initially I was getting file permission error for backend.yml so I used chmod and then run the command again.
[root@dcapmpocappptr1 ~]#cd /etc/sensu
[root@dcapmpocappptr1 sensu]#ls -lth
total 4.0K
-rw-r----- 1 root root 1.8K May 12 07:11 backend.yml
[root@dcapmpocappptr1 sensu]#chmod a+r+w backend.yml
[root@dcapmpocappptr1 sensu]#ls -lth
total 4.0K
-rw-rw-rw- 1 root root 1.8K May 12 07:11 backend.yml
rt -c /etc/sensu/backend.yml sudo -u sensu /usr/sbin/sensu-backend sta
{“component”:“etcd”,“level”:“info”,“msg”:“listening for peers on “,“pkg”:“embed” ,“time”:“2021-05-13T10:41:22+05:30”}
{“component”:“etcd”,“level”:“info”,“msg”:“http: //127.0.0.1:2380”,“pkg”:“embed”,” time”:“2021-05-13T10:41:22+05:30”}
{“component”:“etcd”,“level”:“info”,“msg”:“listening for client requests on “,“pk g”:“embed”,“time”:“2021-05-13T10:41:22+05:30”}
{“component”:“etcd”,“level”:“info”,“msg”:“127.0.0.1:2379”,“pkg”:“embed”,“time”:” 2021-05-13T10:41:22+05:30”}
{“component”:“etcd”,“level”:“info”,“msg”:“name = default”,“pkg”:“etcdserver”,“ti me”:“2021-05-13T10:41:22+05:30”}
{“component”:“etcd”,“level”:“info”,“msg”:“data dir = /var/lib/sensu/sensu-backen d/etcd/data”,“pkg”:“etcdserver”,“time”:“2021-05-13T10:41:22+05:30”}
{“component”:“etcd”,“level”:“info”,“msg”:“member dir = /var/lib/sensu/sensu-back end/etcd/data/member”,“pkg”:“etcdserver”,“time”:“2021-05-13T10:41:22+05:30”}
{“component”:“etcd”,“level”:“info”,“msg”:“dedicated WAL dir = /var/lib/sensu/sen su-backend/etcd/wal”,“pkg”:“etcdserver”,“time”:“2021-05-13T10:41:22+05:30”}
{“component”:“etcd”,“level”:“info”,“msg”:“heartbeat = 100ms”,“pkg”:“etcdserver”, “time”:“2021-05-13T10:41:22+05:30”}
{“component”:“etcd”,“level”:“info”,“msg”:“election = 1000ms”,“pkg”:“etcdserver”, “time”:“2021-05-13T10:41:22+05:30”}
{“component”:“etcd”,“level”:“info”,“msg”:“snapshot count = 100000”,“pkg”:“etcdse rver”,“time”:“2021-05-13T10:41:22+05:30”}
{“component”:“etcd”,“level”:“info”,“msg”:“advertise client URLs = http: //localho st:2379”,“pkg”:“etcdserver”,“time”:“2021-05-13T10:41:22+05:30”}
{“component”:“etcd”,“level”:“info”,“msg”:“initial advertise peer URLs = http ://1 27.0.0.1:2380”,“pkg”:“etcdserver”,“time”:“2021-05-13T10:41:22+05:30”}
{“component”:“etcd”,“level”:“info”,“msg”:“initial cluster = default=http://127.0 .0.1:2380”,“pkg”:“etcdserver”,“time”:“2021-05-13T10:41:22+05:30”}
{“component”:“etcd”,“level”:“info”,“msg”:“starting member 8927110dc66458af in cl uster 3b0efc7b379f89be”,“pkg”:“etcdserver”,“time”:“2021-05-13T10:41:22+05:30”}
{“component”:“etcd”,“level”:“info”,“msg”:“8927110dc66458af became follower at te rm 0”,“pkg”:“raft”,“time”:“2021-05-13T10:41:22+05:30”}
{“component”:“etcd”,“level”:“info”,“msg”:“newRaft 8927110dc66458af [peers: , t erm: 0, commit: 0, applied: 0, lastindex: 0, lastterm: 0]”,“pkg”:“raft”,“time”:" 2021-05-13T10:41:22+05:30"}
