University Computer Systems
Linux is segmented into many sub-classes. These sub-classes are called distributions. Distributions are split upon many different features however a good set of features to split distributions (or distro’s) upon is package management. In the Linux world, there are two main forms of package management. One stems from the Red Hat Distro and uses packages called .rpm’s, the other stems from the Debian distribution and uses .deb packages. The Linux systems in University is called CentOS (CentOS Linux release 6.0 (Final)) and is binary compatible with Red Hat Linux, hence it uses packages in the .rpm format.
Choosing your own Linux distribution
It is likely that as a CS student you will have a need to run a Unix OS on your own machine. If you are a Mac user, great, you’re already sorted. If you are coming from the Windows world, I would recommend you choose a Linux distribution and install it locally on your Laptop. This has got a lot easier over the years and is now at a stage that most people’s grandmothers could probably manage an installation. I recommend a guide here which will select an appropriate distro for your needs. As the university systems use .rpm management and CentOS, for 100% compatibility you should go for CentOS however in practise it really doesn’t matter which distro you choose. I am currently running Linux Mint/Mac and I must say, I’ve never had an issue with either (Mac isn’t even based on Linux). Linux Mint is a nice easy drop in Linux system which offers a windows like environment while also offering all the UNIX goodies.
In your Linux travels you may also come across different installation methods with the Ubuntu based distro’s . These will be native install or wubi. I will spend a little time explaining the differences between them.
A native install creates a dual boot configuration. This configuration partitions your Windows Hard drive and creates a Linux Partition and a swap partition. This is the Vanilla install and offers the most speed. At boot time it will give you a menu choice of windows or linux. This is supported by all Linux distro’s. Although better for speed and experience, it also comes with the drawback of being harder to reverse back to a windows only install.
A Wubi install is less persistent. What this install does is it creates a file on your windows computer which is a disk image for Linux. you can boot in and out the same way you would a native install however it is much easier to remove. Wubi can be removed in the same way as any windows program, allowing easy unistallation. Wubi is much better for newcomers to linux as it brings less of a chance to mess up your computer. Wubi will however run slower on your computer due to how it is installed.
Terminal
The terminal program is the main underpinning of any UNIX operating system. Here you are able to issue commands to instruct the OS to carry out certain actions. I will detail some of the most basic commands you may use day to day as a CS student.
| cd | ./ | ls | mv |
| mkdir | cp | rm | !! |
| chmod | find | grep | man |
cd
“cd” changes directory. e.g to move to the ugrads directory at /home/ugrads:
cd /home/ugrads
To go to the home directory use this shortcut:
cd ~/
./
“./” means current directory
“../” means parent directory
Therefore to execure a file called main in the current directory:
./main
ls
The “ls” command is one of the most common commands used. It lists the contents of a directory. Usage is below.
ls
To get a more detailed listing of a directory including permissions, file owners, size and date’s use:
ls -l
You can also add a -h to give a more human readable view of filesizes
ls -lh
You can also show hidden files by adding -a
ls -lah
mv
“mv” is the move command. Much like cut and paste, “mv” will move a file or folder from location1 to location2. It can be used to rename files.
mv location1 location2
mkdir
To create a a directory under the current directory called “java”
mkdir java
To create intermediate directories as required add a -p. e.g:
mkdir -p ~/java/2012/09/26/src
cp
“cp” is the copy command. It copies a file or folder from location1 to location2
cp location1 location2
rm
“rm” is the remove command. Use with caution. Flags to watch out for are -r and -f.
-r = recursive
-f = forcefully
-rf = recursive forcefully
* = everything
therefore:
rm -rf ./* = remove recursively forcefully everything in the current directory
DO NOT USE THIS COMMAND. I include it so you know to steer clear of it.
To remove a file called main.c from the current directory:
rm ./main.c
!!
“!!” means the same as the previous command.
If I type first:
ls
and then decide I wish to add a -l flag I type:
!! -l
This is the same as:
ls -l
chmod
To understand “chmod” you must first understand Linux user permissions. I reccomend Wikipedia.
Linux has 3 types of permission; User, Group and Everyone.
Owner is your permission on a file or directory
Group is the permission assigned to users in the file or directory’s Group
Everyone is the permission that any user on the system has over the file or directory.
Permissions are octal, the values are:
| # | Permission | rwx |
|---|---|---|
| 7 | full | 111 |
| 6 | read and write | 110 |
| 5 | read and execute | 101 |
| 4 | read only | 100 |
| 3 | write and execute | 011 |
| 2 | write only | 010 |
| 1 | execute only | 001 |
| 0 | none | 000 |
To give rwx permissions to Owner, Group and Everyone on someFile or folder:
chmod 777 someFile
To only allow the Owner access read and execute access to a file or folder:
chmod 500 someFile
To give the Owner full access and Group read access:
chmod 740 someFile
I recommend you set your home directory to only allow you access:
chmod 700 -R ~/
The -R makes changes recursively
find
The “find” command finds files in the directory structure. To find all files ending in .c (C source files) in the current directory and below:
find ./ -name "*.c"
To find a file you know the name of (e.g. myAwesomeProgram.o):
find ./ -name "myAwesomeProgram.o"
You can use Regular Expressions to find any file using this style syntax.
grep
“grep” makes heavy usage of Regular Expressions to locate files which contain a match to a given pattern. “grep” searches internally in files.
The usage of grep is as such:
grep "regular expression pattern" locationToFiles
If you know a chunk of text inside a file but don’t know which file contains the text, grep is your new best friend. It’s extremely useful for debugging log files.
e.g. I know there is a C source file which imports stdlib.h in my current folder but can’t remember which file. I search for string “# import <stdlib.h>”. I can use grep to find the location of this file.
grep "#include <stdlib.h>" ./*.c
man
The “man” command is probably the most important command of all. “man” gives you the manual pages for other commands. I have given an extremely brief overview of some useful commands and their usage. Each of these commands can be used in extremely complex ways to solve different problems and can be used together by piping input between commands. If you ever need to reference how to use a particular command just type
man <command>
So to open the manual for grep, type:
man grep
Press the q character to return to the terminal.
Text Editors
The war of which text editor is best is a long and everlasting battle. Personally I use nano/pico however every programmer has different preferences. The main ones are:
Terminal:
Graphical:
Tips/Tricks
This is a small section of standard tricks I use to speed up my life as a Computer scientist. I have only added one trick for now as I’m bored of writing guides however in time I’m sure this section will expand.
.bashrc
The “.bashrc” file is a magical file that is run every time your terminal loads. As such it is a great time saver as you can run certain commands every time you login.
The .bashrc file is located at “~/.bashrc”. It is a hidden file (hence having the full stop in front of it’s name). You can add any command you wish to be run at startup. Please note, on the mac the .bashrc file is replaced with the .bash_profile file.
To add a text based welcome message:
echo "echo Welcome" | cat >> ~/.bashrc
To add a custom ascii art welcome message create a text file filled with ascii art called .art located at ~/.art and type:
echo "cat ~/.art" | cat >> ~/.bashrc
To add aliases add an alias line to the end of the .bashrc file. e.g
echo "alias snowy='ssh username@snowy.cs.bris.ac.uk'" | cat >> ~/.bashrc
You can edit this file manually with a text editor like:
nano ~/.bashrc
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Mortensson out 🙂