Transcript Linux Envrironment

Chapter 1
LINUX Environment
Heejune AHN
Topics:
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Linux History
Linux User Environment
Linux Development Environment
What is Operating Systems ?
Application Program vs System Program
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Provides uniform resource (hardware) access mechanism to
Application Program/programmer
 same access mechanism to different hardware: Resources
include CPU, memory, disk, tape, printers, terminals, modems,
etc.
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Resource Efficiency and Protection: multi-tasking, multiprocessing, multiuser
 Provide HW resources to multiple task, and protect mis- or
over-use of one task.
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BASIC-OS, MSDOS, Unix OS, Linux OS, Windows OS, Apple
OS
SNUT, Heejune AHN
History of Linux
Unix
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developed at Bell Labs (AT&T, Kerningham ) in 1969 for
minicomputer
coded over 90% in C, not assembler: easy port to different
machines
Xnix family
 UC Berkely BSD, At&T SVR4 version
 SUN Solaris, IBM AIX, HP UNIX, SCO-Xenix etc
GNU(Gnu's not Unix) project
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–3–
Richard Stallman
started in early 80's to create and promote free software
SNUT, Heejune AHN
Linux’ Birth
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Linus Torvalds in the 1990's, released to the Internet in 1994
about 1/3 of Linux is GNU code from the Free Software
Foundation - a Linux distribution consists of Linux kernel +
GNU compilers/tools/utilities + other free software
Popularity
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Linux uses the Open Source model for development - code
is placed on the Internet, users download and test it,
programmers improve it and place it back on the web there
is competition among programmers to fix bugs and improve
Linux
Packages : Redhat (now Fedora), Suse Linux, IBM etc
Latest version : Release 2.6.x
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Linux Internal
Linux (wide-sense) = Linux Kernel + Utilities + alpha
Utilities + Applications
Shell
Linux Kernel + Drivers
HW (CPU + MEM + Peripherals)
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Linux Internal
Hardware : CPU, Memory, Disk, Peripherals, surrounded by Kernel
UNIX Kernel (basic OS)
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Process Management : CPU scheduling
Memory Management : Memory allocation, protection, Paging etc.
File system : secondary/permanent data management
Device Drivers : peripherals control
IPC (inter-process communication) : signal, pipe, fifo, semaphore,
message queue, share memory etc
Network : TCP/IP, IPX, UNIX protocols etc
Utilities/applications (or commands)
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mozila, telnet, apache, mincom, gcc, make etc.
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Shell (user interface, command interpreter, and some built-in
commands)
 Bourne shell (sh), C shell (csh), Korn shell (ksh), Bourne again shell
(bash), TC shell (tcsh), Z shell (zsh)
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–7–
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Yes, I am a Linuxer!
Entering Commands, Logging In & Out
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To login, use a telnet program, and provide userid and
password
DOS>telnet 10.2.32.210
login:yourId
Password:
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To logout, use logout, exit, or control-d
Use passwd to change password
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Unix File system
Linux File Structure
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Everything in Linux is file : file, directory, devices …
hierarchical (tree, directory within directory)
 root directory is / - ancestor of all files and directories on
system
 directories contain files and/or other directories to be safe, for file and
directory names use alphabetics, numerics, underscore, period, or
comma some UNIX systems allow up to 255 characters in a filename,
others only allow up to 14
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Filename
 absolute pathname : starting with ‘/’, I.e. root )
 relative pathname : not starting with /, relative to your current
directory
 . (current), .. (parent directory)
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Access Permission
Linux is multi-user minded OS
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User (me), Group (my team), and Others
Permission
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Read
Write
Execute
chmod (explain later)
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used to alter access permissions to a file or directory
read/write/execute for user(owner)/group/other
chmod xxx filename (xxx is 3 octal digits representing the binary
string rwxrwxrwx where the first three characters are
read/write/execute permission for the user, the next three for the
user's group, and the last three for all others)
 chmod 640 file1
 chmod u+r filename
 chmod u+x file1
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Unix Journey
standard directories & files
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/home typically contains the home directories of all users
/usr/bin or /bin contains standard utility programs
/sbin and /usr/sbin contain utilities for system administration
/etc contains admin & configuration files, such as
/etc/passwd
/var contains files that vary as the system is running, such
as temp, log, spool, and mailbox files
/dev contains files representing peripheral devices (device
drivers)
/tmp is used by some programs for temporary files
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Basic Linux commands: 1
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cd [dirPath]
 change current directory , cd (to hone directory)
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ls
