chmod command

chmod: command is used to set the access permissions of a specific file or directory.

Example:

chmod who=permissions filename   (This gives “who” the specified permissions for a given filename.) 

Permissions: 

Of course, the permissions are the same letters that you see in the directory listing: 

r	Permission to read the file.
w	Permission to write the file.
x	Permission to execute the file, or, in the case of a directory, search it.

who: 

The “who” is a list of letters that specifies whom you’re going to be giving permissions to. These may be specified in any order. 

Letter	Meaning
u	The user who owns the file (this means “you.”)
g	The group the file belongs to.
o	The other users
a	all of the above (an abbreviation for ugo)