umask

umask stands for user file creation mode mask.
777 stands for rwxrwxrwx. first set of rwx is for user, second set of rwx for group and last set is for others. to know what umask u have, at the prompt type umask, which will return a value, say 022.
What does that mean o22?
Its simple.
777-022=755.
umask 022 = rwxr-xr-x, meaning, user has all permissions, group has read and execute, others have read and execute.
To understand umask in permissions mode try this command, umask -S
for example
$ umask
022
$ umask -S
u=rwx,g=rx,o=rx