macOS Mojave Software Update error - "A server with the specified hostname could not be found." How do I get rid of this message and in fact manage to update the machine?


A server with the specified hostname could not be found.
An error occurred while installing the selected updates.

I can browse internal and external websites fine, name resolution works fine, a packet capture tcpdump -i en7 port 53 and subsequent analysis of the dump using tshark shows that the name software update requires resolves just fine:
1   0.000000 ww.xx.yy.zz → vv.ww.xx.yy  DNS 76 Standard query 0xc474 A swscan.apple.com
2   0.014597  vv.ww.xx.yy → ww.xx.yy.zz DNS 210 Standard query response 0xc474 A swscan.apple.com CNAME swscan-cdn.apple.com.akadns.net CNAME swdist.apple.com.edgekey.net CNAME e5977.e9.akamaiedge.net A 104.113.184.251
I've been having this problem myself recently. What just happened to work for me (after already attempting restarts, dns flushes, dns server changes) is to disable Content Caching. Content Caching can be found in System Settings ➡︎ Sharing.

After this the update started to download immediately.