- lists information about files and directories
 Ls –al - "a"ll files (including hidden), "l"ong form
 ls -F - indicates file type, / for directory, * for executable
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pwd : show your current directory
mkdir - to create directories
 mkdir -p - to create any parent directories not already existing
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mv - move (rename) filet/directory
rmdir - to delete empty directories, eg. rmdir directory-list
rm - to delete files, eg. rm file-list
 rm -r - to delete directories including files and subdirectories
 rm -ir - to delete directories including files and subdirectories, with
prompt to confirm removal
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Basic Linux commands: 2
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head -n filename - displays first n lines, 10 is default
tail -n filename - displays last n lines, 10 is default
sort filename - displays in sorted order
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more or less - displays file contents one page at a time
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 <space bar> - will go to next page
 b - will go to previous page
 <enter> - will go down one line
 /string - will search for string within document being viewed
 q - will quit
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touch - creates a new file, or updates stats on an existing file
diff file1 file2 - compares 2 files
 indicates lines to add, delete, or change to convert file1 to file2
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wc - displays various counts of the contents of a file
 wc –l | c | w filename - number of lines / character/ words
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Basic Linux commands: 3
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cp source-file destination-file
 to copy files (careful, overwrites destination with no warning)
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mv existing-file new-file - to rename files & directories
file filename
 gives info about the contents of the file
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whereis utility
 lists all libraries in your path containing a utility of this name
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which utility
 lists specific library in your path that would be used to access this
utility
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ln (link) command gives a file an additional name, or pointer, from
the same or a different directory
 ln file1 file2 - gives file1 the additional name file2 (hard link)
 ln -s file1 file2 - gives file1 the additional name file2, as an indirect
pointer (symbolic link)
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grep 'string' file - print lines in file that contain the string
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Basic Linux command : 4
Chmod
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Permission
 x permission : execution for normal file, pass-through for a directory
 r permission for a directory allows viewing of file names in the directory,
but no access to the files themselves (regardless of the files'
permission settings)
 x and r permissions for a directory allow viewing of file names, and
access to any files which have appropriate permissions set
 permissions can only be changed by file owner or superuser (system
administrator)
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Usage
 eg. chmod g-w file1 - would take away write permission from the user's
group if they had it before
 eg. chmod o=r file1 - would set all others' permission to read only
regardless of what they had before
 chmod -r ( Recursive)
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umask
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defines default permissions for newly created files, doesn't
change permissions on existing files
default permissions will be 777 minus umask arg for
directories, 666 minus umask arg for files
eg. umask - by itself, shows current umask setting
eg. umask 077 - new files will be 600, new directories will be
700
eg. umask 023 - new files will be 644, new directories will be
754
SNUT, Heejune AHN
Basic Linux commands: 5
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echo
 text or $variable (eg. $USER)
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printf
 similar to echo but can use C-style formatting
 allows escapes: eg. \n (newline) \t (tab)
 eg. printf "This is a menu\n\t1. Item 1\n\t2. Item2\n\t3. Item3\nEnter
choice: "
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date - gives date and time
 allows extensive formatting
 eg.: date +"Today is %A %B %d, %Y"
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Print command
 lpr filenames - to print files, lp on some systems
 lpq - to list print queues, lpstat on some systems
 lprm - to remove files from print queue
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Basic Linux commands: 6
Script
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different from each shells
variables
 String : e.g. var1=“hello heejune!”
 environment variable : $HOME, $PATH, $n (argument)
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flow control
 if, elif, for, while, until, case
 comparison
» string
» numeric
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=, !=, -n, –z
-eq, -ne, -gt, -ge, -lt, -le, !, -d, -d/e/f/g/r/s/u/w/x
list
 process successive command, &&, ||
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function
 user defined function e.g. Fun1(){ echo “this is function1”}
 Shell-Internal function e.g. Echo, eval, exec, exit, export ….etc
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SNUT, Heejune AHN
Configure your environment
configuration file
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Make your life easy / customization
Configuration file is often start with “.”
