I'm installing John the Ripper to check my password security, but under RedHat 9 I get an install error when I use make linux-x86-any-elf, I get install error 1. Am I missing something?

Yes, you're missing the details about that error.

Sorry, I can't really isolate the error, but here's the output:

ln -sf x86-any.h arch.h
make ../run/john ../run/unshadow ../run/unafs ../run/unique \
JOHN_OBJS="DES_fmt.o DES_std.o DES_bs.o BSDI_fmt.o MD5_fmt.o MD5_std.o BF_fmt.o
BF_std.o AFS_fmt.o LM_fmt.o batch.o bench.o charset.o common.o compiler.o config.o cracker.o external.o formats.o getopt.o idle.o inc.o john.o list.o loader.o logger.o math.o memory.o misc.o options.o params.o path.o recovery.o rpp.o rules.o signals.o single.o status.o tty.o wordlist.o unshadow.o unafs.o unique.o DES_bs_b.o x86.o"
make[1]: Entering directory `/root/john-1.6.37/src'
gcc -s DES_fmt.o DES_std.o DES_bs.o BSDI_fmt.o MD5_fmt.o MD5_std.o BF_fmt.o BF_std.o AFS_fmt.o LM_fmt.o batch.o bench.o charset.o common.o compiler.o config.o cracker.o external.o formats.o getopt.o idle.o inc.o john.o list.o loader.o logger.o math.o memory.o misc.o options.o params.o path.o recovery.o rpp.o rules.o signals.o single.o status.o tty.o wordlist.o unshadow.o unafs.o unique.o DES_bs_b.o x86.o -o ../run/john
x86.o(.data+0xf60): In function `DES_std_crypt':
: multiple definition of `DES_std_crypt'
DES_std.o(.text+0x1f08): first defined here
collect2: ld returned 1 exit status
make[1]: *** [../run/john] Error 1
make[1]: Leaving directory `/root/john-1.6.37/src'
make: *** [linux-x86-any-elf] Error 2

Error is

: multiple definition of `DES_std_crypt'

However, as the objects appear to be missing debug code it doesn't tell you what line it was defined on, just a hexadecimal adress..

You'll have to remove one definition of that, and hope you get the right one.