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Linux Commands Tutorial

 Linux Commands Tutorial

Introduction:In this Blog i am going to explain  Linux Commands Tutorial  Linux is a Unix-Like operating system. All the Linux/Unix commands are run in the terminal provided by the Linux system. This terminal is just like the command prompt of Windows OS. Linux/Unix commands are case-sensitive. The terminal can be used to accomplish all Administrative tasks

Let us Start the Process Linux Commands Tutorial

1)logname: It shows current username

# logname

2)pwd: Present working directory which means current folder in linux

# pwd

3)date: it display system date and time

# date

4)clear: to clear the screen

 # clear

5)cal: current month calendar we can call month and year along with cal command  ex: cal 5 1982  which displays may month 1982

 # cal

6)uname:  it dispalys the present os name.

 # uname

7)uname -r:  displays kernal version

 

# uname -r

8)hostname: displays server name

 # hostname

9)hostname -i: display server ip address

# hostname -i

10)who: it shows list  of connect user in that server

 

# who

11)who am i:  current logged user info

# who am i 

12)su:  switch username from one user into another user   ex:su - username(oracle is the username)

 # su - oracle 

13)exit:  logout from current user logged in

 # exit

14)man command name: help of the given command

# man

WORKING WITH FILES:

1)cat:  which is use to create a new file or open to  view existing files

# cat chaitanya.txt

2)cat>>filename: appending data to these file

# cat >> chaitanya.txt

3)$touch filename: which  create an empty file with zero kb

# touch chaitanya.txt

FILE DELETION:

 1)rm: to delete the file

# rm chaitanya1.txt

 2)rm -rf: delete the files forcibly 

# rm - rf chaitanya2.txt

 3)rm -i: delete the file which asks the  user conformation 

 # rm - i chaitanya.txt

 4)rm file1 file2: deleting multiple files

# rm chaitanya1.txt  chaitanya2.txt

WORKING WITH DIRECTORIES:

1)mkdir: To create a new directory (Directory is  nothing  but a drive or folders like windows) in linux (here i am using  Linux Commands Tutorial chaitanya is the directory name)

 # mkdir chaitanya  

2)cd dirname: to change a directory (one directory to another directory)

# cd orabackup

3)cd .. : to moves from  current directory into previous directory

# cd ..

4)cd: to come out entire directory

#  cd 

5)cd /: it changes the root directory

# cd /

REMOVING DIRECTORIES:

1)rmdir: to removing directory it must be empty( here i am using Linux Commands Tutorial chaitanya is the directory in that chaitanya directory it should be empty then only it will be deleted)

# rmdir chaitanya

2)rm -r direcname: it deletes recursively to entire structure

# rm - r chaitanya

3)rm -ri direcname: it deletes recursively to entire structure it will ask the user confirmation (here iam using  Linux Commands Tutorial chaitanya is the directory)

 

 # rm - ri

4)rm -rf direcname: it deletes recursively to entire structure with forcibly

# rm -rf

COPY COMMANDS

1)cp sourcefile targetfile: copying file from existing location into  new location

# cp chaitanya1.txt   chaitanya3.txt

# cp chaitanya3.doc  chaitanya03new.doc

# ls - l * .doc( it will displays all doc related files)

# ls - l *.txt (it will displays all text related files)

COPY MULTIPLE FILES SIMULTANEUOSLY INTO ANOTHER DIRECTORY

# cp main.txt demo.txt libc.txt     backup

If backup is located in /home/project, enter:

#  cp main.txt demo.txt libc.txt     /home/project backup

COPY A FILE TO ANOTHER DIRECTORY  

To copy a file from your current directory into another directory called /tmp/, 

# cp filename /tmp

# ls /tmp/filename

# cd /tmp

# ls

COPYING ALL FILES

The star wildcard represents anything i.e. all files. To copy all the files in a directory to a new directory, enter:

