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] [-c carrier-script] [-D departure-
script] [-d down-script] [-u up-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 (such
as pppoe(4)).
Attention: on current MirBSD, only address additions for pppoe(4) inter-
faces are tested.
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 (such
as 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 ex-
ample 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 al-
ready marked up and, if they are, call the up-script with ap-
propriate parameters. Additionally, if the interface is up and
has a link, ifwatchd will run the carrier script.
Since ifwatchd typically is started late in the system boot se-
quence, 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: addi-
tion 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 ig-
nored during normal operation. You do not want to use this option
in /etc/rc.conf!
ifname(s)
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/mksh
/sbin/route -n 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/mksh
/sbin/route -n 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 per-
manent connected cases. Use
! /sbin/route -n add default -iface 0.0.0.1
in your /etc/hostname.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 prevents
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/mksh
# 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
kill $(</var/run/dhclient.pid)
fi
# 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 ad-
dress.
The program logs to the syslog daemon as facility "daemon". For detailed
debugging use the -v (verbose) option.
pppoe(4), route(4), hostname.if(5), rc.conf(8), route(8)
The ifwatchd utility appeared in NetBSD 1.6 first and was ported to
MirBSD #8.
The program was written by Martin Husemann <martin@NetBSD.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 pos-
sible for a pcmcia card with the name given to be inserted later.
MirBSD #10-current November 4, 2004 2