Erlang: specifying a working directory for mnesia?

Question

How do I specify a working directory for mnesia without resorting to passing the "dir" parameter on the command-line?

In other words, can I specify a "working directory" for mnesia just before calling `mnesia:start()' ?

Koerner

Answer 1

application:set_env(mnesia, dir, Dir).

Iceberg

There is an application_controller process started in Erlang VM. application_controller:set_env is the "API" to this process. application:set_env is a more abstract call, that just deals with applications. No wonder though that currently it only calls into that API. – Iceberg

To answer the question :), I believe that the existence of application_controller server and module should be regarded as "implementation detail", and thus the proper way is to use the application module. – Iceberg

Answer 2

Besides the method call mentioned in other responses here you can also specify this in a system configuration file or .app file specified with the -config parameter. See http://erlang.org/doc/design_principles/applications.html#id2270704 for more information. This allows you keep the configuration seperate from the code and avoid a lot of command line flags.

Conglutinate

I have a similar situation ... and I don't want to set mnesia dir from inside the code ... Can you please elaborate how .app file of an application should be used to set env variable for other application. I understand how this can be done using .config file though. e.g. My application file is test.app and it had mnesia listed in "applications" section, so mnesia is started automatically when I start "test". How can I pass "dir" value to mnesia using test.app? – Lackaday

the relevant documentation for that is here: erlang.org/doc/man/app.html specifically the env tuple in the application file spec. anything you can set with set_env() can also be set there or on the commandline. – Conglutinate