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Blank lines, line beginning by a pound-sign (#) (which are considered comments), leading blanks and tabs are ignored. Each line in a fcrontab file can be either
Any logical line (an entry or an assignment) can be divided into several real lines (the lines which end by a newline character) by placing a backslash (\) before the newline character (\n).
name = value
where the blanks around equal-sign (=) are ignored and optional. Trailing blanks are also ignored, but you can place the value in quotes (simple or double, but matching) to preserve any blanks in the value.
When fcron executes a command, it always sets USER, HOME, and SHELL as defined in /etc/passwd for the owner of the fcrontab from which the command is extracted. HOME and SHELL may be overridden by settings in the fcrontab, but USER may not. Every other environment assignments defined in the user fcrontab are then made, and the command is executed.
Plus, the special variable MAILTO allows you to tell fcron to whom it has to mail the command's output. Note that MAILTO is in fact equivalent to a global declaration of the option mailto (see below). It is only used for backward compatibility, so you should use the option mailto directly.
@options frequency command
where frequency is a time value of the form value*multiplier+value*multiplier+...+value-in-minutes as "12h02" or "3w2d5h1". The first means "12 hours and 2 minutes of fcron execution" while the second means "3 weeks, 2 days, 5 hours and 1 minute of fcron execution". The only valid multipliers are:
In place of options, user can put a time value : it will be interpreted as @first(time). If first option is not set, the value of "frequency" is used.
This kind of entry does not guarantee a time and date of execution (as the job is delayed at each startup by the time elapsed since the shutdown), but should be useful for jobs depending on the number of things done by the users (for instance, the filesystem should better be checked after an certain amount of use by the users rather than every x days, as the system may run from 1 day to x days during that x days interval).
The time remaining before next execution is saved every 1800 seconds (to limit damages caused by a crash) and when fcron exits after having received a SIGTERM signal, i.e. when systems go down. Thus, this kind of entries is particularly useful for systems that don't run regularly. The syntax being very simple, it may also useful for tasks which don't need to be run at a specific time and date.
see also : options first, mail, nolog, serial, lavg, nice, runas (see below).
A field is always filled by either an asterisk (*), which acts as "first-last" range, a single number or a list.
List are numbers or range separated with commas (,). For instance: "2,5,15,23".
Ranges of number are of the form "begin-end", where "begin" and "end" are included. For example, "3-5" specifies the values 3, 4 and 5. You can also add an optional "/number" to a range, where the number specifies skips of the number's value through the range. For example, "0-23/2" can be used in the hours field to specify command execution every other hour. Finally, one or several "~number" can be added to turn off some values in a range. For example, "5-8~6~7" is equivalent to "5,8". The final form of a field is: "a[-b[/c][~d][~e][...]][,f[-g[/h][~i][~j][...]]][,...]", where the letters are integers.
You can also use an asterisk (*) in a field. It acts for "first-last". For example, a "*" in the field minute means all minutes from minute 0 down to minute 59.
Ranges can be included in a list as a single number. For instance: "2,5-10/2~6,15,20-25,30".
Names can also be used for the "month" and "day of week" fields. To do so, use the first three letters of the particular day or month (case doesn't matter). Please note that names are used exactly as numbers: you can use them in a list or a range.
If a day of month and a day of week are given, the command will execute only when both match with the current time and date unless option dayor is set. For example, with the line "5 10 31 * 7 echo ''" , echo will be executed only days which are a Sunday AND a 31th.
see also : options dayor, bootrun, runfreq, mail, nolog, serial, lavg, nice, runas (see below).
and optional options.
The keywords of the first line tell fcron to run the command once from
the beginning of the corresponding interval to the end of that interval :
for instance, the keyword weekly
tells fcron to run a command once between Monday and Sunday each week.
On top of that, the second list acts similarly but from middle to middle of
the corresponding interval : midweekly
will run a command once from Thursday to Wednesday.
Note that nightly is equivalent to middaily.
With this two kind of keywords, user must give the needed time fields (as
defined in "Entries based on time and date" (see above)) to specify when
the command should be run during each interval :
For example : '%nightly * 21-23,3-5 echo "a monthly entry"'
will run the command once each night either between 21:00 and 23:59, or between
3:00 and 5:59.
see also : options lavg, noticenotrun, strict, mail, nolog, serial, nice, runas (see below).
