linux:644, 755, 777 permissions

The first bit 7 equals 4+2+1,rwx, the owner has read, write, execute permission;

The second bit 5 equals 4+1+0,r-x, the same group of users have read, execute permissions but no write permission;

Third bit 5, ditto, is also r-x, other users have read, execute permissions but do not have write permission.

Common Linux file permissions are listed below:

444 r--r--r--
RW-------
644 rw-r--r--
666 rw-rw-rw-
RWX------
744 rwxr--r--
755 Rwxr-xr-x
777 Rwxrwxrwx

RWX permissions digital interpretation under Linux
Chmod can also use numbers to represent permissions such as chmod 777 file
The syntax is: chmod ABC file
Each of the a,b,c is a number that represents the permissions of the user, Group, and other respectively.
R=4,w=2,x=1
To rwx the attribute then 4+2+1=7;
To rw-the attribute then 4+2=6;
To r-x the property, 4+1=7.
Example:
chmod a=rwx File
And
chmod 777 File
Same effect
chmod ug=rwx,o=x File
And
chmod 771 File
Same effect
Use chmod 4755 filename to give this program root privileges

Summary: Permissions total 10 bits from the second position each of the three groups R W x 4 2 1 have the plus

linux:644, 755, 777 permissions