NetBSD/usr.sbin/ifwatchd/ifwatchd.8

.\" $NetBSD: ifwatchd.8,v 1.26 2010/04/16 13:47:50 jmcneill Exp $
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.\" This code is derived from software contributed to The NetBSD Foundation
.\" by Martin Husemann <martin@NetBSD.org>.
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.Dd April 16, 2010
.Dt IFWATCHD 8
.Os
.Sh NAME
.Nm ifwatchd
.Nd "watch for addresses added to or deleted from interfaces and call up/down-scripts for them"
.Sh SYNOPSIS
.Nm
.Op Fl hiqv
.Op Fl A Ar arrival-script
.Op Fl c Ar carrier-script
.Op Fl D Ar departure-script
.Op Fl d Ar down-script
.Op Fl u Ar up-script
.Op Fl n Ar no-carrier-script
.Ar ifname(s)
.Sh DESCRIPTION
.Nm
is used to monitor dynamic interfaces (for example PPP interfaces)
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
.Xr pppd 8
or
.Xr isdnd 8 ) ,
but sometimes the interfaces run completely autonomously (like
.Xr pppoe 4 ) .
.Pp
.Nm
provides a generic way to watch these types of changes.
It works by monitoring the routing socket and interpreting
.Ql RTM_NEWADDR
.Pq address added ,
.Ql RTM_DELADDR
.Pq address deleted
and
.Ql RTM_IFINFO
.Pq 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
.Nm
is run.
.Pp
The following options are available:
.Bl -tag -width indent
.It Fl A Ar arrival-script
Specify the command to invoke on arrival of new interfaces (like
PCMCIA cards).
.It Fl c Ar carrier-script
Specify the command to invoke when the carrier status transitions from
no carrier to carrier.
.It Fl D Ar departure-script
Specify the command to invoke when an interface departs (for example
a PCMCIA card is removed.)
.It Fl d Ar down-script
Specify the command to invoke on
.Dq interface down
events (or: deletion of an address from an interface).
.It Fl h
Show the synopsis.
.It Fl i
Inhibit a call to the up-script on startup for all watched interfaces
already marked up.
If this option is not given,
.Nm
will check all watched interfaces on startup whether they are
already marked up and, if they are, call the up-script with
appropriate parameters.
Additionally, if the interface is up and has a link,
.Nm
will run the carrier script.
.Pp
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
.Nm
calls them on startup to account for this (and make the scripts
easier.)
.It Fl n Ar no-carrier-script
Specify the command to invoke when the carrier status transitions from
carrier to no carrier.
.It Fl q
Be quiet and don't log non-error messages to syslog.
.It Fl u Ar up-script
Specify the command to invoke on
.Dq interface up
events (or: addition of an address to an interface).
.It Fl 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.
.Em You do not want to use this option in
.Pa /etc/rc.conf !
.It Ar ifname(s)
The name of the interface to watch.
Multiple interfaces may be specified.
Events for other interfaces are ignored.
.El
.Sh EXAMPLES
.Bd -literal -offset indent
# ifwatchd -u /etc/ppp/ip-up -d /etc/ppp/ip-down pppoe0
.Ed
.Pp
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:
.Bd -literal -offset indent
#! /bin/sh
/sbin/route add default $5
/sbin/route add -inet6 default fe80::2 -iface ifp $1
.Ed
.Pp
As described below the fifth command line parameter will contain
the peer address of the pppoe link.
The corresponding ip-down script is:
.Bd -literal -offset indent
#! /bin/sh
/sbin/route delete default $5
/sbin/route delete -inet6 default fe80::2
.Ed
.Pp
Note that this is not a good idea if you have pppoe0 configured to
connect only on demand (via the link1 flag), but works well for
all permanent connected cases.
Use
.Bd -literal -offset indent
! /sbin/route add default -iface 0.0.0.1
.Ed
.Pp
in your
.Pa /etc/ifconfig.pppoe0
file in the on-demand case.
.Pp
The next example is for dhclient users.
.Bd -literal -offset indent
# ifwatchd -i -c /etc/dhcp/carrier-detect tlp0
.Ed
.Pp
With the above command, the carrier-detect script will be invoked when
a carrier is detected on the interface 
.Ar tlp0 .
Note that the
.Ar -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 
.Cm dhclient .
.Bd -literal -offset indent
#! /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`
fi
# Start dhclient again on this interface
/sbin/dhclient $1
.Ed
.Sh PARAMETERS PASSED TO SCRIPTS
The invoked scripts get passed these parameters:
.Bl -tag -width destination
.It Ar 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).
.It Ar tty
Dummy parameter for compatibility with
.Xr pppd 8
which will always be
.Em /dev/null .
.It Ar speed
Dummy parameter for compatibility with
.Xr pppd 8
which will always be
.Em 9600 .
.It Ar address
The new address if this is an up event, or the no longer valid old
address if this is a down event.
.Pp
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.
.It Ar destination
For point to point interfaces, this is the remote address of the
interface.
For other interfaces it is the broadcast address.
.El
.Sh ERRORS
The program logs to the syslog daemon as facility
.Dq daemon .
For detailed debugging use the
.Fl v
(verbose) option.
.Sh SEE ALSO
.Xr pppoe 4 ,
.Xr route 4 ,
.Xr ifconfig.if 5 ,
.Xr rc.d 8 ,
.Xr route 8
.Sh HISTORY
The
.Nm
utility appeared in
.Nx 1.6 .
.Sh AUTHORS
The program was written by
.An Martin Husemann
.Aq martin@NetBSD.org .
.Sh CAVEATS
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.