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.
163 Display brief usage and exit.
167 List the names of all loaded jobs (whether they are running or not).
168 Use I<--jobs> to list running jobs.
172 List all running jobs.
174 Note that it is possible for the same job to be running more than once
175 (for example, a periodic job that takes longer than the period to run).
181 List the jobs script.
183 =item B<--lib> directory
185 Set the library directory which needs to contain the auxiliary files
186 C<pa_when.cmo> and C<whenlib.cma>. Normally you do not need to
187 specify this. However if you are running whenjobs without installing
188 it, then you need to point this to the C<lib/> directory from the
191 whenjobs --lib $builddir/lib -e
193 =item B<--set> variable=value [variable=value ...]
195 =item B<--type> bool|int|float|string|unit
197 I<--set> sets the variable named C<variable> to the new C<value>. The
198 variable is created if it does not already exist. Note that setting a
199 variable can cause jobs to run immediately.
201 To unset a variable, set it to the empty string like this:
205 By default variables are strings. You can also set the type of a
206 variable when setting it by adding the optional I<--type> parameter.
207 The I<--type> parameter should come I<before> the variable
208 declaration, like this:
210 whenjobs --set --type int free_space=10000
212 See the discussion of variable types in the L</REFERENCE> section
215 You can set multiple variables. When setting multiple variables in a
216 single command, the values are all changed in a single atomic
219 whenjobs --set cat=sushi food=fish
221 When using I<--type> and multiple variables, the type changes the
222 remaining command line parameters until the next I<--type>, eg:
224 whenjobs --set cat=sushi \
225 --type float weight=3.5 \
226 --type string food=fish
228 (C<cat> and C<food> are strings, and C<weight> is a float).
230 =item B<--start> "job name"
232 Start the job immediately and unconditionally.
234 This runs the job even if its normal preconditions are not met. This
235 may cause unexpected results, so use with caution.
237 =item B<--tail> serial
239 Tail the output of the running job identified by its serial number.
240 Use the I<--jobs> flag to get a list of running jobs.
242 =item B<--test> variable=value [variable=value ...]
244 This works the same way as the I<--set> option, but the difference is
245 that the variables are not set. Instead, it lists out the jobs that
246 I<would> run, I<if> the variables were updated to these new values.
248 The variables are not actually updated, and the jobs are not actually
251 The output is a list of job names that would run.
255 Compile the jobs script and upload it to the daemon, without editing.
256 Note that the I<--edit> option does this automatically. Furthermore,
257 when the daemon is started it checks for a jobs script and loads it if
262 Display all the variables and their values, in the format C<name=value>.
268 Display the name and version of the program and exit.
274 A whenjobs file consists of a series of one or more "every" or "when"
277 Comments in the file can be written using C<(* ... *)>. Comments
280 Shell script fragments are written using C<E<lt>E<lt> ... E<gt>E<gt>>.
281 Within shell script fragments, use C<#> for comments (as in ordinary
282 shell scripts). Because C<E<gt>E<gt>> has a special meaning, it
283 cannot be used in the shell script (ie. for redirection). You have to
284 write C<E<gt>\E<gt>> instead which is replaced with C<E<gt>E<gt>> when
285 the shell script is parsed.
287 =head2 EVERY STATEMENTS (PERIODIC JOBS)
289 An every statement has the form:
296 where C<E<lt>periodE<gt>> is a I<period expression>, which may take
297 one of the forms below. Don't forget the colon character between the
298 period expression and the shell script.
