NAME

fchown - change ownership of a file

SYNOPSIS

#include <sys/types.h> /* For uid_t and gid_t / #include <unistd.h> / for fchown prototype */

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

DESCRIPTION

The owner of the file specified by fd is changed. Only the super-user 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. The super-user may change the group arbitrarily.

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-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.

RETURN VALUE

On success, zero is returned. On error, -1 is returned, and errno is set appropriately.

ERRORS

Depending on the file system, other errors can be returned.

EPERM

The effective UID does not match the owner of the file, and is not zero; or the owner or group were specified incorrectly.

EROFS

The named file resides on a read-only file system.

ENOMEM

Insufficient kernel memory was available.

EBADF

The descriptor is not valid.

ENOENT

See above.

EIO

A low-level I/O error occurred while modifying the inode.

NOTES

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).

CONFORMING TO

The fchown call conforms to 4.4BSD and SVr4. SVr4 documents additional EINVAL, EIO, EINTR, and ENOLINK error conditions.

RESTRICTIONS

The fchown(2) 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 fchown(2) 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.

EXAMPLE

/*

• This program creates a file, and uses fchown to change it's ownership.

*

• This program will fail with an error unless run as root.
• /

1. include <sys/stat.h> /* for S_* constants */
2. include <sys/types.h> /* for mode_t for creat(2) */
3. include <unistd.h> /* for fchown(2) prototype */
4. include <string.h> /* for strerror(3) prototype */
5. include <fcntl.h> /* for creat(2) prototype */
6. include <stdio.h> /* for fprintf(3),stderr protype */
7. include <errno.h> /* for errno prototype */
8. define FILENAME "/tmp/fchown.example"
9. define UID 100
10. define GID 100

int main(int argc,char **argv) {

int fd;

fd = creat(FILENAME,S_IRUSR|S_IWUSR); if (fd<0) {

fprintf(

stderr, "creat(\"%s\",S_IRUSR|S_IWUSR): %s (%i)\n", FILENAME, strerror(errno), errno);

return 1;

} if (fchown(fd,UID,GID)==-1) {

fprintf(

stderr, "fchown(fd,%i,%i): %s (%i)\n", UID, GID, strerror(errno), errno);

return 1;

} close(fd); printf(

"%s successfully changed to uid=%i, gid=%i\n", FILENAME, UID, GID);

return 0;

}

SEE ALSO

chown(2), lchown(2), chmod(2), flock(2)