Chroot actually appeared in 7th Edition Unix.

[imp]

Summary

Chroot appeared during the development of 7th edition Unix. The FreeBSD jail
documents, incorrectly, that Bill Joy added this to 4.2BSD on 18 March

1982. That was when Bill Joy converted from a statically coded system call glue

to dynamically generated assembler. Chroot was present in 32V, 3BSD, 4.0BSD, 4.1BSD
and 4.1cBSD well in advance of this.

See also:
V7: https://minnie.tuhs.org/cgi-bin/utree.pl?file=V7/usr/src/libc/sys/chroot.s
32V: https://minnie.tuhs.org/cgi-bin/utree.pl?file=32V/usr/src/libc/sys/chroot.s
3BSD: https://minnie.tuhs.org/cgi-bin/utree.pl?file=3BSD/usr/src/libc/sys/chroot.s
4BSD: https://minnie.tuhs.org/cgi-bin/utree.pl?file=4BSD/usr/src/libc/sys/chroot.s
4.1cBSD: https://minnie.tuhs.org/cgi-bin/utree.pl?file=4.1cBSD/usr/src/libc/sys/chroot.s

The 6th edition does not have this system call, nor does it have anything named
chroot in the tree available from TUHS.

[allanjude]

Reviewed by: allanjude

[imp]

Sent a similar thing to Kirk and he agrees.