How to Change Permissions in Absolute Mode

1. If you are not the owner of the file or directory, become superuser.

   Only the current owner or superuser can use the chmod command to change file permissions on a file or directory.

2. Change permissions in absolute mode by using the chmod command.

   $ chmod nnn filename

   nnn	Specifies the octal values that represent the permissions for the file owner, file group, and others, in that order. See Table 17-5 for the list of valid octal values.
   filename	Specifies the file or directory.

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   Note -

   If you use chmod to change the file group permissions on a file with ACL entries, both the file group permissions and the ACL mask are changed to the new permissions. Be aware that the new ACL mask permissions can change the effective permissions for additional users and groups who have ACL entries on the file. Use the getfacl(1) command to make sure the appropriate permissions are set for all ACL entries.

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3. Verify the permissions of the file have changed.

   $ ls -l filename

Example--Changing Permissions in Absolute Mode

The following example shows changing the permissions of a public directory from 744 (read/write/execute, read-only, and read-only) to 755 (read/write/execute, read/execute, and read/execute).

$ ls -ld public_dir
drwxr--r--  1 ignatz   staff    6023 Aug  5 12:06 public_dir
$ chmod 755 public_dir
$ ls -ld public_dir
drwxr-xr-x  1 ignatz   staff    6023 Aug  5 12:06 public_dir

The following example shows changing the permissions of an executable shell script from read/write to read/write/execute.

$ ls -l my_script
-rw------- 1 ignatz   staff    6023 Aug  5 12:06 my_script
$ chmod 700 my_script
$ ls -l my_script
-rwx------ 1 ignatz   staff    6023 Aug  5 12:06 my_script