On a linux server, how do you find out how long the DNS cache expiry time is?
Use dig to query for the hostname in question.
In the case above, the TTL is 3550.
In a normal DNS server, this is usually configured at the zone level, in the SOA line. That's where you specify the default TTL for the domain. But it can also be set for a hostname specifically, with a syntax similar to the output of dig above.