4921662 Introduction to Linux 2

8/6/2019 4921662 Introduction to Linux 2

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Introduction to Linux

Lei Zhang

UCLA Linux Users Group

http://linux.ucla.edu/~leiz/linuxintro.ppt


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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 beendeveloped ever since


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Why Use Linux?

Multi-Tasking / Multi-User

Stability / Reliability

Portable

Comes with a complete development

enviroment (C, C++, Fortran, Java, Perl,Python, etc...)


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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


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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


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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


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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


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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


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Tree Structure/

/bin

/boot

/dev

/etc

/home/lib

/mnt

/opt

/proc

/root

/sbin

/tmp

/usr

/usr/bin

/usr/lib

/usr/sbin/var

root directory

essential user programs

kernels and boot loader

device files

configuration files

home directories essential libraries and kernel modules

mount point for other filesystems

addon (optional) software

system internals

the root user's home directory

essential system binaries

temporary files

user programs (not as essential)

| similar hierachy to root dir

various other files (lo s, mail, etc)


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Types of files

Everything is a file!

Ordinary files - text, data or programs

Directories - contain other files/directories

Links - pointers to other files

Special filesDevices - represent hardware (e.g. /dev/fd0)

Others - pipes, sockets


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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


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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


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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$


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Command Line Cycle

Display Prompt

User types command and enter

Shell executes the command


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Getting Help (The Manual)

Man command

man sections:

e.g. man 3 printf

n. New

8. System Management7. Miscellaneous

6. Games5. File Format + conversion

4. Devices3. Library Calls

2. System Calls1. User Commands


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ls output

Permissions

links

owner

owners group

size of file/dir date of last modification

name of file/dir


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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


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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


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Examples of permissions

-rw-r--r-- foo

dr-xr-xr-x bar

-rwxr-xr-- prog.c

lrwxrwxrwx prog


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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

e.g. chmod a+x foo

e.g. chmod 644 bar


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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


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Wildcards and Filename

completion The wildcard character is * and matches

zero or more characters.

*.txt = all files that end in .txta* = 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


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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


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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


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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


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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


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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


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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


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The End

(For Now)

4921662 Introduction to Linux 2

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