5 whenjobs - A powerful but simple cron replacement
9 Editing the jobs script:
14 Get and set variables:
16 whenjobs --get variable
17 whenjobs --set variable=value [variable=value ...]
20 Start and stop the per-user daemon:
22 whenjobs --daemon-start
23 whenjobs --daemon-stop
24 whenjobs --daemon-status
25 whenjobs --daemon-restart
30 whenjobs --cancel serial
31 whenjobs --start "name"
32 whenjobs --tail serial
36 Whenjobs is a powerful but simple replacement for cron. It lets you
37 run jobs periodically like cron, but it also lets you trigger jobs to
38 run when user-defined variables are set or change value.
40 Periodic jobs are written like this:
44 # Get the current load average.
45 load=`awk '{print $1}' /proc/loadavg`
46 whenjobs --set --type float load=$load
49 When-statements let you create jobs that run based on variables set
54 mail -s "ALERT: high load average: $load" $LOGNAME < /dev/null
57 (When statements are "edge-triggered", meaning that this job will only
58 run when the load goes from under 6 to E<ge> 6).
60 Like L<crontab(5)>, whenjobs are controlled by a jobs file which can
61 be edited from the command line:
65 Whenjobs uses a daemon called L<whenjobsd(8)>. Unlike crond, this
66 daemon runs as the same user. Each user who wants to use whenjobs
67 starts their own daemon:
69 $ whenjobs --daemon-start
71 You can also have the daemon start as you when the machine boots by
72 adding the following line to a boot file such as C</etc/rc.local>.
73 Replace C<username> with your username:
75 su username -c /usr/sbin/whenjobsd
77 Variables are the key to expressing dependencies between whenjobs.
78 Variables are stored (per-user) in the daemon. You can use the
79 command line tool to examine and set variables:
81 $ whenjobs --variables
83 libguestfs_build_local=1.17.16
84 libguestfs_commit=7e32d892d76a31f55e2a4151902623b9949e3efa
85 libguestfs_dist=1.17.16
86 libguestfs_release=1.17.16
87 libguestfs_stable_build_local=1.16.10
88 libguestfs_stable_commit=27433a0a335301441b1eb6244ba425c2c44b2d99
89 libguestfs_stable_dist=1.16.10
90 libguestfs_stable_release=1.16.10
91 libguestfs_stable_version=1.16.10
92 libguestfs_version=1.17.16
93 $ whenjobs --set cat=sushi
97 Note: The act of setting a variable (using I<--set>) can trigger jobs
100 You can also list out what jobs are running:
103 287 libguestfs-stable: fedora 16
104 running in: /tmp/whenjobsa2afc44fd757465f95438309f1a51609
105 started at: 2012-03-13 10:59:37
107 and you can 'tail' the output of running jobs which is useful for
110 $ whenjobs --tail 287
111 Uploading: 147496271972717053d46b82a07435ca libguestfs-1.16.10.tar.gz
113 You can start and cancel jobs manually:
115 $ whenjobs --start 'libguestfs: poll'
116 $ whenjobs --cancel 287
122 =item B<--cancel> serial
124 Cancel the job with the given serial number.
126 Use I<--jobs> to list running jobs along with their serial numbers.
127 The serial number is also available in the job script (as
128 C<$JOBSERIAL>) and in the log file.
130 =item B<--daemon-start>
132 =item B<--daemon-stop>
134 Start and stop the per-user daemon.
136 =item B<--daemon-status>
138 Prints the status of the daemon: C<up> or C<down>.
140 =item B<--daemon-restart>
142 Restart the daemon. (If it is not running, then this command
149 Edit the jobs script. If you make changes to the jobs script, then it
150 is automatically uploaded to the daemon.
152 The C<$EDITOR> environment variable is used for editing. If not set,
155 =item B<--get> variable
157 Print the value of a variable.
161 List the names of all loaded jobs (whether they are running or not).
162 Use I<--jobs> to list running jobs.
166 List all running jobs.
168 Note that it is possible for the same job to be running more than once
169 (for example, a periodic job that takes longer than the period to run).