# cp *  /u01/oracle/backup

The star wildcard represents anything whose name ends with the .doc extension. So, to copy all the document files (*.doc) in a directory to a new directory, enter:

# cp *.doc  /u01/oracle/backup

To copy a directory, including all its files and subdirectories, to another directory, enter (copy directories recursively):

# cp -R *  /u01/oracle/backup

To copy a file to a new file and preserve the modification date, time, and access control list associated with the source file, enter:

# cp -p chaitanya.txt  /dir1/dir2/

$ cp -p filename /path/to/new/location/myfile

MOVING COMMANDS

1)mv old file newlocation: using these command we can move a file from one folder into  another  folder or we can rename file also

Move mainc.txt defh.txt  files to /u01/oracle/oracbackup/ directory:

# mv mainc.txt defh.txt   /u01/oracle/orabackup/

Move all C files in current directory to subdirectory orabackup :

# mv *.c orabackup

Move all files in subdirectory orabackup to current directory :

# mv orabackup/* .

Rename file main.c to main.backup:

# mv main.c main.backup

Rename directory bak to bak3:

# mv bak bak3

 

Update - move when main.c is newer:

# mv -u main.c bak

#

Move main.c and prompt before overwrite bak/main.c:

# mv -v main.c bak

'bak/main.c' -> 'bak/main.c'

#

VIEWING FILE COMMANDS

1)ls : it's listing files which are in that directory with  ascending order

# ls

2)ls -a: listed all files including  hidden files also

# ls -a 

3)ls -l: listed all files in long list  format i.e 9 field

# ls -1

4)ls -t: listed all files based on date and time of creation

# ls -t

5)ls -r: listed all files on descending order or sin reverse

# ls -r

6)ls -R: listed all files recursively

# ls -R

CREATING HIDDEN FILES

1)cat>.filename

# cat > .chaitanya9.txt

2)mv filename .filename

# mv chaitanya1.txt  .chaitanya6.txt

3)mkdir .dirname

# mkdir  .chaitanya

UNHIDE FILES

1)mv .chaitanya chaitanya

# mv  .chaitanya chaitanya

2)mv .dirname dirname

# mv . chaitanya chaitanya

Note: Info on  Linux Commands Tutorial it may be differ in your environment like production,testing development and naming conventions etc

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Oracle 18c New Features

 Oracle 18c New Features

Introduction

In this blog i am going to explain three new Oracle 18c New Features which is useful for oracle database administrators 

SET ROWLIMIT 

ORAVERSION UTILITY

SET FEEDBACK OPTION

SET ROWLIMIT command enables users to set a limit for the number of rows displayed for a query.

for limiting number  of rows to 5 in Oracle 18c New Features

SQL> set rowlimit 5

SQL> select username from dba_users;

USERNAME

—————————

SYS

SYSTEM

ABHIRAM

CHAITANYA

MANASA

5 rows selected. (rowlimit reached)

for limiting number  of rows to 3

SQL> set rowlimit 3

SQL> select username from dba_users;

USERNAME

————————

SYS

SYSTEM

CHAITANYA

3 rows selected. (rowlimit reached)

Oraversion Utility in Oracle 18c New Features

A new utility Oraversion has been introduced in Oracle 18c New Features Which provides Oracle database version/release related information.

oraversion -help

This program prints release version information.

These are its possible arguments:

-compositeVersion: Print the full version number: a.b.c.d.e.

-baseVersion: Print the base version number: a.0.0.0.0.

-majorVersion: Print the major version number: a.

-buildStamp: Print the date/time associated with the build.

-buildDescription: Print a description of the build.

-help: Print this message.

$ oraversion -compositeVersion

18.3.0.0.0

 

$ oraversion -baseVersion

18.0.0.0.0

 

$ oraversion -majorVersion

18

 

$ oraversion -buildStamp

180628094320

 

$ oraversion -buildDescription

Release_Update

In Oracle 18c New Features, we can display the sql_id of the sql queries we are running using set feedback option.

By default it will be OFF.