 Look after ls –a in your HOME
 .bash_profile, .bashrc, .bash_login, .bash_logout, .exrc etc
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.bash_profile
 Started when you log-in/new terminal
 Put your preference there
if [ -f ~/.bashrc ]; then
. ~/.bashrc
fi
# User specific environment and startup programs
PATH=$PATH:$HOME/bin
export PATH
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SNUT, Heejune AHN
Communication with Others : Optional
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Who
 w - information about users logged on to system
 who am i, whoami - information about your session
 who -T - displays additional info, such as message acceptance
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finger - info about users on system
 finger username [@remotemachine]
» info about a specific user on system - looked up in /etc/passwd file, can
also use first or last name instead of userid
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talk user : character by character conversation with another user,
end with delete
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write user : line by line conversation with another user, end with
control-d
mesg n, mesg y - deny or accept messages (or mesg -n, mesg -y)
mail users - mails a message to users, end with control-d on line by
itself
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mail [email protected] < filename - mails a file to a user
pine - another mail program
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Help me !!
Online Documentation
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man command
 online help for command, if online documentation installed by
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Unix administrator
man -k keyword - eg. man -k sort - searches through all man
sections
man uses more to display information:
<space bar> - will go to next page
b - will go to previous page
<enter> - will go down one line
/string - will search for string within document being viewed
q - will quit
info - is replacing man on Linux
SNUT, Heejune AHN
Software development tool flow
Gnu tool-chain
Editor (vi, emacs)
Source (*.c, *.cc,
*.h)
preprocessor
compiler (front/backend)
Object files (*.o, *.obj)
archiver
linker
Library
*.a
*.so
Executable (a.out, *)
loader
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SNUT, Heejune AHN
vi editor 사용법
Vi Editor
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Most popular, simple, but sill powerful editor in Linux
Provides visual env. Without window system
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No menu scheme
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사용법
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 vi 파일명
 view 파일명
: vi in read-only mode
 PC 버전 (freeware) 도 있음
Mode
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3 modes
 input (editing) mode : 내용 입력, 타이핑한 내용이 화면에 나옴
 command mode
 last line mode
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: 간단한 editor 명령지원, 화면에 타이핑이 나오지 않음.
: 복합 명령 지원
SNUT, Heejune AHN
Mode change
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to input mode:
 insert - i, I (before cursor, beginning of line)
 append - a, A (after cursor, end of line)
 open - o, O (below, above)
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to command mode
 <escape>
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to last-line mode
 (from command mode)
 “:”
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SNUT, Heejune AHN
Symbols in VI
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w (word) , c (character)
$ (endof line, end of file), 0 (begin of line, file),
(, ) ( beginning or end of sentence
{, } - beginning or end of paragraph
Cursor 이동
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return, space, arrow keys, or h, j, k, l (left, down, up, right)
 repetition factor, eg. 12j will move down 12 lines
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H, M, L - move cursor to top, middle, bottom of screen
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^d, ^u, ^f, ^b (^는 CTRL key)
 scroll forward 1/2 screen, backward 1/2 screen, forward full
screen, backward full screen
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nG - move to line n, or last line if n not specified
SNUT, Heejune AHN
Delete
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x - delete character under cursor ( repetition factor, eg. 3x )
dw, dd - delete text (word to the right, line) and copy to buffer
can use repetition factor, eg. 5x, 7dw or d7w, 12dd or d12d
D - delete to end of line
Copy & Past
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yw, yy - yank - copy text (word, line) to buffer
 can use repetition factor eg. 5yw or y5w, 12yy or y12y
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Y - copy to end of line
p, P - paste buffer after or before cursor if buffer contains
words, and below or above current line if buffer contains
lines
SNUT, Heejune AHN
Linux Internal
Replace
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r - replace character under cursor
ns - substitute number of characters specified by n
cw, cc - change - delete text (word, line), copy text to buffer,
and leave in input mode (repetition factor, eg. 5cw or c5w,
12cc or c12c)
Undo & repeat
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u - multiple levels on some systems, one level on others
. - repeat most recent command that made a change
C - change to end of line
J - join current and following line
SNUT, Heejune AHN
last-line mode
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/pattern - searches for the next occurrence of pattern after
the current cursor position
?pattern - searches backwards through the file
 n - repeat last search, N will repeat in opposite direction
 / - repeat last search forward, ? to repeat backward
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Finish vi
 “ZZ” or “:wq” (write and quit)
 “:q!” (quit without writing), “:q” (quit, only allowed if not
changed since last save)
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GNU C Compiler
GCC ( Gnu C Compiler /Gnu compiler collection)
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Global command, ie. it deos not do work itself
gcc call C preprocessor, compiler, assembler and linker
Cf ) g++ for compiling cpp code
{cpu}-{loader}-gcc e.g.) arm-linux-gcc
사용 법: gcc [options] file
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E.g. gcc -o test test.c
For full description, read Manual
 --help Display this information
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Output Options
 -c Compile and assemble, but do not link
 -o Place the output into
 -E Preprocess only; do not compile, assemble or link
 -S Compile only; do not assemble or link
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Code generation
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-g Include Debugging Information
-On Optimization (n = 1,2,3), speed, memory, but longer compile time
-Wn Warning (e.g. -Wall, ...)