175 List the jobs script.
177 =item B<--lib> directory
179 Set the library directory which needs to contain the auxiliary files
180 C<pa_when.cmo> and C<whenlib.cma>. Normally you do not need to
181 specify this. However if you are running whenjobs without installing
182 it, then you need to point this to the C<lib/> directory from the
185 whenjobs --lib $builddir/lib -e
187 =item B<--set> variable=value [variable=value ...]
189 =item B<--type> bool|int|float|string|unit
191 I<--set> sets the variable named C<variable> to the new C<value>. The
192 variable is created if it does not already exist. Note that setting a
193 variable can cause jobs to run immediately.
195 To unset a variable, set it to the empty string like this:
199 By default variables are strings. You can also set the type of a
200 variable when setting it by adding the optional I<--type> parameter.
201 The I<--type> parameter should come I<before> the variable
202 declaration, like this:
204 whenjobs --set --type int free_space=10000
206 See the discussion of variable types in the L</REFERENCE> section
209 You can set multiple variables. When setting multiple variables in a
210 single command, the values are all changed in a single atomic
213 whenjobs --set cat=sushi food=fish
215 When using I<--type> and multiple variables, the type changes the
216 remaining command line parameters until the next I<--type>, eg:
218 whenjobs --set cat=sushi --type float weight=3.5 --type string food=fish
220 (C<cat> and C<food> are strings, and C<weight> is a float).
222 =item B<--start> "job name"
224 Start the job immediately and unconditionally.
226 This runs the job even if its normal preconditions are not met. This
227 may cause unexpected results, so use with caution.
229 =item B<--tail> serial
231 Tail the output of the running job identified by its serial number.
232 Use the I<--jobs> flag to get a list of running jobs.
234 =item B<--test> variable=value [variable=value ...]
236 This works the same way as the I<--set> option, but the difference is
237 that the variables are not set. Instead, it lists out the jobs that
238 I<would> run, I<if> the variables were updated to these new values.
240 The variables are not actually updated, and the jobs are not actually
243 The output is a list of job names that would run.
247 Compile the jobs script and upload it to the daemon, without editing.
248 Note that the I<--edit> option does this automatically. Furthermore,
249 when the daemon is started it checks for a jobs script and loads it if
254 Display all the variables and their values, in the format C<name=value>.
260 Display the name and version of the program and exit.
266 Display brief usage and exit.
272 A whenjobs file consists of a series of one or more "every" or "when"
275 Comments in the file can be written using C<(* ... *)>. Comments
278 Shell script fragments are written using C<E<lt>E<lt> ... E<gt>E<gt>>.
279 Within shell script fragments, use C<#> for comments (as in ordinary
280 shell scripts). Because C<E<gt>E<gt>> has a special meaning, it
281 cannot be used in the shell script (ie. for redirection). You have to
282 write C<E<gt>\E<gt>> instead which is replaced with C<E<gt>E<gt>> when
283 the shell script is parsed.
285 =head2 EVERY STATEMENTS (PERIODIC JOBS)
287 An every statement has the form:
294 where C<E<lt>periodE<gt>> is a I<period expression>, which may take
295 one of the forms below. Don't forget the colon character between the
296 period expression and the shell script.
