DCRON - SIMPLE CRON PROGRAM
				Matthew Dillon

			Originally written: 1 May 1994


CREDITS

    I finally got tired of all of these wild cron programs that take the
    task of running timed jobs to ridiculous extremes in terms of 
    capabilities and unnecessary features.  So here is my entry:  a 
    crond/crontab combination that is simple and elegant, and hopefully
    secure to boot.  This cron implements reasonable features in terms
    of field specification in the crontab and allows individual user 
    crontabs.  

    This program is written entirely from scratch by yours Truely (sig
    at bottom).

    All jobs are run with /bin/sh for conformity and portability, thereby
    avoiding the mess that occurs with other cron's that try to use the
    user's perfered shell, which breaks down for special users and even makes
    some of us normal users unhappy (for example, /bin/csh does not use a true
    O_APPEND mode and has difficulty redirecting stdout and stderr both to
    different places!).  You can, of course, run shell scripts in whatever
    language you like by making them executable with #!/bin/csh or whatever
    as the first line.  If you don't like the extra processes, just 'exec'
    them.

    Under the same reasoning, this cron does not allow you to specify
    environment variables or other stuff better left specified as
    arguments to a shell script.  Talk about nonsense!

    The programs were written with an eye towards security, hopefully I
    haven't forgotton anything.  The programs were also written with an
    eye towards nice, clean, algorithmically sound code.  It's small, and
    the only fancy code is that which deals with child processes.  I do
    not try to optimize with vfork() since it causes headaches and is
    rather pointless considering I'm execing a shell most of the time,
    and I pay close attention to leaving descriptors open in the crond
    and close attention to preventing crond from running away.

COMPILATION

    This is an ANSI program, you must use a compiler that understands
    prototypes, such as GCC.  I will not accept bug reports related
    to hacking the program to work with a non-ANSI compiler.

    Note that the source code, especially in regard to changing the
    effective user, is Linux specific (SysVish).  I welcome any changes
    in regard to making the mechanism work with other platforms.

    (1) Edit the Makefile, adding -D overrides to defines in defs.h as
	appropriate for your machine.  (Or just edit defs.h, but as
	people introduce fixes to make the program work on other
	platforms, I want most overrides to be in the CFLAGS for the
	Makefile).

    (2) You may need to edit the #include lines in defs.h for your 
	machine.  The goal is to include everything necessary such that
	the program can be compiled in the most ansi-strict manner.  Amoung
	other things, prototypes for system functions must come from 
	external include files and NOT from defs.h or any source file.   
	If no prototype exists for a particular function, contact your 
	vendor to get an update for your includes.

    (3) make

INSTALLATION

    Permissions should be as outlined below.  You will want to create a
    special 'cron' group in which you put those users that are allowed
    to use the crontab program. 

    -rwx------   1 root     wheel       24864 Apr 27 09:02 /usr/bin/crond*
    -rwsr-x---   1 root     cron        24311 Apr 27 09:02 /usr/bin/crontab*

    crond should be run automatically at system startup from /etc/rc.local 
    (or equivalent).  It automatically detaches.  A log level of 8 is
    normally specified, and you normally append using /bin/sh's >>, allowing
    the log file to backed up and cleared with an 'echo >/var/log/cron' in
    your cron scripts.

    /usr/bin/crond -l8 >>/var/log/cron 2>&1

    The crontab files are normally located in /var/spool/cron/crontabs.  The
    directories normally have permissions:

    drwxr-x---   3 root  wheel  1024 Feb 24 18:17 /var/spool/cron/
    drwxr-x---   2 root  wheel  1024 May  1 10:28 /var/spool/cron/crontabs

TESTING

    Use the crontab program to create a personal crontab with the following
    two lines:

    * * * * *  date >>/tmp/test
    * * * * *  date

    Check the log output of crond to ensure the cron entries are being
    run once a minute, check /tmp/test to ensure the date is being
    appended to it once a minute, and check your mail to ensure that crond
    is mailing you the date from the other entry once a minute.

    After you are through testing cron, delete the entries with crontab -e
    or crontab -d

BUG REPORTS, SUBMISSIONS

    Send any bug reports and source code changes to me, Matthew Dillon:

	dillon@apollo.backplane.com

    Note carefully that I will not accept any local ANSI prototypes for 
    system calls that should properly be in an external include file,
    that I will probably not accept additional features to the program,
    and I will not accept any changes to make the source compile under
    a non-ANSI compiler.  I will not accept any radical code changes...
    the purpose being that I want this cron to be made bug free rather
    then feature full.

    Changes to overridable defaults in defs.h should be made in the
    Makefile, you may submit a Makefile for your platform.  Changes
    to the #include's in defs.h should be made by a combination of an
    -D options in the Makefile and #ifdef's for that option in defs.h, 
    and not rely on pre-definitions made by the C compiler.

    Changes to source code to accomodate one platform or other should
    be made in the same manner.


    Matthew Dillon		dillon@apollo.backplane.com
    [always include a portion of the original email in any response!]