Note: this is now largely a historical document. More modern distributions have better ways of doing this, and with the demise of the Fedora Legacy project in 2007, Red Hat 9 is now entirely unsupported.
I needed, in Red Hat 9, to spoof the MAC address of an ethernet card. This is easy to do:
ifconfig eth0 hw ether 01:02:03:04:05:06
But I wanted it to happen automatically every time the interface
was brought up. I had some trouble working out the Right Way to hook
this into RH9's configuration, and eventually came up with the
following hack: a line at the start of
DUMMY_GHGHGH=`if ! ip link | grep -q 'eth0:.*UP' ; then ifconfig eth0 hw ether 01:02:03:04:05:06 ; echo "$0: Pont's MAC munger activated." 1>&2; fi` DEVICE=eth0 ONBOOT=yes [... etc.]
This seems to work. (The interface has to be down to allow the
address change, hence the
ip link | grep
ifcfg-eth0 appears to be sourced at various points,
but the only important thing is that it's sourced at least once by
Addendum: Red Hat appears to keep three copies of each ifcfg file, and I have not yet discovered how it chooses which one to execute. It's not always the same one. I dealt with it by hard linking them all to the same file (which appeared to be partially the case already).
$ locate ifcfg-eth0 /etc/sysconfig/network-scripts/ifcfg-eth0 /etc/sysconfig/networking/devices/ifcfg-eth0 /etc/sysconfig/networking/profiles/default/ifcfg-eth0
This is not ideal. I should tighten up that regular expression:
I'm worried about false
eth0.*[<,]UP[,>] should be good, but don't
have time to test it now. But attempting an ifconfig on an
active interface probably isn't disastrous anyway.
Footnote, 2008: looking back at this, I have no idea why the "DUMMY_GHGHGH=" is necessary, unless RH9 actively enforces the VARIABLE=VALUE format of that file. I don't have a RH9 installation to test it on any more, so I'm going to leave it in.