{"id":286,"date":"2008-01-08T08:24:49","date_gmt":"2008-01-08T12:24:49","guid":{"rendered":"http:\/\/onlineappsdba.com\/index.php\/2008\/01\/08\/linuxunix-basics\/"},"modified":"2008-01-08T08:24:49","modified_gmt":"2008-01-08T12:24:49","slug":"linuxunix-basics","status":"publish","type":"post","link":"https:\/\/onlineappsdba.com\/index.php\/2008\/01\/08\/linuxunix-basics\/","title":{"rendered":"Linux\/Unix Basics"},"content":{"rendered":"

‘ROOT<\/strong>‘ on linux is the centre of all power.\u00a0This account\/user\u00a0is the system administrator who has the access to all files & folders & can add or delete users or change their passwords.<\/p>\n

Some of the basic commands used on linux useful for Oracle Apps DBA’s are:<\/p>\n

1. useradd <\/strong>
\nThe general syntax for the useradd command is :<\/p>\n

useradd -d home_directory -e expire_date -g initial_group -p password login_name<\/p>\n

home_directory : Is the main directory within which the user is expected to store all his files and subdirectories.
\nFor a user named ‘neha’ the home directory generally is \/home\/neha
\nexpire_date : This is the date on which the user’s account expires and he\/she cannot access the computer anymore unless the account is renewed.
\ninitial_group : Every user in Linux belongs to a group which affects his file permissions. The initial group must be a group which already exists.
\nPassword : This will be the user’s password to access his account
\nlogin_name : This will be the user name with which the user will access his account.<\/p>\n

Eg :<\/p>\n

useradd -d \/home\/neha -e 2009-12-03 -g root -p talent123 neha
\n<\/em><\/p>\n

creates a user named neha on my computer.<\/p>\n

Home directory for user Neha is \/home\/neha
\nExpirty date is 3rd december,2009
\nBelongs to the ‘root’ group
\nPassword is talent123<\/p>\n

Incase you do not enter one of the parameters group, home, expire or shell they are replaced by their default values. These default values can be viewed using the “ useradd -D” <\/em>command and can also be changed.<\/p>\n

2) ls <\/strong>
\nThe ls <\/strong>command is equivalent of the DOS dir<\/strong> command. It lists the files and subdirectories contained within the present directory.<\/p>\n

Some possible flags which can be used with the ls command are :<\/p>\n

ls -l\u00a0<\/strong><\/em><\/p>\n

Uses a long listing format,which contains lots of useful information,like the exact size of file,who owns the file\u00a0, who has the right to look at it & when it was last modified.
\nls -a<\/strong><\/em><\/p>\n

List all files including the one’s starting with ‘.’ (Some configuration files starting with a dot ‘.’ are otherwise not listed).<\/p>\n

ls<\/em> | more<\/em><\/strong><\/p>\n

Lists files and directories page after page on keystroke. The above command actually is a combination of two commands. It introduces a new concept called ‘Piping’.\u00a0 In Linux it is possible to give the output of one command to another command as an input.The ls command lists files & subdirectories and the more commands divides its input into page length views. Thus piping the ls output to more results in page length views of files and subdirectories.<\/p>\n

ls -R<\/strong><\/em><\/p>\n

It lists the files and subdirectories of a directory and further lists the contents of each subdirectory recursively. <\/em><\/strong><\/p>\n

3)\u00a0pwd
\n<\/strong>The pwd or the present working directory command gives you the path to the directory in which you presently are. It is used without flags simply as ‘pwd’<\/p>\n

4) su <\/strong><\/p>\n

Many a times you might have logged in as a normal user and might need to be root (or any other user)\u00a0to install a software or for some other small task. You could logout then login as\u00a0that particular user,\u00a0complete the work logout and login back as a normal user. Instead, you can just use the su<\/strong> command. The format is :<\/p>\n

su {username}<\/strong><\/p>\n

eg : su root<\/p>\n

when you ‘su’ to become root from a normal user, you are asked for the root password. But if you are root, you can use ‘su’ to become any user without using a password. Once your work is finished, use ‘exit’ to become yourself.<\/p>\n

* Check for – (hyphen) with su command <\/em><\/strong><\/p>\n

5)<\/strong> whoami
\n<\/strong>Will tell you which user you are logged in as. Useful when you have used ‘su’ many times and now don’t know who you are.<\/p>\n

6) cp
\n<\/strong>This one copies files \/ directories from one place to another .It’s syntax is<\/p>\n

cp source_file_path destination_path<\/strong><\/p>\n

eg : cp \/home\/neha\/abctxt\u00a0 \/ftp\/xyz<\/p>\n

The cp command can be used with some useful flags also :<\/p>\n

cp -i<\/strong><\/p>\n

Interactive copying, prompts before overwriting files or directories<\/p>\n

cp -l source_file_with_path destination_path<\/strong><\/p>\n

Makes a link (shortcut) to the source_file at the destination path instead of actually copying it there.<\/p>\n

cp -p<\/strong><\/p>\n

Preserve file attributes while copying if possible<\/p>\n

cp -R<\/strong><\/p>\n

Copy Recursively . Used when copying directories. This command also copies the contents of the subdirectories.<\/p>\n

cp -u<\/strong><\/p>\n

Update i.e. Copy only if the source file is newer than the destination file or the destination file does not exist.<\/p>\n

7)\u00a0rm <\/strong>
\nThe rm command is used to remove or delete files or directories. Its general syntax is:<\/p>\n

rm -flag file_or_directory_with_path<\/strong><\/p>\n

eg : rm \/home\/neha\/scrap.txt<\/p>\n

Some flags which can be used with the rm command are<\/p>\n

rm -v file.txt<\/em><\/strong><\/p>\n

Remove verbosely, explain what is being done.<\/p>\n

rm -r my_directory<\/em><\/strong><\/p>\n

Remove the directory and its contents recursively.<\/p>\n

8) mkdir<\/strong><\/p>\n

This command is used to create new a new directory. Its syntax is<\/p>\n

mkdir -optional_flag directory_name<\/strong><\/p>\n

The possible flags are<\/p>\n

mkdir -v directory_name<\/strong><\/em><\/p>\n

Tell what is going on.<\/em>mkdir -p directory_with_path<\/strong><\/em><\/em><\/p>\n

\u00a0Suppose you need a directory named\u00a0ABC within another directory called\u00a0XYZ in \/usr\/local and the parent directory XYZ\u00a0itself does not exist, then you can use :<\/p>\n

mkdir -p \/usr\/local\/XYZ\/ABC<\/p>\n

This command creates the\u00a0XYZ directory and the\u00a0ABC subdirectory in one go.<\/p>\n

9) man
\n<\/strong>Suppose you have not understood fully one of the above commands or want to find out about a new command you have learnt , the man command provides a manual for that command. The syntax is:<\/p>\n

man command_name<\/strong><\/p>\n

Thus<\/p>\n

man cp<\/strong><\/p>\n

will show you a manual on the cp command and so on<\/p>\n

More on linux basics coming soon ….
\n<\/strong>
\nRelated
\nhttps:\/\/onlineappsdba.com\/index.php\/2007\/12\/11\/linux-common-queries\/<\/a><\/strong><\/p>\n","protected":false},"excerpt":{"rendered":"

‘ROOT‘ on linux is the centre of all power.\u00a0This account\/user\u00a0is the system administrator who has the access to all files 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