SQL> set feedback ON SQL_ID

SQL> select name from v$database;

NAME

———

ORA18C

1 row selected.

SQL_ID: 0btb065ytg2v0 –  > This is the sql_id of the query . 

Note : Info on  Oracle 18c New Features it maybe differ in your environment like production,testing,development etc and naming conventions

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Crontab Linux

Crontab Linux

Introduction:

Crontab Linux system has a useful task scheduler named crontab, to automate the scheduled to run the process as a Root, the Unix Scheduling tool, The Cron tab commands opens the cron table for editing.The cron table is the list of tasks scheduled to run at regulartime intervals on the system

The Daemon which reads the crontab and executes the commands at the right time is called Crontab Linux for instance you can automate like backup,schedule updates andsynchroniztion files and many more

In Crontab Linux Oracle DBA jobs to be managed

Analyze Database

Rman backups

Datapump jobs

Hot/cold backups

Archive log backups

House keeping jobs --Cleaning alert log/Trace files

Gathering stats

Delete old log files

Send out any notification email such as newsletter,passwords,expiration mail

Regular cleaned up of cached data

Crontab Linux is used to automate sytem mainatanace

Let us Start the process

Crontab Linux Format

MIN   HOUR   DOM  MON   DOW   CMD

Field Description     Allowed Value

MIN Minute field      0 to 59

HOUR Hour field       0 to 23

DOM Day of Month       1-31

MON Month field        1-12

DOW Day Of Week          0-6

CMD Command       Any command to be executed.

 

Asterics(*) : use for matching

Define Range : Allows you to define range with the help of hypen like 1-10 or 30 -40 or jan-mar,mon-wed

Define Multiple Ranges: Alows you to define various ranges with command separated like apr-jun,oct-dec

Crontab Linux Commands

How to Add /Modify crontab job  with the help of cron tab command

$ crontab -u -e 

To List the Crontab jobs 

$ crontab -l

To Remove the Crontab tasks 

$ crontab -r

To add or update job in crontab 

$ crontab -e

Command to edit others users crontab

$ crontab -u username -e

Command to view crontab entries of current user

$ crontab -l

Command to view crontab entries of a specific user

crontab -u username -l

Here Some of the Crontab Examples

Crontab Linux to do the various scheduling jobs. Below given command execute at 7 AM and 5 PM daily.

0 7,17 * * * /orabackup/scripts/scriptjob.sh

Command to execute a cron after every 5 minutes.

*/5* * * * * /orabackup/scripts/scriptjob.sh

Cron scheduler command helps you to execute the task on every Monday at 5 AM. This command is helpful for doing weekly tasks like system clean-up.

0 5 * * mon  /orabackup/scripts/scriptjob.sh

Command run your script on 3 minutes interval.

*/3 * * * * /orabackup/scripts/scriptjob.sh

Command to schedule a cron to which executes for a specific month. This command to run tasks run in Feb, June and September months. Sometimes we need to schedule a task to execute a select monthly task.

* * * feb,jun,sep * /orabackup/scripts/scriptjob.sh

Command to execute on selected days. This example will run each Monday and Wednesday at 5 PM.

0 17 * * mon,wed  /orabackup/scripts/scriptjob.sh

This command allows cron to execute on first Saturday of every month.

0 2 * * sat  [ $(date +%d) -le 06 ] && /orabackup/scripts/scriptjob.sh

Command to run a script for 6 hours interval so it can be configured like below.

0 */6 * * * /orabackup/scripts/scriptjob.sh

This command schedule a task to execute twice on Monday and Tuesday. Use the following settings to do it.

0 4,17 * * mon,tue /orabackup/scripts/scriptjob.sh

Command schedule a cron to execute after every 15 Seconds.

* * * * * /orabackup/scripts/scriptjob.sh

* * * * *  sleep 15; /orabackup/scripts/scriptjob.sh

Command to schedule tasks on a yearly basis.

