gentoo-overlay/sys-cluster/ceph/files/ceph-osd_at.service

[Unit]
Description=Ceph object storage daemon
After=network-online.target local-fs.target
Wants=network-online.target local-fs.target
PartOf=ceph.target

[Service]
Environment=CLUSTER=ceph
ExecStart=/usr/bin/ceph-osd -f --cluster ${CLUSTER} --id %i
ExecStartPre=/usr/libexec/ceph/ceph-osd-prestart.sh --cluster ${CLUSTER} --id %i

[Install]
WantedBy=ceph.target