Use command db2ilist to lists all the instances that are available on a system.
-w: Lists the 31-, 32-, or 64-bit instances. The -w option can be specified with the -p option, and is superseded by the -a option.
-p: Lists the DB2 install path that an instance is running from. The -p option can be used with the -a option, and is superseded by the -a option.
-a: Lists information including the DB2 install path associated with an instance, as well as its bit width (32 or 64). The returned information for 32-bit indicates 31-bit for DB2 on Linux (on S/390 and zSeries).
-inst_name: Lists the information for the specified instance. If no instance is named,db2ilist lists information about all instances of the current DB2 release.
-h: Displays usage information.
> db2ilist db2itsiti db2deeaya