We did not have any cephfs or mds involved. But since you haven’t even started a ceph upgrade in earnest, I have to wonder about your nautilus versions. Maybe you have a mismatch there? I would definitely share the output of `ceph versions` and `ceph features`. If you’re not 14.2.22 across the board, I would at least upgrade your mon, mgr, and mds services. Then check release notes to see if there’s any clues there. Thank you, Josh Beaman From: Götz Reinicke <goetz.reinicke@filmakademie.de> Date: Friday, August 4, 2023 at 9:02 AM To: ceph-users@ceph.io <ceph-users@ceph.io> Subject: [EXTERNAL] [ceph-users] cephfs mount problem - client session lacks required features Hi, During the upgrade from centos7/nautilus to ubuntu 18/nautilus (still updating the MONs) I got a cephfs client who refuses or is refused to mount the ceph fs again. The clients says: mount error 13 = Permission denied The cephmds log: lacks required features 0x0000000000001000 client supports 0x00000000000000ff The mds/mon is still centos7/nautilus. The Clients centos7 as well. Any ideas ? Thx for suggestions and hints . Best Götz