AIX Basics
Short Description
unix basics...
Description
UNIX Structure
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Kernel ± The Kernel interfaces directly with the hardware devices and controls their access. ± It also controls the processes that are started by users.
Shell is a command interpreter and acts as an interface between user and kernel. ± Also the Shell is a programming language. ± We can write Shell scripts to automate tasks.
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Logging In Logging In
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Passwd ± Passwd command is used to change the user password.
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Command Format ± The general format of an AIX command is ± command option (s) argument (s)
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Clear,echo and banner ± The Clear command clears the terminal window.
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Who, Finger commands ± The Who and Finger commands are used to find information about the users.
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write ± write provides a conversation like communication with each user alternatively sending and recieving messages.
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wall ± The wall command writes to all terminals and useful to notify all users of a system event.
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talk ± The talk command allows two users to hold a conversation.
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Files and Directories ± A file is a collection of data.
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File Structure ± AIX has a Hierarchial File Structure.
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File Structure ± AIX has a Hierarchial File Structure.
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File Structure ± AIX has a Hierarchial File Structure.
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File Structure ± AIX has a Hierarchial File Structure.
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pwd command ± The print working directory prints your current directory
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list command
ls [ directory ]
± The list command is used to list the contents of a directory.
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cd command
cd [ directory ]
± The cd command changes our current directory.
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mkdir command
mkdir [ directory ]
± The mkdir command creates one or more new directories.
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rmdir command
rmdir [ directory ]
± The rmdir command removes a directory.
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rmdir command
rmdir [ directory ]
± The rmdir command removes a directory.
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display directory info ± The istat command displays the i-node information for a particular file or dir. ± Every file has an associated §
± When a file is accessed the filename is matched with the corresponding i-node number and the data is located. name
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links User Group Date
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cat, pg and more commands ± The cat command lists a file but if the file is longer than one screen space it scrolls down to the end of the file. ± The pg command displays the file one page at a time. ± The more command also works the same way but you can scroll one line at a time by pressing ÿ and one screen at a time by pressing the .
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wc command wc [-c] [-l] [-w] filename ± The wc command counts the number of lines,words and bytes in a named file. ± This command is very useful when comparing files.
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± If no options are used the order will be lines,words and characters
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link command
ln source_file target_file
± The ln command allows one file to have more than one name. ± Both copies have the same i-node.
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print command
qprt filenameÔ filename2
± To queue files to the printer we use the qprt command. ± The qchk command displays the current status of a print queue. ± To cancel a print job use the qcan command.
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Standard files and Redirection ± Three files are automatically opened for each process. ± standard input ( ) x default is keyboard ---- stdin < ± standard output (Ô) ± ± standard error (2)
---- stdout > x default is screen ---- stderr 2>
± These defaults can be changed by redirection.
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Pipes ± A pipe is a sequence of one or more commands where the i of one command becomes the i § of the next command.
7R& )4 Filters ± A filter is a command that reads from i §, processes it and then writes it to i
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Tee ± The tee command reads i § and sends the data to both i and a file.
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command grouping ± Multiple commands can be entered on the same line seperated by a semi-colon.
&C >S Line continuation ± \ can be used to continue a command on a seperate line. ± A µ>¶ prompt id issued by the shell to indicate line continuation.
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Shell Variables ± Variables represent data whose value may change. ± Shell variables define your environment...HOME,TERM,PATH etc., ± Shell variable names are case sensitive. ± The convention is that UPPERCASE are used for system-defined variables and lowercase are used for user-defined variables.
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Setting and Referencing Shell Variables 'U#;;I::7:7 x % % 7 0I 0
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Commmand substitution . 3!)343++) / I . 3!)343++) /
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Quoting Metacharacters ± µ µ Single Quotes
Ignores all metacharacters between the quotes.
