These system calls change the owner and group of the file specified by
path or by fd. 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
If the owner or group is specified as -1, then that ID is not
When the owner or group of an executable file are changed by a non-super-user,
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 behaviour
depends on the kernel version. In case of a non-group-executable file (with
clear S_IXGRP bit) the S_ISGID bit indicates mandatory locking, and is not
cleared by a chown.
In versions of Linux prior to 2.1.81 (and distinct from 2.1.46), chown
did not follow symbolic links. Since Linux 2.1.81, chown does follow
symbolic links, and there is a new system call lchown that does not
follow symbolic links. Since Linux 2.1.86, this new call (that has the same
semantics as the old chown) has got the same syscall number, and
chown got the newly introduced number.
The prototype for fchown is only available if _BSD_SOURCE is
defined (either explicitly, or implicitly, by not defining _POSIX_SOURCE or
compiling with the -ansi flag).
The chown call conforms to SVr4, SVID, POSIX, X/OPEN. The 4.4BSD version
can only be used by the superuser (that is, ordinary users cannot give away
files). SVr4 documents EINVAL, EINTR, ENOLINK and EMULTIHOP returns, but no
ENOMEM. POSIX.1 does not document ENOMEM or ELOOP error conditions.
The fchown call conforms to 4.4BSD and SVr4. SVr4 documents additional
EINVAL, EIO, EINTR, and ENOLINK error conditions.
The chown() semantics are deliberately violated on NFS file systems which
have UID mapping enabled. Additionally, the semantics of all system calls
which access the file contents are violated, because chown() may cause
immediate access revocation on already open files. Client side caching may
lead to a delay between the time where ownership have been changed to allow
access for a user and the time where the file can actually be accessed by the
user on other clients.