300 An every statement is a job which runs periodically.
302 =head3 PERIOD EXPRESSIONS
306 =item B<every second>
308 The job runs every second.
310 =item B<every minute>
312 The job runs every minute.
316 The job runs every hour.
320 The job runs every day, at midnight UTC.
324 The job runs every week, on a Thursday at midnight UTC.
328 The job runs every month, on the first of the month at midnight UTC.
332 The job runs every year, on the first day of the year at midnight UTC.
334 =item B<every decade>
336 =item B<every century>
338 =item B<every millenium>
340 The job runs every 10, 100 or 1000 years.
342 =item B<every I<N> seconds>
344 The job runs every I<N> seconds (I<N> is any number E<ge> 1).
346 =item B<every I<N> minutes>
348 The job runs every I<N> minutes.
350 =item B<every I<N> hours>
352 The job runs every I<N> hours.
354 =item B<every I<N> days>
356 The job runs every I<N> days.
358 =item B<every I<N> weeks>
360 The job runs every I<N> weeks.
362 =item B<every I<N> months>
364 The job runs every I<N> months.
366 =item B<every I<N> years>
368 =item B<every I<N> decades>
370 =item B<every I<N> centuries>
372 =item B<every I<N> millenia>
374 The job runs every I<N>, I<10*N>, I<100*N> or I<1000*N> years.
378 =head2 WHEN STATEMENTS (DEPENDENT JOBS)
380 A when statement has the form:
387 where C<E<lt>exprE<gt>> is a I<when expression>, described below.
388 Don't forget the colon character between the period expression and the
391 A when statement is a job which runs when the conditions described in
392 its when-expression become true.
394 When jobs are I<edge triggered>. This means that they run when the
395 condition changes from false to true (or in the case where the
396 expression has not been evaluated before, when it evaluates initially
399 =head3 WHEN EXPRESSIONS
401 When expressions are fully recursive expressions constructed from the
406 =item I<expr> B<&&> I<expr>
408 =item I<expr> B<||> I<expr>
410 The boolean "and" or "or" of the two sub-expressions.
412 =item I<expr> B<E<lt>> I<expr>
414 =item I<expr> B<E<lt>=> I<expr>
416 =item I<expr> B<==> I<expr>
418 =item I<expr> B<E<gt>=> I<expr>
420 =item I<expr> B<E<gt>> I<expr>
422 The two sub-expressions are evaluated and the usual comparison
423 operator is performed.
425 If the sub-expressions are numeric, then numeric comparison is done.
426 If either sub-expression is non-numeric, then both expressions are
427 converted (if necessary) to strings and string comparison is done.
431 Boolean negative of I<expr>.
433 =item I<expr> B<+> I<expr>
435 For numeric sub-expressions, this performs addition.
437 If both sub-expressions are strings, this performs string
440 Other types give an error.
442 =item I<expr> B<-> I<expr>
444 =item I<expr> B<*> I<expr>
446 =item I<expr> B</> I<expr>
448 =item I<expr> B<mod> I<expr>
450 Both sub-expressions are evaluated, and if both are numeric, then the
451 result is subtraction, multiplication, division or modulo.
453 Other types give an error. Note that I<mod> really is an infix
458 If I<expr> is a string, this returns the length of the string.
462 The value of the named variable.
464 Previously undefined variables are automatically initialized to the
467 =item B<prev> I<variable>
469 The I<previous> value of the named variable. This means, the value
470 that it had last time this when-job ran.
472 If the when-job has not run yet, then this returns C<"">.
474 Job state is preserved across file reloads, but I<only> for jobs that
475 are explicitly named. If you find that jobs using C<prev>, C<changes>
476 etc are running unnecessarily when the jobs file is edited or
477 uploaded, try giving the jobs an explicit name.
479 =item B<changes> I<variable>
481 If the named variable has changed since this job last ran, then this
482 evaluates to true, else false.
484 This is the same as writing C<prev variable == variable>.
486 =item B<increases> I<variable>
488 If the named variable has changed and increased since this job last
489 ran, then this evaluates to true, else false.
491 This is the same as writing C<prev variable E<lt> variable>.
493 =item B<decreases> I<variable>
495 If the named variable has changed and decreased since this job last
496 ran, then this evaluates to true, else false.
498 This is the same as writing C<prev variable E<gt> variable>.
500 B<Note:> There is a subtle gotcha with the I<decreases> operator: The
501 first time the expression is evaluated, the job has (by definition)
502 not yet run. Therefore C<prev variable> evaluates to C<""> (see
503 definition of I<prev> above). Since it is always true that
507 the I<decreases> operator evaluates to false, and since this usually
508 means the job does not run, the operator always evaluates to false.
