03 Essential Unix (and Linux) for the Oracle DBA

Revision no.: PPT/2K403/02

Essential Unix (and Linux) for the Oracle DBA


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2

Architecture of UNIX Systems



3

UNIX System Structure

Operating system interacts directly with Hardware

Provides common services to programs

Insulating from Hardware

Kernel is treated as an operating system

Programs are independent of the Hardware

Easy to move on different processing environment

Programs should be independent of Hardware



4

UNIX System Structure (contd.)

Programs in the upper layer communicate with Kernel using

defined set of system calls

System calls instruct the Kernel to do various operations

System calls also exchange the data between Kernel and

program

Some Standard programs also fall in this layer i.e. executable

files by C compiler

Top most layer is used for other application programs eg. C

compiler (CC)



5

SHELL

It is a program that interprets the commands.

If the command is valid then the shell directs the kernel to

carry out the request

If invalid then an error message is displayed.

Shell starts when an user logs in, and terminates when the

user logs out.

Presence of shell is indicated by a special symbol known as

the shell prompt ( $ or # ).



6

SHELL (contd.)

Several shells are available to handle the same hardware in

different ways.

Redirection of data : the shell facilitates chaining or

"pipelining" of commands, i.e. the output of one program flows

down the pipe and becomes an input to the next program.



7

SHELL (contd.)

Interpretiveprogramming

language

Program execution

Pipeline hookup

SHELLSHELL

Environmentcontrol

I/O Redirectio

n

File name substitutio

n



8

Different shells

Bourne shell or Standard shell (sh) :

Introduced in 1978 and is widely used in AT&T Unix.

Gives "$" as the prompt to the user and " # " to the superuser

(root).

One disadvantage is that it does not provide command history.



9

Different shells (contd.)

C shell (csh) :

Gives "%" as the prompt to user.

It is different from the sh.

Syntax is similar to the C language programming.

It is quite popular among the programmers.

Provides aliasing of the command i.e. the ability to customize the

command names.



10


Restricted shell (rsh) :

Basically designed to restrict the rights of normal users

It cannot execute

cd command

path variable

command containing "/

redirect outputs



11


The Korn Shell

The Korn shell is a product of AT&T Bell labs & was developed

by David Korn.

It has many novel features like the facility to edit the command

line,the history mechanism, aliases & job control.

Moreover the Korn shell also lets you handle computations

awk-like formatted printing & simplified menu routines.



12

Accessing the Unix System

Directly from the server hosting the database itself

Via a UNIX workstation

Through a Windows NT Server front end.



13

Basic Unix Commands

Display the machines symbolic nameuname

Display present working directorypwdTo change users passwordpasswd

Gives you the commands entered previously by users.$ history 3

historyIs a pattern-recognition command.grepDisplay text on your screenecho

Display time & datedateChange directoriescd



14

Basic Unix Commands

As the name of this command indicates, whereis will give you the exact location of the executable file for the utility inquestion.$ whereis who: /usr/bin/who /usr/share/man1.z/who.1$

whereis

Indicates who you are logged in as.whoami

Display list of all the users currently logged into the system.

who

Enables you to find out which version of a command the shell is using.$ /bin/cat$$ which cat

which



15

Linux Environment

/etc/profile file owned and managed by the system administrator.

It is used to automatically set the environment variables for users at login time.

The shell looks in users home directory as an alternative location for environment information in the .profile file.

env command is used to display the entire set of environment variables.

Use export command to set any environment variable. Eg export ORACLE_SID=prod2



16

Input & output in Unix

$ date > file1.txt$ file1 < file2.txt$ date | file2

Eg.

Redirects standard error2>

Appends standard input to a file>

Redirects standard output>

Redirects standard input /dev/rmt/0m

Will copy the contents of the entire directory to the tape name

/dev/rmt/0m

cpio i < /dev/rmt/0m

The cpio command with the i option restores all the contents

of the tape named /dev/rmt/0m to the current directory



46

The Crontab and Automation of Scripts

DBAs will have to schedule their shell programs and other data loading programs for regular execution by the Unix administrator

Unix provides the cron table to schedule database tasks. One can invoke the crontab by crontab 1. To add programs to the schedule or make scheduling

changes, the command is crontab e. #-----------------------------------------------------------------------

minute hour date month day of week command30 18 * * 1-6 analyze.ksh#--------------------------------------------------------------------------------------

The preceding code indicates that the program analyze.ksh will be run Monday through Saturday at 6:30 P.M.



47

The Crontab and Automation of Scripts



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03 Essential Unix (and Linux) for the Oracle DBA

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