Taking the following into consideration, you should specify "setuid no" when mounting (the default is yes):

• UNIX files and directories are contained in MVS™ data sets.
• UNIX users using these files and directory do not need access to these MVS data sets.
• Only the kernel and the storage administrators needs access to the data sets.
• If you give the users direct access to the MVS data sets by giving them UPDATE access in a RACF® profile protecting the data sets, or by naming the data sets with the user ID as the HLQ, and you do not specify "setuid no" when mounting, you have a security exposure