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Linux 2.6 - man page for fchmod (linux section 3)

FCHMOD(P)						     POSIX Programmer's Manual							 FCHMOD(P)

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. 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. If fildes refers to a STREAM (which is fattach()-ed into the file system name space) the call returns successfully, doing nothing.
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: 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 privilege. EROFS The file referred to by fildes resides on a read-only file system. The fchmod() function may fail if: EINTR The fchmod() function was interrupted by a signal. EINVAL The value of the mode argument is invalid. EINVAL 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/exe- cute 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>
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol- ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at .
/The Open Group 2003 FCHMOD(P)