{“component”:“etcd”,“level”:“info”,“msg”:“8927110dc66458af became follower at te rm 1”,“pkg”:“raft”,“time”:“2021-05-13T10:41:22+05:30”}
{“component”:“etcd”,“level”:“warning”,“msg”:“simple token is not cryptographical ly signed”,“pkg”:“auth”,“time”:“2021-05-13T10:41:22+05:30”}
{“component”:“etcd”,“level”:“info”,“msg”:“starting server… [version: 3.3.22, c luster version: to_be_decided]”,“pkg”:“etcdserver”,“time”:“2021-05-13T10:41:22+0 5:30”}
{“component”:“etcd”,“level”:“info”,“msg”:“8927110dc66458af as single-node; fast- forwarding 9 ticks (election ticks 10)”,“pkg”:“etcdserver”,“time”:“2021-05-13T10 :41:22+05:30”}
{“component”:“etcd”,“level”:“info”,“msg”:“added member 8927110dc66458af [http:// 127.0.0.1:2380] to cluster 3b0efc7b379f89be”,“pkg”:“etcdserver/membership”,“time “:“2021-05-13T10:41:22+05:30”}
{“component”:“etcd”,“level”:“info”,“msg”:“8927110dc66458af is starting a new ele ction at term 1”,“pkg”:“raft”,“time”:“2021-05-13T10:41:23+05:30”}
{“component”:“etcd”,“level”:“info”,“msg”:“8927110dc66458af became candidate at t erm 2”,“pkg”:“raft”,“time”:“2021-05-13T10:41:23+05:30”}
{“component”:“etcd”,“level”:“info”,“msg”:“8927110dc66458af received MsgVoteResp from 8927110dc66458af at term 2”,“pkg”:“raft”,“time”:“2021-05-13T10:41:23+05:30” }
{“component”:“etcd”,“level”:“info”,“msg”:“8927110dc66458af became leader at term 2”,“pkg”:“raft”,“time”:“2021-05-13T10:41:23+05:30”}
{“component”:“etcd”,“level”:“info”,“msg”:“raft.node: 8927110dc66458af elected le ader 8927110dc66458af at term 2”,“pkg”:“raft”,“time”:“2021-05-13T10:41:23+05:30” }
{“component”:“etcd”,“level”:“info”,“msg”:“published {Name:default ClientURLs:[ht tp://localhost:2379]} to cluster 3b0efc7b379f89be”,“pkg”:“etcdserver”,“time”:“20 21-05-13T10:41:23+05:30”}
{“component”:“sensu-etcd”,“level”:“info”,“msg”:“Etcd ready to serve client conne ctions”,“time”:“2021-05-13T10:41:23+05:30”}
{“component”:“etcd”,“level”:“info”,“msg”:“ready to serve client requests”,“pkg”: “embed”,“time”:“2021-05-13T10:41:23+05:30”}
{“component”:“etcd”,“level”:“info”,“msg”:“setting up the initial cluster version to 3.3”,“pkg”:“etcdserver”,“time”:“2021-05-13T10:41:23+05:30”}
{“component”:“etcd”,“level”:“warning”,“msg”:“set the initial cluster version to 3.3”,“pkg”:“etcdserver/membership”,“time”:“2021-05-13T10:41:23+05:30”}
{“component”:“etcd”,“level”:“info”,“msg”:“enabled capabilities for version 3.3”, “pkg”:“etcdserver/api”,“time”:“2021-05-13T10:41:23+05:30”}
{“component”:“etcd”,“level”:“warning”,“msg”:“serving insecure client requests on 127.0.0.1:2379, this is strongly discouraged!”,“pkg”:“embed”,“time”:“2021-05-13 T10:41:23+05:30”}
{“component”:“backend”,“level”:“debug”,“msg”:“Registering backend…”,“time”:“20 21-05-13T10:41:23+05:30”}
{“component”:“backend”,“level”:“debug”,“msg”:“Done registering backend.”,“time”: “2021-05-13T10:41:23+05:30”}
