dhclient and dhcp update require restart?

David Cantrell dcantrell at redhat.com
Wed Sep 2 20:33:25 UTC 2009


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On Wed, 2 Sep 2009, Dennis J. wrote:

> On 08/27/2009 07:49 PM, David Cantrell wrote:
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>> On Wed, 26 Aug 2009, Dariusz J. Garbowski wrote:
>> 
>>> Hi, something that bothers me a bit... More and more system restart
>>> requests with each update (even if one doesn't use the package at the
>>> time).
>>> 
>>> Is this necessary for dhclient and dhcp update packages to require
>>> restart?
>>> Wouldn't "service network restart" and "service dhcpd restart" in the
>>> install/upgrade
>>> scripts do the trick (after checking that the service is actually
>>> running)?
>>> Ssh used to do that since, well, as far as I remember.
>> 
>> Yes, 'service dhcpd restart' will work fine for dhcpd. For dhclient, it's
>> not necessarily as simple as restarting the network service. If you are
>> using
>> the network service, that will work fine. If you are using NetworkManager,
>> you'll need to either restart NetworkManager or have it down the connection
>> you're using dhclient on and bring it back up.
>
> Why is a restart of NetworkManager necessary in this case? If dhclient 
> reinitializes the interface and gets the old dhcp data then nothing really 
> changes and NetworkManager shouldn't have to care. If e.g. der IP changes 
> then NetworkManager should detect that and reinitialize the connection info 
> on its end (after all the "new" interface might not be connected to anything 
> and thus have to be marked as down anyway).

It doesn't work that way.  dhclient isn't a service with an init.d script.  If
you are using NetworkManager, dhclient is a child process of NetworkManager.
You can't just restart dhclient since NetworkManager is controlling it.  You
have to either tell NetworkManager to down the interface, stop dhclient, and
bring it back up -- or restart NetworkManager.  Either way, the result is the
same.

If you are using the network service, dhclient is run when the interface is
ifup'ed (so either restart the network service or ifup/ifdown the interface in
that case).

- -- 
David Cantrell <dcantrell at redhat.com>
Red Hat / Honolulu, HI

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