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How to change existing permissions symbolically

After you have determined what permissions are in effect, you can change them by executing the command chmod (change mod). chmod has two options; symbolic mode (using alphabetic characters) and absolute mode (uses numbers).

First of all we will deal with symbolic mode. In this mode the command is used with the following syntax:


WHO represents one or a combination of three classes (u,g, or o) where u is for user (owner), g is for group, and o is for other. The use of '+' allows us to add permissions to those already in existence, where as '-' removes permissions from those currently in use. '=' set the permissions specified and removes any permissions which are not mentioned explicitly. Permission is any combination of r, w, and x. Finally filename is the name of a file or directory. Note that there is no space between the arguments who[+-=]permission.

For example, assume 'myfile' has the following default permissions:

-rwxr-----.  1 john staff 500 Nov 18 12:25 myfile
If we wished to give the group 'staff' write access to 'myfile' we could use the following command:
% chmod g+w myfile
% ls -l myfile
-rwxrw----.  1 john staff 500 Nov 18 12:25 myfile

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