Hello! This occurs if for some reason the prefill file happens to be empty: kresd[11812]: [prefill] root zone file valid for 17 hours 01 minutes, reusing data from disk kresd[11812]: segfault at 0 ip 00007f9b06017436 sp 00007ffc3142bb58 error 4 in libc-2.28.so[7f9b05fa1000+148000] Apr 30 20:26:13 scruffy kernel: Code: 0f 1f 40 00 66 0f ef c0 66 0f ef c9 66 0f ef d2 66 0f ef db 48 89 f8 48 89 f9 48 81 e1 ff 0f 00 00 48 81 f9 cf 0f 00 00 77 6a <f3> 0f 6f 20 66 0f 74 e0 66 0f d7 d4 85 d2 74 04 0f bc c2 c3 48 83 This happens in a loop until systemd gives up trying to start kresd. Solved by removing /var/cache/knot-resolver/root.zone (0 bytes). kresd version: 4.0.0 We use your example config from: https://knot-resolver.readthedocs.io/en/stable/modules.html#cache-prefilling kind regards, Christoph