CentralNotice From Wikipedia, the free encyclopedia Jump to: navigation , search In Unix and related computers operating systems, a file descriptor ( FD , less frequently fildes ) is an abstract indicator used to access a file or other input/output resource, such as a pipe or network connection. File descriptors are part of the POSIX application programming interface . A file descriptor is a non-negative integer , represented in C programming language as the type int . It typically serves as an index into a table maintained by the kernel that tracks which files are "opened" by a process for performing input/output. There are three standard POSIX file descriptors, corresponding to the three standard streams , which presumably every process (save perhaps a daemon ) should expect to have: Integer value Name <unistd.h> symbolic constant [ 1 ] <stdio.h> file stream [ ...