Krusader can use several external programs for additional functionality, from
diff utilities to email programs.

https://docs.kde.org/trunk5/en/extragear-utils/krusader/konfig-dependencies.html
contains a list of programs Krusader optionally looks for.

To use 'update DB' button in the locate dialog, open "Settings->Configure
Krusader -> Dependencies" and write '/usr/libexec/locate.updatedb' into the
field 'updatedb'.