Using the Linux Desktop

1
Using the Linux Desktop

• In this lecture you will learn
• How to navigate a Linux desktop
• How to add and remove software
• How to use essential command line tools
• and the basics of Linux programming

2
First Steps

• Starting desktop applications
• Click the 'Applications' menu bar
• Under 'Accessories', find 'Text Editor'
• Click on it.
• Now try to find and run Firefox
• Go to OpenMigration.net

3
Installing applications

• Click on the 'System' tab at the upper left hand
  corner of the screen
• Under 'Administration', click on 'Synaptic
  Package Manager'
• Search for 'kenolaba'
• Click on it and select 'mark for installation'
• Hit the 'apply' button

4
Using the terminal

• To start the terminal, go to
  Applications-gtAccessories-gtTerminal
• To run an application, type its name, then its
  arguments, then hit enter
• Try it out with 'ls'. It will print a list of the
  contents of the current directory.

5
Special Characters

• Tabs are used for automatic command completion
• is the 'wildcard' character
• 'command ' runs command in the background
• 'command gt filename' pipes the output of command
  to filename
• 'command1 command2' pipes the output of
  command1 to the input of command2
• '' references the current user's home directory

6
Basic Commands

• Use 'man commandname' to find out more about a
  command
• Use 'apropos keywords' to find commands related
  to the keywords
• 'sudo command' allows you to run command as root

7
Aside root

• On every Linux machine, there is a user named
  root
• root is a user with total privilege- ie, they can
  run any program, edit any file, format any disk
• root powers can turn an innocent mistake or minor
  mischief into an absolute disaster
• Use root only as absolutely necessary

8
File Commands

• 'ls' lists the current directory
• 'cd directory' changes the current directory to
  directory
• 'find name' finds files by name
• 'rm filename' removes filename
• 'mkdir name' makes a directory called name
• 'cp name destination' copies file to destination
• 'mv name destination' moves file to destination

9
File Commands II

• 'chmod options filename' changes the file
  permissions on filename
• 'chown username filename' makes username the
  owner of filename
• 'chattrs options filename' changes extended file
  attributes on filename

10
Aside permissions

• File permissions are a fundamental part of Linux
  security
• Base file permissions are read(4), write(2), and
  execute(1), and are set for the owner, owning
  group, and everybody else
• Ex 'chmod 754 test.txt' marks test.txt readable,
  writeable, and executable by its owner, readable
  and executable by members of the owning group,
  and readable by everyone else

11
Process Control

• 'ps' lists processes and has a LOT of options-'ps
  -aux' and 'ps axjf' are the most common
  invocations
• 'pgrep expression' uses a regular expression to
  match processes
• 'top' interactively lists the top processes
• 'kill' sends signals to running processes

12
Linux Directory Structure

• It makes sense, I promise- just not at first.
• The top of the hierarchy is called '/'- Linux
  doesn't use '\'
• There are no such things as drive letters- it's
  one big tree.
• Files are separated by what they do, not where
  they came from

13
Linux Directory Structure II

• User stuff goes in /home
• Variable data goes in /var
• User applications go in /usr
• System binaries go in /bin
• System static binaries go in /sbin
• System libraries go in /lib
• Configuration files go in /etc

14
Linux Directory Structure III

• Just about everything in Linux is a file.
• There are several special directories for special
  'files'
• /proc stores data about the running system,
  including hardware configuration and process
  data.
• /dev stores all device pseudo-files, including
  hard disks, CD-ROMs, and terminals.

15
Linux Directory Structure IV

• A handful of useful commands
• 'mount device directory' adds the device's
  filesystem below the named directory
• 'umount device' reverses the above
• 'fdisk device' formats the device
• 'du filename' determines the amount of disk space
  occupied by the file

16
Programming on Linux

• Linux programming can be very different from
  programming on Windows
• Heavy use of free external libraries and
  utilities
• Very little static compilation
• Reliance upon coding standards
• Configuration files vs registry
• IDEs vs command line tools

17
GCC

• GCC- Gnu Compiler Collection
• Part of the build-essentials package
• Basic C invocation 'gcc filename'
• Simple C invocation 'g filename'
• Java invocation 'gcj filename'
• Also supports Fortran, Ada, and others

18
GCC II

• Substitute the appropriate compiler, ie, g for
  C
• Multiple source files 'gcc source1 source2'
• Named output file 'gcc source -o output'
• Debugging symbols 'gcc -g source'
• Compile but do not link 'gcc -c source'
• Report all warnings 'gcc -Wall source'
• Optimize by size 'gcc -Os source'
• Optimize lots 'gcc -O3 source'

19
Scripting

• Start every script with '! /path/to/interpreter'
• Some consider '! /usr/bin/env interpreter' a
  more portable alternative
• Common languages include Bash shell, Python,
  Perl, and PHP
• Make sure to mark scripts executable 'chmod x
  file'

20
Debugging

• GDB- the Gnu DeBugger
• Must compile with the -g option 'gcc -g code'
• Invoke with 'gdb /path/to/executable'
• Use strace to trace system calls
• Standard invocation 'strace filename'
• Use gcov/gprof for coverage and profiling
• If in doubt, -v and -

21
Further Reading

• OpenMigration.net/downloads.html
• For desktop help, try the official Ubuntu book,
  available at Books-A-Million or free online
• For a more in-depth look, try the Ubuntu Linux
  Toolbox, a handy (but non-techical) look at
  practical Ubuntu
• For help with writing code for Linux, try The
  Definitive Guide to GCC and Advanced Programming
  for the Linux Environment.