Backtrace:
In ice-9/boot-9.scm:
 157: 10 [catch #t #<catch-closure 113f560> ...]
In unknown file:
   ?: 9 [apply-smob/1 #<catch-closure 113f560>]
   ?: 8 [call-with-input-string "(use-modules (mcron config))(if config-debug (begin (debug-enable 'debug)                        (debug-enable 'backtrace)))(use-modules (ice-9 regex) (ice-9 rdelim))(define command-name (match:substring (regexp-exec (make-regexp \"[[:alpha:]]*$\")                                                   (car (command-line)))))(define (mcron-error exit-code . rest)  (with-output-to-port (current-error-port)    (lambda ()      (for-each display (append (list command-name \": \") rest))      (newline)))  (if (and exit-code (not (eq? exit-code 0)))      (primitive-exit exit-code)))(defmacro catch-mcron-error (. body)  `(catch 'mcron-error          (lambda ()            ,@body)          (lambda (key exit-code . msg)            (apply mcron-error exit-code msg))))(define command-type (cond ((string=? command-name \"mcron\") 'mcron)                           ((or (string=? command-name \"cron\")                                (string=? command-name \"crond\")) 'cron)                           ((string=? command-name \"crontab\") 'crontab)                           (else                            (mcron-error 12 \"The command name is invalid.\"))))(use-modules (ice-9 getopt-long))(define options  (catch   'misc-error   (lambda ()     (getopt-long (command-line)                  (append                   (case command-type                     ((crontab)                      '((user     (single-char #\\u) (value #t))                        (edit     (single-char #\\e) (value #f))                        (list     (single-char #\\l) (value #f))                        (remove   (single-char #\\r) (value #f))))                     (else `((schedule (single-char #\\s) (value #t)                                       (predicate                                        ,(lambda (value)                                           (string->number value))))                             (daemon   (single-char #\\d) (value #f))                             (noetc    (single-char #\\n) (value #f))                             (stdin    (single-char #\\i) (value #t)                                       (predicate                                        ,(lambda (value)                                           (or (string=? \"vixie\" value)                                               (string=? \"guile\" value))))))))                   '((version  (single-char #\\v) (value #f))                     (help     (single-char #\\h) (value #f))))))   (lambda (key func fmt args . rest)     (mcron-error 1 (apply format (append (list #f fmt) args))))))(if (option-ref options 'version #f)    (begin      (display (string-append \"\\n\" command-name \"  (\" config-package-string \")\\nWritten by Dale Mellor\\n\\nCopyright (C) 2003, 2006, 2014  Dale Mellor\\nThis is free software; see the source for copying conditions.  There is NO\\nwarranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.\\n\"))      (quit)))(if (option-ref options 'help #f)    (begin      (display (string-append \"Usage: \" (car (command-line))(case command-type  ((mcron)\" [OPTIONS] [FILES]\\nRun an mcron process according to the specifications in the FILES (`-' for\\nstandard input), or use all the files in ~/.config/cron (or the \\ndeprecated ~/.cron) with .guile or .vixie extensions.\\n\\n  -v, --version             Display version\\n  -h, --help                Display this help message\\n  -sN, --schedule[=]N       Display the next N jobs that will be run by mcron\\n  -d, --daemon              Immediately detach the program from the terminal\\n                              and run as a daemon process\\n  -i, --stdin=(guile|vixie) Format of data passed as standard input or\\n                              file arguments (default guile)\")  ((cron)\" [OPTIONS]\\nUnless an option is specified, run a cron daemon as a detached process, \\nreading all the information in the users' crontabs and in /etc/crontab.\\n\\n  -v, --version             Display version\\n  -h, --help                Display this help message\\n  -sN, --schedule[=]N       Display the next N jobs that will be run by cron\\n  -n, --noetc               Do not check /etc/crontab for updates (HIGHLY\\n                              RECOMMENDED).\")  ((crontab)           (string-append \" [-u user] file\\n\"           \"       \" (car (command-line)) \" [-u user] { -e | -l | -r }\\n\"           \"               (default operation is replace, per 1003.2)\\n\"           \"       -e      (edit user's crontab)\\n\"           \"       -l      (list user's crontab)\\n\"           \"       -r      (delete user's crontab)\\n\"))  (else \"rubbish\"))\"\\n\\nReport bugs to \" config-package-bugreport \".\\n\"))      (quit)))(define (delete-run-file)  (catch #t (lambda () (delete-file config-pid-file)                       (delete-file config-socket-file))            noop)  (quit))(if (eq? command-type 'cron)    (begin      (if (not (eqv? (getuid) 0))          (mcron-error 16                       \"This program must be run by the root user (and should \"                       \"have been installed as such).\"))      (if (access? config-pid-file F_OK)          (mcron-error 1\t\t       \"A cron daemon is already running.\\n\"\t\t       \"  (If you are sure this is not true, remove the file\\n\"\t\t       \"   \"\t\t       config-pid-file\t\t       \".)