Linux permissions are a set of flags associated with each file determines who can access that file, and how they can access it. These flags are called file permissions or modes, as in "mode of access." The command name chmod stands for "change mode." It restricts the way a file can be accessed.
user group others
r w x r w x r w x
4 2 1 4 2 0 4 0 1
4+2+1 = 7 (rwx) # user
4+2 = 6 (rw) # group
4+1 = 5 (rx) # others
Absolute permission doen't really work well with recursion and wildcards, as it is absolute and likely change required permissions that are unknown to the administrator:
chomd 600 <filename> # Configure rw for user and no permissions for assigned group and others
u user
g group
o others
r read
w write
e execute
+ Adds the selected file mode bits to the file/pattern
- Removes the selected file mode bits from the file/pattern
Relative permissions can be set using symbolic permission notation:
chmod u+rw <filename> # Add rw to user
chmod ug-rw <filename> # Remove read write from user & group