Table 3. Controlling User Access to at

/etc/at.allow       /etc/at.deny                  Resulting Policy
------------------------------------------------------------------------------------------------
Does not exist               Does not exist                  Only the root user has permission.
------------------------------------------------------------------------------------------------
Exists                           ----                        Only the users listed in /etc/at.allow
                                                             have permission.
------------------------------------------------------------------------------------------------
Does not exist               Exists                          All users have permission except those
                                                             listed in /etc/at.deny. This is
                                                             typically the default configuration
                                                             when Linux is installed.