Pacemaker fails to start after running crm cluster init

Pacemaker fails to start after running crm cluster init -y

sles15sp5-node1:~ # crm cluster init -y
INFO: Loading "default" profile from /etc/crm/profiles.yml
INFO: SSH key for root does not exist, hence generate it now
INFO: SSH key for hacluster does not exist, hence generate it now
INFO: Configuring csync2
INFO: Starting csync2.socket service on sles15sp5-node1
INFO: BEGIN csync2 checking files
INFO: END csync2 checking files
INFO: Configuring corosync (unicast)
WARNING: Not configuring SBD - STONITH will be disabled.
INFO: Hawk cluster interface is now running. To see cluster status, open:
INFO:   https://192.168.150.40:7630/
INFO: Log in with username 'hacluster', password 'linux'
WARNING: You should change the hacluster password to something more secure!
INFO: BEGIN Waiting for cluster
.............................................................                                                                                                                                           ERROR: FAIL Waiting for cluster
ERROR: cluster.init: Time out waiting for cluster.

Pacemaker fails to start because it depends on Corosync which has failed to start due to an error writing to /dev/shm/

sles15sp5-node1:~ # journalctl -u pacemaker -e --no-pager
Mar 11 14:32:39 sles15sp5-node1 systemd[1]: Dependency failed for Pacemaker High Availability Cluster Manager.
Mar 11 14:32:39 sles15sp5-node1 systemd[1]: pacemaker.service: Job pacemaker.service/start failed with result 'dependency'.

sles15sp5-node1:~ # journalctl -u corosync -e --no-pager
...text truncated for brevity...
Mar 11 14:32:38 sles15sp5-node1 corosync[1981]:   [QB    ] couldn't allocate file /dev/shm/qb-1981-2283-19-HKPoVX/qb-request-cfg-data: No space left on device (28)
Mar 11 14:32:38 sles15sp5-node1 corosync[1981]:   [QB    ] couldn't create file for mmap
Mar 11 14:32:38 sles15sp5-node1 corosync[1981]:   [QB    ] qb_rb_open:/dev/shm/qb-1981-2283-19-HKPoVX/qb-request-cfg: No space left on device (28)
Mar 11 14:32:38 sles15sp5-node1 corosync[1981]:   [QB    ] shm connection FAILED: No space left on device (28)
Mar 11 14:32:38 sles15sp5-node1 corosync[1981]:   [QB    ] Error in connection setup (/dev/shm/qb-1981-2283-19-HKPoVX/qb): No space left on device (28)
Mar 11 14:32:38 sles15sp5-node1 corosync[1975]: Starting Corosync Cluster Engine (corosync): [FAILED]
...text truncated for brevity...

The cause in this case is that a tmpfs file-system is not mounted at /dev/shm/

sles15sp5-node1:~ # grep -c /dev/shm /proc/mounts
0

sles15sp5-node1:~ # mount -o nosuid,nodev,strictatime,mode=1777 -t tmpfs tmpfs /dev/shm
sles15sp5-node1:~ # grep /dev/shm /proc/mounts
tmpfs /dev/shm tmpfs rw,nosuid,nodev,inode64 0 0
sles15sp5-node1:~ # crm cluster init -y
INFO: Loading "default" profile from /etc/crm/profiles.yml
INFO: Configuring csync2
INFO: Starting csync2.socket service on sles15sp5-node1
INFO: BEGIN csync2 checking files
INFO: END csync2 checking files
INFO: Configuring corosync (unicast)
WARNING: Not configuring SBD - STONITH will be disabled.
INFO: Hawk cluster interface is now running. To see cluster status, open:
INFO:   https://192.168.150.40:7630/
INFO: Log in with username 'hacluster'
INFO: BEGIN Waiting for cluster
...........                                                                                                                                                                                             INFO: END Waiting for cluster
INFO: Loading initial cluster configuration
INFO: Done (log saved to /var/log/crmsh/crmsh.log)