How to flush DNS cache on HPUX

[Douglas D. Denney]

Hello,

I have a few general questions regarding DNS on HPUX.

1. Does DNS on HPUX honor TTL? For example, Sun Solaris ignores TTL and caches all entries.
2. Is it possible to flush the local DNS cache on an HPUX system without rebooting?

[John Kittel · Accepted solution]

some relevant info here:
http://forums1.itrc.hp.com/service/forums/bizsupport/questionanswer.do?threadId=993552

[rick jones]

IIRC the DNS _resolver_ library on HP-UX does no caching, other than the IP addresses of the DNS servers themselves. As such, there is no need to "flush" any cache as there is none.

If you change the IPs of the DNS servers, you will need to restart processes.

Now, if you decided to run a caching-only DNS server on the HP-UX system, and then point the /etc/resolv.conf file at _it_ then you would follow "standard" cache flushing for BIND named. It could be as simple as killing and restarting named.

Again though, IIRC there is no caching in the HP-UX resolver library itself.

And if Sun's resolver library caches and ignores TTL's it is fundamentally broken... :)

[Douglas D. Denney]

Issue resolved.

[Joshua Laden]

How did you end up resolving this issue.

I have changed ips on my dns servers, and have hpux systems not resolving properly.

[rick jones]

While there is no cache of responses kept in the HP-UX resolver library, the resolver library does in effect "cache" the settings in /etc/resolv.conf as it only reads the file once in the life of a process. So, if you change the IP addresses of your DNS servers, those processes must be restarted to have them see the new IPs you have placed in /etc/resolv.conf.