Estratto da man 2 chown
Only a privileged process (Linux: one with the CAP_CHOWN capability)
may change the owner of a file. The owner of a file may change the
group of the file to any group of which that owner is a member. A
privileged process (Linux: with CAP_CHOWN) may change the group arbi‐
trarily.
If the owner or group is specified as -1, then that ID is not changed.
When the owner or group of an executable file are changed by a non-
superuser, the S_ISUID and S_ISGID mode bits are cleared. POSIX does
not specify whether this also should happen when root does the chown();
the Linux behavior depends on the kernel version. In case of a non-
group-executable file (i.e., one for which the S_IXGRP bit is not set)
the S_ISGID bit indicates mandatory locking, and is not cleared by a
chown().