510 To fix this, ensure that the variable is initialized (see
511 L</SETTING THE INITIAL VALUE OF VARIABLES> below).
515 This evaluates to true the first time the expression is evaluated
516 after the jobs file has been reloaded or the daemon restarted.
517 Thereafter it evaluates to false.
519 Don't use this to initialize variables: it won't do what you mean.
525 Constants that evaluate to boolean false or true respectively.
527 =item I<"any string">
531 In a boolean context, the empty string evaluates to false, and
532 non-empty strings evaluate to true.
536 Any integer. (Arbitrarily large integers are supported.)
538 In a boolean context, 0 evaluates to false, and non-zero evaluates to
549 Any floating point number.
551 In a boolean context, 0 evaluates to false, and non-zero evaluates to
558 The code between C<E<lt>E<lt> ... E<gt>E<gt>> is a shell script. It
559 is executed using C<$SHELL>, or if that environment variable is not
562 =head3 SHELL SCRIPT VARIABLES
564 Every variable that has been set (using the whenjobs I<--set> option)
565 is exported to the script, so you can simply get the value of any
566 variable by writing C<$name>.
568 In addition, there are some special variables available:
574 The name of the job. If the job has been named explicitly, then that
575 name is available through this variable, else it will be some implicit
580 The serial number of the job. This is simply a variable that
581 increments each time a job is run, and is unique to that run of the
586 Other environment variables such as C<$HOME>, C<$LOGNAME> etc are
589 =head3 SHELL SCRIPT TEMPORARY CURRENT DIRECTORY
591 The shell script runs with its current directory set to a temporary
592 directory. The temporary directory is removed when the shell script
593 exits. Therefore you can write temporary files here without worrying
594 about cleaning them up.
596 If you want to store permanent state, then you have to save it to a
597 well-known directory, eg. C<$HOME>, C</var> etc.
599 =head3 SHELL SCRIPT USER
601 The shell script runs as the ordinary user. It has no special
606 Jobs are given implicit names (C<job$1>, C<job$2> etc.). You can also
607 name jobs explicitly by preceeding the "every" or "when" statement
616 The job name is passed to the shell script in the C<$JOBNAME>
617 environment variable.
619 =head2 OCAML EXPRESSIONS
621 As well as simple "every" and "when" expressions, advanced users may
622 want to use arbitrary OCaml expressions, functions, etc in the jobs
623 script. These are useful for factoring common code or strings, for
624 setting the initial values of variables, or for defining pre and post
627 A simple example of an OCaml expression is:
629 let prefix = "daily_"
631 job (prefix ^ "virus_scan")
637 job (prefix ^ "disk_check")
643 which creates two jobs called C<"daily_virus_scan"> and
644 C<"daily_disk_check"> (C<^> is the OCaml string concatenation
647 OCaml expressions have access to a library of functions called
648 B<Whentools> which is described below. It lets you set variables,
649 create jobs algorithmically, etc.
651 The OCaml expressions run once, when the jobs file is being loaded or
654 =head3 SETTING THE INITIAL VALUE OF VARIABLES
656 Variables are created when they are referenced, and until set they
657 have the value empty string (just like the shell). Across file
658 reloads, the previous values of variables are preserved.
660 To initialize a variable to a known value when the jobs file is
661 loaded, call one of the C<Whentools.set_variable*> functions as in
665 Whentools.set_variable "name" "Richard";
666 Whentools.set_variable_int "counter" 0
670 Before a job runs, you can arrange that a C<pre> function is called.
671 This function may decide not to run the job (by returning C<false>).
673 One use for this is to prevent a particular job from running if there
674 is already an instance of the same job running:
677 pre (Whentools.one ())
680 # Takes longer than 10 seconds to run, but 'Whentools.one ()'
681 # will ensure only one is ever running.
685 When using pre functions, jobs must be given an explicit name, ie.
686 you must use the C<job> statement.
