fchmod - Man Page

change mode of a file


This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.


#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.

Return Value

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 privileges.


The file referred to by fildes resides on a read-only file system.

The fchmod() function may fail if:


The fchmod() function was interrupted by a signal.


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 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);

Application Usage




Future Directions


See Also

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

The Base Definitions volume of POSIX.1-2017, <sys_stat.h>

Referenced By


2017 IEEE/The Open Group POSIX Programmer's Manual