\"))      (if (not (option-ref options 'schedule #f))          (with-output-to-file config-pid-file noop))      (setenv \"MAILTO\" #f)      (c-set-cron-signals)))(use-modules (mcron core)             (mcron job-specifier)             (mcron vixie-specification))(define (stdin->string)  (with-output-to-string (lambda () (do ((in (read-char) (read-char)))                                        ((eof-object? in))                                        (display in)))))(if (eq? command-type 'crontab)    (begin(let ((hit-server       (lambda (user-name)         (catch #t (lambda ()                     (let ((socket (socket AF_UNIX SOCK_STREAM 0)))                       (connect socket AF_UNIX config-socket-file)                       (display user-name socket)                       (close socket)))                (lambda (key . args)                  (display \"Warning: a cron daemon is not running.\\n\")))))      (in-access-file?       (lambda (file name)         (catch #t (lambda ()                     (with-input-from-file                         file                       (lambda ()                         (let loop ((input (read-line)))                           (if (eof-object? input)                               #f                               (if (string=? input name)                                   #t                                   (loop (read-line))))))))                (lambda (key . args) '()))))      (crontab-real-user (passwd:name (getpw (getuid)))))  (if (or (eq? (in-access-file? config-allow-file crontab-real-user) #f)          (eq? (in-access-file? config-deny-file crontab-real-user) #t))      (mcron-error 6 \"Access denied by system operator.\"))  (if (> (+ (if (option-ref options 'edit #f) 1 0)            (if (option-ref options 'list #f) 1 0)            (if (option-ref options 'remove #f) 1 0))         1)      (mcron-error 7 \"Only one of options -e, -l or -r can be used.\"))  (if (and (not (eqv? (getuid) 0))           (option-ref options 'user #f))      (mcron-error 8 \"Only root can use the -u option.\"))  (let (        (crontab-user (option-ref options 'user crontab-real-user))        (crontab-file (string-append config-spool-dir \"/\" crontab-user))        (get-yes-no (lambda (prompt . re-prompt)                      (if (not (null? re-prompt))                          (display \"Please answer y or n.\\n\"))                      (display (string-append prompt \" \"))                      (let ((r (read-line)))                        (if (not (string-null? r))                            (case (string-ref r 0)                              ((#\\y #\\Y) #t)                              ((#\\n #\\N) #f)                              (else (get-yes-no prompt #t)))                            (get-yes-no prompt #t))))))    (cond ((option-ref options 'list #f)  (catch #t (lambda ()              (with-input-from-file crontab-file (lambda ()                 (do ((input (read-char) (read-char)))                     ((eof-object? input))                   (display input)))))         (lambda (key . args)           (display (string-append \"No crontab for \"                                   crontab-user                                   \" exists.\\n\"))))) ((option-ref options 'edit #f)  (let ((temp-file (string-append config-tmp-dir                                  \"/crontab.\"                                  (number->string (getpid)))))    (catch #t (lambda () (copy-file crontab-file temp-file))              (lambda (key . args) (with-output-to-file temp-file noop)))    (chown temp-file (getuid) (getgid))    (let retry ()      (system (string-append               (or (getenv \"VISUAL\") (getenv \"EDITOR\") \"vi\")               \" \"               temp-file))      (catch 'mcron-error             (lambda () (read-vixie-file temp-file))             (lambda (key exit-code . msg)               (apply mcron-error 0 msg)               (if (get-yes-no \"Edit again?\")                   (retry)                   (begin                     (mcron-error 0 \"Crontab not changed\")                     (primitive-exit 0))))))    (copy-file temp-file crontab-file)    (delete-file temp-file)    (hit-server crontab-user))) ((option-ref options 'remove #f)  (catch #t (lambda () (delete-file crontab-file)                       (hit-server crontab-user))            noop)) ((not (null? (option-ref options '() '())))  (let ((input-file (car (option-ref options '() '()))))    (catch-mcron-error     (if (string=? input-file \"-\")         (let ((input-string (stdin->string)))           (read-vixie-port (open-input-string input-string))           (with-output-to-file crontab-file (lambda ()                                               (display input-string))))         (begin           (read-vixie-file input-file)           (copy-file input-file crontab-file))))    (hit-server crontab-user))) (else  (mcron-error 15 \"usage error: file name must be specified for replace.\")))))       (quit)))(define (regular-file? file)  (catch 'system-error\t (lambda ()\t   (eq? (stat:type (stat file)) 'regular))\t (lambda (key call fmt args . rest)\t   (mcron-error 0 (apply format (append (list #f fmt) args)))\t   #f)))(define guile-file-regexp (make-regexp \"\\\\.gui(le)?$\"))(define vixie-file-regexp (make-regexp \"\\\\.vix(ie)?