298 An every statement is a job which runs periodically.
300 =head3 PERIOD EXPRESSIONS
304 =item B<every second>
306 The job runs every second.
308 =item B<every minute>
310 The job runs every minute.
314 The job runs every hour.
318 The job runs every day, at midnight UTC.
322 The job runs every week, on a Thursday at midnight UTC.
326 The job runs every month, on the first of the month at midnight UTC.
330 The job runs every year, on the first day of the year at midnight UTC.
332 =item B<every decade>
334 =item B<every century>
336 =item B<every millenium>
338 The job runs every 10, 100 or 1000 years.
340 =item B<every I<N> seconds>
342 The job runs every I<N> seconds (I<N> is any number E<ge> 1).
344 =item B<every I<N> minutes>
346 The job runs every I<N> minutes.
348 =item B<every I<N> hours>
350 The job runs every I<N> hours.
352 =item B<every I<N> days>
354 The job runs every I<N> days.
356 =item B<every I<N> weeks>
358 The job runs every I<N> weeks.
360 =item B<every I<N> months>
362 The job runs every I<N> months.
364 =item B<every I<N> years>
366 =item B<every I<N> decades>
368 =item B<every I<N> centuries>
370 =item B<every I<N> millenia>
372 The job runs every I<N>, I<10*N>, I<100*N> or I<1000*N> years.
376 =head2 WHEN STATEMENTS (DEPENDENT JOBS)
378 A when statement has the form:
385 where C<E<lt>exprE<gt>> is a I<when expression>, described below.
386 Don't forget the colon character between the period expression and the
389 A when statement is a job which runs when the conditions described in
390 its when-expression become true.
392 When jobs are I<edge triggered>. This means that they run when the
393 condition changes from false to true (or in the case where the
394 expression has not been evaluated before, when it evaluates initially
397 =head3 WHEN EXPRESSIONS
399 When expressions are fully recursive expressions constructed from the
404 =item I<expr> B<&&> I<expr>
406 =item I<expr> B<||> I<expr>
408 The boolean "and" or "or" of the two sub-expressions.
410 =item I<expr> B<E<lt>> I<expr>
412 =item I<expr> B<E<lt>=> I<expr>
414 =item I<expr> B<==> I<expr>
416 =item I<expr> B<E<gt>=> I<expr>
418 =item I<expr> B<E<gt>> I<expr>
420 The two sub-expressions are evaluated and the usual comparison
421 operator is performed.
423 If the sub-expressions are numeric, then numeric comparison is done.
424 If either sub-expression is non-numeric, then both expressions are
425 converted (if necessary) to strings and string comparison is done.
429 Boolean negative of I<expr>.
431 =item I<expr> B<+> I<expr>
433 For numeric sub-expressions, this performs addition.
435 If both sub-expressions are strings, this performs string
438 Other types give an error.
440 =item I<expr> B<-> I<expr>
442 =item I<expr> B<*> I<expr>
444 =item I<expr> B</> I<expr>
446 =item I<expr> B<mod> I<expr>
448 Both sub-expressions are evaluated, and if both are numeric, then the
449 result is subtraction, multiplication, division or modulo.
451 Other types give an error. Note that I<mod> really is an infix
456 If I<expr> is a string, this returns the length of the string.
460 The value of the named variable.
462 Previously undefined variables are automatically initialized to the
465 =item B<prev> I<variable>
467 The I<previous> value of the named variable. This means, the value
468 that it had last time this when-job ran.
470 If the when-job has not run yet, then this returns C<"">.
472 Job state is preserved across file reloads, but I<only> for jobs that
473 are explicitly named. If you find that jobs using C<prev>, C<changes>
474 etc are running unnecessarily when the jobs file is edited or
475 uploaded, try giving the jobs an explicit name.
477 =item B<changes> I<variable>
479 If the named variable has changed since this job last ran, then this
480 evaluates to true, else false.
482 This is the same as writing C<prev variable == variable>.
484 =item B<increases> I<variable>
486 If the named variable has changed and increased since this job last
487 ran, then this evaluates to true, else false.
489 This is the same as writing C<prev variable E<lt> variable>.
491 =item B<decreases> I<variable>
493 If the named variable has changed and decreased since this job last
494 ran, then this evaluates to true, else false.
496 This is the same as writing C<prev variable E<gt> variable>.
498 B<Note:> There is a subtle gotcha with the I<decreases> operator: The
499 first time the expression is evaluated, the job has (by definition)
500 not yet run. Therefore C<prev variable> evaluates to C<""> (see
501 definition of I<prev> above). Since it is always true that
505 the I<decreases> operator evaluates to false, and since this usually
506 means the job does not run, the operator always evaluates to false.
508 To fix this, ensure that the variable is initialized (see
509 L</SETTING THE INITIAL VALUE OF VARIABLES> below).
513 This evaluates to true the first time the expression is evaluated
514 after the jobs file has been reloaded or the daemon restarted.
