Hue server failed to start with exit code 255

[lyuyunbo]

Hi, I'm deploying Hue through Cloudera Manager. After adding the service and roles, I have Hue Server, Kerberos Ticket Renewer, and Load Balancer on the same host. The Kerberos Ticket Renewer and Load Balancer can start just fine, but the Hue server fails to start with exit code 255. There are no more explicit errors or exceptions in the logs. Could anyone please advise on how to fix it?

My environment is CDP 7.1.9, Hue 4.11.0, Ubuntu 20.04, JDK 8, Python 3.8.12, MySQL 8.0.36.

/var/log/hue/error.log ends with

[08/Mar/2024 23:41:41 -0800] schemas      DEBUG    Schema targetNamespace is 'http://www.w3.org/2001/XMLSchema'
[08/Mar/2024 23:41:41 -0800] schemas      DEBUG    Declared namespaces: {'xml': 'http://www.w3.org/XML/1998/namespace', 'xs': 'http://www.w3.org/2001/XMLSchema', '': ''}
[08/Mar/2024 23:41:41 -0800] schemas      INFO     Resource 'XMLSchema.xsd' is already loaded
[08/Mar/2024 23:41:41 -0800] schemas      DEBUG    Read schema from 'file:///opt/cloudera/parcels/CDH-7.1.9-1.cdh7.1.9.p0.44702451/lib/hue/build/env/lib/python3.8/site-packages/xmlschema/schemas/VC/XMLSchema-versioning.xsd'
[08/Mar/2024 23:41:41 -0800] schemas      DEBUG    Schema targetNamespace is 'http://www.w3.org/2007/XMLSchema-versioning'
[08/Mar/2024 23:41:41 -0800] schemas      DEBUG    Declared namespaces: {'xml': 'http://www.w3.org/XML/1998/namespace', 'xs': 'http://www.w3.org/2001/XMLSchema', '': ''}
[08/Mar/2024 23:41:42 -0800] rungunicornserver INFO     Welcome to Hue from Gunicorn server 4.11.0

lsof -i:8888 shows nothing.

stdout looks normal and only says:

HIVE_CONF_DIR=/var/run/cloudera-scm-agent/process/5104-hue-HUE_SERVER/hive-conf
...
ALERT: This appears to be a CM Managed environment
ALERT: HUE_CONF_DIR must be set when running hue commands in CM Managed environment
ALERT: Please run 'hue <command> --cm-managed'

stderr shows no errors, but only a couple warnings:

[08/Mar/2024 23:56:12 -0800] hiveserver2  WARNING  Job Browser app is not enabled
/opt/cloudera/parcels/CDH-7.1.9-1.cdh7.1.9.p0.44702451/lib/hue/build/env/lib/python3.8/site-packages/oauth2/grant.py:320: SyntaxWarning: "is" with a literal. Did you mean "=="?
  if isinstance(value, tuple) and len(value) is 2:
[08/Mar/2024 23:56:12 -0800] api          WARNING  Oozie application is not enabled: Model class oozie.models.Job doesn't declare an explicit app_label and isn't in an application in INSTALLED_APPS.

What does exit code 255 mean? I would really appreciate any help here.