chown()

Change the user ID and group ID of a file

Synopsis:

#include <sys/types.h>
#include <unistd.h>

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

Arguments:

path

The name of the file whose ownership you want to change.

owner

The user ID of the new owner.

group

The group ID of the new owner.

Library:

libc

Use the -l c option to qcc to link against this library. This library is usually included automatically.

Description:

The chown() function changes the user ID and group ID of the file specified by path to be the numeric values contained in owner and group, respectively.

If the named file is a symbolic link, chown() changes the ownership of the file or directory to which the symbolic link refers; lchown() changes the ownership of the symbolic link file itself.

Only processes with an effective user ID equal to the user ID of the file or with appropriate privileges (for example, the superuser) may change the ownership of a file.

In QNX Neutrino, the _POSIX_CHOWN_RESTRICTED flag (tested via the _PC_CHOWN_RESTRICTED flag in pathconf()), is enforced for path. This means that only the superuser may change the ownership or the group of a file to anyone. Normal users can't give a file away to another user by changing the file ownership, nor to another group by changing the group ownership.

If the path argument refers to a regular file, the set-user-ID (S_ISUID) and set-group-ID (S_ISGID) bits of the file mode are cleared, if the function is successful.

If chown() succeeds, the st_ctime field of the file is marked for update.

Returns:

0

Success.

-1 (no changes were made in the user ID and group ID of the file).

An error occurred (errno is set).

Errors:

EACCES

Search permission is denied on a component of the path prefix.

ELOOP

Too many levels of symbolic links or prefixes.

ENAMETOOLONG

The length of the path string exceeds PATH_MAX, or a pathname component is longer than NAME_MAX.

ENOENT

A component of the path prefix doesn't exist, or the path arguments points to an empty string.

ENOSYS

The chown() function isn't implemented for the filesystem specified in path.

ENOTDIR

A component of the path prefix isn't a directory.

EPERM

The effective user ID doesn't match the owner of the file, or the calling process doesn't have appropriate privileges.

EROFS

The named file resides on a read-only filesystem.

Examples:

/*
 * Change the ownership of a list of files
 * to the current user/group
 */
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <unistd.h>

int main( int argc, char** argv )
  {
    int i;
    int ecode = 0;

    for( i = 1; i < argc; i++ ) {
      if( chown( argv[i], getuid(), getgid() ) == -1 ) {
        perror( argv[i] );
        ecode++;
      }
    }
    exit( ecode );
  }

Classification:

POSIX 1003.1

See also:

chmod(), errno, fchown(), fstat(), lchown(), open(), stat()