How to do it...

In order to set permissions for files, we use the chmod command.

Assume that we need to set the permission, rwx rw- r-.

Set these permissions with chmod:

    $ chmod u=rwx g=rw o=r filename

The options used here are as follows:

• u: This specifies user permissions
• g: This specifies group permissions
• o: This specifies others permissions

Use + to add permission to a user, group, or others, and use - to remove the permissions.

Add the executable permission to a file, which has the permission, rwx rw- r-:

    $ chmod o+x filename

This command adds the x permission for others.

Add the executable permission to all permission categories, that is, for user, group, and others:

    $ chmod a+x filename

Here a means all.

In order to remove a permission, use -. For example, $ chmod a-x filename.

Permissions can be denoted with three-digit octal numbers in which each digit corresponds to user, group, and other, in that order.

Read, write, and execute permissions have unique octal numbers, as follows:

• r = 4
• w = 2
• x = 1

We calculate the required combination of permissions by adding the octal values. Consider this example:

• rw- = 4 + 2 = 6
• r-x = 4 + 1 = 5

The permission rwx rw- r-- in the numeric method is as follows:

• rwx = 4 + 2 + 1 = 7
• rw- = 4 + 2 = 6
• r-- = 4

Therefore, rwx rw- r-- is equal to 764, and the command to set the permissions using octal values is $ chmod 764 filename.