15.1.9 debug

This variable may be set to enable debugging output from various components of GRUB. The value is an ordered list of debug facility names separated by whitespace or ‘,’. If the special facility named ‘all’ is present then debugging output of all facility names is enabled at the start of processing the value of this variable. A facility’s debug output can then be disabled by prefixing its name with a ‘-’. The last occurence facility name with or without a leading ‘-’ takes precendent over any previous occurence. This allows the easy enabling or disabling of facilities by appending a ‘,’ and then the facility name with or without the leading ‘-’, which will preserve the state of the rest of the facilities. The facility names are the first argument to grub_dprintf. Consult the source for more details.