CLI - commands and their uses

1)What is the difference between Service and Application?

• Service(API) is a kind of work/process which is mostly used by other programs, whereas Application(Software) is a service offered to the user or any other application to manage the process/work.

2)What are these wildcards ~, ., .., * and ??

• Wildcards are special characters which are used to ease the search process. It is used for identifying multiple items but not identical data.
  • ~ Home directory
  • . Current working directory
  • .. Prev to the current directory
  • * Any number of characters.

3)What are the different flags for the kill? Why do we use kill -9 in general?

• Kill command is used to kill the process in Linux systems but also we can use it to halt/interrupt/continue the process. To do that we can use the command

kill SignalName/ID PID

4)Are you clear about file permissions? Explain them. chmod and chown commands?

• CHMOD cmd is used to alter the permission(Read, Write, Execute) of the file. Two different ways of representation.

  • Absolute - CHMOD 755 file.txt
  • Symbolic - CHMOD a=rwx file.txt

• CHOWN cmd is used to update the user/group of the file.

  • To update the user - Sudo CHOWN user filename
  • To update user & group - Sudo CHOWN user: group filename

5)Usage of Ctrl+R to search previously run commands, arrow keys and tab autocompletion.

• Tab - Autocomplete the word based on what we have typed.
• Arrow Keys - up/down keys Navigate to frequently used commands.
• CTRL+R - It's like a search box to find the previously ran command.