How to get a unix script to run every 15 seconds

Question

I ve seen a few solutions  including watch and simply running a looping  and sleeping  script in the background  but nothing has been ideal   I have a script that needs to run every 15 seconds  and since cron won t support seconds  I m left to figuring out something else   What s the most robust and efficient way to run a script every 15 seconds on unix  The script needs to also run after a reboot

User · Answer

To avoid possible overlapping of execution  use a locking mechanism as described in that thread

User · Answer

Since my previous answer I came up with another solution that is different and perhaps better  This code allows processes to be run more than 60 times a minute with microsecond precision  You need the usleep program to make this work  Should be good to up to 50 times a second       bin sh    Microsecond Cron   Usage  cron-ms start   Copyright 2014 by Marc Perkel   docs at http   wiki junkemailfilter com index php How to run a Linux script every few seconds under cron    Free to use with attribution  basedir  etc cron-ms  if      -eq 0   then    echo    echo  cron-ms by Marc Perkel     echo    echo  This program is used to run all programs in a directory in parallel every X times per minute      echo  Think of this program as cron with microseconds resolution      echo    echo  Usage  cron-ms start     echo    echo  The scheduling is done by creating directories with the number of     echo  executions per minute as part of the directory name      echo    echo  Examples      echo     etc cron-ms 7        Executes everything in that directory  7 times a minute     echo     etc cron-ms 30       Executes everything in that directory 30 times a minute     echo     etc cron-ms 600      Executes everything in that directory 10 times a second     echo     etc cron-ms 2400     Executes everything in that directory 40 times a second     echo    exit fi    If  start  is passed as a parameter then run all the loops in parallel   The number of the directory is the number of executions per minute   Since cron isn t accurate we need to start at top of next minute  if    1   start   then    for dir in  basedir     do        0   dir      60000000  amp     done    exit fi    Loops per minute and the next interval are passed on the command line with each loop  loops  1 next interval  2    Sleeps until a specific part of a minute with microsecond resolution  60000000 is full minute  usleep      next interval - 10   date   S N    1000       Run all the programs in the directory in parallel  for program in  basedir  loops     do    if   -x  program       then        program  amp  gt   dev null  amp     fi done    Calculate next interval  next interval     next interval   60000000    60000000    loops        If minute is not up - call self recursively  if    next interval -lt     60000000    loops    loops     then       0  loops  next interval  amp  fi    Otherwise we re done

User · Answer

bin sh    Run all programs in a directory in parallel   Usage  run-parallel directory delay   Copyright 2013 by Marc Perkel   docs at http   wiki junkemailfilter com index php How to run a Linux script every few seconds under cron    Free to use with attribution  if      -eq 0   then    echo    echo  run-parallel by Marc Perkel     echo    echo  This program is used to run all programs in a directory in parallel      echo  or to rerun them every X seconds for one minute      echo  Think of this program as cron with seconds resolution      echo    echo  Usage  run-parallel  directory   delay      echo    echo  Examples      echo     run-parallel  etc cron 20sec 20     echo     run-parallel 20     echo       Runs all executable files in  etc cron 20sec every 20 seconds or 3 times a minute      echo     echo  If delay parameter is missing it runs everything once and exits      echo  If only delay is passed then the directory  etc cron  delay sec is assumed      echo    echo  if  cronsec  is passed then it runs all of these delays 2 3 4 5 6 10 12 15 20 30     echo  resulting in 30 20 15 12 10 6 5 4 3 2 executions per minute       echo    exit fi    If  cronsec  is passed as a parameter then run all the delays in parallel  if    1   cronsec   then     0 2  amp      0 3  amp      0 4  amp      0 5  amp      0 6  amp      0 10  amp      0 12  amp      0 15  amp      0 20  amp      0 30  amp     exit fi    Set the directory to first prameter and delay to second parameter  dir  1 delay  2    If only parameter is 2 3 4 5 6 10 12 15 20 30 then automatically calculate    the standard directory name  etc cron  delay sec  if      1       2 3 4 5 6 10 12 15 20 30      then    dir   etc cron  1sec     delay  1 fi    Exit if directory doesn t exist or has no files  if        ls -A  dir      then    exit fi    Sleep if both  delay and  counter are set  if     -z  delay    amp  amp      -z  counter   then    sleep  delay fi    Set counter to 0 if not set  if   -z  counter   then    counter 0 fi    Run all the programs in the directory in parallel   Use of timeout ensures that the processes are killed if they run too long  for program in  dir     do    if   -x  program       then       if    0 delay  -gt 1          then          timeout  delay  program  amp  gt   dev null  amp        else           program  amp  gt   dev null  amp        fi    fi done    If delay not set then we re done  if   -z  delay   then    exit fi    Add delay to counter  counter      counter    delay       If minute is not up - call self recursively  if    counter -lt 60   then       0  dir  delay  amp  fi    Otherwise we re done

User · Answer

I would use cron to run a script every minute  and make that script run your script four times with a 15-second sleep between runs    That assumes your script is quick to run - you could adjust the sleep times if not    That way  you get all the benefits of cron as well as your 15 second run period   Edit  See also  bmb s comment below

User · Answer

If you insist of running your script from cron              foo bar your script           sleep 15   foo bar your script           sleep 30   foo bar your script           sleep 45   foo bar your script   and replace your script name amp path to  foo bar your script

User · Answer

Use nanosleep 2   It uses structure timespec that is used to specify intervals of time with nanosecond precision   struct timespec              time t tv sec            seconds               long   tv nsec           nanoseconds

User · Answer

Modified version of the above   mkdir  etc cron 15sec mkdir  etc cron minute mkdir  etc cron 5minute   add to  etc crontab             root run-parts  etc cron 15sec  gt   dev null 2 gt   dev null           root sleep 15  run-parts  etc cron 15sec  gt   dev null 2 gt   dev null           root sleep 30  run-parts  etc cron 15sec  gt   dev null 2 gt   dev null           root sleep 45  run-parts  etc cron 15sec  gt   dev null 2 gt   dev null            root run-parts  etc cron minute  gt   dev null 2 gt   dev null   5         root run-parts  etc cron 5minute  gt   dev null 2 gt   dev null

User · Answer

Won t running this in the background do it      bin sh while   1    do     echo  Hell yeah    amp      sleep 15 done   This is about as efficient as it gets   The important part only gets executed every 15 seconds and the script sleeps the rest of the time  thus not wasting cycles

User · Answer

I wrote a scheduler faster than cron  I have also implemented an overlapping guard  You can configure the scheduler to not start new process if previous one is still running  Take a look at https   github com sioux1977 scheduler wiki

[unix] How to get a unix script to run every 15 seconds?

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