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;;;; crontab -- edit user's cron tabs
;;; Copyright © 2003, 2004 Dale Mellor <>
;;; Copyright © 2016 Mathieu Lirzin <mthl@gnu.org>
;;;
;;; 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 scripts crontab)
#:use-module (ice-9 rdelim)
#:use-module (mcron config)
#:use-module (mcron utils)
#:use-module (mcron vixie-specification)
#:export (main))
(define (hit-server user-name)
"Tell the running cron daemon that the user corresponding to
USER-NAME has modified his crontab. USER-NAME is written to the
'/var/cron/socket' UNIX socket."
(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"))))
;; Display the prompt and wait for user to type his choice. Return #t if the
;; answer begins with 'y' or 'Y', return #f if it begins with 'n' or 'N',
;; otherwise ask again.
(define (get-yes-no prompt . re-prompt)
(unless (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))))
(define (in-access-file? file name)
"Scan FILE which should contain one user name per line (such as
'/var/cron/allow' and '/var/cron/deny'). Return #t if NAME is in there, and
#f otherwise. if FILE cannot be opened, a error is signaled."
(catch #t
(lambda ()
(with-input-from-file file
(lambda ()
(let loop ((input (read-line)))
(cond ((eof-object? input)
#f)
((string=? input name)
#t)
(else
(loop (read-line))))))))
(const '())))
;;;
;;; Entry point.
;;;
(define (main --user --edit --list --remove files)
(when config-debug (debug-enable 'backtrace))
(let ((crontab-real-user
;; This program should have been installed SUID root. Here we get
;; the passwd entry for the real user who is running this program.
(passwd:name (getpw (getuid)))))
;; If the real user is not allowed to use crontab due to the
;; /var/cron/allow and/or /var/cron/deny files, bomb out now.
(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."))
;; Check that no more than one of the mutually exclusive options are
;; being used.
(when (< 1 (+ (if --edit 1 0) (if --list 1 0) (if --remove 1 0)))
(mcron-error 7 "Only one of options -e, -l or -r can be used."))
;; Check that a non-root user is trying to read someone else's files.
(when (and (not (zero? (getuid))) --user)
(mcron-error 8 "Only root can use the -u option."))
(letrec* (;; Iff the --user option is given, the crontab-user may be
;; different from the real user.
(crontab-user (or --user crontab-real-user))
;; So now we know which crontab file we will be manipulating.
(crontab-file
(string-append config-spool-dir "/" crontab-user)))
;; There are four possible sub-personalities to the crontab
;; personality: list, remove, edit and replace (when the user uses no
;; options but supplies file names on the command line).
(cond
;; In the list personality, we simply open the crontab and copy it
;; character-by-character to the standard output. If anything goes
;; wrong, it can only mean that this user does not have a crontab
;; file.
(--list
(catch #t
(λ ()
(with-input-from-file crontab-file
(λ ()
(do ((input (read-char) (read-char)))
((eof-object? input))
(display input)))))
(λ (key . args)
(display (string-append "No crontab for "
crontab-user
" exists.\n")))))
;; In the edit personality, we determine the name of a temporary file
;; and an editor command, copy an existing crontab file (if it is
;; there) to the temporary file, making sure the ownership is set so
;; the real user can edit it; once the editor returns we try to read
;; the file to check that it is parseable (but do nothing more with
;; the configuration), and if it is okay (this program is still
;; running!) we move the temporary file to the real crontab, wake the
;; cron daemon up, and remove the temporary file. If the parse fails,
;; we give user a choice of editing the file again or quitting the
;; program and losing all changes made.
(--edit
(let ((temp-file (string-append config-tmp-dir
"/crontab."
(number->string (getpid)))))
(catch #t
(λ () (copy-file crontab-file temp-file))
(λ (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
(λ () (read-vixie-file temp-file))
(λ (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)))
;; In the remove personality we simply make an effort to delete the
;; crontab and wake the daemon. No worries if this fails.
(--remove (catch #t (λ () (delete-file crontab-file)
(hit-server crontab-user))
noop))
;; XXX: This comment is wrong.
;; In the case of the replace personality we loop over all the
;; arguments on the command line, and for each one parse the file to
;; make sure it is parseable (but subsequently ignore the
;; configuration), and all being well we copy it to the crontab
;; location; we deal with the standard input in the same way but
;; different. :-) In either case the server is woken so that it will
;; read the newly installed crontab.
((not (null? files))
(let ((input-file (car files)))
(catch-mcron-error
(if (string=? input-file "-")
(let ((input-string (read-string)))
(read-vixie-port (open-input-string input-string))
(with-output-to-file crontab-file
(λ () (display input-string))))
(begin
(read-vixie-file input-file)
(copy-file input-file crontab-file))))
(hit-server crontab-user)))
;; The user is being silly. The message here is identical to the one
;; Vixie cron used to put out, for total compatibility.
(else (mcron-error 15
"usage error: file name must be specified for replace."))))))
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