unzip the file, use the gunzip command.
% gunzip science.txt.gz
The bzip2 and xz programs work analogously, but are a slower and compress a bit better, with xz being more extreme in both cases.
file classifies the named files according to the type of data they contain, for example ascii (text), pictures, compressed data, etc.. To report on all files in your home directory, type
% file *
The shell keeps an ordered list of all the commands that you have entered. Each command is given a number according to the order it was entered.
% history (show command history list)
% !! (run last command)
% !-3 (run third most recent command)
% !5 (run 5th command in list)
% !grep (run last command starting with grep)
% grep !$ (run grep with the same argument as the last command)