WARNING: index 'main1': lock: failed to lock

[Axel]

Hi all.

Starting searchd via PuTTy  I receive the following:

precaching index 'main1'
WARNING: index 'main1': lock: failed to lock /var/piler/sphinx/main1.spl: Resource temporarily unavailable; NOT SERVING

Same for main2, main3 and main4.

Sphinx 2.2.11 runs on Ubuntu 18 LTS.

Any suggestions what Sphinx is telling me?

Regards

Axel