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IFWATCHD(8)               BSD System Manager's Manual              IFWATCHD(8)

     ifwatchd -- watch for addresses added to or deleted from interfaces and
     call up/down-scripts for them

     ifwatchd [-hiqv] [-A arrival-script] [-D departure-script]
              [-d down-script] [-u up-script] [-c carrier-script]
              [-n no-carrier-script] ifname(s)

     ifwatchd is used to monitor dynamic interfaces (for example PPP inter-
     faces) for address changes, and to monitor static interfaces for carrier
     changes.  Sometimes these interfaces are accompanied by a daemon program,
     which can take care of running any necessary scripts (like pppd(8) or
     isdnd(8)), but sometimes the interfaces run completely autonomously (like

     ifwatchd provides a generic way to watch these types of changes.  It
     works by monitoring the routing socket and interpreting 'RTM_NEWADDR'
     (address added), 'RTM_DELADDR' (address deleted) and 'RTM_IFINFO'
     (carrier detect or loss of carrier) messages.  It does not need special
     privileges to do this.  The scripts called for up or down events are run
     with the same user id as ifwatchd is run.

     The following options are available:

     -A arrival-script
             Specify the command to invoke on arrival of new interfaces (like
             PCMCIA cards).

     -c carrier-script
             Specify the command to invoke when the carrier status transitions
             from no carrier to carrier.

     -D departure-script
             Specify the command to invoke when an interface departs (for
             example a PCMCIA card is removed.)

     -d down-script
             Specify the command to invoke on ``interface down'' events (or:
             deletion of an address from an interface).

     -h      Show the synopsis.

     -i      Inhibit a call to the up-script on startup for all watched inter-
             faces already marked up.  If this option is not given, ifwatchd
             will check all watched interfaces on startup whether they are
             already marked up and, if they are, call the up-script with
             appropriate parameters.

             Since ifwatchd typically is started late in the system boot
             sequence, some of the monitored interfaces may already have come
             up when it finally starts, but their up-scripts have not been
             called.  By default ifwatchd calls them on startup to account for
             this (and make the scripts easier.)

     -n no-carrier-script
             Specify the command to invoke when the carrier status transitions
             from carrier to no carrier.

     -q      Be quiet and don't log non-error messages to syslog.

     -u up-script
             Specify the command to invoke on ``interface up'' events (or:
             addition of an address to an interface).

     -v      Run in verbose debug mode and do not detach from the controlling
             terminal.  Output verbose progress messages and flag errors
             ignored during normal operation.  You do not want to use this
             option in /etc/rc.conf!

             The name of the interface to watch.  Multiple interfaces may be
             specified.  Events for other interfaces are ignored.

           # ifwatchd -u /etc/ppp/ip-up -d /etc/ppp/ip-down pppoe0

     If your pppoe0 interface is your main connection to the internet, the
     typical use of the up/down scripts is to add and remove a default route.
     This is an example for an up script doing this:

           #! /bin/sh
           /sbin/route add default $5

     As described below the fifth command line parameter will contain the peer
     address of the pppoe link.  The corresponding ip-down script is:

           #! /bin/sh
           /sbin/route delete default $5

     Note that this is not a good idea if you have pppoe0 configured to con-
     nect only on demand (via the link1 flag), but works well for all perma-
     nent connected cases.  Use

           ! /sbin/route add default -iface

     in your /etc/ifconfig.pppoe0 file in the on-demand case.

     The next example is for dhclient users.

           # ifwatchd -i -c /etc/dhcp/carrier-detect tlp0

     With the above command, the carrier-detect script will be invoked when a
     carrier is detected on the interface tlp0.  Note that the -i flag pre-
     vents any action based on the initial state.  A script like the following
     should work for most users, although it will not work for machines with
     multiple interfaces running dhclient.

           #! /bin/sh
           # Arguments:  ifname tty speed address destination
           # If there is a dhclient already running, kill it.
           # (This step could be put in a distinct no-carrier script,
           # if desired.)
           if [ -f /var/run/dhclient.pid ]; then
                  /bin/kill `/bin/cat /var/run/dhclient.pid`
           # Start dhclient again on this interface
           /sbin/dhclient $1

     The invoked scripts get passed these parameters:

     ifname       The name of the interface this change is for (this allows to
                  share the same script for multiple interfaces watched and
                  dispatching on the interface name in the script).

     tty          Dummy parameter for compatibility with pppd(8) which will
                  always be /dev/null.

     speed        Dummy parameter for compatibility with pppd(8) which will
                  always be 9600.

     address      The new address if this is an up event, or the no longer
                  valid old address if this is a down event.

                  The format of the address depends on the address family, for
                  IPv4 it is the usual dotted quad notation, for IPv6 the
                  colon separated standard notation.

     destination  For point to point interfaces, this is the remote address of
                  the interface.  For other interfaces it is the broadcast

     The program logs to the syslog daemon as facility ``daemon''.  For
     detailed debugging use the -v (verbose) option.

     pppoe(4), route(4), ifconfig.if(5), rc.d(8), route(8)

     The ifwatchd utility appeared in NetBSD 1.6.

     The program was written by Martin Husemann <martinATNetBSD.org>.

     Due to the nature of the program a lot of stupid errors can not easily be
     caught in advance without removing the provided facility for advanced
     uses.  For example typing errors in the interface name can not be
     detected by checking against the list of installed interfaces, because it
     is possible for a pcmcia card with the name given to be inserted later.

BSD                             January 4, 2004                            BSD