Ubuntu – How to make sure one Upstart job starts before other Upstart jobs


This is a general Upstart question, but let me use a specific case:

Centrify is a NIS to ActiveDirectory gateway. It needs to load before any service that will depend the authentication service that it provides, e.g. autofs, cron, nis, et al.

This has proven to be quite challenging to achieve, even when trying to change the dependencies of the other services (which I don't think we should be doing anyway, I don't want to touch the other Upstart jobs if at all possible).


Best Answer

The solution is to approach the problem from the other direction: to satisfy the start criteria for Centrify, it is not necessary to make existing services depend on the new Centrify service, rather make the new Centrify service depend on existing services.

For example, an Upstart configuration file /etc/init/centrify.conf could say:

start on (starting cron or starting autofs or starting nis)

Converting this into English, this would translate as:

start the Centrify service just before either cron, autofs or nis start (whichever starts first).

The order in which cron, autofs or nis start is irrelevant: Upstart will ensure that Centrify will start before whichever service starts first, thus ensuring that Centrify is running before any one of those services start.

Note too that Upstart will block the start of the first service that wants to start until Centrify has started running.

Very elegant and simple once you get used to thinking in this manner.