Advance System administrations commands

Essential of vi editor

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In our last section your have learnt about cat command. cat is a very basic command you cannot depend on cat command in exam to create files as cat is a very essential command.
Before we go further just learn how to create a hidden file in linux and see it.

$cat > [.name of file]

A single dot in front of the file will make it hidden. For example to make a file named secret to hidden use this command

$cat > .secret This is a secret file

Now normal ls command will not list this file. Do a ls form current directory

$ls

As you can see in output .secret file is not shown here. But can see hidden file with –a switch.

$ls –a .secret

Now rename and make it unhidden. Use mv command to rename the file

$mv .secret test $ls test

If we want to change the matter of file cat will not do it for us. So we will use vi editor to change matter of file.

$vi test

This will open a window with bilking cursor. vi editor work in three different mode.

Esc Command mode [press Esc key before giving any command]
Insert Insert mode [ to start editing use press Insert key ]
Exit Exit mode [ Exit mode can be access via press Ecs key and :]

Beside it there are various command which can be used to control the behavior of vi editor, some of them most command are there to remember

Esc +:+w+q      save and exit form file
Esc+:+q+!       exit without saving
Esc+:+set nu    to show hidden line
Esc+:+/test     to find test word in forward directions
Esc+:+21        to move cursor in line number 21
Esc+:+2+yy      to copy 2 line form cursor
Esc+:+p         to paste the copied line below the crusor
Esc+:+dd        to remove the entire line
Esc+:+4+dd      to remove 4 line below of cursor
Esc+:+x         to remove single character
Esc+:+e         to go to end of the word
Esc+:+h         to go one character back

Vi Editor Command

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Linux and Unix are managed through a series of text files. Linux administrators do not normally use graphical editors to manage these configuration files. Editors such as WordPerfect, starOffice, and yes, even Microsoft Word normally save files in a binary format that Linux can't read. Popular text editors for Linux configuration files include emacs, pico, joe, and vi.
While emacs may be the most popular text editor in the world of Linux, every administrator needs at least a basic knowledge of vi. While emacs may be more popular and flexible, vi may help you save a broken system. If you ever have to restore a critical configuration file using an emergency boot floppy, vi is probably the only editor that you'll have available. You need to know how to restore your system from a rescue floppy, which does not have enough room to carry any editor other than vi.So should know how to use vi editor.

$ vi /tmp/test
~
~
~
~
~ 
 “/tmp/test” [New File]
 

If this is a new file, you should see something similar to above.
The box at the top represents where your cursor is. The bottom line keeps you informed about what is going on with your editing (here you just opened a new file). In between, there are tildes (~) as filler because there is no text in the file yet. Now here's the intimidating part: There are no hints, menus, or icons to tell you what to do. On top of that, you can't just start typing. If you do, the computer is likely to beep at you. And some people complain that Linux isn't friendly.
The first things you need to know are the different operating modes: command and input. The vi editor always starts in command mode. Before you can add or change text in the file, you have to type a command (one or two letters and an optional number) to tell vi what you want to do. Case is important, so use uppercase and lowercase exactly as shown in the examples! To get into input mode, type an input command. To start out, type either of the following:

• a-The add command. After it, you can input text that starts to the right of the cursor.
• i-The insert command. After it, you can input text that starts to the left of the cursor.

Type a few words and then press Enter. Repeat that a few times until you have a few lines of text. When you're finished typing, press Esc to return to command mode. Now that you have a file with some text in it, try moving around in your text with the following keys or letters: Remember the Esc key! It always places you back into command mode.
Arrow keys-Move the cursor up, down, left, or right in the file one character at a time. To move left and right you can also use Backspace and the space bar, respectively. If you prefer to keep your fingers on the keyboard, move the cursor with h (left), l (right), j (down), or k (up).

• w-Moves the cursor to the beginning of the next word.
• b-Moves the cursor to the beginning of the previous word.
• 0 (zero)-Moves the cursor to the beginning of the current line.
• $-Moves the cursor to the end of the current line.
• H-Moves the cursor to the upper-left corner of the screen (first line on the screen).
• M-Moves the cursor to the first character of the middle line on the screen.
• L-Moves the cursor to the lower-left corner of the screen (last line on the screen).

The only other editing you need to know is how to delete text. Here are few vi commands for deleting text:

• x-Deletes the character under the cursor.
• X-Deletes the character directly before the cursor.
• dw-Deletes from the current character to the end of the current word.
• d$-Deletes from the current character to the end of the current line.
• d0-Deletes from the previous character to the beginning of the current line.

To wrap things up, use the following keystrokes for saving and quitting the file:

• ZZ-Save the current changes to the file and exit from vi.
• :w-Save the current file but continue editing.
• :wq-Same as ZZ.
• :q-Quit the current file. This works only if you don't have any unsaved changes.
• :q!-Quit the current file and don't save the changes you just made to the file.

