Ubuntu Manpage: dacssched - rule-based command scheduling

NAME

       dacssched - rule-based command scheduling

SYNOPSIS


       dacssched [-h | -help] [-ll log_level] [-q] [{-r | -rules} rules_uri] [{-s | -sched} sched_uri] [-v]

       dacssched --version

DESCRIPTION

This program is part of the DACS suite. It is a stand-alone program that neither accepts the usual DACS
command line options (dacsoptions) nor accesses any DACS configuration files.

The dacssched command runs other programs when specified conditions have been met. It does this by
periodically examining a schedule, which, for each scheduled event, identifies the necessary conditions
and the command line to be executed should the conditions be satisfied. Rules are stored separately from
the schedule, although in a future version it might be possible to contain them with their schedule.

Although dacssched is conceptually similar to cron(8)[1], atrun(8)[2], and other programs used to
schedule a command to be executed or a reminder to be sent at certain times or dates, there are some
important differences. First, because the DACS rule evaluation engine is used, conditions much more broad
and complex than simply the time or date can be used to schedule a command - DACS expressions[3] are
available. For instance, a rule to manage automated file backup could be written to take into account
context other than simply the day of the week and the time of day, if necessary even running external
programs to assist in making the determination. Second, both a schedule and the rules referenced by a
schedule are accessed through the DACS virtual filestore, which means they can be stored in file or
database, retrieved by HTTP, and so on.

Note

Although this program may be useful, it is currently merely a prototype intended for demonstration
and experimentation purposes. Some configuration capabilities, features, and security steps required
by a production version have not been implemented. The prototype must be invoked periodically; a
production version would run in the background and automatically rescan the schedule at a given
frequency. Note that because of its flexibility, the schedule must be polled at a suitable frequency
- in general, the program cannot compute when the next scheduled event will occur. Also because
events need not be triggered by a time or date, some events may need to "self-disabling" so that they
are not repeatedly executed unintentionally.

Operation
The program loads a schedule, which either comes from a default file or a location specified on the
command line. A schedule is an ordinary text file, each line of which is either blank, a comment, or a
scheduled event. The file is processed in the order in which the events appear from the top. Initial
whitespace on any line is ignored. A comment line begins with a "#" character. A scheduled event consists
of a name, followed by whitespace, followed by a command. If name evaluates to True (i.e., it grants
access), the command is executed through system(3)[4]. If rule evaluation fails because of an error, the
event is not executed. Events are not removed from the schedule after their command has been executed.

A name, which must begin with a slash, has no significance to dacssched; it is simply a label that is
used to identify the rule to apply and is matched against a rule's service element.

Here is a simple schedule containing one event:

# A simple schedule
/setdate /usr/local/sbin/rdate -a

If the condition labelled /setdate is True the specified command will be executed.

A simple rule such as the following might be associated with the event:

<acl_rule status="enabled">
<services>
<service url_pattern="/setdate"/>
</services>

This rule enables the event /setdate at 2:00am every day. We will assume that the schedule is processed
exactly once per minute.

Internally, dacssched converts the scheduled event above into the expression:

rule("/setdate", rule_uri)

(where rule_uri specifies the ruleset to use) and then evaluates the expression. Please refer to the rule
predicate[5] for additional information.

OPTIONS

       The arguments are processed as they are examined (left-to-right) and their ordering can be significant.

       By default, the program will look for a schedule in the file ${Conf::DACS_HOME}/dacssched/sched.
       (default: /usr/local/dacs/dacssched/sched) The default location for the rules is
       ${Conf::DACS_HOME}/dacssched/acls. (default: /usr/local/dacs/dacssched/acls)

       The following command line flags are recognized:

       -h
           Prints the usage blurb.

       -ll log_level
           Set the debugging output level to log_level (see dacs(1)[6]). The default level is warn, and the -v
           flag bumps the level to debug or trace.

       -q
           Be quiet, except for error messages. The -v and -ll flags are independent of this.

       -r rule_uri
       -rules rule_uri
           This flag specifies the ruleset to be used. It can be an absolute pathname or a URI in the syntax of
           the VFS[7] configuration directive. Examples:

               -r "[acls1]dacs-fs:/local/acls"
               -rules /usr/local/myrules

       -s sched_uri
       -sched sched_uri
           This flag specifies the schedule. It can be an absolute pathname or a URI in the syntax of the VFS[7]
           configuration directive.

       -v
           Increase the level of debugging output. The flag may be repeated.

       --version
           Display the program's version information and then exit.

DIAGNOSTICS

       The program exits 0 if everything was fine, 1 if an error occurred.

AUTHOR

       Distributed Systems Software (www.dss.ca[9])

COPYING

       Copyright © 2003-2018 Distributed Systems Software. See the LICENSE[10] file that accompanies the
       distribution for licensing information.

NOTES

        1. cron(8)
           https://www.freebsd.org/cgi/man.cgi?query=cron&apropos=0&sektion=8&manpath=FreeBSD+10.3-RELEASE&format=html

        2. atrun(8)
           https://www.freebsd.org/cgi/man.cgi?query=atrun&apropos=0&sektion=8&manpath=FreeBSD+10.3-RELEASE&format=html

        3. expressions
           http://dacs.dss.ca/man/dacs.exprs.5.html

        4. system(3)
           https://www.freebsd.org/cgi/man.cgi?query=system&apropos=0&sektion=3&manpath=FreeBSD+10.3-RELEASE&format=html

        5. rule predicate
           http://dacs.dss.ca/man/dacs.exprs.5.html#rule

        6. dacs(1)
           http://dacs.dss.ca/man/dacs.1.html

        7. VFS
           http://dacs.dss.ca/man/dacs.conf.5.html#VFS

        8. dacs.acls(5)
           http://dacs.dss.ca/man/dacs.acls.5.html

        9. www.dss.ca
           http://www.dss.ca

       10. LICENSE
           http://dacs.dss.ca/man/../misc/LICENSE

DACS 1.4.40                                        02/19/2019                                       DACSSCHED(1)