SVR4, or System V Release 4, is a version of System V, ie. Unix. The tools in this chapter aim to help working with such an environment on an LFS system. There are a few caveats as a result of dealing with an old operating system.
The packages in this chapter are installed to various non-standard
locations inside /usr. The purpose
behind this is to be more accurate to where UNIXen from where these
tools were ported put said files, and an explanation of where said
paths came from is provided below.
/bin and /sbin: the traditional, pre-dating formal
standardization, general toolsets; from a
post-formal-standardization viewpoint, commands that conform
to the System V Interface Definition and the X/Open
Portability Guide version 3 (or, in Linux's case, standard
Linux tools)
/usr/ucb: UCB (i.e. BSD)
compatibility directory with BSD-compatible tools
/5bin and /usr/5bin: SVID3-adhering tools, aka tools
compatible with AT&T Unix System 5 Release 4.0 or Solaris
2
/usr/5bin/s42: SVID4-adhering
tools, aka tools compatible with Unix System 5 Release 4.2MP
/usr/5bin/posix: POSIX.2 and
SUSv2-adhering tools
/usr/5bin/posix2001: tools
adhering to POSIX.1-2001 with SUSv3 extensions
/usr/ccs/bin: various developer
tools
/usr/sadm/bin: pkgadd internal
tooling
The rest of the non-standard folders' meanings can be easily deduced from basic Linux knowledge and the above.
If you want to know more about old UNIXen' path conventions, and are willing to fall down a rabbit hole of 80s-90s UNIX variants, DEC equipment and various other old UNIX conventions, old hardware and everyday jobs of UNIX sysops of the 90s, a much more comprehensive guide can be found here.
It is also of note that Linux tools are much closer in UI and parameters to their BSD counterparts than their SVR4 ones. If you want to use tools from this category on a daily basis and you're not familiar with UNIX SVR4, you might first need to learn how SVR4 tools work.