The Open Group Base Specifications Issue 8
IEEE Std 1003.1-2024
Copyright © 2001-2024 The IEEE and The Open Group

NAME

fchmod — change mode of a file

SYNOPSIS

#include <sys/stat.h>

int fchmod(int
fildes, mode_t mode);

DESCRIPTION

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

[SHM] [Option Start] 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. [Option End]

[TYM] [Option Start] If fildes references a typed memory object, the behavior of fchmod() is unspecified. [Option End]

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

RETURN VALUE

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

ERRORS

The fchmod() function shall fail if:

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

The fchmod() function may fail if:

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

The following sections are informative.

EXAMPLES

Changing the Current Permissions for a File

The following example shows how to change the permissions for a file named /home/cnd/mod1 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);

APPLICATION USAGE

None.

RATIONALE

None.

FUTURE DIRECTIONS

None.

SEE ALSO

chmod , chown , creat , fcntl , fstatat , fstatvfs , mknod , open , read , write

XBD <sys/stat.h>

CHANGE HISTORY

First released in Issue 4, Version 2.

Issue 5

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.

Issue 6

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

Issue 8

Austin Group Defect 1330 is applied, removing obsolescent interfaces.

End of informative text.

 

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