$\"))(define (process-user-file file-path . assume-guile)  (cond ((string=? file-path \"-\")               (if (string=? (option-ref options 'stdin \"guile\") \"vixie\")                   (read-vixie-port (current-input-port))                   (eval-string (stdin->string))))        ((or (not (null? assume-guile))             (regexp-exec guile-file-regexp file-path))         (load file-path))        ((regexp-exec vixie-file-regexp file-path)         (read-vixie-file file-path))))(define (process-files-in-user-directory)  (let ((errors 0)        (home-directory (passwd:dir (getpw (getuid)))))    (map (lambda (config-directory)          (catch #t                 (lambda ()                   (let ((directory (opendir config-directory)))                     (do ((file-name (readdir directory) (readdir directory)))                         ((eof-object? file-name) (closedir directory))                       (process-user-file (string-append config-directory                                                         \"/\"                                                         file-name)))))                 (lambda (key . args)                   (set! errors (1+ errors)))))          (list (string-append home-directory \"/.cron\")                (string-append (or (getenv \"XDG_CONFIG_HOME\")                                   (string-append home-directory \"/.config\"))                               \"/cron\")))    (if (eq? 2 errors)        (mcron-error 13                     \"Cannot read files in your ~/.config/cron (or ~/.cron) \"                     \"directory.\"))))(define (valid-user user-name)  (setpwent)  (do ((entry (getpw) (getpw)))      ((or (not entry)           (string=? (passwd:name entry) user-name))       (endpwent)       entry)))(use-modules (srfi srfi-2)) (define (process-files-in-system-directory)  (catch #t         (lambda ()           (let ((directory (opendir config-spool-dir)))             (do ((file-name (readdir directory) (readdir directory)))                 ((eof-object? file-name))               (and-let* ((user (valid-user file-name)))                         (set-configuration-user user)                          (catch-mcron-error                          (read-vixie-file (string-append config-spool-dir                                                          \"/\"                                                          file-name)))))))         (lambda (key . args)           (mcron-error            4            \"You do not have permission to access the system crontabs.\"))))(case command-type  ((mcron) (if (null? (option-ref options '() '()))                (process-files-in-user-directory)                (for-each (lambda (file-path)                            (process-user-file file-path #t))                          (option-ref options '() '()))))  ((cron) (process-files-in-system-directory)   (use-system-job-list)   (catch-mcron-error    (read-vixie-file \"/etc/crontab\" parse-system-vixie-line))   (use-user-job-list)   (if (not (option-ref options 'noetc #f))       (begin         (display\"WARNING: cron will check for updates to /etc/crontab EVERY MINUTE. If you do\\nnot use this file, or you are prepared to manually restart cron whenever you\\nmake a change, then it is HIGHLY RECOMMENDED that you use the --noetc\\noption.\\n\")         (set-configuration-user \"root\")         (job '(- (next-minute-from (next-minute)) 6)              check-system-crontab              \"/etc/crontab update checker.\")))))(and-let* ((count (option-ref options 'schedule #f)))          (set! count (string->number count))          (display (get-schedule (if (<= count 0) 1 count)))          (quit))(if (option-ref options 'daemon (eq? command-type 'cron))    (begin      (if (not (eqv? (primitive-fork) 0))          (quit))      (setsid)      (if (eq? command-type 'cron)          (with-output-to-file config-pid-file            (lambda () (display (getpid)) (newline))))))(define fd-list '())(if (eq? command-type 'cron)    (catch #t           (lambda ()             (let ((socket (socket AF_UNIX SOCK_STREAM 0)))               (bind socket AF_UNIX config-socket-file)               (listen socket 5)               (set! fd-list (list socket))))           (lambda (key . args)             (delete-file config-pid-file)             (mcron-error 1                          \"Cannot bind to UNIX socket \"                          config-socket-file))))\t\t     (define (process-update-request)  (let* ((socket (car (accept (car fd-list))))         (user-name (read-line socket)))    (close socket)    (set-configuration-time (current-time))    (catch-mcron-error     (if (string=? user-name \"/etc/crontab\")         (begin           (clear-system-jobs)           (use-system-job-list)           (read-vixie-file \"/etc/crontab\" parse-system-vixie-line)           (use-user-job-list))         (let ((user (getpw user-name)))           (remove-user-jobs user)           (set-configuration-user user)           (read-vixie-file (string-append config-spool-dir \"/\" user-name)))))))(catch-mcron-error (while #t        (run-job-loop fd-list)        (if (not (null? fd-list))            (process-update-request))))" ...]
In ice-9/boot-9.scm:
2401: 7 [save-module-excursion #<procedure 1466f30 at ice-9/eval-string.scm:65:9 ()>]
In ice-9/eval-string.scm:
  44: 6 [read-and-eval #<input: string fcc750> #:lang ...]
  37: 5 [lp (if (eq? command-type (quote crontab)) (begin (let # # # # #) (quit)))]
In ice-9/eval.scm:
 432: 4 [eval # ()]
 411: 3 [eval # #]
 387: 2 [eval # #]
 393: 1 [eval # #]
In unknown file:
   ?: 0 [memoize-variable-access! #<memoized crontab-user> #<directory # 101bc60>]

ERROR: In procedure memoize-variable-access!:
ERROR: Unbound variable: crontab-user