Welcome to Linux

1
Welcome to Linux

• A quick overview of some ideas and commands of
  most frequent use to programmers using Linux

2
Two interface options

• The modern graphical desktop interface
• Objects are represented as colorful icons
• Users operate mainly by clicking the mouse
• Its intuitive (like Macintosh or Windows)
• The legacy command-line interface
• Objects are accessed by their file-names
• Users operate by typing in commands
• Its flexible and powerful, but demands
  knowledge!

3
Toggle between interfaces

• If your workstation is configured for the
  Graphical Desktop Interface by default (also
  known as runlevel 5), it is easy to switch to
  the Command-Line Interface by typing a
  keystroke-combination
• ltCNTRLgtltALTgt-Fn (for n 1, 2, ..., 6)
• You can return to your Graphical Desktop by
  typing ltALTgt-F7

4
All Linuxs objects are files

• All ordinary files are sequences of bytes
• Some store data, others store programs
• Also there are some special files (such as
  directories, device-files, and pseudo-files)
• Each file has a unique name
• Each file has a specific owner
• Each file has a set of access permissions

5
File permissions
Owner
Group
All
r
w
x
r
w
x
w
w
x
Legend r read access
(1 yes, 0 no) w write access (1 yes, 0
no) x execute access (1 yes, 0 no)
Bitmap-example 110-100-100 Octal
representation 0644 ASCII-representation
rw-r--r--
6
Directory Tree
/
/var
/usr
/etc
/bin
/boot
/home
Linux organizes its hundreds of thousands of
files into a tree-like hierarchy.
For a current Linux installation (such as Fedora
Core 5), the topmost directory (named
/) will typically contain only about two-dozen
sub-directories.
7
Directory Tree
/
/var
/usr
/etc
/bin
/boot
/home

/root
/parr
/brooks
/cruse
superuser
The /home directory contains a sub-directory
for each authorized user.
8
Directory Tree
/
/var
/usr
/etc
/bin
/boot
/home

/System.map
/vmlinuz
/grub
compressed kernel
The /boot directory contains the files and
directories that are needed to select, load,
decompress, and begin executing the Linux kernel
9
Directory Tree
/
/var
/usr
/etc
/bin
/boot
/home

/X11
/hosts
/fstab
/inittab
The /etc directory stores files concerned with
the systems configuration-options.
10
Directory Tree
/
/var
/usr
/etc
/bin
/boot
/home

/mkdir
/chown
/kill
The /bin directory contains about a hundred of
the most necessary and basic binary-executables
(such as the programs which implement the minimal
set of commands you need for system-recovery in
the unlikely event of a crash ).
11
Directory Tree
/
/var
/usr
/etc
/bin
/boot
/home

/local
/lib
/src
/include
/bin
The /usr directory contains about a dozen
sub-directories which organize the vast majority
of the various kinds files needed for a useful
work-environment. Together these sub-directories
contain tens of thousands of files and programs.
12
Directory Tree
/
/var
/usr
/etc
/bin
/boot
/home

/lock
/log
/spool
The /var directory contains about two-dozen
sub-directories that pertain to various
value-added resourses (such as system log-files
or users email).
13
Unique filenames

• To give each file a name thats unique, the
  directory-tree hierarchy is utilized

/
/home
/brooks
/cruse
/hello
/hello
/home/cruse/hello
/home/brooks/hello
14
The online manual

• Linux offers online documentation for all of its
  commands (and for its library functions)
• You type man ltcommand-namegt to view the
  relevant page of this online manual
• Example man ls view ls options
• Some commands have numerous options that are
  explained (but seldom illustrated)

15
Command-usage examples ls

• The LiSt command ls
• ls files in present working directory
• ls / files in the topmost (root) directory
• ls files in YOUR home-directory
• ls l files with their attributes
• ls a files (all including the hidden
  ones)
• ls .c files having the .c filename-suffix
• ls files in every immediate sub-directory
• ls .. files in the parent-directory
• ls my files whose names begin with my

16
My own top-30 commands

• cd Change Directory
• cp CoPy file (or files)
• mv MoVe file (or files)
• rm ReMove file (or files)
• rename RENAME a file (or files)
• who who else is using station
• mkdir MaKe a new DIRectory
• rmdir ReMove DIRectory

17
My top-30 (continued)

• scp Secure CoPy
• ssh Secure Shell
• lpr Line-Printer
• cat conCATenate file(s)
• grep global reg-expr printer
• uname -r shows kernel-release
• ln s creates a soft link

18
My top-30 (continued)

• vi VIsually edit a text file
• gcc Gnu C Compiler
• g Gnu C compiler
• as Assembler
• ld Linker
• make compile-and-link script
• objdump -d disassemble program

19
My top-30 (continued)

• tar uncompresses a file
• diff compares two textfiles
• exit terminates a user-session
• time time a programs execution
• chmod change files access-mode
• su Substitute User
• more view textfile page-at-a-time

20
Recommend keeping a journal

• Some notes I find useful for reference
• For extracting a new Linux kernel release
• tar xvf linux-2.6.16.6.tar
• For combining several files of a new project
• tar cvf linux-2.6.16.6.tar

21
Some practice exercises

• Switch from your Graphical Desktop to a Text-Mode
  Console Interface (6 choices)
• Switch from one text-console to another
• Login to that console
• Type the ls command
• Log out from that console
• Return to your Graphical Desktop

22
Some exploration exercises

• Use cat to look at one of the hidden files in
  your own home directory, like this
• cat .bash_history
• Use ls to look at the names of all the files in
  your own Desktop directory, like this
• ls -a Desktop
• Use cd to change your current directory to the
  root directory, like this
• cd /

23
An advanced exercise

• Create a subdirectory named bin in your own
  home directory, like this
• cd is your home-directory
• mkdir bin creates bin sub-directory
• Copy a program-file from a class-website, then
  compile it, move the executable into your /bin
  subdirectory, and finally execute it, like this
• cp /home/web/cruse/cs630/dump.cpp .
• g dump.cpp -o dump
• mv dump bin
• dump dump.cpp