Python | os.dup() method

OS module in Python provides functions for interacting with the operating system. OS comes under Python’s standard utility modules. This module provides a portable way of using operating system dependent functionality.

A file descriptor is small integer value that corresponds to a file or other input/output resource, such as a pipe or network socket. A File descriptor is an abstract indicator of a resource and act as handle to perform various lower level I/O operations like read, write, send etc.

For Example: Standard input is usually file descriptor with value 0, standard output is usually file descriptor with value 1 and standard error is usually file descriptor with value 2.
Further files opened by the current process will get the value 3, 4, 5 an so on.

os.dup() method in Python is used to duplicate the given file descriptor. The duplicated file descriptor is non-inheritable, But on Windows platform, file descriptor associated with standard stream (standard input : 0, standard output : 1, standard error : 2) which can be inherited by child processes.

Inheritable file descriptor means if the parent process has a file descriptor 4 in use for a particular file and parent creates a child process then the child process will also have file descriptor 4 in use for that same file.

Syntax: os.dup(fd)

fd: A file descriptor, which is to be duplicated.

Return Type: This method returns the duplicated file descriptor, which is an integer value.

Code: Use of os.dup() method to duplicate a file descriptor





# Python program to explain os.dup() method 
# importing os module 
import os
# File path 
path = "/home/ihritik/Desktop/file.txt"
# open the file and get
# the file descriptor associated
# with it using method
fd =, os.O_WRONLY)
# Print the value of
# file descriptor
print("Original file descriptor:", fd)
# Duplicate the file descriptor
dup_fd = os.dup(fd)
# The duplicated file will have 
# different value but it 
# will correspond to the same 
# file to which original file
# descriptor was refering 
# Print the value of
# duplicated file descriptor
print("Duplicated file descriptor:", dup_fd)
# Get the list of all 
# file Descriptors Used
# by the current Process
# (below code works on UNIX systems)
pid = os.getpid()
os.system("ls -l/proc/%s/fd" %pid)
# Close file descriptors
print("File descriptor duplicated successfully")



Original file descriptor: 3
Duplicated file descriptor: 4
total 0
lrwx------ 1 ihritik ihritik 64 Jun 14 06:45 0 -> /dev/pts/0
lrwx------ 1 ihritik ihritik 64 Jun 14 06:45 1 -> /dev/pts/0
lrwx------ 1 ihritik ihritik 64 Jun 14 06:45 2 -> /dev/pts/0
l-wx------ 1 ihritik ihritik 64 Jun 14 06:45 3 -> /home/ihritik/Desktop/file.txt
l-wx------ 1 ihritik ihritik 64 Jun 14 06:45 4 -> /home/ihritik/Desktop/file.txt
File descriptor duplicated successfully
My Personal Notes arrow_drop_up

Check out this Author's contributed articles.

If you like GeeksforGeeks and would like to contribute, you can also write an article using or mail your article to See your article appearing on the GeeksforGeeks main page and help other Geeks.

Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below.

Article Tags :

Be the First to upvote.

Please write to us at to report any issue with the above content.