VU!-# U!-# ± ³ ³ Double Quotes
Ignore all metachar., except for $,` and \
U!-# : : ± \Backslash
Ignore the special meaning of the following character
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Process ± A program or a command that is actually running on a system is referred to as a process. ± Every process has a Process ID (PID). ± PID Ô is always assigned to the §§ process which is the first process that is started during the boot process. ± A PPID is the parent PID. ± The variable $$ shows the PID of the current shell.
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The Login Process ± When a user logs into a system a new process is started with a PID that is randomly allocated by the Kernel. ± The program usr/bin/ksh is loaded into this process.
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Variables and Processes ± w § iare part of the process environment Processes cannot access or change variables from another process.
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Shell Script ± A shell script is a collection of commands stored in a text file. ± Any text editor can be used to create a shell script. ± Here we start ksh and pass the script name as an argument.
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Invoking Shell Script ± The shell uses the PATH variable to find executable programs. ± The directory in which the script is stored must be defined in the path variable.
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Invoking Shell Script ± Each Shell Script is executed in a subshell. ± Variables defined in a shell script cannot be passed back to the parent shell. ± If the script is invoked with a .(dot) it runs in the current shell.
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Exit Codes ± A command returns an exit value to the parent process. ± The environment variable $? contains the exit value of last command.
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ps command ± The ps command displays process status information.
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Types of Processes ± Processes that are started from and require interaction with the terminal are called - iii. ± Processes that can run independently are called iii
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Terminating Processes
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Termination Signals ' -
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Daemons ± A daemon is a never ending process that controls a system resource (printer queue). ± It starts when the system is started and runs until the system is down. ± For example qdaemon tracks print job requests and the printers available to handle them.
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User Environment ± Login Files ± The first file that the OS uses at login time is the /etc/environment file which contains variables specifying the basic environment for all processes. ± The second file is the /etc/profile file which controls systemwide default variables. ± The third file is the .profile file which resides in a user¶s login login directory and enables the user to customize their working environment.
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User Environment ± Login Files M
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sample /etc/environment ::% Z18C"A",. 0 7 Z% % 7 >#
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sample .profile > 8.UI:7::7:U!-#:7 ' IV1 x . 70 0 > x U 0 >
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sample .kshrc >= Z
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ksh features-Aliases ± The alias command invoked with no arguments prints the list of aliases in the form name=value. ± The unalias command will cancel the alias named and removes it from the alias list. IV? IV ? 0IV ? IV ? IV? IV &? = å
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ksh features-History ± The last Ô2å commands are stored in $HOME/.sh_history. ± The r command allows you to recall previously entered commands. & x ): : 3 & 4 & +
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AIX Utilities find command (find path expression) ± Searches one or more dir structures recursively for files meeting certain specified criteria and displays those filenames or executes commands against them.
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Executing commands with find ± The exec command executes a command on each of the files found.
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Interactive command execution ± The ok option causes command execution on an interactive basis.
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Additional Options
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find examples >& VQ &0 &D)& & ^_TS ???]& 9 3+4+ )3 3+ > ??]& 9 4+43 )3 )> >& 544& 4& >: : >& && >: : >: :& V0 &)> :% :0 :: 7:0
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find with the ±links option : &0 & = R & )6&???& 3 +5)* ) +: : )6&???& 3 +5)* ) +: : 0 )6&???& 3 +5)* ) +: : 0)
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The ±links +Ô option lists the files that have more than one link associated with them.
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grep command (grep [options] pattern [fileÔ file2....]) ± Searches for lines matching specified pattern and also displays the name of the file containing the pattern.
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grep with regular expressions ± When * is used with the grep command ti will match zero or more occurences of the previous character.
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grep examples & R + 4 3)+4 *+4++: ?= V`H H = 9
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head and tail commands ± head command can be used to view the first few lines of a file or files. ± tail command displays a file beginning at a specified point and displaying a specified number of lines.
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xargs ± The xargs command reads a group of commands from stdin and runs an AIX command with that group of arguments. ± Here cat passes xargs the list of files and allows xargs to pass them to rm. ± The ±t flag echoes the constructed command line to stderr.
