How to Change Special File Permissions in Absolute Mode

1. If you are not the owner of the file or directory, become superuser or assume an equivalent role.

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

2. Change special permissions in absolute mode.

   % chmod nnnn filename

   nnnn

   Specifies the octal values that change the permissions on the file or directory. The leftmost octal value sets the special permissions on the file. For the list of valid octal values for special permissions, see Table 7–6.

   filename

   Specifies the file or directory.

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   Note –

   When you use the chmod command 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 permissions for additional users and groups who have ACL entries on the file. Use the getfacl command to make sure that the appropriate permissions are set for all ACL entries. For more information, see the getfacl(1) man page.

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3. Verify that the permissions of the file have changed.

   % ls -l filename

Example 7–5 Setting Special File Permissions in Absolute Mode

In the following example, the setuid permission is set on the dbprog file.

# chmod 4555 dbprog
# ls -l dbprog
-r-sr-xr-x   1 db     staff        12095 May  6 09:29 dbprog

In the following example, the setgid permission is set on the dbprog2 file.

# chmod 2551 dbprog2
# ls -l dbprog2
-r-xr-s--x   1 db     staff       24576 May  6 09:30 dbprog2

In the following example, the sticky bit permission is set on the public_dir directory.

# chmod 1777 public_dir
# ls -ld public_dir
drwxrwxrwt   2 ignatz   staff          512 May 15 15:27 public_dir