# Linux

### User:
1. Regular user (only has access in their home directory only)
2. Root user or Super user (Admin)

- $ : Regular User
- (#) : Sudo user/Super user

- Absolute Path : cd/bin/fo1
- Relative Path : cd fo2

### Basic Linux commands

- pwd : print working directory
- ls : Lists all files and directories in the present working directory
- ls-R : Lists files in sub-directories as well
- ls-a : Lists hidden files as well
- ls-al : Lists files and directories with detailed information like permissions,size, owner, etc.
- ls -lart : list files with read/write acess
- cd or cd ~ : Navigate to HOME directory
- cd .. : Move one level up
- cd : To change to a particular directory
- cd / : Move to the root directory
- cat > filename : Creates a new file
- cat filename : Displays the file content
- cat file1 file2 > file3 : Joins two files (file1, file2) and stores the output in a new file (file3)
- mv file "new file path" : Moves the files to the new location
- mv filename new_file_name : Renames the file to a new filename
- sudo : Allows regular users to run programs with the security privileges of the superuser or root
- rm filename : Deletes a file
- man : Gives help information on a command
- history : Gives a list of all past commands typed in the current terminal session
- clear : Clears the terminal
- mkdir directoryname : Creates a new directory in the present working directory or a at the specified path
- rmdir : Deletes a directory
- mv : Renames a directory

- pr -x : Divides the file into x columns
- pr -h : Assigns a header to the file
- pr -n : Denotes the file with Line Numbers
- lp -nc , lpr c : Prints “c” copies of the File
- lp-d lp-P : Specifies name of the printer
- apt update : Command used to check update
- apt upgrade : command for installing update
- touch harry.txt : create harry.txt file

### File Permission commands

- ls-l : to show file type and access permission
- r : read permission
- w : write permission
- x : execute permission
- -= : no permission
- Chown user : For changing the ownership of a file/directory
- Chown user:group filename : change the user as well as group for a file or directory

### Environment Variables command

- echo $VARIABLE : To display value of a variable
- env : Displays all environment variables
- VARIABLE_NAME= variable_value : Create a new variable
- Unset : Remove a variable
- export Variable=value : To set value of an environment variable

### User management commands of linux

- sudo adduser username : To add a new user
- sudo passwd -l 'username' : To change the password of a user
- sudo userdel -r 'username' : To remove a newly created user
- sudo usermod -a -G GROUPNAME USERNAME : To add a user to a group
- sudo deluser USER GROUPNAME : To remove a user from a group
- finger : Shows information of all the users logged in
- finger username : Gives information of a particular user

### Networking command

- SSH username@ip-address or hostname : login into a remote Linux machine using SSH
- Ping hostname="" or ="" : To ping and Analyzing network and host connections
- dir : Display files in the current directory of a remote computer
- cd "dirname" : change directory to “dirname” on a remote computer
- put file : upload ‘file’ from local to remote computer
- get file : Download ‘file’ from remote to local computer
- quit : Logout

### Process command

- bg : To send a process to the background
- fg : To run a stopped process in the foreground
- top : Details on all Active Processes
- ps : Give the status of processes running for a user
- ps PID : Gives the status of a particular process
- pidof : Gives the Process ID (PID) of a process
- kill PID : Kills a process
- nice : Starts a process with a given priority
- renice : Changes priority of an already running process
- df : Gives free hard disk space on your system
- free : Gives free RAM on your system

### VI Editing Commands

- i : Insert at cursor (goes into insert mode)
- a : Write after cursor (goes into insert mode)
- A : Write at the end of line (goes into insert mode)
- ESC : Terminate insert mode
- u : Undo last change
- U : Undo all changes to the entire line
- o : Open a new line (goes into insert mode)
- dd : Delete line
- 3dd : Delete 3 lines
- D : Delete contents of line after the cursor
- C : Delete contents of a line after the cursor and insert new text. Press ESC key to end insertion.
- dw : Delete word
- 4dw : Delete 4 words
- cw : Change word
- x : Delete character at the cursor
- r : Replace character
- R : Overwrite characters from cursor onward
- s : Substitute one character under cursor continue to insert
- S : Substitute entire line and begin to insert at the beginning of the line
- ~ : Change case of individual character

### chmod : Change file mode

- Go to chmod calculator, select your permission in different segment like (Owner, Group, other
- Copy that number/ or use this number to change mode of a file.

- chmod 732 1.tx

### vim : is a edtior

- apt install vim
- vim harry.txt - harry.txt file open in vim editor.
- i - to go to insert mode to write.
- esc - to escape from insert mode. then
- colon(:) - if you want to exit without save write q! or if you want to save and exit then write wq and enter.