fd - file descriptor files
The /dev/fd file system is a pseudo-file system layered beneath the Virtual File System (VFS). The file descriptor files (fd*) are those files that are accessible through file descriptors. The file descriptors use the naming convention /dev/fd/0, /dev/fd/1, /dev/fd/2 and so on up to any number.
To make the /dev/fd file system known to the operating system, you must create the directory with the correct privileges, then you must mount the file system. The following steps describe how to create the directory, mount the file system both manually and automatically, and how to dismount the file system: Create the directory using the mkdir and chmod commands: mkdir /dev/fd; chmod 777 /dev/fd Mount the file system manually using the mount command: mount -t fdfs /dev/fd /dev/fd Mount the file system automatically by editing either the /etc/fstab file or the /sbin/bcheckrc file.
The /dev/fd file descriptors should not be exported.
The following example show how the open and dup functions have the same effect if file descriptor n is opened:
fd = open("/dev/fd/n", mode);
fd = dup(n);
In the above example, the open function is equal to the creat function and mode is ignored. Using the dup function, subsequent reads or writes on the fd file descriptor files fail unless the original file descriptor enables the operation.
The following error condition exists: The file descriptor is not valid.
Commands: chmod(1), mkdir(1), mount(8).
Functions: creat(2), dup(2), open(2). delim off