Which is the first version of the linux-kernel implementing the system call write? (sys_write)
As you might expect, given that the
write system call is a staple of Unix-style kernels, Linux had it as soon as it was “grown up” enough to be a kernel. You can see its implementation in version 0.01 from 1991.
At the risk of repeating information that is undoubtedly documented in a million places:
“Unix Version 6” (or “Unix Sixth Edition”) was the first version of Unix released outside of AT&T Bell Laboratories (the birthplace of Unix). I know this happened by 1975 at the latest. I know nothing about versions before that. (Chronology note: “Version 7”, naturally, came shortly after “Version 6”. Then “System III” and “System V” came long after that.)
write system call was present in Unix Version 6.
Here is the
write(II) man page from Unix Version 6;
note that it is dated 8/5/73.
Here is an index of all the man pages.
Linux was announced in 1991; see, for example, Wikipedia. This answer to the U&L question Is it true that the first version of Linux was based on parts of Unix? claims that Linus Torvalds based the Linux system calls on the Unix man pages, saying that this information comes from the book Just for Fun.
write system call was in Unix long before Linux existed.
The yggdrasil tarball from November 1994 has
/usr/src/linux/fs/read_write.c (actually gzip'd).
That file has this: Copyright (C) 1991, 1992 Linus Torvalds which indicates it was added in 1991 or 1992. There was no version-control system in use at that time, so details are scarce.