In Unix like system File descriptor is
abstract indicator for accessing file and are represented in integer value. FD
is a computer program term and highly used while programming in Unix like
system using language like C, This is similar to file handle in windows
like system.
By default operating system 3 file descriptor namely from 0-2.
Where 0 represent standard input (stdin),
1 for standard output (stdout)
and 2 for standard errors (stderr).
Operating system keeps index entry of opened files somewhere
in Kernal’s address space which can be generally referred as file
descriptor table. When a user process use open() or socket() (system
calls to interface to the kernel) you are returned a file descriptor, which is an integer (These entries are
represented by integers like ...100, 101, 102....) And are maintains its file descriptor table in its address space. When a process want to
access the file it passes the file descriptor to kernel with system call which
in turns reads the file on behalf and returns the handle or result.
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