Malwaredomains list doesn't exist

https://mirror1.malwaredomains.com/files/justdomains
that url results in not found error in web browser.

and using

pihole -g

[i] Target: https://mirror1.malwaredomains.com/files/justdomains
[✗] Status: Not found
[✗] List download failed: no cached list available

after deleting gravity.db and gravity_temp.db, runing pihole -g should fix it

This list is obsolete and no longer maintained. You should delete it.

thanks for the update. pihole basic-install.sh script still has it default set to on @line 1291

1291 MalwareDom "MalwareDomains" on)

This is because the changed code has not yet been incorporated in the master branch of Pi-hole.

It is in the development branch only at this point.

FYI - Have noticed the last 2 updates (sudo pihole -up) has an error, source not found, for the malware domain list.

riskanalytics has a notification of shutting off the feed (Nov/2019) and provides a new source for the feed to the list malware domains.