[[remsim_logging]]
== osmo-remsim logging

All programs within the osmo-remsim project use the logging sub-system of `libosmocore`.

Contrary to the larger Osmocom projects with their own VTY + configuration file, the
logging configuration for osmo-remsim programs must happen via command line arguments.

Also, contrary to the larger Osmocom projects, only logging to `stderr` is supported;
no direct logging to log files, syslog, systemd, etc. is supported at this point.

=== `-d` command line argument

Every osmo-remsim program like `osmo-remsim-bankd`, `osmo-remsim-server` or
`osmo-remsim-client-st2` supports a `-d` command line argument.  This argument
takes one mandatory parameter configuring the log level for each log sub-system
as follows:

`-d SUBSYS,num_lvl[:SUBSYS,num_lvl[:...]]`

So basically, a colon-separated list of tuples, where each tuple contains the
sub-system name and the _numeric_ log level.

Below is the list of sub-systems and a table of numerical levels:

.libosmocore log levels and their numeric values
[options="header",width="30%",cols="1,1"]
|===
|Level name|Numeric value
|DEBUG|1
|INFO|3
|NOTICE|5
|ERROR|7
|FATAL|8
|===

.osmo-remsim log sub-system names and their description
[options="header",width="50%",cols="1,2"]
|===
|Sub-System Name|Description
|DMAIN|respective main program code
|DST2|SIMtrace2 `cardem` firmware interaction via USB
|DRSPRO|RSPRO protocol between bankd, server and client
|DREST|REST interface of `osmo-remsim-server`
|DSLOTMAP|slotmap code shared by `osmo-remsim-server` and `osmo-remsim-bankd`
|DBANKDW|worker threads of `osmo-remsim-bankd`
|===

=== Example

Putting the above in a concrete example:

`-d DMAIN,5:DRSPRO,1`

would perform the following configuration:

* log only NOTICE (or higher) messages in the DMAIN subsystem (low verbosity)
* log DEBUG (or higher) messages in the DRSPRO subsystem (very high verbosity)