Transcript Introduction to *nix Systems

Introduction to *nix Systems
HKOI Training Team
Sidney Fong
Overview of this presentation
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What to expect
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Brief introduction to UNIX-like systems
Brief history of Linux
Introduction to basic Linux commands and
environment
Linux as competition environment
What not to expect
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Detailed instructions on how to install Linux
Setting up Linux as a server
What is *nix?
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“*nix” refers to a class of UNIX-like operating
systems
The term “UNIX” is sometimes used to refer to *nix
systems
Examples of *nix systems:
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Linux (or GNU/Linux)
BSD (FreeBSD, NetBSD, OpenBSD, etc)
Solaris
Mac OS X (Darwin)
GNU Hurd
Typical Features of *nix Systems
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Geared towards being a “server” / “networking” OS
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Multi-user
Multi-tasking
Tends to focus more on command line interface
The Unix Philosophy
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Write programs that do one thing and do it well
Write programs to work together
Write programs to handle text streams, because that is a
universal interface
Linux - Overview
For the rest of the
session, we will focus
on Linux
Important Figures
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Linus Torvalds
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Creator of Linux Kernel
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Richard M. Stallman
(RMS)
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Founder of GNU and
the Free Software
Movement
Names
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Pronunciation of “Linux”
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Pronunciation of “GNU”
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“guh-noo” ( /gnu/ )
GNU
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“lee-nix” ( /linəks/ )
recursive acronym for “GNU’s not UNIX”
“Linux” vs “GNU/Linux” debate
The GNU Project
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Started by RMS to create a complete UNIX-like
system in 1983
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Ideology of Free Software Movement
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Kernel, system tools, compilers, documentation, editors, etc.
Free: “Free” as in Freedom
“Copyleft” Software: GNU General Public License (GPL)
Related: Open Source Movement
Most GNU tools were ready by the early 90’s.
… Except the kernel: “GNU Hurd”
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Hurd was supposed to be a microkernel
Over-design? Wrong approach?
BSD
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At the same time, another open source UNIX
distribution, the BSD, was being sued by UNIX
System Labs. (USL v. BSDi)
The lawsuit cast doubt upon the legal status of the
BSD’s. The case was finally settled in 1994, with
both parties agreeing not to litigate further.
This, together with the lack of a kernel in the GNU
project, created a demand for a free UNIX-like kernel,
which was fulfilled by Linux
Linux
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Started by Linus Torvalds as a hobby project
Inspired by Minix, an OS used as an example
in teaching principles of operating systems
First release of Linux in September 1991
Free of the problems of GNU Hurd and BSD
Eventually joined by other developers
More:
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Just for Fun: The Story of an Accidental
Revolutionary
A Typical Linux System
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Linux Kernel
User space programs (many are GNU software)
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Shell (command line): bash
Utilities: ls, cp, mv, rm, cat, grep, ...
Compiler: gcc
… and more …
X Window System (for desktops/workstations)
Various daemons (a.k.a. services)
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Eg.: syslogd, httpd, cron, inetd
A Rough Graphical Representation of a
Linux System
Hardware
Kernel
Daemons
X Server
User space programs
Shell
X Client
Linux “Distributions”
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Since most software on Linux can be freely modified and redistributed, people began packaging these software into
“distributions”
A “distribution” is responsible for most of the software installed on
the Linux system, including the base “operating” system and any
other applications the user installs
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rpm, deb/apt, tgz
Each distribution has it’s own “character”, differing in
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Purpose : Server, Workstation, Firewall, etc…
Installation / upgrade method
Choice of software
Way of packaging software (tgz, rpm, deb)
Default configuration
Aims and Ideology – Commercial, Promote Free Software, etc
Linux Distributions – Redhat / Fedora
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The “standard” Linux
Has a relatively high level of support from third party
vendors
Geared towards commercial / corporate
environments
Initial set up is generally easy
Rather expensive if you buy the enterprise edition
(hundreds of USD!)
Maintenance is a nightmare! ;-p
www.redhat.com
Mandriva (was “Mandrake”)
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Originally based on Redhat, therefore
somewhat similar to Redhat
Geared towards desktop and newbies
www.mandrivalinux.com
Slackware
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Stable, simplistic
One man distribution
Zipslack, which works without having
separate Linux partition(s)
Relatively UNIX-like compared to other
distributions
www.slackware.com
Gentoo
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Source based installation!