{“component”:“backend”,“entity”:{“entity_class”:“backend”,“system”:{“hostname”:” dcapmpocappptr1”,“os”:“linux”,“platform”:“redhat”,“platform_family”:“rhel”,“plat form_version”:“7.9”,“network”:{“interfaces”:[{“name”:“lo”,“addresses”:[“127.0.0. 1/8”]},{“name”:“eth0”,“mac”:“00:50:56:85:61:41”,“addresses”:[“10.5.129.11/24”]}] },“arch”:“amd64”,“libc_type”:“glibc”,“vm_system”:"",“vm_role”:"",“cloud_provider “:””,“processes”:null},“subscriptions”:null,“last_seen”:0,“deregister”:false,“de registration”:{},“metadata”:{“name”:“dcapmpocappptr1”},“sensu_agent_version”:""} ,“level”:“info”,“msg”:“backend entity information”,“time”:“2021-05-13T10:41:23+0 5:30”}
{“cache”:"/var/cache/sensu/sensu-backend",“component”:“asset-manager”,“level”:“d ebug”,“msg”:“initializing cache directory”,“time”:“2021-05-13T10:41:23+05:30”}
{“cache”:"/var/cache/sensu/sensu-backend",“component”:“asset-manager”,“level”:“d ebug”,“msg”:“done initializing cache directory”,“time”:“2021-05-13T10:41:23+05:3 0”}
{“component”:“store”,“key”:"/sensu.io/entity_configs/",“level”:“debug”,“msg”:“st arting a watcher”,“time”:“2021-05-13T10:41:23+05:30”}
{“component”:“store”,“key”:"/sensu.io/api/enterprise/federation/v1/etcd-replicat ors/",“level”:“debug”,“msg”:“starting a watcher”,“time”:“2021-05-13T10:41:23+05: 30”}
{“component”:“eventd”,“level”:“info”,“msg”:“no event log file specified, event l ogging is disabled”,“time”:“2021-05-13T10:41:23+05:30”}
{“component”:“licensing”,“level”:“info”,“msg”:“starting the license watcher”,“ti me”:“2021-05-13T10:41:23+05:30”}
{“component”:“licensing”,“level”:“info”,“msg”:“no enterprise license found”,“tim e”:“2021-05-13T10:41:23+05:30”}
{“component”:“store”,“key”:"/sensu.io/api/enterprise/licensing/v2/license",“leve l”:“debug”,“msg”:“starting a watcher”,“time”:“2021-05-13T10:41:23+05:30”}
{“component”:“store-providers”,“level”:“info”,“msg”:“starting the event store pr oviders watcher”,“time”:“2021-05-13T10:41:23+05:30”}
{“component”:“store”,“key”:"/sensu.io/api/enterprise/store/v1/provider/",“level” :“debug”,“msg”:“starting a watcher”,“time”:“2021-05-13T10:41:23+05:30”}
{“component”:“store-providers”,“level”:“info”,“msg”:“no event store provider fou nd”,“time”:“2021-05-13T10:41:23+05:30”}
{“component”:“agentd”,“level”:“info”,“msg”:“starting agentd on address: [::]:808 1”,“time”:“2021-05-13T10:41:23+05:30”}
{“component”:“store”,“key”:"/sensu.io/checks/",“level”:“debug”,“msg”:“starting a watcher”,“time”:“2021-05-13T10:41:23+05:30”}
{“component”:“backend”,“level”:“info”,“msg”:“shutting down event-store-providers -watcher”,“time”:“2021-05-13T10:41:23+05:30”}
{“component”:“backend”,“level”:“info”,“msg”:“shutting down backend_id_getter”,“t ime”:“2021-05-13T10:41:23+05:30”}
{“component”:“backend”,“level”:“info”,“msg”:“shutting down message_bus”,“time”:" 2021-05-13T10:41:23+05:30"}