If you've really trashed the file by mistake, the :q! command is the best way to exit and abandon your changes.
The file reverts to the most recently changed version. So, if you just did a :w, you are stuck with the changes up to that point. If you just want to undo a few bad edits, press u to back out of changes.
You have learned a few vi editing commands. I describe more commands in the following sections. First, however,
here are a few tips to smooth out your first trials with vi:

• Esc-Remember that Esc gets you back to command mode. (I've watched people press every key on the keyboard trying to get out of a file.) Esc followed by ZZ gets you out of command mode, saves the file, and exits.
• u-Press u to undo the previous change you made. Continue to press u to undo the change before that, and the one before that.
• Ctrl+R-If you decide you didn't want to undo the previous command, use Ctrl+R for Redo. Essentially, this command undoes your undo.
• Caps Lock-Beware of hitting Caps Lock by mistake. Everything you type in vi has a different meaning when the letters are capitalized. You don't get a warning that you are typing capitals-things just start acting weird.
• :! command-You can run a command while you are in vi using :! followed by a command name. For example,
• type :!date to see the current date and time,
• type :!pwd to see what your current directory is,
• type :!jobs to see if you have any jobs running in the background.
• INSERT-When you are in insert mode, the word INSERT appears at the bottom of the screen.
• Ctrl+G-If you forget what you are editing, pressing these keys displays the name of the file that you are editing and the current line that you are on at the bottom of the screen. It also displays the total number of lines in the file, the percentage of how far you are through the file, and the column number the cursor is on.

Moving Around the File

Besides the few movement commands described earlier, there are other ways of moving around a vi file. To try these out, open a large file that you can't do much damage to. (Try copying /var/log/ messages to /tmp and opening it in vi.) Here are some movement commands you can use:

• Ctrl+F-Page ahead, one page at a time.
• Ctrl+B-Page back, one page at a time.
• Ctrl+D-Page ahead one-half page at a time.
• Ctrl+U-Page back one-half page at a time.
• G-Goto the last line of the file.
• 1G-Go to the first line of the file. (Use any number to go to that line in the file.)

Searching for Text

To search for the next occurrence of text in the file, use either the slash (/) or the question mark (?) character. Follow the slash or question mark with a pattern (string of text) to search forward or backward, respectively, for that pattern. Within the search, you can also use metacharacters. Here are some examples:

• /hello-Searches forward for the word hello.
• ?goodbye-Searches backward for the word goodbye.
• /The.*foot-Searches forward for a line that has the word The in it and also, after that at some point, the word foot.
• ?[pP]rint-Searches backward for either print or Print. Remember that case matters in Linux, so make use of brackets to search for words that could have different capitalization.

The vi editor was originally based on the ex editor, which didn't let you work in full-screen mode. However, it did enable you to run commands that let you find and change text on one or more lines at a time. When you type a colon and the cursor goes to the bottom of the screen, you are essentially in ex mode. Here is an example of some of those ex commands for searching for and changing text. (I chose the words Local and Remote to search for, but you can use any appropriate words.)

• :g/Local-Searches for the word Local and prints every occurrence of that line from the file. (If there is more than a screenful, the output is piped to the more command.)
• :s/Local/Remote-Substitutes Remote for the word Local on the current line.
• :g/Local/s//Remote-Substitutes the first occurrence of the word Local on every line of the file with the word Remote.
• :g/Local/s//Remote/g-Substitutes every occurrence of the word Local with the word Remote in the entire file.
• :g/Local/s//Remote/gp-Substitutes every occurrence of the word Local with the word Remote in the entire file, and then prints each line so that you can see the changes (piping it through more if output fills more than one page).

Using Numbers with Commands

You can precede most vi commands with numbers to have the command repeated that number of times. This is a handy way to deal with several lines, words, or characters at a time. Here are some examples:

• 3dw-Deletes the next three words.
• 5cl-Changes the next five letters (that is, removes the letters and enters input mode).
• 12j-Moves down 12 lines.

Putting a number in front of most commands just repeats those commands. At this point, you should be fairly proficient at using the vi command. Once you get used to using vi, you will probably find other text editors less efficient to use.

System administrator commands in linux

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Critical to a Linux administrator is knowledge of one or more text editors to manage the many configuration files on a Linux system. The Linux file system hierarchy organizes hardware, drivers, directories, and of course, files. Printer configuration can be a complex topic. Shell scripts enable you to automate many everyday processes. Security is now a huge issue that Linux can handle better than other operating systems; locally, and on larger networks such as the Internet. You need to master a number of basic commands to manage Linux.
First we would cover those commands which can be run from a normal user. To complete this practice login from a normal user.

How to count line word and character form a file

 $wc [file name]

This command is used to count line words and character of file. Out will first show the line number word and in the end characters.

 $wc test 2 4 23 test

In this example there are 2 lines 4 words and 23 character in test file.

how to display top and bottom line form files

 $head –n [number] [file name]

head command is used to display specific number of line from top for given file.

 $head –n 4 test

For example this command will show the 4 top most line of file test.

