[BUG] Initial startup of nav service by package fails, second startup works fine

[lunkwill42]

Describe the bug

When installing the nav-debian package from scratch, the package initially tries to start the nav services after the package is configured. This appears to fail in many instances, but since the package startup is "behind the scenes" without verbose logging, it's not clear why this happens.

Attempting a manual start after the failure seems to work just fine.

The tracebacks provided further down seem to indicate a problem with using the NET-SNMP library, which seems strange, since that package should have been installed as part of the process (and starting a second time does not produce this error)

To Reproduce

Steps to reproduce the behavior:

1. Start a Debian Buster docker container
2. Follow the package install procedure from https://nav.uninett.no
3. See error at end of package installation

Expected behavior

The initial service startup should succeed.

Tracebacks

I patched the package to use the --verbose flag to the nav start command, and these two tracebacks provide some hints into why the full startup fails.

ipdevpoll:

Traceback (most recent call last):
  File "/usr/bin/ipdevpolld", line 23, in <module>
    from nav.ipdevpoll.daemon import main
  File "/opt/venvs/nav/lib/python3.7/site-packages/nav/ipdevpoll/daemon.py", line 45, in <module>
    from nav.ipdevpoll import ContextFormatter, schedule, db
  File "/opt/venvs/nav/lib/python3.7/site-packages/nav/ipdevpoll/schedule.py", line 35, in <module>
    from nav.ipdevpoll.snmp import SnmpError, AgentProxy
  File "/opt/venvs/nav/lib/python3.7/site-packages/nav/ipdevpoll/snmp/__init__.py", line 21, in <module>
    import pynetsnmp.twistedsnmp
  File "/opt/venvs/nav/lib/python3.7/site-packages/pynetsnmp/twistedsnmp.py", line 11, in <module>
    from . import netsnmp
  File "/opt/venvs/nav/lib/python3.7/site-packages/pynetsnmp/netsnmp.py", line 55, in <module>
    lib.netsnmp_get_version.restype = c_char_p
  File "/usr/lib/python3.7/ctypes/__init__.py", line 369, in __getattr__
    func = self.__getitem__(name)
  File "/usr/lib/python3.7/ctypes/__init__.py", line 374, in __getitem__
    func = self._FuncPtr((name_or_ordinal, self))
AttributeError: /opt/venvs/nav/bin/python: undefined symbol: netsnmp_get_version

snmptrapd:

Traceback (most recent call last):
  File "/usr/sbin/snmptrapd.py", line 42, in <module>
    from nav.snmptrapd import agent
  File "/opt/venvs/nav/lib/python3.7/site-packages/nav/snmptrapd/agent.py", line 17, in <module>
    from nav.Snmp import BACKEND
  File "/opt/venvs/nav/lib/python3.7/site-packages/nav/Snmp/__init__.py", line 38, in <module>
    from .pynetsnmp import *
  File "/opt/venvs/nav/lib/python3.7/site-packages/nav/Snmp/pynetsnmp.py", line 36, in <module>
    from pynetsnmp import netsnmp
  File "/opt/venvs/nav/lib/python3.7/site-packages/pynetsnmp/netsnmp.py", line 55, in <module>
    lib.netsnmp_get_version.restype = c_char_p
  File "/usr/lib/python3.7/ctypes/__init__.py", line 369, in __getattr__
    func = self.__getitem__(name)
  File "/usr/lib/python3.7/ctypes/__init__.py", line 374, in __getitem__
    func = self._FuncPtr((name_or_ordinal, self))
AttributeError: /opt/venvs/nav/bin/python: undefined symbol: netsnmp_get_version

Environment (please complete the following information):

• OS on the NAV server: Debian Buster
• NAV version installed: 5.5