user-tools/cronrun

   1 #!/bin/bash
   2
   3 {
   4
   5 true <<'EOF'
   6 =pod
   7
   8 =head1 NAME
   9
  10 cronrun - convenience features to run commands in task scheduler environment
  11
  12 =head1 SYNOPSIS
  13
  14 cronrun [I<OPTIONS>] <I<COMMAND>> [I<ARGS>]
  15
  16 Run I<COMMAND> in a way most scheduled jobs are intended to run, ie:
  17
  18 =over 4
  19
  20 =item Set computing priority (nice(1), ionice(1)) to low
  21
  22 =item Delay start for random amount of time, thus avoiding load-burst when multiple jobs start at the same time
  23
  24 =item Allow only one instance at a time (by locking)
  25
  26 =back
  27
  28 =head1 OPTIONS
  29
  30 =over 4
  31
  32 =item --random-delay, -d I<SEC>
  33
  34 Delay program execution at most I<SEC> seconds.
  35 Default is to wait nothing.
  36
  37 =item --wait-lock, -W
  38
  39 Wait for the lock to release.
  40 By default cronrun(1) fails immediately if locked.
  41
  42 =back
  43
  44 =head1 DESCRIPTION
  45
  46 Lock is based on C<CRONJOBID> environment, or I<COMMAND> if C<CRONJOBID> is not set.
  47
  48 If C<CRONJOBID> is set, STDIO goes to syslog too, in the "cron" facility, stdout at info level, stderr at error level.
  49 If not set, STDIO is not redirected.
  50
  51 =head1 FILES
  52
  53 =over 4
  54
  55 =item F<~/.cache/cronrun>
  56
  57 Lock files stored in this directory.
  58
  59 =back
  60
  61 =head1 ENVIRONMENT
  62
  63 =over 4
  64
  65 =item CRONJOBID
  66
  67 Recommended practice is to set C<CRONJOBID=something> in your crontab before each C<cronrun ...> job definition.
  68
  69 =back
  70
  71 =head1 LIMITATIONS
  72
  73 =head1 SEE ALSO
  74
  75 =cut
  76
  77 EOF
  78
  79
  80
  81
  82 scriptname=${0##*/}
  83 random_delay_sec=0
  84 wait_lock=''
  85
  86 while [ $# != 0 ]
  87 do
  88         case "$1" in
  89         --help)
  90                 exit;;
  91         -d|--random-delay)
  92                 shift
  93                 random_delay_sec=$1
  94                 ;;
  95         -W|--wait-lock)
  96                 wait_lock=1
  97                 ;;
  98         --)     shift; break;;
  99         -*)     echo "$scriptname: unknown option: $1" >&2
 100                 exit -1;;
 101         *)      break;;
 102         esac
 103         shift
 104 done
 105
 106 if [ `id -u` = 0 ]
 107 then
 108         lockdir=/var/run/lock/cronrun
 109 else
 110         lockdir=~/.cache/cronrun/locks
 111 fi
 112 cmd_hash=`echo -n "${CRONJOBID:-$1}" | md5sum | cut -c1-32`
 113
 114
 115 # delay random amount of seconds
 116 sleep $[RANDOM % ($random_delay_sec + 1)]
 117
 118
 119 # set up logging
 120 if [ -n "$CRONJOBID" ]
 121 then
 122         syslog_ident=$LOGNAME.${CRONJOBID//\//.}
 123         exec 1> >(exec logger -p cron.info -t "$syslog_ident" -s 2>&1) 2> >(exec logger -p cron.error -t "$syslog_ident" -s 1>&2)
 124 fi
 125
 126
 127 # scheduled jobs are likely good to run at low priority
 128 renice -n 19 -p $$ >/dev/null
 129 ionice -c 3 -p $$
 130
 131
 132 # check the lock
 133 mkdir -p "$lockdir"
 134 lockfile=$lockdir/$cmd_hash
 135 exec {lock_fd}>>"$lockfile"
 136 flock --exclusive --nonblock $lock_fd
 137 errno=$?
 138 if [ $errno != 0 ]
 139 then
 140         if [ $wait_lock ]
 141         then
 142                 echo "cronrun: waiting on lock..." >&2
 143                 flock --exclusive $lock_fd
 144                 errno=$?
 145                 if [ $errno != 0 ]
 146                 then
 147                         exit $errno
 148                 fi
 149                 echo "cronrun: lock acquired" >&2
 150         else
 151                 exit $errno
 152         fi
 153 fi
 154
 155 # ---- lock acquired ----
 156
 157 # run the job
 158 exec "$@"
 159
 160 exit $?
 161 }