Unable to run mongo - mongodb

Question

I have problems when running mongo on my Ubuntu.
When I try mongo I got:
MongoDB shell version v4.4.12
connecting to: mongodb://127.0.0.1:27017/?compressors=disabled&gssapiServiceName=mongodb
Error: couldn't connect to server 127.0.0.1:27017, connection attempt failed: SocketException: Error connecting to 127.0.0.1:27017 :: caused by :: Connection refused :
connect#src/mongo/shell/mongo.js:374:17
#(connect):2:6
exception: connect failed
exiting with code 1
When I try sudo rm /var/lib/mongodb/mongod.lock and mongod --repair I got
{"t":{"$date":"2022-03-03T15:32:19.454+01:00"},"s":"I", "c":"CONTROL", "id":23285, "ctx":"main","msg":"Automatically disabling TLS 1.0, to force-enable TLS 1.0 specify --sslDisabledProtocols 'none'"}
{"t":{"$date":"2022-03-03T15:32:19.457+01:00"},"s":"W", "c":"ASIO", "id":22601, "ctx":"main","msg":"No TransportLayer configured during NetworkInterface startup"}
{"t":{"$date":"2022-03-03T15:32:19.458+01:00"},"s":"I", "c":"NETWORK", "id":4648601, "ctx":"main","msg":"Implicit TCP FastOpen unavailable. If TCP FastOpen is required, set tcpFastOpenServer, tcpFastOpenClient, and tcpFastOpenQueueSize."}
{"t":{"$date":"2022-03-03T15:32:19.458+01:00"},"s":"I", "c":"STORAGE", "id":4615611, "ctx":"initandlisten","msg":"MongoDB starting","attr":{"pid":37243,"port":27017,"dbPath":"/data/db","architecture":"64-bit","host":"prace"}}
{"t":{"$date":"2022-03-03T15:32:19.458+01:00"},"s":"I", "c":"CONTROL", "id":23403, "ctx":"initandlisten","msg":"Build Info","attr":{"buildInfo":{"version":"4.4.12","gitVersion":"51475a8c4d9856eb1461137e7539a0a763cc85dc","openSSLVersion":"OpenSSL 1.1.1f 31 Mar 2020","modules":[],"allocator":"tcmalloc","environment":{"distmod":"ubuntu1804","distarch":"x86_64","target_arch":"x86_64"}}}}
{"t":{"$date":"2022-03-03T15:32:19.458+01:00"},"s":"I", "c":"CONTROL", "id":51765, "ctx":"initandlisten","msg":"Operating System","attr":{"os":{"name":"Ubuntu","version":"20.04"}}}
{"t":{"$date":"2022-03-03T15:32:19.458+01:00"},"s":"I", "c":"CONTROL", "id":21951, "ctx":"initandlisten","msg":"Options set by command line","attr":{"options":{"repair":true}}}
{"t":{"$date":"2022-03-03T15:32:19.459+01:00"},"s":"E", "c":"STORAGE", "id":20557, "ctx":"initandlisten","msg":"DBException in initAndListen, terminating","attr":{"error":"NonExistentPath: Data directory /data/db not found. Create the missing directory or specify another path using (1) the --dbpath command line option, or (2) by adding the 'storage.dbPath' option in the configuration file."}}
{"t":{"$date":"2022-03-03T15:32:19.459+01:00"},"s":"I", "c":"REPL", "id":4784900, "ctx":"initandlisten","msg":"Stepping down the ReplicationCoordinator for shutdown","attr":{"waitTimeMillis":10000}}
{"t":{"$date":"2022-03-03T15:32:19.460+01:00"},"s":"I", "c":"COMMAND", "id":4784901, "ctx":"initandlisten","msg":"Shutting down the MirrorMaestro"}
{"t":{"$date":"2022-03-03T15:32:19.460+01:00"},"s":"I", "c":"SHARDING", "id":4784902, "ctx":"initandlisten","msg":"Shutting down the WaitForMajorityService"}
{"t":{"$date":"2022-03-03T15:32:19.460+01:00"},"s":"I", "c":"NETWORK", "id":4784905, "ctx":"initandlisten","msg":"Shutting down the global connection pool"}
{"t":{"$date":"2022-03-03T15:32:19.460+01:00"},"s":"I", "c":"STORAGE", "id":4784906, "ctx":"initandlisten","msg":"Shutting down the FlowControlTicketholder"}
{"t":{"$date":"2022-03-03T15:32:19.460+01:00"},"s":"I", "c":"-", "id":20520, "ctx":"initandlisten","msg":"Stopping further Flow Control ticket acquisitions."}
{"t":{"$date":"2022-03-03T15:32:19.460+01:00"},"s":"I", "c":"NETWORK", "id":4784918, "ctx":"initandlisten","msg":"Shutting down the ReplicaSetMonitor"}
{"t":{"$date":"2022-03-03T15:32:19.460+01:00"},"s":"I", "c":"SHARDING", "id":4784921, "ctx":"initandlisten","msg":"Shutting down the MigrationUtilExecutor"}
{"t":{"$date":"2022-03-03T15:32:19.460+01:00"},"s":"I", "c":"CONTROL", "id":4784925, "ctx":"initandlisten","msg":"Shutting down free monitoring"}
{"t":{"$date":"2022-03-03T15:32:19.460+01:00"},"s":"I", "c":"STORAGE", "id":4784927, "ctx":"initandlisten","msg":"Shutting down the HealthLog"}
{"t":{"$date":"2022-03-03T15:32:19.460+01:00"},"s":"I", "c":"STORAGE", "id":4784929, "ctx":"initandlisten","msg":"Acquiring the global lock for shutdown"}
{"t":{"$date":"2022-03-03T15:32:19.460+01:00"},"s":"I", "c":"-", "id":4784931, "ctx":"initandlisten","msg":"Dropping the scope cache for shutdown"}
{"t":{"$date":"2022-03-03T15:32:19.460+01:00"},"s":"I", "c":"FTDC", "id":4784926, "ctx":"initandlisten","msg":"Shutting down full-time data capture"}
{"t":{"$date":"2022-03-03T15:32:19.460+01:00"},"s":"I", "c":"CONTROL", "id":20565, "ctx":"initandlisten","msg":"Now exiting"}
{"t":{"$date":"2022-03-03T15:32:19.460+01:00"},"s":"I", "c":"CONTROL", "id":23138, "ctx":"initandlisten","msg":"Shutting down","attr":{"exitCode":100}}
What is the problem, please?

Answer 1

Normally this is caused because you didn't start the mongod process before you try starting the mongo shell.
Start mongod server
mongod
Open another terminal window
Start mongo shell
mongo

Answer 2

I think the log identifies your problem:
{..."error":"NonExistentPath: Data directory /data/db not found. Create the missing directory or specify another path using (1) the --dbpath command line option, or (2) by adding the 'storage.dbPath' option in the configuration file."}}
How are you starting the mongod server? Here's a sample command line:
mkdir -p /some/path
# dbpath must name a dir, not a file
# logpath must name a file, not a dir
# Use a port different than 27017 for extra defense in depth safety
mongod --dbpath /some/path --logpath /some/path/mongo.log --port 47016 --fork