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diff --git a/scm/mcron/mcron-core.scm b/scm/mcron/mcron-core.scm
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+;;   Copyright (C) 2003 Dale Mellor
+;; 
+;;   This file is part of GNU mcron.
+;;
+;;   GNU mcron is free software: you can redistribute it and/or modify it under
+;;   the terms of the GNU General Public License as published by the Free
+;;   Software Foundation, either version 3 of the License, or (at your option)
+;;   any later version.
+;;
+;;   GNU mcron is distributed in the hope that it will be useful, but WITHOUT
+;;   ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+;;   FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+;;   more details.
+;;
+;;   You should have received a copy of the GNU General Public License along
+;;   with GNU mcron.  If not, see <http://www.gnu.org/licenses/>.
+
+
+
+(define-module (mcron core)
+  #:use-module (mcron environment)
+  #:export     (add-job
+                remove-user-jobs
+                get-schedule
+                run-job-loop
+                   ;; These three are deprecated and not documented.
+                use-system-job-list
+                use-user-job-list
+                clear-system-jobs)
+  #:re-export  (clear-environment-mods
+                append-environment-mods))
+
+
+(use-modules (srfi srfi-1)    ;; For remove.
+             (srfi srfi-2))   ;; For and-let*.
+
+
+
+;; The list of all jobs known to the system. Each element of the list is
+;;
+;;  (vector user next-time-function action environment displayable next-time)
+;;
+;; where action must be a procedure, and the environment is an alist of
+;; modifications that need making to the UNIX environment before the action is
+;; run. The next-time element is the only one that is modified during the
+;; running of a cron process (i.e. all the others are set once and for all at
+;; configuration time).
+;;
+;; The reason we maintain two lists is that jobs in /etc/crontab may be placed
+;; in one, and all other jobs go in the other. This makes it possible to remove
+;; all the jobs in the first list in one go, and separately we can remove all
+;; jobs from the second list which belong to a particular user. This behaviour
+;; is required for full vixie compatibility.
+
+(define system-job-list '())
+(define user-job-list '())
+
+(define configuration-source 'user)
+
+(define (use-system-job-list) (set! configuration-source 'system))
+(define (use-user-job-list) (set! configuration-source 'user))
+
+
+
+;; Convenience functions for getting and setting the elements of a job object.
+
+(define (job:user job)                (vector-ref job 0))
+(define (job:next-time-function job)  (vector-ref job 1))
+(define (job:action job)              (vector-ref job 2))
+(define (job:environment job)         (vector-ref job 3))
+(define (job:displayable job)         (vector-ref job 4))
+(define (job:next-time job)           (vector-ref job 5))
+
+
+
+;; Remove jobs from the user-job-list belonging to this user.
+
+(define (remove-user-jobs user)
+  (if (or (string? user)
+          (integer? user))
+      (set! user (getpw user)))
+    (set! user-job-list
+          (remove (lambda (job) (eqv? (passwd:uid user)
+                                      (passwd:uid (job:user job))))
+                  user-job-list)))
+
+
+
+;; Remove all the jobs on the system job list.
+
+(define (clear-system-jobs) (set! system-job-list '()))
+
+
+
+;; Add a new job with the given specifications to the head of the appropriate
+;; jobs list.
+
+(define (add-job time-proc action displayable configuration-time
+                 configuration-user)
+  (let ((entry (vector configuration-user
+                       time-proc
+                       action
+                       (get-current-environment-mods-copy)
+                       displayable
+                       (time-proc configuration-time))))
+    (if (eq? configuration-source 'user)
+      (set! user-job-list (cons entry user-job-list))
+      (set! system-job-list (cons entry system-job-list)))))
+
+
+
+;; Procedure to locate the jobs in the global job-list with the lowest
+;; (soonest) next-times. These are the jobs for which we must schedule the mcron
+;; program (under any personality) to next wake up. The return value is a cons
+;; cell consisting of the next time (maintained in the next-time variable) and a
+;; list of the job entries that are to run at this time (maintained in the
+;; next-jobs-list variable).
+;;
+;; The procedure works by first obtaining the time of the first job on the list,
+;; and setting this job in the next-jobs-list. Then for each other entry on the
+;; job-list, either the job runs earlier than any other that have been scanned,
+;; in which case the next-time and next-jobs-list are re-initialized to
+;; accomodate, or the job runs at the same time as the next job, in which case
+;; the next-jobs-list is simply augmented with the new job, or else the job runs
+;; later than others noted in which case we ignore it for now and continue to
+;; recurse the list.
