Use the undocumented switch /FORCE for this filesystem to force immediate access to a "dirty" HPFS partition. HPFS partitions get "dirty" if you don't shutdown OS/2 (e.g. after crashing the system).
Use the undocumented switch /QUIET for this filesystem to suppress all messages from CHKDSK. Note that /QUIET cannot be the last parameter.
Example:
IFS=C:\OS2\BOOT\HPFS.IFS /FORCE /AUTOCHECK:C
Warning: Use these parameters with extreme care! Use it only when you really need it!