2390478 - Cannot fork: Resource temporarily unavailable

SUM aborts with the following error message in log file SAPup.log.

=================================================================
CURRENTPHASE PREP_SPACECALC/TR_GET_SPCREQ_ADD
...started at <Time Stamp>
# Using phase log file 'TRADIMP.LOG'.
..finished at <Time Stamp> with status ABORTED.
# Error message set: 'Cannot fork: Resource temporarily unavailable'
# WARNING: Could not create trouble ticket: Cannot fork: Resource temporarily unavailable!
...begin dialog at <Time Stamp>

=================================================================

This may happen in different phases while you find that the hardware resource is sufficient.

Netweaver based upgrade in AIX

cannot fork, resource temporarily unavailable, the fork function failed, too many processes already exist, PARCONV_UPG_DS , KBA , BC-UPG-TLS-TLA , Upgrade tools for ABAP , Problem