[erlang-questions] Mnesia folder

Dániel Szoboszlay dszoboszlay@REDACTED
Thu Jul 11 23:30:44 CEST 2019

This directory was created because you once called mnesia:create_schema/1
on a node called nonode@REDACTED (that is, on a non-distributed node).

By the way, nonode@REDACTED is not really an error, per se. Every Erlang node
has a name (see erlang:node/0 <http://erlang.org/doc/man/erlang.html#node-0>).
For distributed nodes the name is important, because other nodes can find
and connect to it via its name. But there can be non-distributed nodes too.
They don't listen to incoming connections and don't attempt to connect to
other nodes either. So their name is completely irrelevant, and by
definition they are always called nonode@REDACTED (It is also possible to
stop <http://erlang.org/doc/man/net_kernel.html#stop-0> and start
<http://erlang.org/doc/man/net_kernel.html#start-1> distribution on a node
without stopping it. If you do so, it will change its name.)

Now, the documentation sometimes calls nodes where distribution is running "
*alive*, and nodes where it is stopped "*not alive"*. These names may be a
bit confusing. A "not alive" node is still alive in the sense that it is
running and executing code. It is just not accessible to other nodes via
the Erlang distribution protocol.

Back to Mnesia: Mnesia allows you to create a distributed database, but it
can work perfectly on a single node as well. So it's even valid to use
Mnesia on a non-distributed node. If you do so, you will get the directory
you found. Of course, if you no longer want to use non-distributed nodes
and don't need this DB instance, you can just delete it now.


On Thu, 11 Jul 2019 at 07:39, Peter J Etheridge <petergi@REDACTED>

> dear list,
> having recently discovered that nonode@REDACTED is an error, i now find a
> folder;
> Mnesia.nonode@REDACTED
> containing files;
> etc
> could this be because i did not name my node?
> thank you in advance,
> peter
> _______________________________________________
> erlang-questions mailing list
> erlang-questions@REDACTED
> http://erlang.org/mailman/listinfo/erlang-questions
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