Introduction to Linux
Lei Zhang UCLA Linux Users Group
http://linux.ucla.edu/~leiz/linuxintro.ppt
What is Linux?
UNIX-like Operating System Developed by Finnish computer science student Linus Torvalds as an OS project in 1991. Made available on the net and has been developed ever since
Why Use Linux?
Multi-Tasking / Multi-User Stability / Reliability Portable Comes with a complete development enviroment (C, C++, Fortran, Java, Perl, Python, etc...)
Why Use Linux?
It's Free Software
Free as in beer Free as in speech
It's Open Source
You can see the source code You can modify the source code
Users in Linux
Every User has: username, group(s), password, home directory Root User vs Regular User
Root == Administrator == God
Use sparingly, only when necessary Remember, it's your bed, don't Sh** in it
Regular Users
Limited privileges
Home Dir and Path
Home Directory
Location of user files Start point when logging in
Path
Used to search for commands Colon separated e.g. /usr/bin:/bin:/usr/X11R6/bin
The filesystem (fs)
Linux supports many filesystems
Native fs (ext2, ext3, reiserfs, etc)
UNIX permissions, links, special devices
Microsoft fs (fat, ntfs)
Read/write support for fat, readonly for ntfs
Network fs (nfs, smb, afs, etc)
Support for accessing files on other computers
Structure of fs
The fs is conceptualised as a tree / is the root directory and everything is a subdirectory of it branching downwards Other drives are attached to the tree
No C drive Attach other filesystem using the mount and umount command
umount is the unmount command, not a typo Normally only root can (un)mount
Tree Structure
root directory / essential user programs /bin kernels and boot loader /boot device files /dev configuration files /etc home directories /home essential libraries and kernel modules /lib mount point for other filesystems /mnt addon (optional) software /opt system internals /proc the root user's home directory /root essential system binaries /sbin temporary files /tmp user programs (not as essential) /usr /usr/bin | similar hierachy to root dir /usr/lib /usr/sbin various other files (logs, mail, etc) /var
Types of files
Everything is a file! Ordinary files - text, data or programs Directories - contain other files/directories Links - pointers to other files Special files
Devices - represent hardware (e.g. /dev/fd0) Others - pipes, sockets
The Linux User Interface
Command line interface (CLI)
Command line type commands at a prompt Can be more flexible / powerful
Graphical user interface (GUI)
Point and click windows interface Familiar / easy to use
The GUI
X Window System
underlying graphics system
Desktop Environments (the actual GUI)
e.g. KDE, GNOME
Useful Apps
Konsole runs a shell (the CLI) OpenOffice wordprocessor/spreadsheet Mozilla Web Browser Gaim AIM / MSN / Yahoo IM client
The Shell (CLI)
Command Interpreter Runs programs on the user's behalf varieties csh, tcsh, bash, zsh, etc
Bash is the most popular
The prompt e.g.
user@computer:/current_dir$
Command Line Cycle
Display Prompt User types command and enter Shell executes the command
Getting Help (The Manual)
Man command man sections:
1. User Commands 3. Library Calls 5. File Format + conversion 7. Miscellaneous n. New 2. System Calls 4. Devices 6. Games 8. System Management
e.g. man 3 printf
ls output
Permissions links owner owners group size of file/dir date of last modification name of file/dir
Permissions
Multi-user OS needs access mechanism for files Each file/dir has permissions for its owner, its owners group and everyone else on the system (u,g,o) The permissions are for the ability to read, write and execute a file/dir
RWX
Output of ls -l if permission is on a letter appears if it is off there will be a minus sign (-) first one is - for a file or d for dir next 3 are the users perms next 3 are the groups perms last 3 are everyone else's perms
Examples of permissions
-rw-r--r-dr-xr-xr-x -rwxr-xr-lrwxrwxrwx foo bar prog.c prog
Changing permissions
Chmod command - has 2 modes
number (convert bits to decimal number)
directly set the permission read = 4, write = 2, execute = 1 e.g. 750 is equivalent to rwxr-x---
add/remove perms: {a,u,g,o} {+,-} {r,w,x}
chmod permission <filename>
e.g. chmod a+x foo e.g. chmod 644 bar
Navigation
Absolute - full pathnames (/) Relative - pathnames relative to were you are in the fs (. .. ~) Shortcuts
. is current directory .. is the parent of current directory
~ is your home directory
Wildcards and Filename completion
The wildcard character is * and matches zero or more characters.
*.txt = all files that end in .txt a* = all files that start with the letter a d*.c = all files that start with d and have .c at the end
Filename completion - type first few characters of a file/command and press tab, the shell will fill in the rest
Basic commands
cd change directory
e.g. cd /usr/bin
cp copy files
e.g. cp ~/cs111/source.c /mnt/floppy
mv move files
e.g. mv /tmp/mystuff/* ../somewhere
rm remove files
e.g. rm ee115c/hwk*
mkdir, rmdir make and remove directories
Standard input/output
3 special file handles for input/output of programs
standard input (stdin) file handle 0 standard output (stdout) - file handle 1 standard error (stderr) - file handle 2
By default for programs:
stdout and stderr are the screen stdin is the keyboard
Pipes
The pipe character is: | The output of the command on the left of the pipe becomes the input to the command on the right
ls | wc -l output of ls as input to wc
Can create complex commands to perform difficult tasks
Processes
ps command lists processes on the system
e.g. ps auwx shows all processes running on the system at the time
Processes can be killed
Using the kill command
You must be owner of process, or root e.g. kill 500 will kill process #500 Can also be used to send processes signals
Compiling Programs
gcc GNU C Compiler Simple compiler usage
gcc o hello hello.c
Compile only
gcc c hello.c gcc c functions.c
Link files together
gcc o newhello hello.o functions.o
Run the program
./hello
Network Utils
ping - tells if a machine is on the network
e.g. ping www.ucla.edu will keep sending packets until CTRL + C
traceroute - shows all points between machine and machine you are looking for
e.g. traceroute www.yahoo.com shows all the hops to yahoo
netstat - show network connections
The End
(For Now)
