## 8 Appendix A: Mnesia Error Messages

Whenever an operation returns an error in Mnesia, a description of the error is available. For example, the functions `mnesia:transaction(Fun)`, or `mnesia:create_table(N,L)` may return the tuple `{aborted, Reason}`, where `Reason` is a term describing the error. The following function is used to retrieve more detailed information about the error:

- `mnesia:error_description(Error)`

### 8.1 Errors in Mnesia

The following is a list of valid errors in Mnesia.

- `badarg`. Bad or invalid argument, possibly bad type.
- `no_transaction`. Operation not allowed outside transactions.
- `combine_error`. Table options were illegally combined.
- `bad_index`. Index already exists, or was out of bounds.
- `already_exists`. Schema option to be activated is already on.
- `index_exists`. Some operations cannot be performed on tables with an index.
- `no_exists`.; Tried to perform operation on non-existing (non-alive) item.
- `system_limit`.; A system limit was exhausted.
- `mnesia_down`. A transaction involves records on a remote node which became unavailable before the transaction was completed. Record(s) are no longer available elsewhere in the network.
- `not_a_db_node`. A node was mentioned which does not exist in the schema.
- `bad_type`.; Bad type specified in argument.
- `node_not_running`. Node is not running.
- `truncated_binary_file`. Truncated binary in file.
- `active`. Some delete operations require that all active records are removed.
- `illegal`. Operation not supported on this record.

The following example illustrates a function which returns an error, and the method to retrieve more detailed error information.

The function `mnesia:create_table(bar, [{attributes, 3.14}])` will return the tuple `{aborted,Reason}`, where `Reason` is the tuple `{bad_type,bar,3.14000}`.

The function `mnesia:error_description(Reason)`, returns the term `{"Bad type on some provided arguments",bar,3.14000}` which is an error description suitable for display.

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