 $tail –n [number] [file name]

tail command will display the specific number of line form bottom for given file.

 $tail –n 3 test

This command will display the 3 line from bottom of file test

how to find wrong spelling and correct them

$spell [file name]

spell command will display the wrong spelling of files.

 $spell test 

This command will display the wrong spelling of test file. If there is no spelling mistake no out will show.

 $aspell check [file]

This command is used to correct the spelling related mistake in any given files.

 $aspell check test 

This command will show the all wrong spelling from test file and there possible corrections. To use correction just press the number shown in front of words.

how display logged in user information and terminal number

 $who am i 

This command is use to display the username of currently logged.

 $who 

This command will display all the user currently logged in all terminals.

 $tty 

This command is used to display the terminal number of currently logged in terminals.

how to display date time and calendar

 $cal 

This command will display the calendar of current month. You can see the calendar of any specific year also.

 $cal 2010 |more 

This will display the calendar of year 2010. As output will be more than a page so use more switch with commands.

 $date 

This will the current system times and date.

how to use calculator

 $bc 

This command will launch the calculator at command prompt. Write down your calculations and press enter to get the answer. Use CTRL+D key combination to exit from calculator.

how to get help about commands

 $info [command]

info command is used to get help about any commands.

 $info cat 

This will display the help about cat commands. Generally output of info commands is more a then a page. You can quit form this out by just pressing q.

 $command - - help

This help options is really very useful when do not want to be read full manual page for help. This will provide very basic help like which switch will work with this command.

 $cat - - help

This will show the available switch cat command and a very brief descriptions about these switches.

 $man [command]

If want to read the detail about any command use this command. This will give you the complete detail about commands.

 $man cat

This command will give the complete details about the cat commands including switches and their usages. Use q to quit from the output of this commands.

 $less [file]

When you have a file more than one pages use less command to read the output of file despite of using cat command with more switch. As with more switch you cannot scroll the text in both directions.

 $cat [file] |more 

If you have a file more than one page than use |more switch with cat to read the output. Without this switch matter of file will scroll too fast that you will see only texts of last pages

recommended you to complete that first.
System administrator commands in linux
Login from normal user

How to redirect the content of files in a new file

Create two file and write some text in them.

$cat > one
This is first file
$cat > second
This is second file
 

Now we will combine these two files in a single file. In standard linux its call redirection of output.

 $cat one second > new
 $cat new
 This is first file This is second files 

Then what exactly this command did? As you know cat command is used to display the content of file so it will first display the content of first file and then it will display the content of second file. But as you put a > sign at the end of command so despite of showing this output on screen command will redirect these contents to a file.

How to execute multiple commands in a single line

 $[command] ; [command] ; [command] ;[command]…….. 

To execute multiple commands from single line use a ; between them form example

$cat new ; mkdir xyz ; mkdir rat ; ls
This is first file
This is second files
new xyz rat 

this command will first execute the first command which is cat new so it will display the matter of new file, further is mkdir xyz so it will create a xyz directory , further is mkdir rat so will create a rat directory and in the end we use ls command so it will list the contain of current directory.

How to create multiple sub directory form single command

To create multiple sub directory from a single command use –p switch with mkdir command for example

 $mkdir –p a/b/c/d/f/g/h/i/j 

In this example we created 9 subdirectories form a single mkdir command. Now verify it by listing.

 $ls new xyz rat a 

now change the directory to verify the depth of directories.

 $cd a/b/c/d/f/g/h/i/j $pwd /home/vinita/a/b/c/d/f/g/h/i/j 

Come back to home directory. Simple cd command without passing any argument will do this.

 $cd 

How to move multiple file in directory with a single commands?

Give all files name one by one with a single space between them and in the end give the destination directory name for example
$mv new first second xyz

This command will move three files new, one, second to the xyz directory.

$cd xyz 
$ls New one second 
$cd .. 

how to take back-up and restore files and directories.

tar command is used to take the back up with –cvf switches and the same tar command is used to restore the matter with –xvf switches. For example

$tar –cvf backup.tar xyz 
$ls
$rm –rf xyz 

In linux you cannot restore the data once deleted unless you have backup. Now restore these files and directory.

$tar –xvf backup.tar
$ls $cd xyz 
$ls new first second 
$cd .. 

How to compress files to save disk space?

Create a large file and check how much disk space is consumed by this file

$man ls > manoj
$du –h manoj
12k manoj 

File manoj is using 12k space on hard disk. For exam prospective you should familiar with two compress utilities.

$bzip2 [file name] {command syntax}
$bzip2 manoj
$ls
$du -h  manoj.bz2
4k manoj.bz2 

To decompress file
$bzip2 –d manoj.bz2
$ls manoj
as you can show file has been decompressed. Now use other utility to compress the file.

$gzip manoj
$ls manoj.gz 
$du –h manoj.gz 4k manoj.gz
$gzip –d manoj.gz 
$ls manoj