Memcached changes to the memcached user from root before writing the PID
file. This means that it must be able to write the PID file as the memcached
user.
To make this work, create the /var/run/memcached directory when the service
starts, make it owned by memcached, and change memcached to write the PID file
to /var/run/memcached/pid.
This wasn't picked up by the system test as the "service running" part was too
permissive, and only failed on an error. Instead, test the response from
calling start-service and check that the PID is a number.
* gnu/services/databases.scm (memcached-activation): New variable.
(memcached-shepherd-service): Change PID file location.
(memcached-service-type): Extend the activation-service-type.
* gnu/tests/databases.scm (run-memcached-test)[test]: Change the "service
running" test to check the response from the shepherd.
* gnu/services/databases.scm (memcached-service-type, %memcached-accounts):
New variables.
(<memcached-configuration>): New record type.
(memcached-service-type): New procedures.
* gnu/tests/databases.scm: New file.
* doc/guix.texi (Database Services): Document the new memcached service.
* gnu/local.mk (GNU_SYSTEM_MODULES): Add entry for tests/databases.scm.
