To check the status of Ceph's MDS, run ceph mds stat or ceph mds dump.

# ceph mds stat
e85: 1/1/1 up {0=ceph-mds001=up:active}
    
# ceph mds dump
dumped mdsmap epoch 85
epoch    85
flags    0
created 2017-10-20 11:11:11.1138
modified 2017-10-22 13:13:13.1701
tableserver     0
root     0
session_timeout 60
session_autoclose        300
max_file_size   1099511627776
last_failure    0
last_failure_osd_epoch   666
compat  compat={},rocompat={},incompat={1=base v0.20,2=client writeable ranges,3=default file layouts on dirs,4=dir inode in separate object,5=mds uses versioned encoding,6=dirfrag is stored in omap}
max_mds   1
in        0
up        {0=1138}
failed
stopped
data_pools       0
metadta_pool     1
inline_data      disabled
1138:  196.168.1.1:6800/2046 'ceph-mds001' mds.0 13 up; active seq 4252