Linux SysAdmin [RHEL] - Lesson #1

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Linux SysAdmin [RHEL] - Lesson #1

This thread is start of Linux System Administrator topic based on RedHat.


General Information and Terms:
Recursive - Changes affected by only existing components, new components will NOT be affected.
Default - Changes affected by only new components, existing components will NOT be affected.
[TAB] button - It is used to complete which we have partially typed commands or directories
| (Pipe) - It used for sending a command's output to other command's input.
Example: ls | grep "a" - ls lists files/folders in current directory, grep filters and shows only files/folders including "a" letter.
man command_name - shows document of command/tool. Example: man ls - it shows document of ls command.


Basic Commands

1. ls - Lists file/folders in current directory.

2. pwd - Shows current directory location/path.

3. cd - Changes directory, example: cd /usr/bin
After, checking with pwd command

4. cat file_name.ext - Prints inside of file on terminal in plaintext

5. tac file_name.ext - Prints reversed (starts from last line) inside of file on terminal in plaintext.

6. rm file_name/folder_name - Removes file and folders.
Best Practise: rm -rf file_name/folder_name - Removes files/folders Recursively* (-r) and forced (-f)

7. touch file_name.ext - Creates empty file.

8. mkdir folder_name - Creates folder.
Best Practise: mkdir -p not_existing_folder/folder_name - Creates folder with parents (-p), it means creating not existing folder in directory too.
If you do not use -p option, not_existing_folder/folder_name will be failed.

9. mv - moves files/folders, more options to apply
General: mv file_name.ext1 file_name.ext2 - renames (moves) file file_name.ext1 to file_name.ext2

9.1. mv folder_name1 folder_name 2 - renames (moves) folder folder_name1 to folder_name2

9.2. mv file_name.ext/folder_name /path/to/file_name.ext - moves file's current directory to /path/to folder

10. cp - copies files/folders, more options to apply
For copying folder, must use with Recursive (-r/-R) option.

11. grep "filter_word" - finds lines which includes given word.
Best Practise: command | grep "filter_word"

12. wc - shows word count.
1 (Line Count), 1(Word count), 6(byte size)
P.S> hello is 5 byte, but Linux adds \n (break line) end of the file, making it 6 byte total.

13. head - shows first 10 lines.
Best Practise: head -n total_line_number

14. tail - shows last 10 lines reversed.
Best Practise: tail -n total_line_number

15. history - shows user's history.

15.1. history -c - removes current user terminal session's command history, not all command history.

15.2. history -w - writes current user terminal session's command history to ~/.bash-history

15.3. history -c && history -w - deletes permanently user's command history.

15.4. !command_number - executes history numbered command

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