fchown(2) - NetBSD Manual Pages

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CHOWN(2)                  NetBSD System Calls Manual                  CHOWN(2)


NAME

     chown, lchown, fchown, fchownat -- change owner and group of a file


LIBRARY

     Standard C Library (libc, -lc)


SYNOPSIS

     #include <unistd.h>

     int
     chown(const char *path, uid_t owner, gid_t group);

     int
     lchown(const char *path, uid_t owner, gid_t group);

     int
     fchown(int fd, uid_t owner, gid_t group);

     #include <fcntl.h>

     int
     fchownat(int fd, const char *path, uid_t owner, gid_t group, int flag);


DESCRIPTION

     The owner ID and group ID of the file named by path or referenced by fd
     is changed as specified by the arguments owner and group.  The owner of a
     file may change the group to a group of which he or she is a member, but
     the change owner capability is restricted to the super-user.

     When called to change the owner of a file, chown(), lchown() and fchown()
     clear the set-user-id (S_ISUID) bit on the file.  When a called to change
     the group of a file, chown(), lchown() and fchown() clear the set-group-
     id (S_ISGID) bit on the file.  These actions are taken to prevent acci-
     dental or mischievous creation of set-user-id and set-group-id programs.

     lchown() is like chown() except in the case where the named file is a
     symbolic link, in which case lchown() changes the owner and group of the
     link, while chown() changes the owner and group of the file the link ref-
     erences.

     fchown() is particularly useful when used in conjunction with the file
     locking primitives (see flock(2)).

     fchownat() works the same way as chown() (or lchown() if
     AT_SYMLINK_NOFOLLOW is set in flag) except if path is relative.  In that
     case, it is looked up from a directory whose file descriptor was passed
     as fd.  Search permission is required on this directory.  fd can be set
     to AT_FDCWD in order to specify the current directory.

     One of the owner or group id's may be left unchanged by specifying it as
     (uid_t)-1 or (gid_t)-1 respectively.


RETURN VALUES

     The chown(), lchown(), fchown(), and fchownat() functions return the
     value 0 if successful; otherwise the value -1 is returned and the global
     variable errno is set to indicate the error.


ERRORS

     chown(), lchown() and fchownat() will fail and the file will be unchanged
     if:

     [EACCES]           Search permission is denied for a component of the
                        path prefix.

     [EFAULT]           path points outside the process's allocated address
                        space.

     [EIO]              An I/O error occurred while reading from or writing to
                        the file system.

     [ELOOP]            Too many symbolic links were encountered in translat-
                        ing the pathname.

     [ENAMETOOLONG]     A component of a pathname exceeded {NAME_MAX} charac-
                        ters, or an entire path name exceeded {PATH_MAX} char-
                        acters.

     [ENOENT]           The named file does not exist.

     [ENOTDIR]          A component of the path prefix is not a directory.

     [EPERM]            The effective user ID is not the super-user.

     [EROFS]            The named file resides on a read-only file system.

     In addition, fchownat() will fail if:

     [EBADF]            path does not specify an absolute path and fd is nei-
                        ther AT_FDCWD nor a valid file descriptor open for
                        reading or searching.

     [ENOTDIR]          path is not an absolute path and fd is a file descrip-
                        tor associated with a non-directory file.

     fchown() will fail if:

     [EBADF]            fd does not refer to a valid descriptor.

     [EINVAL]           fd refers to a socket, not a file.

     [EIO]              An I/O error occurred while reading from or writing to
                        the file system.

     [EPERM]            The effective user ID is not the super-user.

     [EROFS]            The named file resides on a read-only file system.


SEE ALSO

     chgrp(1), chmod(2), flock(2), symlink(7), chown(8)


STANDARDS

     The chown() function deviates from the semantics defined in ISO/IEC
     9945-1:1990 (``POSIX.1''), which specifies that, unless the caller is the
     super-user, both the set-user-id and set-group-id bits on a file shall be
     cleared, regardless of the file attribute changed.  The lchown() and
     fchown() functions, as defined by X/Open Portability Guide Issue 4,
     Version 2 (``XPG4.2''), provide the same semantics.  fchownat() conforms
     to IEEE Std 1003.1-2008 (``POSIX.1'').

     To retain conformance to these standards, compatibility interfaces are
     provided by the POSIX Compatibility Library (libposix, -lposix) as fol-
     lows:
     ·   The chown() function conforms to ISO/IEC 9945-1:1990 (``POSIX.1'')
         and X/Open Portability Guide Issue 4, Version 2 (``XPG4.2'').
     ·   The lchown() and fchown() functions conform to X/Open Portability
         Guide Issue 4, Version 2 (``XPG4.2'').


HISTORY

     The chown() function call appeared in Version 1 AT&T UNIX.  The fchown()
     function call appeared in 4.2BSD.

     The chown() and fchown() functions were changed to follow symbolic links
     in 4.4BSD.  The lchown() function call appeared in NetBSD 1.3.

NetBSD 9.2                     September 1, 2019                    NetBSD 9.2