The keywords of the third list act differently, as follows:
run this command once during EACH interval specified, ignoring the fields
below the keyword in the interval definition
(a hours prevents the mins field to be considered as an interval,
but it will be used to determine when the line should be run during an
interval : see the note below) (dow means
"day of week").
Such a keyword is followed by 5 time and date fields (the same fields used
for a line based on absolut time (see above)).
Furthermore, there must be some non-matching time and dates in the lines
with that kind of keyword (i.e. the following is not allowed :
"%hours * 0-23 * * * echo", but "%hours * 0-22 * * * echo" is allowed).
Note : a single number in a field is considered as an interval :
"%mins 15 2-4 * * * echo" will run at 2:15, 3:15
AND 4:15 every day.
But every fields below the keywords are ignored in interval definition :
"%hours 15 2-4 * * * echo" will run only ONCE either at 2:15, 3:15
OR 4:15.
option[(arg1[,arg2][...])][,option[(arg1[...])]][...]
where option is either the name of an option or its abbreviation. The options are (abbreviation and default value between brackets):
A boolean argument can be inexistent, in which case brackets are not used and it means true; the string "true", "yes" or 1 to mean true; and the string "false", "no" or 0 to mean false. See above for explanations about time value (section "entries based on elapsed system up time").
Note that dayand and dayor are in fact the same option : a false value to dayand is equivalent to a true to dayor, and reciprocally a false value to dayor is equivalent a true value to dayand. It is the same for lavgand and lavgor.
Note a special case to be handled :
A job should be entered into the
serial
queue, *but* the previous entry
for this job has not been completed yet, because of high system load or some
external event. Option
serialonce
answers the question : should the new entry of the job be ignored ? This way
one can distinguish between jobs required to run a certain number of times,
preferably at specified times, and tasks to be performed irrespective of their
number (-> serialonce(true)), which make the system respond faster.
The same considerations apply for the load average queue, and can
be expressed with option
lavgonce.
Moreover, if the serial or the lavg queue contains respectively more than 30 and 30 jobs, the next job in the serial queue or the job nearest to the until timeout in the lavg queue will be executed before adding a new job.
Finally, if jobs remain in the lavg or serial queues when fcron stops, they will be put once in the corresponding queue on startup (their order may not be conserved).
An example of an option declaration would be :
!reset,serial(true),dayor,bootrun(0),mailto(root),lavg(.5,2,1.5)
# use /bin/bash to run commands, ignoring what /etc/passwd says SHELL=/bin/bash # mail output to thib, no matter whose fcrontab this is !mailto(thib) # define a variable which is equivalent to " Hello thib and paul ! " # here the newline characters are escaped by a backslash (\) # and quotes are used to force to keep leading and trailing blanks TEXT= " Hello\
thib and\
paul ! " # we want to use serial but not bootrun: !serial(true),b(0) # run after five minutes of execution the first time, # then run every hours @first(5) 1h echo "Run every hours" # run every days @ 1d echo "fcron daily" # run once between in the morning and once in the afternoon # if systems is running at any moment of these intervals &hours * 8-12,14-18 * * * echo "Hey boss, I'm working today !" # run once a week during our lunch %weekly * 12-13 echo "I left my system on at least once \ at lunch time this week." # run every Sunday and Saturday at 9:05 5 9 * * sat,sun echo "Good morning Thibault !" # run every peer days of march at 18:00, except on 16th 0 18 2-30/2~16 Mar * echo "It's time to go back home !" # the line above is equivalent to & 0 18 2-30/2~16 Mar * echo "It's time to go back home !" # reset options to default and set runfreq for lines below !reset,runfreq(7) # run once every 7 matches (thanks to the declaration above), # so if system is running every day at 10:00, this will be # run once a week & 0 10 * * * echo "if you got this message last time 7 days ago,\ this computer has been running every day at 10:00 last week.\ If you got the message 8 days ago, then the system has been down \ one day at 10:00 since you got it, etc" # wait every hour for a 5 minutes load average under 0.9 @lavg5(0.9) 1h echo "The system load average is low" # wait a maximum of 5 hours every day for a fall of the load average @lavgand,lavg(1,2.0,3.0),until(5h) 1d echo "Load average is going down" # wait for the best moment to run a heavy job @lavgor,lavg(0.8,1.2,1.5),nice(10) 1w echo "This is a heavy job" # run once every night between either 21:00 and 23:00 or # between 3:00 and 6:00 %nightly,lavg(1.5,2,2) * 21-23,3-6 echo "It's time to retrieve \ the last release of Mozilla !"