From GridLAB-D Wiki
The warn option produces all the warning output from GridLAB-D. It is managed by the global variable warn, which is by default FALSE.
GLM
To enable warn mode use the directive
#set warn=1
To disable warn mode use the directive
#set warn=0
Command line
To toggle warn mode use the option
host% gridlabd --warn
To enable warn mode use the option
host% gridlabd -D warn=1
To disable warn mode use the option
host% gridlabd -D warn=0