Remove ambiguity about systemd service files being separate.
Add URL for more information about systemd service files.
Add note about public keys being mandatory for self-signed certs.
Make cert/key file naming consistent throughout document.

Improve documentation for artifact cache installation

See merge request !777

Daniel Silverstone authored Sep 04, 2018 and Tristan Maat committed Sep 04, 2018

The garbage collector can take too long to get around to cleaning
up the Queue and Process instances in completed Job instances.  As
such, FDs tend to leak and in very large projects this can result
in running out of FDs before a build, fetch, track, or other process
can complete.  This patch reduces the chance of that by only creating
the queue when it's needed, and forcing the queue and process instances
to be deleted when the parent is finished with them.

Signed-off-by: Daniel Silverstone <daniel.silverstone@codethink.co.uk>

jobs.py: Reduce FD leaks from queues and process objects

See merge request !778

This is what the whole resource.py thing was created for, the
cleanup job must have exclusive access to the cache, while the pull
and build jobs which result in adding new artifacts, must only require
shared access.

This is a part of #623

This means there is no cap for shared resource requests.

Together with the previous commit, this causes the cleanup
job and the pull/build jobs to all require unlimited shared
access to the CACHE resource; while only the cleanup job
requires exclusive access to the resource.

This is a part of #623

This runs after every pull, and does not need the cache exclusively,
only the cleanup job requires the cache exclusively.

Without this, every time a cache_size job is queued, all pull and
build jobs need to complete before cache_size job can run exclusively,
which is not good.