can dhclient trigger actions when it gets ip from DHCP server ?

5883 · 04-03-2014, 10:09 AM

normally if eth cable up/down can trigger the scripts in the if-up.d, if-down.d.

Now sometimes our DHCP server is not good, you plugin your eth cable for your system, it won't get ip.
sometime later it gets ip.

when it gets it, is there a way i get notified and do some actions ?

allend · 04-04-2014, 07:17 AM

As far as I know, dhclient cannot do this. However, if you are using DHCP and getting DNS addresses, these will be saved in /etc/resolv.conf. You could monitor that file for changes using inotify.

rknichols · 04-04-2014, 02:18 PM

You didn't mention which distro you are using, but for the Red Hat family, if you have an executable script dhclient-exit-hooks in $(ETCDIR} (normally either /etc/dhclient or /etc), then it will be sourced by /sbin/dhclient-script each time a dhclient event occurs. Since it is sourced, not called, all of the internal variables in dhclient-script are available, in particular $reason, which might be "BOUND", "RENEW", "REBIND", etc. You'll need to look at /sbin/dhclient-script for further info.

5883 · 04-04-2014, 05:11 PM

with stunnel on, it shows sth. like 127.0.0.1, not the real one.

Quote:

Originally Posted by allend

As far as I know, dhclient cannot do this. However, if you are using DHCP and getting DNS addresses, these will be saved in /etc/resolv.conf. You could monitor that file for changes using inotify.

---------- Post added 04-04-14 at 05:12 PM ----------

looks like this is what i want, using ubuntu, where should it be pls ?

Quote:

Originally Posted by rknichols

You didn't mention which distro you are using, but for the Red Hat family, if you have an executable script dhclient-exit-hooks in $(ETCDIR} (normally either /etc/dhclient or /etc), then it will be sourced by /sbin/dhclient-script each time a dhclient event occurs. Since it is sourced, not called, all of the internal variables in dhclient-script are available, in particular $reason, which might be "BOUND", "RENEW", "REBIND", etc. You'll need to look at /sbin/dhclient-script for further info.

rknichols · 04-04-2014, 08:19 PM

You couldn't find it?? /sbin/dhclient-script is in exactly the same place, and in the /etc/dhcp directory you will find subdirectories dhclient-enter-hooks.d and dhclient-exit-hooks.d, both with some scripts for you to look at. This is on a Ubuntu 13.04 Live CD.

5883 · 04-07-2014, 05:38 PM

found it, thanks so much !

Quote:

Originally Posted by rknichols

You couldn't find it?? /sbin/dhclient-script is in exactly the same place, and in the /etc/dhcp directory you will find subdirectories dhclient-enter-hooks.d and dhclient-exit-hooks.d, both with some scripts for you to look at. This is on a Ubuntu 13.04 Live CD.