Difference between APPLPTMP and APPLTMP Directories in EBS (Doc ID 1355735.1)

APPLPTMP:

"APPLPTMP is a special directory used only for PLSQL temporary files. When a concurrent program uses the FND_FILE package, the concurrent manager uses APPLPTMP as the directory to which it writes temporary files. FND_FILE uses the UTL_FILE package, which can only write to directories specified in init.ora. Thus, APPLPTMP must be one of the directories listed in init.ora in order for FND_FILE to work.
Ensure that the virtual path assigned to the APPLPTMP environment variable is valid, writable, and is referenced at the beginning of the UTL_FILE_DIR database parameter."

Also as per Note:123977.1 using multiple instances, a unique APPLPTMP directory will be needed for each instance environment used.

So, in case multiple instances running on the same box, please have different directories for each instance, something like

Instance 1: APPLPTMP=/usr/tmp/ or /usr/tmp/<SID1>
Instance 2: APPLPTMP=/usr/tmp2/ or /usr/tmp/<SID2>

with Full permission on them and first entry in UTL_FILE_DIR on Database Node only.


APPLTMP:

APPLTMP does not need a utl_file_dir entry. It is a pointer to the the temporary directory used by the application, and is not referenced by the database. It is generally recommended that the location be the same simply to avoid any confusion that might be caused by multiple temporary file locations, but this is not a requirement, and you may certainly use different and non-shared locations for each host if you wish.

i.e  you can have APPLTMP='/usr/tmp' (Apps Node) or '$INST_TOP/appltmp' with Full permission.