fchmod() — Change the mode of a file or directory by descriptor

Standards

Standards / Extensions	C or C++	Dependencies
POSIX.1a XPG4.2 Single UNIX Specification, Version 3	both

Format

#define _POSIX1_SOURCE 2
#include <sys/stat.h>

int fchmod(int fildes, mode_t mode);

General description

Sets the S_ISUID, S_ISGID, and file permission bits of the open file identified by fildes, its file descriptor.

The mode argument is created with one of the symbols defined in the sys/stat.h header file. For more information on these symbols, refer to chmod() — Change the mode of a file or directory.

Returned value

If successful, fchmod() marks for update the st_ctime field of the file and returns 0.

If unsuccessful, fchmod() returns -1 and sets errno to one of the following values:

Error Code: Description
EBADF: fildes is not a valid open file descriptor.
EPERM: The effective user ID (UID) does not match the owner of the file, and the calling process does not have appropriate privileges.
EROFS: The file resides on a read-only file system.

Example

CELEBF03

/* CELEBF03

   This example changes a file permission.

 */
#define _POSIX_SOURCE
#include <fcntl.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>
#undef _POSIX_SOURCE
#include <stdio.h>

main() {
  char fn[]="temp.file";
  int  fd;
  struct stat info;

  if ((fd = creat(fn, S_IWUSR)) < 0)
    perror("creat() error");
  else {
    stat(fn, &info);
    printf("original permissions were: %08x\n", info.st_mode);
    if (fchmod(fd, S_IRWXU|S_IRWXG) != 0)
      perror("fchmod() error");
    else {
      stat(fn, &info);
      printf("after fchmod(), permissions are: %08x\n", info.st_mode);
    }
    close(fd);
    unlink(fn);
  }
}

Output

original permissions were: 03000080
after fchmod(), permissions are: 030001f8