I originally posted this at http://www.318.com/TechJournal By default the global permissions for new files written into an Xsan volume are 644 (rw-r–r–). This can result in a permissions problem where one user can read another userâ€™s posted items, but not make changes to it. This can be resolved by changing the default umask value for groups. Itâ€™s a simple command line: sudo defaults write -g NSUmask 23 In this case, the 23 is a decimal equivalent of â€œrw-â€. So the result of running this command line is that files posted to the shared volume will have 664 permissions (rw-rw-r–), allowing other users in the group to modify the files. Note that this command must be run on all machines accessing the Xsan shared volume (it cannot be applied globally from the Xsan controller).