+
+(define (find-next-jobs)
+  (let ((job-list (append system-job-list user-job-list)))
+    
+    (if (null? job-list)
+        
+        '(#f . '())
+        
+        (let ((next-time 2000000000)
+              (next-jobs-list '()))
+
+          (for-each
+           (lambda (job)
+             (let ((this-time (job:next-time job)))
+               (cond ((< this-time next-time)
+                          (set! next-time this-time)
+                          (set! next-jobs-list (list job)))
+                     ((eqv? this-time next-time)
+                          (set! next-jobs-list (cons job next-jobs-list))))))
+           job-list)
+
+          (cons next-time next-jobs-list)))))
+
+
+
+;; Create a string containing a textual list of the next count jobs to run.
+;;
+;; Enter a loop of displaying the next set of jobs to run, artificially
+;; forwarding the time to the next time point (instead of waiting for it to
+;; occur as we would do in a normal run of mcron), and recurse around the loop
+;; count times.
+;;
+;; Note that this has the effect of mutating the job timings. Thus the program
+;; must exit after calling this function; the internal data state will be left
+;; unusable.
+
+(define (get-schedule count)
+  (with-output-to-string
+    (lambda ()
+      (do ((count count (- count 1)))
+          ((eqv? count 0))
+        (and-let* ((next-jobs (find-next-jobs))
+                   (time (car next-jobs))
+                   (date-string (strftime "%c %z\n" (localtime time))))
+          (for-each (lambda (job)
+                      (display date-string)
+                      (display (job:displayable job))
+                      (newline)(newline)
+                      (vector-set! job
+                                   5
+                                   ((job:next-time-function job)
+                                                          (job:next-time job))))
+                    (cdr next-jobs)))))))
+
+
+
+;; For proper housekeeping, it is necessary to keep a record of the number of
+;; child processes we fork off to run the jobs.
+
+(define number-children 0)
+
+
+
+;; For every job on the list, fork a process to run it (noting the fact by
+;; increasing the number-children counter), and in the new process set up the
+;; run-time environment exactly as it should be before running the job proper.
+;;
+;; In the parent, update the job entry by computing the next time the job needs
+;; to run.
+
+(define (run-jobs jobs-list)
+  (for-each (lambda (job)
+              (if (eqv? (primitive-fork) 0)
+                  (begin
+                    (setgid (passwd:gid (job:user job)))
+                    (setuid (passwd:uid (job:user job)))
+                    (chdir (passwd:dir (job:user job)))
+                    (modify-environment (job:environment job) (job:user job))
+                    ((job:action job))
+                    (primitive-exit 0))
+                  (begin
+                    (set! number-children (+ number-children 1))
+                    (vector-set! job
+                                 5
+                                 ((job:next-time-function job)
+                                                            (current-time))))))
+            jobs-list))
+
+
+
+;; Give any zombie children a chance to die, and decrease the number known to
+;; exist.
+
+(define (child-cleanup)
+  (do () ((or (<= number-children 0)
+	      (eqv? (car (waitpid WAIT_ANY WNOHANG)) 0)))
+    (set! number-children (- number-children 1))))
+
+
+
+;; Now the main loop. Loop over all job specifications, get a list of the next
+;; ones to run (may be more than one). Set an alarm and go to sleep. When we
+;; wake, run the jobs and reap any children (old jobs) that have
+;; completed. Repeat ad infinitum.
+;;
+;; Note that, if we wake ahead of time, it can only mean that a signal has been
+;; sent by a crontab job to tell us to re-read a crontab file. In this case we
+;; break out of the loop here, and let the main procedure deal with the
+;; situation (it will eventually re-call this function, thus maintaining the
+;; loop).
+
+(define (run-job-loop . fd-list)
+
+  (call-with-current-continuation
+   (lambda (break)
+     
+     (let ((fd-list (if (null? fd-list) '() (car fd-list))))
+
+       (let loop ()
+
+         (let* ((next-jobs      (find-next-jobs))
+                (next-time      (car next-jobs))
+                (next-jobs-list (cdr next-jobs))
+                (sleep-time     (if next-time (- next-time (current-time))
+                                    2000000000)))
+
+           (and (> sleep-time 0)
+                (if (not (null?
+                          (catch 'system-error
+                                 (lambda ()
+                                   (car (select fd-list '() '() sleep-time)))
+                                 (lambda (key . args) ;; Exception add by Sergey
+						                              ;; Poznyakoff.
+                                   (if (member (car (last args))
+                                               (list EINTR EAGAIN))
+                                       (begin
+                                         (child-cleanup) '())
+                                       (apply throw key args))))))
+                    (break)))
+
+           (run-jobs next-jobs-list)
+
+           (child-cleanup)
+           
+           (loop)))))))