The isis.[date].[time].log file keeps track of events while isis is initializing and is essentially the output file for the nms-isis start script. It is located in $NMS_LOG_DIR (or under $ISIS_LOG_DIR if it is set). The isis.[date].[time].log file contains clues if there is any difficulty in starting isis.

This is the directory where the Protos and Incarnation logs reside. The location of this directory is defined in the isis.rc file, and is typically found in $NMS_LOG_DIR/run.isis (or under $ISIS_LOG_DIR/run.isis, if $ISIS_LOG_DIR is defined).

Protos is the isis protocol process. This process logs its messages to $NMS_LOG_DIR/run.isis/[Site No.].logdir.[port]/[Site No.]_protos.YYYYMMDD.HHMMSS.log or similar under the $ISIS_LOG_DIR directory if $ISIS_LOG_DIR is defined. Check here for runtime problems with isis. Each time isis is restarted, the previous protos log is moved to the old_log subdirectory. The retention period for logs in the old_log directory is driven by the $NMS_DAYS_TO_LOG environment variable or for 7 days, if the environment variable is not set. Each time isis is restarted it will delete logs older than the retention period.

There is a short file called $NMS_LOG_DIR/run.isis/[Site No.].logdir./[Site No.].incarn and it usually includes a single line containing the incarnation number for the particular site.