The Open Group Base Specifications Issue 6
IEEE Std 1003.1, 2004 Edition
Copyright © 2001-2004 The IEEE and The Open Group, All Rights reserved.
A newer edition of this document exists here


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() 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.

[XSR] [Option Start] If fildes refers to a STREAM (which is fattach()-ed into the file system name space) the call returns successfully, doing nothing. [Option End]


Upon successful completion, fchmod() shall return 0. Otherwise, it shall return -1 and set errno 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 privilege.
The file referred to by fildes resides on a read-only file system.

The fchmod() function may fail if:

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

The following sections are informative.


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);








chmod(), chown(), creat(), fcntl(), fstatvfs(), mknod(), open(), read(), stat(), write(), the Base Definitions volume of IEEE Std 1003.1-2001, <sys/stat.h>


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.

End of informative text.

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