install/umask is a SAP Parameter attribute which is used to control mask for modifying the file permission bits information. This is available within R/3 SAP systems depending on the version and release level.
Below is the standard documentation available and a few details of the attributes values .
Whenever files need to be created, the kernel often uses this mask to
modify the permission bits intended for the file in question.
See SAP Parameter Documentation for full SAP documentation for this profile parameter.