playumidi directly opens, writes midi-event data,
and closes the umidi* device files.
So, it is necessary to grant the R/W privileges(666)
to umidi* device file before use playumidi.

Therefore, there is a need to grant permissions to R/W
prior to use.
An example of the setting method is shown below.

 1. Append to devfs.rules (in etc dir.) the following lines.
   ------------------------------------------
   [system=10]
    add path 'umidi*' mode 0666 group wheel
   ------------------------------------------

 2.  Append to rc.conf (in etc dir.) the following three lines.
   ------------------------------------------
   devfs_enable="YES"
   ------------------------------------------

 3.  Reboot FreeBSD (shutdown -r now)