688 A number of pre functions are available in the library; see below.
690 You can also write your own post functions (in OCaml). The function
691 is passed one argument which is a C<Whentools.preinfo> struct, defined
692 below. It should return a boolean: C<true> if the job should run, and
693 C<false> if the job should not run.
695 Note that a fresh serial number (see L</JOBSERIAL>) is assigned to
696 each run, whether or not the job actually runs because of
699 =head3 POST FUNCTIONS
701 After a job runs, you can control what happens to its output by
702 writing a C<post> function. To write a post function you have to
703 name the job (ie. have an explicit C<job> statement). Put C<post ...>
704 after the job name like this:
707 post (Whentools.mailto "you@example.com")
713 A number of post functions are available in the library; see below.
715 You can also write your own post functions (in OCaml). The
716 function is passed one argument which is a C<Whentools.result> struct,
719 =head3 WHENTOOLS LIBRARY
725 =item B<Whentools.mailto> [I<~only_on_failure:true>]
726 [I<~from:from_address>] I<email_address> I<result>
728 This built-in post function sends the result of the script by email to
729 the given email address.
731 If the optional C<~only_on_failure:true> flag is set, then it is only
732 sent out if the script failed.
734 If the optional C<~from> flag is set, then the from address is set
735 accordingly. This is sometimes needed when sending mail.
737 Note the C<result> parameter is passed implicitly by the daemon. You
738 do not need to add it.
740 Here are some examples of using the mailto function:
743 post (Whentools.mailto "you@example.com")
750 post (Whentools.mailto ~only_on_failure:true
757 let from = "me@example.com"
758 let to_addr = "you@example.com"
761 post (Whentools.mailto ~from to_addr)
767 =item B<Whentools.max> I<n>
769 This built-in pre function ensures that a maximum of I<n> instances of
772 It checks the list of running jobs, and if I<n> or more instances are
773 already running, then it returns C<false>, which ensures that the new
776 =item B<Whentools.one> I<()>
778 This built-in pre function ensures that only one instance of the job
779 is running. It is the same as calling:
783 =item B<Whentools.set_variable> I<name> I<string>
785 Set variable I<name> to the string.
787 =item B<Whentools.set_variable_bool> I<name> I<b>
789 Set variable I<name> to the boolean value I<b>.
791 =item B<Whentools.set_variable_int> I<name> I<i>
793 Set variable I<name> to the integer value I<i>.
795 =item B<Whentools.set_variable_string> I<name> I<s>
797 Set variable I<name> to the string value <s>. This is
798 the same as I<Whentools.set_variable>.
800 =item B<Whentools.set_variable_float> I<name> I<f>
802 Set variable I<name> to the floating point value I<f>.
810 =item B<Whentools.preinfo>
812 This structure is passed to pre functions. It has the following
816 pi_job_name : string; # Job name.
817 pi_serial : Big_int.big_int; # Job serial number.
818 pi_variables : (string * variable) list; # Variables set in job.
819 pi_running : preinfo_running_job list; # List of running jobs.
821 and preinfo_running_job = {
822 pirun_job_name : string; # Running job name.
823 pirun_serial : Big_int.big_int; # Running job serial number.
824 pirun_start_time : float; # Running job start time.
825 pirun_pid : int; # Running job process ID.
828 =item B<Whentools.result>
830 This structure is passed to post functions. It has the following
834 res_job_name : string; # job name
835 res_serial : big_int; # job serial (same as $JOBSERIAL)
836 res_code : int; # return code from the shell script
837 res_tmpdir : string; # temporary directory script ran in
838 res_output : string; # filename of stdout/stderr output
839 res_start_time : float; # when the job started
848 =head1 ENVIRONMENT VARIABLES
858 Richard W.M. Jones L<http://people.redhat.com/~rjones/>
862 Copyright (C) 2012 Red Hat Inc.
864 This program is free software; you can redistribute it and/or modify
865 it under the terms of the GNU General Public License as published by
866 the Free Software Foundation; either version 2 of the License, or
867 (at your option) any later version.
869 This program is distributed in the hope that it will be useful,
870 but WITHOUT ANY WARRANTY; without even the implied warranty of
871 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
872 GNU General Public License for more details.
874 You should have received a copy of the GNU General Public License
875 along with this program; if not, write to the Free Software
876 Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.