Changing file permissions on Linux Operating System

To change a file's permissions, you need to use a program called chmod. With that command you can change
one or multiple file permissions. Here are a few examples:
$ chmod 755 file
$ ls -l file
-rwxr-xr-x 1 root users 1656 Mar 22 00:27 file
$ chmod 700 file
$ ls -l file
-rwx------ 1 root users 1656 Mar 22 00:27 file
$ chmod 664 file
$ ls -l file
-rw-rw-r-- 1 root users 1656 Mar 22 00:27 file
The numbers are based on the 3 types of permissions. Read = 4, write = 2 and execute = 1. A permission of
755 means the user will have read, write and execute permissions (4 + 2 + 1 = 7), and everyone else will have
read and execute permissions (4 + 1 = 5).