再現実験

console_log

$ ls /
Applications
Library
Network
System
Users
Volumes
bin
cores
dev
etc
home
mach_kernel
net
private
sbin
tmp
usr
var
ユーザ情報
$ locale
LANG="en_US.UTF-8"
LC_COLLATE="en_US.UTF-8"
LC_CTYPE="en_US.UTF-8"
LC_MESSAGES="en_US.UTF-8"
LC_MONETARY="en_US.UTF-8"
LC_NUMERIC="en_US.UTF-8"
LC_TIME="en_US.UTF-8"
LC_ALL=
$ ros -L sbcl-bin run
* (let ((dir (sb-posix:opendir "/")))
    (unwind-protect
       (block dir-loop
         (loop for dirent = (sb-posix:readdir dir)
               until (sb-alien:null-alien dirent)
               when (not (stringp (sb-posix:dirent-name dirent)))
                 do (return-from dir-loop nil)
               finally (return t)))
      (sb-posix:closedir dir)))

T
* (quit)
$ export LANG=C
$ locale
LANG="C"
LC_COLLATE="C"
LC_CTYPE="C"
LC_MESSAGES="C"
LC_MONETARY="C"
LC_NUMERIC="C"
LC_TIME="C"
LC_ALL=
$ ros -L sbcl-bin run
* (let ((dir (sb-posix:opendir "/")))
    (unwind-protect
       (block dir-loop
         (loop for dirent = (sb-posix:readdir dir)
               until (sb-alien:null-alien dirent)
               when (not (stringp (sb-posix:dirent-name dirent)))
                 do (return-from dir-loop nil)
               finally (return t)))
      (sb-posix:closedir dir)))

debugger invoked on a SB-INT:C-STRING-DECODING-ERROR:
  :ASCII c-string decoding error: the octet sequence #(227) cannot be decoded.

Type HELP for debugger help, or (SB-EXT:EXIT) to exit from SBCL.

restarts (invokable by number or by possibly-abbreviated name):
  0: [ABORT] Exit debugger, returning to top level.

(SB-INT:C-STRING-DECODING-ERROR :ASCII #.(SB-SYS:INT-SAP #X05800435) 0 1)
0] 0

* (quit)