Using ISC-DHCPD to renew DHCP leases in an Active Directory domain. This requires using ktutil to generate a keytab for DHCPd to use in order to update secure dynamic DNS.

What I need to do is to be able to auto-renew the credential in the keytab. I'm aware of krenew and kinit -R, but what I need is something to automatically refresh them (indefinitely). I have near zero experience with bash or creating daemons.

I see that DHCPd is running as root, and I do have a Kerberos cache file at /tmp/krb5cc_0.

I'm using the Raspbian distribution.


use a cron job with kinit and the keytab (man kinit, look at options -k, eventually -t if you use other keytab than the host's).

Raspian is debian based, I believe, so maybe you can use the k5start package that should automate this for you.

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  • I was looking at k5start as well, but I must be doing something wrong with the syntax as I don't see it detach. Note that the keytab/cred cache is created using sudo as I figure root needs to be the one that owns it. sudo k5start -p /var/run/k5start.pid -b -f /etc/dhcp/user.keytab -U -K 10 -l 10h -- sh -c 'ls -l /tmp/krb5cc_0' – Trevor Seward Mar 27 '16 at 17:51
  • try getting a root prompt instead of using it under sudo. You should consider using -L to see eventual errors in syslog as well. – natxo asenjo Mar 27 '16 at 19:42
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    This worked for me: sudo k5start -f /etc/dhcp/user.keytab -U -k /tmp/krb5cc_0 -K 10 -l 10h -p /var/run/k5start.pid -L -b. I can see k5start running as root via ps. Obviously I'll need to monitor to make sure the ticket renewal is functional, but I think this is what I need. – Trevor Seward Mar 27 '16 at 19:43

Not familiar with krenew, kinit or Kerberos myself but how regularly do you want the credential to be renewed? If it is once per some time interval then cron is a good tool for that.

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