FCHMOD(3) Library Functions Manual FCHMOD(3)

fchmod — change mode of a file

#include <sys/stat.h>

int fchmod(int fildes, mode_t mode);

The fchmod () function shall be equivalent to chmod(3) except that the file whose permissions are changed is specified by the file descriptor fildes.

If fildes references a shared memory object, the fchmod () function need only affect the S_IRUSR, S_IWUSR, S_IRGRP, S_IWGRP, S_IROTH, and S_IWOTH file permission bits.

If fildes references a typed memory object, the behavior of fchmod () is unspecified.

If fildes refers to a socket, the behavior of fchmod () is unspecified.

Upon successful completion, fchmod () shall return 0. Otherwise, it shall return -1 and set to indicate the error.

The fchmod () function shall fail if:

The fildes argument is not an open file descriptor.
The effective user ID does not match the owner of the file and the process does not have appropriate privileges.
The file referred to by fildes resides on a read-only file system.

The fchmod () function may fail if:

[XSI] The fchmod () function was interrupted by a signal.
[XSI] The value of the mode argument is invalid.
The fildes argument refers to a pipe and the implementation disallows execution of fchmod () on a pipe.

The following example shows how to change the permissions for a file named so that the owner and group have read/write/execute permissions, but the world only has read/write permissions.

#include <sys/stat.h>
#include <fcntl.h>


mode_t mode;
int    fildes;
...
fildes = open("/home/cnd/mod1", O_RDWR);
fchmod(fildes, S_IRWXU | S_IRWXG | S_IROTH | S_IWOTH);

None.

None.

None.

chmod(3), chown(3) , creat(3), fcntl(3), fstatat(3), fstatvfs(3), mknod(3), open(3), read(3), write(3)

XBD <sys/stat.h>

First released in Issue 4, Version 2.

Moved from X/OPEN UNIX extension to BASE and aligned with fchmod () in the POSIX Realtime Extension. Specifically, the second paragraph of the DESCRIPTION is added and a second instance of [EINVAL] is defined in the list of optional errors.

The DESCRIPTION is updated for alignment with IEEE Std 1003.1j-2000 by stating that fchmod () behavior is unspecified for typed memory objects.

Austin Group Defect 1330 is applied, removing obsolescent interfaces.

June 14, 2024 posix.fail