Chroot actually appeared in 7th Edition Unix.

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. Kirk McKusick agrees with this analysis.

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 and earlier editions do not have this system call, nor do they have
anything named chroot in the trees available from TUHS.

Reviewed by: allanjude@
Differential Revision: https://reviews.freebsd.org/D25475