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The standard way of installing new software on
the system is to compile it from source (using the
“portage” system)
This is equivalent to the BSD ports system
Takes LoOOong time to install / upgrade
www.gentoo.org
Debian
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Made by a worldwide non-profit organization,
with thousands of volunteers helping to
maintain packages
Quality and quantity of packages are
generally quite high
Slow release cycle – the last “stable” release
was in July 2002!!
www.debian.org
Linux - Basics
An introduction to using
Linux as a normal user
Post-Login Screen
“Message of
the day”
Usually contains
important notices
Username
Hostname
Current directory
Why is the username and hostname
displayed in the command prompt?
Hint: You may press
<Ctrl+Alt+F1> to <Ctrl+Alt+F6>
for multiple terminals if you are
using Linux on the local machine
(instead of over network)
Basic Commands
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“ls” – List directory contents
“cd” – Change directory
“cp” – Copy file(s)
“rm” – Remove file(s)
“mv” – Move file(s)
“echo” – Display a line (or lines) of text
“mkdir” – Make (i.e. Create) Directory
“cat” – Concatenate files and print to stdout
“exit” / “logout” – Exit the shell
Example I
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Try the following commands
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ls
echo HKOI Cows
ls -l
mkdir hello
cd hello
cp /etc/motd .
ls -la
cat motd
rm /etc/motd
mv motd ..
cd ..
# list directory
# print a message on screen
# list directory (long format)
# create directory “hello”
# change directory to hello
# copy file to current dir
# list directory
# display contents of file
# try to remove file (fails ;-p)
# move file to parent dir
# change to parent directory
Linux File System Hierarchy
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In Linux, the file system is a (single) tree
Everything begins from the root directory: /
Non-exclusive listing of commonly used directories
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/home – User home directories
/bin, /usr/bin – Binaries (executables, programs)
/lib, /usr/lib – Libraries (similar to “DLL”s in Windows)
/etc – System configuration files
/var, /usr/var – Stores files that are often modified (eg. log files,
database files, mail spool, print spool)
/dev – special device files
/tmp – Temporary files
In general, a normal user cannot modify the files outside his
home directory (except /tmp)
Exploring the system
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Try to navigate your way around the system
with the above commands
You may view the contents of a file with the
“cat” command
You can return to your home directory with
the “cd” command (no arguments)
Make good use of tab completion
Text Editors
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Vi (VIM)
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Emacs
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Visual Editor
VIM: Vi Improved.
Editor Macros
Nickname: Esc-Meta-Alt-Control-Shift
Nano
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“Notepad”-like
Easy to use but less powerful than Vi / Emacs
Text Editors (How to quit)
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Some programs may launch text editors that you
may not know how to use -- even quitting is difficult!
VIM
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Emacs
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<Esc> :q! (Quit without saving)
<Ctrl-X> <Ctrl-C> (Quit)
Although not required, it is strongly recommended
that you learn one of the above editors since they
can increase your productivity quite significantly
Man(ual) pages
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Example: man cp
Different
usages
Detailed
description of
command and
its options
Purpose of
command
Hint:
Press ‘q’ to quit
*nix Quirks (compared to MSDOS)
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Path separator is a slash “/” instead of backslash “\”
Files are case sensitive
“File extensions” are “meaningless”
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The “.” character in a file has no special meaning unless it is
in the beginning of a filename
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“.file” – hidden file
“.” – current directory
“..” – parent directory
Executable files have an “executable bit” set, instead of a
“.exe” extension
<Ctrl-D> is End of File (<Ctrl-Z> in DOS)
*nix Quirks II
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There must be a space between the command and subsequent
arguments
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Command line arguments start with “-” or “--” instead of “/”
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Eg. “cd /” works, “cd/” does not
DOS: dir /OD
Linux: ls -t
Unix text format vs MSDOS text format
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A line in *NIX systems ends with a ‘\n’ (ASCII 10)
A line in MSDOS ends with ‘\r\n’ (ASCII 13, 10)
The relevant functions of the C library in DOS/Windows converts
‘\n’ to ‘\r\n’ automatically
*nix Quirks III
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Unless the path the command is specified,
the shell will only run commands located in
the $PATH environment variable (why?)
