IFACE OPTIONS
       The  following  "command" options are available for every family and method.  Each of these options can be given multiple times in a single stanza, in which case the commands are executed in the order in which they appear in
       the stanza.  (You can ensure a command never fails by suffixing "|| true".)

       pre-up command
              Run command before bringing the interface up.  If this command fails then ifup aborts, refraining from marking the interface as configured, prints an error message, and exits with status 0.  This behavior  may  change
              in the future.

       up command

       post-up command
              Run command after bringing the interface up.  If this command fails then ifup aborts, refraining from marking the interface as configured (even though it has really been configured), prints an error message, and exits
              with status 0.  This behavior may change in the future.

       down command

       pre-down command
              Run command before taking the interface down.  If this command fails then ifdown aborts, marks the interface as deconfigured (even though it has not really been deconfigured), and exits with status 0.   This  behavior
              may change in the future.

       post-down command
              Run command after taking the interface down.  If this command fails then ifdown aborts, marks the interface as deconfigured, and exits with status 0.  This behavior may change in the future.

       There exists for each of the above mentioned options a directory /etc/network/if-<option>.d/ the scripts in which are run (with no arguments) using run-parts(8) after the option itself has been processed. Please note that as
       post-up and pre-down are aliases, no files in the corresponding directories are processed.  Please use if-up.d and if-down.d directories instead.

       All of these commands have access to the following environment variables.

       IFACE  physical name of the interface being processed

       LOGICAL
              logical name of the interface being processed

       ADDRFAM
              address family of the interface

       METHOD method of the interface (e.g., static)

       MODE   start if run from ifup, stop if run from ifdown

       PHASE  as per MODE, but with finer granularity, distinguishing the pre-up, post-up, pre-down and post-down phases.

       VERBOSITY
              indicates whether --verbose was used; set to 1 if so, 0 if not.

       PATH   the command search path: /usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin

       Additionally, all options given in an interface definition stanza are exported to the environment in upper case with "IF_" prepended and with hyphens converted to underscores and non-alphanumeric characters discarded.

       When ifupdown is being called with the --all option, before doing anything to interfaces, if calls all the hook scripts (pre-up or down) with IFACE set to "--all", LOGICAL set to the current value of  --allow  parameter  (or
       "auto" if it's not set), ADDRFAM="meta" and METHOD="none".  After all the interfaces have been brought up or taken down, the appropriate scripts (up or post-down) are executed.