@yearly timestamp is= to "0 0 5 1 *". This executes the task in the fifth minute of every year. You can use it to send for new year greetings.

@yearly /orabackup/scripts/scriptjob.sh

Command tasks to execute on a monthly basis.

@monthly timestamp is similar to "0 0 1 * *". This command expression allows the execution of a task in the first minute of the month.

@monthly /orabackup/scripts/scriptjob.sh

Command to execute multiple tasks using a single cron.

* * * * * /orabackup/scripts/scriptjob.sh; /orabackup/scripts/scriptjob2.sh

Command to schedule tasks to execute on a weekly basis.

@weekly timestamp is similar to "0 0 4 * sun". This is used to perform the weekly tasks like the system cleanup etc.

@weekly /bin/orabackup/scripts/scriptjob.sh

Task will be scheduled to execute on a daily basis.

@daily timestamp is similar to "0 2 * * *". It executes the task in the second minute of every day.

@daily /orabackup/scripts/scriptjob.sh

Allows tasks to execute on an hourly.

@hourly timestamp is similar to "0 * * * *". This command executes a task in the first minute of every hour.

@hourly /orabackup/scripts/scriptjob.sh

Allows tasks to execute on system reboot.

@reboot expression is useful for those tasks that the system wants to run on your system startup. This is helpful to begin tasks background automatically.

@reboot /orabackup/scripts/scriptjob.sh

we use shell scripts to create jobs

.sh /.ksh (types of shell are korn(IBM-AIX) / bash (linux c shell)

scripts in /orabackup/scripts

Sample Scenario

32  11  *  *  */orabackups/script/scriptjob.sh

create the script

$ vi scriptjob.sh

#!/bin/sh

find /archives/prod-name " *.arc" -mtime +1-exec gzip{ }\;

find /archives/prod-name " *.gz"  mtime +7 -exec rm-rf{ }\;

now save  :wq!

Give execution permission

$ chmod +x scriptjob.sh

edit the crontab

$ crontab -e

# give an entry as follows 

30  11  4  6  *  / orabackup/script/scriptjob.sh

then save it

*   *  *  *  *  * command to executed

Min  (0-59)

  Hour      (0-23)

     Day of Month  (1-31)

               month        (1-12)

       Day of the week   (0-6)  (0/7 is sunday  sunday =0 or7)

Note : Info on Crontab Linux it may be differ in yourenvironment like production,testing,development and naming conventions etc

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Shell Script Basics

 Shell Script Basics

Let us start the process in this Blog i am going to explain  Shell Script Basics and shell script  if condition statement ,else if condition statement, and or operators in bash shell 

Introduction

Shell: When ever you login to  a unix system you are placed in a program called the shell acts as a command interpreter , it takes each command and passes it to the operating system kernel to be acted upon it then displays the results of this operation on completion on your screen

DIFFERENT FLAVOURS OF SHELL IN UNIX

Bourne Shell: Bourne Shell scripts to specify the shell to use for the scripts. The default prompt on the Unix for this is $

#!/bin/bsh

C Shell:C Shell Scripts to specify the shell to use for the scripts.The default prompt on the Unix for this is %,  

#!/bin/csh

Korn Shell: Korn Shell Scripts  to specify the shell to use for the scripts.The default prompt on the Unix for this is $,

#!/bin/ksh

Shell Script: Shell Scripts collection of command which are executed in a order given. There are conditional statement and looping also available like if ,while which helps in finding if a particular value is greater than another value .

To write any comments in the shell scripts ,it has to be written with # preceded

Example

# Author of the script is

There are some variables Shell Script Basics which are set internally by the shell and which are available to the user

$1 – $9 Variables are the positional parameters.

$0 Name of the command currently being executed.

$# Number of positional arguments given to this invocation of the shell.

$? Exit status of the last command executed is given as a decimal string. When a command completes successfully, it returns the exit status of 0 (zero), otherwise it returns a non-zero exit status.

$$ Process number of this shell – useful for including in filenames, to make them unique.

