The meaning of Linux system level and special characters

Operating level:

0 is shutdown

1 is single-user mode

2 is a multi-user mode with no NFS

3 is multi-user mode, command-line mode

4 is not used

5 is the graphical desktop

6 is reboot

Special character Meaning:

~ Is home directory/root

-The path where the user was last

. A dot is another feature of the current directory, regular, any single character.

.. Parent directory for current directory

| Pipeline

> Output redirection >> Append output redirection

< input redirection << append input redirection

1) The!+ letter indicates that the most recent command that starts this letter is recalled.

2)!! Represents a command that uses the most recent operation.

3)!+ number indicates the first order to recall history

The meaning of Linux system level and special characters