{“component”:“backend”,“level”:“info”,“msg”:“shutting down pipelined”,“time”:“20 21-05-13T10:41:23+05:30”}
{“component”:“store”,“key”:"/sensu.io/api/enterprise/store/v1/provider/",“level” :“debug”,“msg”:“stopping the watcher”,“time”:“2021-05-13T10:41:23+05:30”}
{“component”:“store-providers”,“level”:“warning”,“msg”:“the postgres store watch er has been stopped”,“time”:“2021-05-13T10:41:23+05:30”}
{“component”:“backend”,“level”:“info”,“msg”:“shutting down eventd”,“time”:“2021- 05-13T10:41:23+05:30”}
{“component”:“eventd”,“level”:“info”,“msg”:“shutting down eventd”,“time”:“2021-0 5-13T10:41:23+05:30”}
{“component”:“backend”,“level”:“info”,“msg”:“shutting down schedulerd”,“time”:“2 021-05-13T10:41:23+05:30”}
{“component”:“backend”,“level”:“info”,“msg”:“shutting down etcd”,“time”:“2021-05 -13T10:41:23+05:30”}
{“component”:“store”,“key”:"/sensu.io/checks/",“level”:“debug”,“msg”:“stopping t he watcher”,“time”:“2021-05-13T10:41:23+05:30”}
{“component”:“etcd”,“level”:“info”,“msg”:“skipped leadership transfer for single member cluster”,“pkg”:“etcdserver”,“time”:“2021-05-13T10:41:23+05:30”}
{“component”:“backend”,“level”:“error”,“msg”:“error starting agentd: failed to s tart agentd: listen tcp 0.0.0.0:8081: bind: address already in use”,“time”:“2021 -05-13T10:41:23+05:30”}
{“component”:“sensu-enterprise”,“error”:“error starting agentd: failed to start agentd: listen tcp 0.0.0.0:8081: bind: address already in use”,“level”:“fatal”," msg":“error executing sensu-backend”,“time”:“2021-05-13T10:41:23+05:30”}
[root@dcapmpocappptr1 sensu]#sudo systemctl enable --now sensu-backend
[root@dcapmpocappptr1 sensu]#systemctl status sensu-backend
? sensu-backend.service - The Sensu Backend service.
Loaded: loaded (/usr/lib/systemd/system/sensu-backend.service; enabled; vendor preset: disabled)
Active: failed (Result: start-limit) since Thu 2021-05-13 10:43:43 IST; 13s ago
Process: 25323 ExecStart=/usr/sbin/sensu-backend start -c /etc/sensu/backend.yml (code=exited, status=1/FAILURE)
Main PID: 25323 (code=exited, status=1/FAILURE)
May 13 10:43:42 dcapmpocappptr1 systemd[1]: Unit sensu-backend.service entered failed state.
May 13 10:43:42 dcapmpocappptr1 systemd[1]: sensu-backend.service failed.
May 13 10:43:43 dcapmpocappptr1 systemd[1]: sensu-backend.service holdoff time over, scheduling restart.
May 13 10:43:43 dcapmpocappptr1 systemd[1]: Stopped The Sensu Backend service…
May 13 10:43:43 dcapmpocappptr1 systemd[1]: start request repeated too quickly for sensu-backend.service
May 13 10:43:43 dcapmpocappptr1 systemd[1]: Failed to start The Sensu Backend service…
May 13 10:43:43 dcapmpocappptr1 systemd[1]: Unit sensu-backend.service entered failed state.
May 13 10:43:43 dcapmpocappptr1 systemd[1]: sensu-backend.service failed.