File Permissions

r = READ (View the file/directory)
w = WRITE (Change/modify the file/directory)
x = EXECUTE (Run code/program or enter directory)

rwx = 7
rw- = 6
r-x = 5
r– = 4
— = 0

Each group of 3 permissions is in the following order:
user:group:others

Common Permissions
777 = rwxrwxrwx
770 = rwxrwx—
755 = rwxr-xr-x
700 = rwx——
666 = rw-rw-rw
644 = rw-r–r–
600 = rw——-

The numbers stand for 1 or 0 in each group of 3. E.g. 6 in binary is 110 = rw but no x.

The first character is either a hyphen or a ‘d.’ A hyphen denotes a regular file, while a ‘d’
denotes a directory.
The next three characters tell us the permissions for the user that owns the file.
The following three characters tell us the permissions for all members of the group
which owns the file.
The final three characters tell us the permissions for all others.

Example
-rwx—— 1 [User] [Group] [size] [Date-Modified] [Filename]
-rwxr–r– 1 root root 5386 Nov 15 14:49 r00ter.c

root user can rwx, root group can read, others can read only. Size=5385, date as shown, filename=r00ter.c

Changing permissions
chmod 777 filename gives rwx user, group and others
chmod +x filename gives x to user group and others

Change ownership
chown root filename changes file ownership to root
chgrp root filename changes group for file to root