What is dup2 in Linux?

The dup2() system function is used to create a copy of an existing file descriptor. In Linux, there are 3 standard file descriptors. They are: stdin: This is the standard input file descriptor. It is used to take input from the terminal by default.

Is dup2 a system call?

dup2() The dup2() system call performs the same task as dup(), but instead of using the lowest-numbered unused file descriptor, it uses the file descriptor number specified in newfd.

What is the difference between dup and dup2?

The difference between dup and dup2 is that dup assigns the lowest available file descriptor number, while dup2 lets you choose the file descriptor number that will be assigned and atomically closes and replaces it if it’s already taken.

What is the point of dup2?

dup/dup2 – Technically the purpose is to share one File table Entry inside a single process by different handles. ( If we are forking the descriptor is duplicated by default in the child process and the file table entry is also shared).

What is Fcntl in Linux?

The fcntl() function provides for control over open files. The fildes argument is a file descriptor. The available values for cmd are defined in the header

Does dup2 close file descriptor?

If fd1 is a valid file descriptor and is equal to fd2, dup2() returns fd2 without closing it; F_CLOEXEC is not cleared. If fd1 is not a valid file descriptor, dup2() fails and does not close fd2. If a file descriptor does not already exist, dup2() can be used to create one, a duplicate of fd1.

What is Fcntl header file?

Description. The /usr/include/fcntl. h file defines the values that can be specified for the Command and Argument parameters of the fcntl subroutine and for the Oflag parameter of the open subroutine. The file-status flags of an open file are described in the following information. Flag Values for open Subroutine.

How do I lock a Fcntl file?

To place a lock on a file, first create and zero out a struct flock variable. Set the l_type field of the structure to F_RDLCK for a read lock or F_WRLCK for a write lock. Then call fcntl, passing a file descriptor to the file, the F_SETLCKW operation code, and a pointer to the struct flock variable.

Does dup2 close FD?

If fildes is a valid descriptor and is equal to fildes2, dup2() returns fildes2 without closing it. If fildes is not a valid descriptor, dup2() fails and does not close fildes2.

What is dup system call return?

The dup() system call duplicates an open file descriptor and returns the new file descriptor. • The new file descriptor has the following properties in common with the original file descriptor: 1. refers to the same open file or pipe.