Rescheduling an at job
Is there a way to change the date of a job that has been issued with the unix at
command?
I need to do this because my Application has scheduled too many jobs at the same time which will bring the machine 开发者_如何学Cto a grinding halt.
This is probably implementation dependent, but on my system I can rename the job like so:
$ # Bash
$ sudo ls -l /var/spool/cron/atjobs
-rwx------ 1 username daemon 3782 Nov 29 11:24 a00078014854e8
$ atq
120 Mon Nov 29 11:44:00 2010 a username
$ printf "%x\n" $((16#14854e8 + 60*2)) # 2 hour delay
1485560
$ sudo mv /var/spool/cron/atjobs/a00078014854e8 /var/spool/cron/atjobs/a0007801485560
$ atq
120 Mon Nov 29 13:44:00 2010 a username
The last 8 hex digits in the filename is the number of minutes from the Unix Epoch that determines the time to run the job. Increment that by the number of minutes to delay.
Edit:
Below is a Bash script to automate the steps above. Here are some example runs:
Create a job:
$ date
Mon Nov 29 20:00:00 CST 2010
$ echo true | at now + 1 hour
$ atq
140 Mon Nov 29 21:00:00 2010 a username
Reschedule the job for one hour later:
$ sudo atrs 140 60
Job 140 in Queue "a" rescheduled
from Mon Nov 29 21:00:00 CST 2010
to Mon Nov 29 22:00:00 CST 2010
Reschedule it for 15 minutes earlier:
$ sudo atrs 140 -15
Job 140 in Queue "a" rescheduled
from Mon Nov 29 22:00:00 CST 2010
to Mon Nov 29 21:45:00 CST 2010
Now add a day:
$ sudo atrs 140 $((60 * 24))
Job 140 in Queue "a" rescheduled
from Mon Nov 29 21:45:00 CST 2010
to Mon Nov 30 21:45:00 CST 2010
You can specify a queue:
$ sudo atrs -q b 141 120
Do a dry run:
$ sudo atrs -n 140 30
Job 140 in Queue "a"
Current job time: Mon Nov 30 21:45:00 2010
Proposed job time: Mon Nov 30 22:15:00 2010
Here's the script:
#!/bin/bash
# atrs - reschedule at jobs
# atrs [-n] [-q queue] job [-|+]minutes
# by Dennis Williamson 2010-11-29
# in response to http://stackoverflow.com/questions/4304631/rescheduling-an-at-job
# for Bash 3.2 or greater
# this script assumes that the last eight characters of the at job filename is
# a sequence of hex digits representing the number of minutes starting at
# the Unix epoch that is the time that the job is scheduled to be run
LC_COLLATE=C
export LC_TIME=C
shopt -s nullglob
mvcmd=/bin/mv
datecmd=/bin/date
GREP_OPTIONS=
grepcmd=/bin/grep
atqcmd=/usr/bin/atq
atjobs=/var/spool/cron/atjobs
declare -r tab=$'\t'
declare -r NOEXIT=0
declare -r EXIT=1
# it's not necessary to bitmap the errors, but I just wanted to
declare -r ERROPTS=1
declare -r ERROARG=2
declare -r ERRARGS=4
declare -r ERRQUNM=8
declare -r ERRNOJB=16
declare -r ERRMVFL=32
declare -r ERRNOCH=64
declare -r ERRNINT=128
declare -r DRYRUN=255 # not otherwise possible to reach this number
queue=a
err=0
error () {
(( err |= ${2:-0} ))
msg+="${3:+$3\n}"
if (( $1 == $EXIT ))
then
printf "$msg"
printf "Usage: ${0##*/} [-n] [-q queue] job [-|+]minutes\n"
printf " the default queue is a\n"
printf " -n = dry run (default if not superuser)\n"
exit $err
else
return
fi
}
# Process options and arguments
options=':q:nh'
while getopts $options option
do
case $option in
q ) queue=$OPTARG;;
n ) execute=1; ret=$DRYRUN;; # do dry run
h ) error $EXIT $DRYRUN;;
\? ) if (( (err & ERROPTS) != ERROPTS ))
then
error $NOEXIT $ERROPTS "Unknown option."
fi;;
* ) error $NOEXIT $ERROARG "Missing option argument.";;
esac
done
shift $(($OPTIND - 1))
if [[ ! $queue =~ ^[a-zA-Z=]$ ]]
then
error $NOEXIT $ERRQUNM "Invalid queue name."
fi
if (( $# != 2 ))
then
error $NOEXIT $ERRARGS "Job number and offset in minutes are required."
fi
if [[ $1 =~ ^[0-9]+$ ]]
then
job=$1
else
error $NOEXIT $ERRNINT "Job number must be a positive integer."
fi
if [[ $2 =~ ^[-+]?[0-9]+$ ]]
then
minutes=$2
else
error $NOEXIT $ERRNINT "Minutes must be an integer."
fi
if (( err != 0 ))
then
error $EXIT
fi
# make preparations
if (( $EUID == 0 ))
then
printf -v old "%05x" "$job"
prefix="$atjobs/$queue$old"
file=($prefix*)
if [[ -z $file || ! -e $file ]]
then
error $EXIT $ERRNOJB "Job not found."
fi
oldhex="${file#$prefix}"
oldminutes=$((16#$oldhex))
newminutes=$((oldminutes + minutes))
printf -v newhex "%08x" "$newminutes"
from=$($datecmd -d @"$(($oldminutes * 60))")
to=$($datecmd -d @"$((newminutes * 60))")
else
if (( execute == 0 ))
then
printf "You must be superuser to reschedule jobs. The job will be listed instead.\n"
execute=1 # do dry run
ret=$DRYRUN
fi
fi
# perform action
if (( execute == 0 ))
then
if [[ $file != $prefix$newhex ]]
then
if $mvcmd "$file" "$prefix$newhex"
then
printf 'Job %s in Queue "%s" rescheduled\n' "$job" "$queue"
printf "from %s\n" "$from"
printf "to %s\n" "$to"
else
error $EXIT $ERRMVFL "Reschedule failed."
fi
else
error $EXIT $ERRNOCH "No change, times are the same."
fi
else
jobdate=$($atqcmd -q $queue | $grepcmd "^$job$tab")
if [[ -n $jobdate ]]
then
jobdate=${jobdate#$job$tab}
jobdate=${jobdate%% $queue *}
newjobdate=$($datecmd +%c -d "$jobdate + $minutes minutes")
if [[ $jobdate != $newjobdate ]]
then
printf 'Job %s in Queue "%s"\n' "$job" "$queue"
printf "Current job time: %s\n" "$jobdate"
printf "Proposed job time: %s\n" "$newjobdate"
else
error $EXIT $ERRNOCH "Proposed time would result in no change."
fi
else
error $EXIT $ERRNOJB "Job not found."
fi
fi
exit $ret
This will assign the job a new id for its new time.
at -c OLDJOBID | at NEWTIME
atrm OLDJOBID
I'm not sure if there is a way to reschedule them for a different time, but you can remove them completely from at
like this:
First list the jobs:
$ at -l
9944 2010-11-29 15:00 a dogbane
9945 2010-11-29 15:00 a dogbane
Then remove them:
$ at -d 9944
$ at -d 9945
You can then recreate them if you want.
精彩评论