what are xnds entries in /var/cpanel/users/[cpaneluser]

[cookiesunshinex]

I was receiving a warning that one of my backups was suddenly failing.

I received an email stating that I should check:
/usr/local/cpanel/logs/error_log

In this log, I found:
info [cpanellogd] Invalid domain in /var/cpanel/users/usernameexample XDNS entry, skipping

In /var/cpanel/users/usernameexample I found 3 entries at the bottom that don't look quite right.

There was a typo in one of them and I cleaned it up.

I'm not sure that they should be there though. Where do these come from and where are they set?

And, why are my backups just suddenly failing, or at least I'm just suddenly getting a notification that it failed?

[PlatinumServerM]

The XDNS are usually removed or incomplete domain entries. You can clean that up manually.

Backups are not related to that. You can check the cpbackup logs to see what is going on there.

[thewebhosting]

You can check the cpbackup logs to see what is going on there.

You can check it from /usr/local/cpanel/logs/cpbackup/xxxxx.log

[InstaCarma_Tech]

And, why are my backups just suddenly failing, or at least I'm just suddenly getting a notification that it failed?

They might not be failing actually. Check the backup file that was created for any discrepancies.

Also, have a look at this
cpbackup failure - permission denied - cPanel Forums

[cookiesunshinex]

OK, this was a false alarm.

It was just a coincidence that I found the xdns errors in the tail of the error log at the same time I was looking for the backup errors.

The backup errors were not actually errors at all, they were just notifications that certain cache files could not be backed up for an account that had OpenX adserver installed.

/bin/gtar: ./public_html/adserver/var/cache/deliverycache_8c55765c48b36458458f4543aca49b9f.php: Cannot open: Permission denied
/bin/gtar: ./public_html/adserver/var/cache/deliverycache_5f9edebdf29ac4edb87729ea6399b1f1.php: Cannot open: Permission denied

These must have started creating what the backup program considers to be an error after an upgrade of OpenX adserver, but I didn't put two and two together at the time and didn't consider too important at the time.

When I did go back in and dig into it, I didn't remember that I had upgraded OpenX at about the same time the errors started appearing.