$! Process id of the last command run in the background.

$* String containing all the arguments to the shell, starting at $1.

Shell scripts and functions are both interpreted. This means they are not compiled.

Commands in Shell

All shell have a number of built in command which are executed in the shell owns process like echo ,cd,  when you enter a command first it will check the built in shell command echo or cd  or it is directly interpreted by the shell,if the command begins with  / shell assumes that command is absolute path name.

unix commands are executabale binary files located in directories with the name bin (for binary) many of the commands that are located in the directory /usr/bin.

Typical path variable might be 

/bin:/usr/bin:/usr/local/utils/bin:$HOME/bin

Shell Script Example

cat chaitanya.sh

#Written by ChaitanyaOracleDbaBlog

TODAY=date '+%m%d%y_%H%M'

echo "This is Chaitanya  at" $TODAY

The Name of each script must reflect its use,and each script must have a suffix that describes the what type of script it is “.sh” for Bourne shell ,“.ksh” for Korn shell or “.cgi” for Common Gateway Interface scripts

Lets start the first shell script

#!/bin/ksh   # This script displays the date, time, username and

# current directory.

# Author Chaitanya

echo "Current date and time is:"

date

echo

echo "Your username is: `whoami` \\n"

echo "Your current directory is: \\c"

pwd echo "Your system name is :`hostname`\\n"   

How to execute the shell script 

Once the shell scripts are created ,they can be executed in two ways 

1. We specify the shell type and then the script name 

 sh  chaitanya.sh

2.We change the permission of the shell scripts to perform execution

 chmod  +x chaitanya.sh

 ./ chaitanya.sh

Bash if statement syntax

1.Bash if ...then..fi statement

if [ conditional expression ]

then

statement1

statement2

.

fi

Bash if then fi example

#!/bin/bash

count=300

if [ $count -eq 300 ]

then

  echo "The Count is 300"

fi

2. Bash if ..then..else..fi statement  syntax

If [ conditional expression ]

then

statement1

statement2

.

else

statement3

statement4

.

fi

Bash if ..then..else..fi statement  Example

#!/bin/bash

count=299

if [ $count -eq 300 ]

then

  echo " The Count is 300"

else

  echo "The Count is not 300"

fi

3. Bash If....elif...else..fi statement syntax

If [ conditional expression1 ]

then

statement1

statement2

.

elif [ conditional expression2 ]

then

statement3

statement4

.

else

statement5

fi

Bash If....elif...else..fi statement Example

#!/bin/bash

count=299

if [ $count -eq 300 ]

then

  echo "Count is 300"

elif [ $count -gt 300 ]

then

  echo "Count is greater than 300"

else

  echo "Count is less than 300"

fi

4. Bash If..then..else..if..then..fi..fi.. syntax

If [ conditional expression1 ]

then

statement1

statement2

.

else

if [ conditional expression2 ]

then

statement3

.

fi

fi

Bash If..then..else..if..then..fi..fi.. Example

#!/bin/bash

count=299

if [ $count -eq 300 ]

then

  echo " The Count is 300"

else

  if [ $count -gt 300 ]

  then

    echo "The Count is greater than 300"

  else

  echo "The Count is less than 300"

  fi

fi

Test for numbers

-eq ------->   equal to--------->   x==y

-ge-------->  greater than or equal to--->  x>=y

-gt --------> greater than    -----> x>y     

-le ---------> less than or equal to  ------>   x<=y

-lt ---------> less than------> x<y

-ne ---------> not equal to ---->   x!=y     

AND and OR  operator 

&& ------> This stand for AND condition( if both the conditions are true then whole Condition will be true)

[[ $1 == yes && -r $1.txt ]]

|| --------> This stand for OR condition (if only one Condition is true then whole Condition will be true

[[ $1 == yes || -r $1.txt ]]

Note : Info on Shell Script Basics it may be differ in your environment like production,testing,development  and naming conventions etc

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