515 Thereafter it evaluates to false.
517 Don't use this to initialize variables: it won't do what you mean.
523 Constants that evaluate to boolean false or true respectively.
525 =item I<"any string">
529 In a boolean context, the empty string evaluates to false, and
530 non-empty strings evaluate to true.
534 Any integer. (Arbitrarily large integers are supported.)
536 In a boolean context, 0 evaluates to false, and non-zero evaluates to
547 Any floating point number.
549 In a boolean context, 0 evaluates to false, and non-zero evaluates to
556 The code between C<E<lt>E<lt> ... E<gt>E<gt>> is a shell script. It
557 is executed using C<$SHELL>, or if that environment variable is not
560 =head3 SHELL SCRIPT VARIABLES
562 Every variable that has been set (using the whenjobs I<--set> option)
563 is exported to the script, so you can simply get the value of any
564 variable by writing C<$name>.
566 In addition, there are some special variables available:
572 The name of the job. If the job has been named explicitly, then that
573 name is available through this variable, else it will be some implicit
578 The serial number of the job. This is simply a variable that
579 increments each time a job is run, and is unique to that run of the
584 Other environment variables such as C<$HOME>, C<$LOGNAME> etc are
587 =head3 SHELL SCRIPT TEMPORARY CURRENT DIRECTORY
589 The shell script runs with its current directory set to a temporary
590 directory. The temporary directory is removed when the shell script
591 exits. Therefore you can write temporary files here without worrying
592 about cleaning them up.
594 If you want to store permanent state, then you have to save it to a
595 well-known directory, eg. C<$HOME>, C</var> etc.
597 =head3 SHELL SCRIPT USER
599 The shell script runs as the ordinary user. It has no special
604 Jobs are given implicit names (C<job$1>, C<job$2> etc.). You can also
605 name jobs explicitly by preceeding the "every" or "when" statement
614 The job name is passed to the shell script in the C<$JOBNAME>
615 environment variable.
617 =head2 OCAML EXPRESSIONS
619 As well as simple "every" and "when" expressions, advanced users may
620 want to use arbitrary OCaml expressions, functions, etc in the jobs
621 script. These are useful for factoring common code or strings, for
622 setting the initial values of variables, or for defining pre and post
625 A simple example of an OCaml expression is:
627 let prefix = "daily_"
629 job (prefix ^ "virus_scan")
635 job (prefix ^ "disk_check")
641 which creates two jobs called C<"daily_virus_scan"> and
642 C<"daily_disk_check"> (C<^> is the OCaml string concatenation
645 OCaml expressions have access to a library of functions called
646 B<Whentools> which is described below. It lets you set variables,
647 create jobs algorithmically, etc.
649 The OCaml expressions run once, when the jobs file is being loaded or
652 =head3 SETTING THE INITIAL VALUE OF VARIABLES
654 Variables are created when they are referenced, and until set they
655 have the value empty string (just like the shell). Across file
656 reloads, the previous values of variables are preserved.
658 To initialize a variable to a known value when the jobs file is
659 loaded, call one of the C<Whentools.set_variable*> functions as in
663 Whentools.set_variable "name" "Richard";
664 Whentools.set_variable_int "counter" 0
668 Before a job runs, you can arrange that a C<pre> function is called.
669 This function may decide not to run the job (by returning C<false>).
671 One use for this is to prevent a particular job from running if there
672 is already an instance of the same job running:
675 pre (Whentools.one ())
678 # Takes longer than 10 seconds to run, but 'Whentools.one ()'
679 # will ensure only one is ever running.
683 When using pre functions, jobs must be given an explicit name, ie.
684 you must use the C<job> statement.