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xargs more examples ± Here we create a list of files to be printed and queue them up for printing through xargs.
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% > ± Here { } is called a placeholder and the ±I flag tells xargs to insert each line of the ls directory listing where { } appears.
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xargs,find and grep ± Using xargs is more efficient and easier to remember than the find commanad
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which,whereis,whence ± which command takes a list of program names and looks for the files that are executed when these names are given as a command. ± whereis also takes a list of program names but only searches in some standard locations. ± Whence is a ksh-specific command which also searches for ksh aliases.
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file command ± The file command can be used to determine the type of a file. ± It also tells us under what OS version it is compiled. ::7:% ::7:% 7 CA' '0 :5 79 ::7 ::7 0
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diff (Differential File Comparator) ± The diff command works only with text files and and reports the differences between the two files. >
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command search order The shell looks for a in the following order.
Qualified pathname Reserved word
if,then,else,while...etc.,
alias built-in command
cd,pwd,umask,read...etc.,
Function path variable ÔÔå
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X Window ± The X-window is a N/W based graphics system. ± It enables us to work with multiple items simultaneously. ± It provides the capability to manage local and remote displays. ± X window uses a client/server environment. ± So the graphic application can run on one system, yet display its output on another system. ± X window is platform independent. ± It allows a keyboard and display attached to one system to use programs running on a completely different system.
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X Window ± The X-window is a N/W based graphics system. :,
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X Window ± X window function is split into terminal and application support. ± Typically the application support runs on a UNIX system and the terminal system can run on any system. ± The system providing application support is called client and the one providing terminal support is called server. ± In most cases both will be on the same system. ± Client is the application that is running and needs to display graphics to a user. ± Clients recieve keyboard and mouse input from the associated x server. ± X servers respond to requests from clients and to actions from users.
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X Clients ± X clients are the aplications which the users run under the X window systemcommon X clients are
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xterm
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Standard terminal emulator
aixterm
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IBM AIX terminal emulator
xclock
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displays a clock
xcalc
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displays a calculator
xwd
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dumps the image of an x window
mwm
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motif window manager
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X Clients ± standard X client command line options are ,
x
specifies the color for window background
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specifies the color for window border
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specifies window border in pixels
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Identifies the host server name and the X server display number where the command is to run.
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specifies the color for the window foreground
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specifies the normal sized text fontset.
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X Server ± Each X server controls one keyboard. one mouse and one or more screens. ± Allows simultaneous access by several clients ± Performs basic graphic operations ± Provides information such as fonts and colors ± Routes keyboard and mouse I/P to the correct clients
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Starting AIXwindow ± The command is used to start the AIXwindows environment. ± If the workstation is not an X Station then will execute the § § command. ± By default startx starts three clients § , and . ± Any errors occuring during will be logged in a file / #+0 MMM. ± We use to close AIXwindows and return to command prompt. ± Some windows like aixterm accept and display information while some like xclock and xcalc simply display information.
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The aixterm Window ± An aixterm can be started in two ways ± In SHELL x § ± Display ´
and select § ± To create an additional aixterm window enter § at the command prompt. ± The aixterm window can be closed by ± Type § or
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Running a Client on Another System ± With AIXwindows it is possible to run a client on a remote system in the network yet display the application window on your screen. ± we need to tell the client process where to display its window. ± AIXwindows uses the DISPLAY environment variable to indicate the name of the server where it should display its output. ± To override this value we need to specify a value using the M 8 Q7 = 0 8 Q %0 8 Q =Q - Q=07 2 0
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Customizing AIXwindows
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.mwmrc
± Root menu,window menu and mouse options can be customized in the .mwmrc file. ± DO NOT MODIFY SYSTEM-WIDE FILE which can be found in /usr/lpp/XÔÔ/defaults/MotifÔ.2/system.mwmrc. ± To customize we need to copy this file to our HOME dir and modify it as it will override the system-wide version.
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