I am using Cromwell version 55 on a MacBook Pro running OS 10.15.7 (Catalina).  I thought I'd learn to use Cromwell, so I started with the 5-minute introduction tutorial found here:

https://cromwell.readthedocs.io/en/stable/tutorials/FiveMinuteIntro/ 

Unfortunately it isn't working quite as advertised.  I followed the instructions exactly, and it does seem to be working in the sense that it produces a directory structure, and a few levels down in that directory structure there is a file "stdout" that contains the words "hello world".  But in the terminal window, I never get my command line back.  The following is the complete output:

[2021-02-01 12:33:10,09] [info] Running with database db.url = jdbc:hsqldb:mem:4b62140f-ee89-4787-b6e5-7d025fe17d5d;shutdown=false;hsqldb.tx=mvcc
[2021-02-01 12:33:21,26] [info] Running migration RenameWorkflowOptionsInMetadata with a read batch size of 100000 and a write batch size of 100000
[2021-02-01 12:33:21,29] [info] [RenameWorkflowOptionsInMetadata] 100%
[2021-02-01 12:33:21,52] [info] Running with database db.url = jdbc:hsqldb:mem:fe4f4034-7ee8-427b-9719-579ee2f6618f;shutdown=false;hsqldb.tx=mvcc
[2021-02-01 12:33:22,24] [info] Slf4jLogger started
[2021-02-01 12:33:22,55] [info] Workflow heartbeat configuration:
{
  "cromwellId" : "cromid-af22feb",
  "heartbeatInterval" : "2 minutes",
  "ttl" : "10 minutes",
  "failureShutdownDuration" : "5 minutes",
  "writeBatchSize" : 10000,
  "writeThreshold" : 10000
}
[2021-02-01 12:33:22,60] [info] Metadata summary refreshing every 1 second.
[2021-02-01 12:33:22,62] [info] KvWriteActor configured to flush with batch size 200 and process rate 5 seconds.
[2021-02-01 12:33:22,62] [info] WriteMetadataActor configured to flush with batch size 200 and process rate 5 seconds.
[2021-02-01 12:33:22,72] [info] CallCacheWriteActor configured to flush with batch size 100 and process rate 3 seconds.
[2021-02-01 12:33:22,72] [warn] 'docker.hash-lookup.gcr-api-queries-per-100-seconds' is being deprecated, use 'docker.hash-lookup.gcr.throttle' instead (see reference.conf)
[2021-02-01 12:33:22,86] [info] JobExecutionTokenDispenser - Distribution rate: 50 per 1 seconds.
[2021-02-01 12:33:22,92] [info] SingleWorkflowRunnerActor: Version 55
[2021-02-01 12:33:22,94] [info] SingleWorkflowRunnerActor: Submitting workflow
[2021-02-01 12:33:23,00] [info] Unspecified type (Unspecified version) workflow b9e4ed10-1e46-4b1f-b5b4-9075fa736f3a submitted
[2021-02-01 12:33:23,04] [info] SingleWorkflowRunnerActor: Workflow submitted b9e4ed10-1e46-4b1f-b5b4-9075fa736f3a
[2021-02-01 12:33:23,05] [info] 1 new workflows fetched by cromid-af22feb: b9e4ed10-1e46-4b1f-b5b4-9075fa736f3a
[2021-02-01 12:33:23,07] [info] WorkflowManagerActor Starting workflow b9e4ed10-1e46-4b1f-b5b4-9075fa736f3a
[2021-02-01 12:33:23,09] [info] WorkflowManagerActor Successfully started WorkflowActor-b9e4ed10-1e46-4b1f-b5b4-9075fa736f3a
[2021-02-01 12:33:23,09] [info] Retrieved 1 workflows from the WorkflowStoreActor
[2021-02-01 12:33:23,11] [info] WorkflowStoreHeartbeatWriteActor configured to flush with batch size 10000 and process rate 2 minutes.
[2021-02-01 12:33:23,29] [info] MaterializeWorkflowDescriptorActor [b9e4ed10]: Parsing workflow as WDL draft-2
[2021-02-01 12:33:24,75] [info] MaterializeWorkflowDescriptorActor [b9e4ed10]: Call-to-Backend assignments: myWorkflow.myTask -> Local
[2021-02-01 12:33:26,12] [info] WorkflowExecutionActor-b9e4ed10-1e46-4b1f-b5b4-9075fa736f3a [b9e4ed10]: Starting myWorkflow.myTask
[2021-02-01 12:33:26,89] [info] Assigned new job execution tokens to the following groups: b9e4ed10: 1
[2021-02-01 12:33:27,10] [info] BackgroundConfigAsyncJobExecutionActor [b9e4ed10myWorkflow.myTask:NA:1]: echo "hello world"
[2021-02-01 12:33:27,21] [info] BackgroundConfigAsyncJobExecutionActor [b9e4ed10myWorkflow.myTask:NA:1]: executing: /bin/bash /Users/mcrepeau/working/cromwell/cromwell-executions/myWorkflow/b9e4ed10-1e46-4b1f-b5b4-9075fa736f3a/call-myTask/execution/script
[2021-02-01 12:33:27,88] [info] Not triggering log of token queue status. Effective log interval = None
[2021-02-01 12:33:32,65] [info] BackgroundConfigAsyncJobExecutionActor [b9e4ed10myWorkflow.myTask:NA:1]: job id: 31514
[2021-02-01 12:33:32,70] [info] BackgroundConfigAsyncJobExecutionActor [b9e4ed10myWorkflow.myTask:NA:1]: Status change from - to WaitingForReturnCode

At that point it stalls forever.  Using top I can see the bash PID 31514 still present with state "sleeping", plus a java PID 31511, also with state sleeping. As far as my java -version, the output I get is:

openjdk version "11.0.2" 2019-01-15
OpenJDK Runtime Environment 18.9 (build 11.0.2+9)
OpenJDK 64-Bit Server VM 18.9 (build 11.0.2+9, mixed mode

I tried the same commands on our Linux server, and they finished and exited properly.  Just not working on my Mac.