-m Machine dependent handling (e.g. -msoft-float -m)
-fxxx code generation (e.g. PIC: relocatable code)
Directory options
 -llibraryname -static, -shared library to link
 -Llibpath non standard library Location
 -Iheaerpath non standard header path
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ETC
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-D Preprocessor Macro-definition
-x Specify the language of the following input files
-Wa, Pass comma-separated on to the assembler
-Wp, Pass comma-separated on to the preprocessor
-Wl, Pass comma-separated on to the linker
SNUT, Heejune AHN
GNU Make utility
Project and Make Utility
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Compile process automation required
 most modern project has more than 100 source files
 Batch file (script) is ok for it.
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Intelligent compilation
 Many c files -> long Compile time
 Make utility checks the dependency and compile only the
required to compile.
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How to make "Makefile"
1.
2.
write definition section : define Macros, eg. CC, CFLAGS etc
write dependency
 target and its sources
3.
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write commands
Notes
 # is for comment
 Variable: $variable, $@ is target, $< is source
 commands must start with "tab" not space or something
How to Run it
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make <-f file> target . . . (eg. make -f mymakefile target1
target2)
make (for gnuMakefile, makefile, Makefile and "all" target)
SNUT, Heejune AHN
Sample (most primitive)
#definition section
CC=gcc
CFLAGS=-O3 –g
# command section
OBJS = main.o first_func.o second_func.o
all : main
main : $(OBJS)
$(CC) -o $@ $(OBJS)
main.o : main.c func.h
first_func.o : first_func.c
second_func.o : second_func.c
.c.o : $(CC) -c $<
clean :
rm -f main *.o
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How it works
read the makefile, parse it (rule check), build the
dependence info
 check the dates of each files
 run the commands (explicit or implicit)
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Details
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Real world is more dirty, see Manual
SNUT, Heejune AHN
Preprocessor
Preprocessor
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Before compiler process the source file, the preprocessor expands
or substitutes MACROs.
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For Conditional compile, in-line function (faster than real function),
include files
Rules
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#include <file> | "file"
 include file from IMPLICIT ( or EXPLICT )
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#define MARCO [DEFINITION] , #undef
 #define DEBUG
#define ADD(a,b) ((a) +(b))
#define EOF (-1)
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#undef DEBUG
#error, #warning
 #warning "this is warning" (error stops the compile process, while
warning does not stops on "most good" tool-chains)
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Conditional Processing
 #if #ifdef #ifndef #else #elif #endif defined()
 #ifdef DEBUG
printf(" data : %0x\n", data);
#endif
 #if CPU == MIPS
....
#elif CPU == x86
....
#endif
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Predefined MACROs
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__DATE__
__FILE__
__LINE__
__STDC__
__TIME__
(%s): Sep 5 2004
(%s): main.c
(%d): 23
(%d): 1
(%s): 02:11:54
SNUT, Heejune AHN
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# : variable name not the variable itself
 #define INTVAR(var) printf("%s:%d \t %s = %d\n", __FILE__,
__LINE__, #var, var);
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## : Concatenate (연결) the variable names
 #define x(i)
x##i
int x(i), x(2), x(3); x(1) = 100; x(2) = 200; x(3) = 300;
int x1,x2, x3 ; x1 = 100; x2 =200; x3 = 300;
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은
과 같음.
SNUT, Heejune AHN
주의 사항
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use the "(" parenthesis not to be mis-expanded
 #define ADD(a +b) (a) + (b)
 ADD(1 + 2) * 3 =====> not 9 but 7 !!
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MARCO does not check the Syntax
 #define MOD(a,b) ((a) % (b))
 MOD(7.0, 5.0) -> ok for preprocessor, but error in compiler!!
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MARCO is always good for performance (speed).
 Abusing Macros make the code lengthy and need more code
memory than Instruction Cache can do.
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Trouble shooting
 “gcc -E src.c” and investigate the bug!
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