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[do3meli <1854236@xxxxxxxxxxxxxxxxxx>]

** Changed in: cloud-init
       Status: Fix Committed => Fix Released

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https://bugs.launchpad.net/bugs/1854236

Title:
  documentation for cc_set_hostname module doesn't mention runs during
  "init" phase

Status in cloud-init:
  Fix Released

Bug description:
  (I'm using cloud-init 19.2 under Ubuntu Bionic.)

  
  The documentation generated for the cc_set_hostname module (as found e.g. at
  https://cloudinit.readthedocs.io/en/latest/topics/modules.html#set-hostname
  )
  includes the paragraph:

  ====
  Module frequency: per instance
  ====

  However, looking carefully at the /var/log/cloud-init.log log, I see
  that the module is actually executed during the "init-local" phase on
  every boot:

  
  ====
  2019-11-20 17:08:08,364 - util.py[DEBUG]: Cloud-init v. 19.2-36-g059d049c-0ubuntu2~18.04.1 running 'init-local' at Wed, 20 Nov 2019 17:08:08 +0000. Up 30.32 seconds.
  [...]
  2019-11-20 17:08:08,411 - handlers.py[DEBUG]: start: init-local/check-cache: attempting to read from cache [check]
  [...]
  2019-11-20 17:08:08,588 - handlers.py[DEBUG]: finish: init-local/check-cache: SUCCESS: restored from checked cache: DataSourceNoCloud [seed=/var/lib/cloud/seed/nocloud-net][dsmode=net]
  [...]
  2019-11-20 17:08:08,849 - cc_set_hostname.py[DEBUG]: Setting the hostname to diggle.doxpop.com (bionic)
  2019-11-20 17:08:08,849 - util.py[DEBUG]: Reading from /etc/hostname (quiet=False)
  2019-11-20 17:08:08,849 - util.py[DEBUG]: Read 7 bytes from /etc/hostname
  2019-11-20 17:08:08,850 - util.py[DEBUG]: Writing to /etc/hostname - wb: [644] 7 bytes
  2019-11-20 17:08:08,851 - __init__.py[DEBUG]: Non-persistently setting the system hostname to bionic
  2019-11-20 17:08:08,851 - util.py[DEBUG]: Running command ['hostname', 'bionic'] with allowed return codes [0] (shell=False, capture=True)
  2019-11-20 17:08:08,908 - atomic_helper.py[DEBUG]: Atomically writing to file /var/lib/cloud/data/set-hostname (via temporary file /var/lib/cloud/data/tmp8p193ijc) - w: [644] 56 bytes/chars
   with allowed return codes [0] (shell=False, capture=True)
  [...]
  2019-11-20 17:08:08,932 - handlers.py[DEBUG]: finish: init-local: SUCCESS: searching for local datasources
  ====

  This is because cmd/main.py:main_init() calls cc_set_hostname (via the
  _maybe_set_hostname() function) without checking the per-instance
  semaphore status.

  Based on the comments in main_init(), it looks like there are good
  reasons that the hostname gets updated on every boot... but currently
  the behavior does not match the cc_set_hostname documentation (and in
  particular, it overwrites a manually-changed /etc/hostname upon reboot
  even when the instance id is not changed).

  I'm not sure exactly how this should be worded, but it would be nice
  if the documentation included an explanation of exactly when the
  cc_set_hostname module is called.

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