Linux basic Commands (3)

1. Use commands with absolute paths, such as

$/bin/ls

2. View the user's preset path

$ echo $PATH

$/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games

Multiple paths separated by colons, if a command has two versions of the path exist, such as/usr/local/bin and/usr/bin, then the former is selected for execution;

3. Add a command path

If the system cannot find a command, the path to the command must be added to the search path

$ export path= $PATH:/usr/bin;

The above command indicates that the path of/usr/bin is added after the original search command.

4. Put the command in the background and back from the background

$ gcc hello.cc &

[1] 21475

After the command & will put the command in the background, return [1] is assigned to the command of the work sequence number, 21475 is the process identification code

$ FG%1

$ FG 21475

These two commands can bring the previous command back to the foreground from the background

$ kill%1

Terminate the command

5. Reference manual, manual pages

$ man ls; View ls command

$ man 1 ls; 1 indicates command code

$ apropos Edit: Query the command related to edit, the system according to the name in the manual find

$ info Find

6. File Ownership and Permissions

Read, readable, write, writable (add or delete files), execute, executable (listing the relevant information in the directory)

UNIX File permissions: Owner (owner), Group of file owner (group), other user (others)

The results of the LS-L command are as follows

7. Change permission Commands

First, you must be a root

$ chown bin sample; Change the owner of the sample program to Bin

$ chgrp bin sample; Change the group of sample programs to Bin

$ chmod +x header; Add executable permission to header file

$ chmod-x Header;

$ chmod u+x header; Set executable permissions only to yourself

$ chmod ug+rwx header; Assign multiple permissions at once

$ chmod Absolute mode header;

$ umask Absolute mode header;

Such as:

$ chmod 777 header; Open all permissions for all users, 7=4+2+1;

$ chmod 741 Header:user All permissions, group Read and execute, other execute permissions

$ umask The absolute mode is reversed, take the complement

such as: $ umask 027 Headr; With the same effect as the chmod