How to change existing permissions

After you have determined what permissions are in effect, you can change them by calling the chmod command in the following format:

   chmod who+permission file(s)

   chmod who-permission file(s)

chmod	name of the program
who	one of three user groups: user group ohers
+ or -	instruction that grants (+) or denies (-) permission
permission	any combination of three authorizations: read write execute
file(s)	file (or directory) name(s) listed; assumed to be branches from your current directory, unless you use full pathnames

The following examples show a few possible ways to use the chmod command. As the owner of display, you can read, write, and run this executable file. You can protect the file against being accidentally changed by denying yourself write (w) permission. To do this, type the command line:

   chmod u-w display

As you can see, you no longer have permission to write changes into the file. You will not be able to change this file until you restore write permission for yourself.

Now consider another example. Notice that permission to write into the file display has been denied to members of your group and other system users. However, they do have read permission. This means they can copy the file into their own directories and then make changes to it. To prevent all system users from copying this file, you can deny them read permission by typing:

   chmod go-r display

For more information, refer to ls(1) and chmod(1).