MAXIOBUFUSER limits each user’s (for example, a single UID) use of persistent kernel storage for I/O buffers when used in a Unicode Services conversion environment. (See AUTOCVT or the description of the _BPXK_AUTOCVT environment variable in _BPXK environment variables.) This storage remains allocated for the life of an open file. The amount allocated for each open depends on the CCSID of the file and the size of a read or write requests used by the process. The limit does not apply to UID 0 processes.

z/OS® UNIX only tracks such storage for the user that opens the file. If the file is inherited by a different user ID, the amount is not propagated. This can occur, for example, when the user identity changes during spawn or exec. A user identity change is an authorized operation, so the extra tracking is not needed.