686 A number of pre functions are available in the library; see below.
688 You can also write your own post functions (in OCaml). The function
689 is passed one argument which is a C<Whentools.preinfo> struct, defined
690 below. It should return a boolean: C<true> if the job should run, and
691 C<false> if the job should not run.
693 Note that a fresh serial number (see L</JOBSERIAL>) is assigned to
694 each run, whether or not the job actually runs because of
697 =head3 POST FUNCTIONS
699 After a job runs, you can control what happens to its output by
700 writing a C<post> function. To write a post function you have to
701 name the job (ie. have an explicit C<job> statement). Put C<post ...>
702 after the job name like this:
705 post (Whentools.mailto "you@example.com")
711 A number of post functions are available in the library; see below.
713 You can also write your own post functions (in OCaml). The
714 function is passed one argument which is a C<Whentools.result> struct,
717 =head3 WHENTOOLS LIBRARY
723 =item B<Whentools.mailto> [I<~only_on_failure:true>]
724 [I<~from:from_address>] I<email_address> I<result>
726 This built-in post function sends the result of the script by email to
727 the given email address.
729 If the optional C<~only_on_failure:true> flag is set, then it is only
730 sent out if the script failed.
732 If the optional C<~from> flag is set, then the from address is set
733 accordingly. This is sometimes needed when sending mail.
735 Note the C<result> parameter is passed implicitly by the daemon. You
736 do not need to add it.
738 Here are some examples of using the mailto function:
741 post (Whentools.mailto "you@example.com")
748 post (Whentools.mailto ~only_on_failure:true
755 let from = "me@example.com"
756 let to_addr = "you@example.com"
759 post (Whentools.mailto ~from to_addr)
765 =item B<Whentools.max> I<n>
767 This built-in pre function ensures that a maximum of I<n> instances of
770 It checks the list of running jobs, and if I<n> or more instances are
771 already running, then it returns C<false>, which ensures that the new
774 =item B<Whentools.one> I<()>
776 This built-in pre function ensures that only one instance of the job
777 is running. It is the same as calling:
781 =item B<Whentools.set_variable> I<name> I<string>
783 Set variable I<name> to the string.
785 =item B<Whentools.set_variable_bool> I<name> I<b>
787 Set variable I<name> to the boolean value I<b>.
789 =item B<Whentools.set_variable_int> I<name> I<i>
791 Set variable I<name> to the integer value I<i>.
793 =item B<Whentools.set_variable_string> I<name> I<s>
795 Set variable I<name> to the string value <s>. This is
796 the same as I<Whentools.set_variable>.
798 =item B<Whentools.set_variable_float> I<name> I<f>
800 Set variable I<name> to the floating point value I<f>.
808 =item B<Whentools.preinfo>
810 This structure is passed to pre functions. It has the following
814 pi_job_name : string; # Job name.
815 pi_serial : Big_int.big_int; # Job serial number.
816 pi_variables : (string * variable) list; # Variables set in job.
817 pi_running : preinfo_running_job list; # List of running jobs.
819 and preinfo_running_job = {
820 pirun_job_name : string; # Running job name.
821 pirun_serial : Big_int.big_int; # Running job serial number.
822 pirun_start_time : float; # Running job start time.
823 pirun_pid : int; # Running job process ID.
826 =item B<Whentools.result>
828 This structure is passed to post functions. It has the following
832 res_job_name : string; # job name
833 res_serial : big_int; # job serial (same as $JOBSERIAL)
834 res_code : int; # return code from the shell script
835 res_tmpdir : string; # temporary directory script ran in
836 res_output : string; # filename of stdout/stderr output
837 res_start_time : float; # when the job started
846 =head1 ENVIRONMENT VARIABLES
856 Richard W.M. Jones L<http://people.redhat.com/~rjones/>
860 Copyright (C) 2012 Red Hat Inc.
862 This program is free software; you can redistribute it and/or modify
863 it under the terms of the GNU General Public License as published by
864 the Free Software Foundation; either version 2 of the License, or
865 (at your option) any later version.
867 This program is distributed in the hope that it will be useful,
868 but WITHOUT ANY WARRANTY; without even the implied warranty of
869 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
870 GNU General Public License for more details.
872 You should have received a copy of the GNU General Public License
873 along with this program; if not, write to the Free Software
874 Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.