Comment 16 for bug 1728739

Same issue for me:

root@myserver:~# uname -r
4.4.0-112-generic
root@myserver:~# ceph version
ceph version 12.2.2 (cf0baeeeeba3b47f9427c6c97e2144b094b7e5ba) luminous (stable)
root@myserver:~# rbd create testimage --size 10G
root@myserver:~# rbd ls -l
NAME SIZE PARENT FMT PROT LOCK
testimage 10240M 2
root@myserver:~# rbd map testimage
rbd: sysfs write failed
In some cases useful info is found in syslog - try "dmesg | tail".
rbd: map failed: (110) Connection timed out
root@myserver:~# dmesg | tail
[ 1392.958472] libceph: mon0 51.254.215.26:6789 feature set mismatch, my 106b84a842a42 < server's 40106b84a842a42, missing 400000000000000
[ 1392.958721] libceph: mon0 51.254.215.26:6789 missing required protocol features

... same last two messages repeat