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Question: how to run a program on the current
directory?
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./command
To see what $PATH contains, you may issue the
command: echo $PATH
To edit the value of $PATH: PATH=(new value)
Task I
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Write a program in Pascal that
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Reads an integer n from standard input
Writes n random integers to standard output
Save it as numbers.pas
Compile the program
Execute the program
Keep a backup copy in
~/backup/numbers.pas
I/O Redirection, Pipes
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“A > B” redirects standard output from program A to file B. This
operation will overwrite original contents of B (if any)
“A >> B” redirects standard output from program A and appends
it to the end of file B.
“A < B“ redirects standard input from file B to program A
“A | B” redirects standard output of program A to standard input
of program B
Try the following commands:
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echo 100 | ./numbers
echo 10 > ten.txt
./numbers < ten.txt
echo 20 | ./numbers | sort –n
Hint: Also works
in MSDOS and
cmd.exe
Task II
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Download http://www.hkoi.org/~sydneyfong/public/openq.zip to
home directory and unzip the contents (use wget / w3m)
Change working directory to ~/prog0
Write a program to solve the HKOI “Open Question” (see
HKOI2005 website)
(You may try to write a “wrong” one (i.e. “incorrect solution 4”)
for checking answers)
Save the program as “program0.pas”
Run the program using inputs from the files input1.txt to
input5.txt, redirect the output to output1.txt to output5.txt
Check your answers by using `diff`
More on bash shell
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alias – substitute a string as a command
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Eg. alias ls=‘ls --color’
You may list current aliases by simply issuing the command “alias”
without arguments
The script ~/.bash_profile is run during login
The script ~/.bashrc is run in non-login shells
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You may set aliases, environment variables and run commands in
these files to customize your shell
You may want to make the two files identical
Aliases that you may want to have by default:
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alias cp=‘cp -i’
alias mv=‘mv -i’
alias rm=‘rm -i’
# asks for confirmation before overwriting a file
# asks for confirmation before overwriting a file
# asks for confirmation before deleting a file
More on man pages
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There are different sections of
man pages
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Section 1: commands
Section 2: system calls
Section 3: C library calls
Section 4: special files (in /dev)
Section 5: (config) file formats
Section 6: “games”
Section 7: Misc
Section 8: System
administration commands
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If there are conflicts in
names, the section of lower
value is displayed. For a
specific section:
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man <section> <page>
Note that you may find
section 3 very useful as a
reference to standard C
functions (eg. printf, fopen,
string functions, etc)
Special files (in /dev)
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/dev/zero – returns an endless stream of ‘\0’
characters
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To create an file of size 1MB:
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dd if=/dev/zero of=myfile.img bs=1k count=1024
/dev/null
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Always return EOF when read
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cat /dev/null > abc – creates empty file of size zero
All data written to /dev/null is discarded
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ls > /dev/null – mutes output of ls
Tips in competitions…
Practical advice for
competition environments
Useful Commands in Competitions
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bc – Arbitrary precision calculator
sort – Sort lines of text files (note the “-n” option)
ps – list running processes on the machine
kill – Sends a signal to running programs (terminates it by default)
date – Print system date/time
time – reports execution time of a command
diff – compares files
head, tail – prints the first/last N lines of the input
wc – word count (also counts characters and lines)
more – pager (allows you to scroll the input for easy viewing)
less – better version of more
grep – print lines matching a pattern
find – search for files
factor – factorize numbers
tsort – perform topological sort
seq – print a sequence of numbers
file – determine file type (sometimes displays other useful information)
tar – Archive files (“glue” multiple files into one, and vice versa)
Compilers - fpc
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In most cases, fpc <file> would do
Useful options
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-Co (check for integer overflow)
-Cr (range check)
-O1, -O2, -O3…
In some systems the man page is outdated
Compilers – gcc/g++
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use -o <output> to specify output file, otherwise the
default is “a.out”
Most gcc options apply to g++
Normally you would do:
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gcc -O2 -o program1 program1.c
g++ -O2 -o program1 program1.cc
Remember to compile your program using the flags
given by the judge/competition. (In particular, the
optimization flags sometimes causes trouble)
If you want, you may also run `make <prog>`