The letters `rwxXstugo' select the new permissions for the
affected users: read (r), write (w), execute (or access
for directories) (x), execute only if the file is a direc
tory or already has execute permission for some user (X),
set user or group ID on execution (s), save program text
on swap device (t), the permissions that the user who owns
the file currently has for it (u), the permissions that
other users in the file's group have for it (g), and the
permissions that other users not in the file's group have
for it (o).