Running a cron every 30 seconds

Question

Ok so I have a cron that I need to run every 30 seconds   Here is what I have     30          bin bash -l -c  cd  srv last song releases 20120308133159  amp  amp  script rails runner -e production     Song insert latest        It runs  but is this running every 30 minutes or 30 seconds    Also  I have been reading that cron might not be the best tool to use if I run it that often  Is there another better tool that I can use or install on Ubuntu 11 04 that will be a better option  Is there a way to fix the above cron

User · Answer

write one shell script create  sh file nano every30second sh and write script    bin bash For     i 1  i  lt   2  i      do     write Command here     sleep 30 done  then set cron for this script crontab -e              home username every30second sh  this cron call  sh file in every 1 min  amp  in the  sh file command is run 2 times in 1 min if you want run script for 5 seconds then replace 30 by 5 and change for loop like this  For     i 1  i  lt   12  i      when you select for any second then calculate 60 your second and write in For loop

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Why not just adding 2 consecutive command entries  both starting at different second  0          bin bash -l -c  cd  srv last song releases 20120308133159  amp  amp  script rails runner -e production     Song insert latest      30          bin bash -l -c  cd  srv last song releases 20120308133159  amp  amp  script rails runner -e production     Song insert latest

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You can run that script as a service  restart every 30 seconds  Register a service  sudo vim  etc systemd system YOUR SERVICE NAME service   Paste in the command below  Description GIVE YOUR SERVICE A DESCRIPTION  Wants network target After syslog target network-online target   Service  Type simple ExecStart YOUR COMMAND HERE Restart always RestartSec 10 KillMode process   Install  WantedBy multi-user target   Reload services  sudo systemctl daemon-reload   Enable the service  sudo systemctl enable YOUR SERVICE NAME   Start the service  sudo systemctl start YOUR SERVICE NAME   Check the status of your service  systemctl status YOUR SERVICE NAME

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If you are running a recent Linux OS with SystemD  you can use the SystemD Timer unit to run your script at any granularity level you wish  theoretically down to nanoseconds   and - if you wish - much more flexible launching rules than Cron ever allowed  No sleep kludges required  It takes a bit more to set up than a single line in a cron file  but if you need anything better than  Every minute   it is well worth the effort   The SystemD timer model is basically this  timers are units that start service units when a timer elapses   So for every script command that you want to schedule  you must have a service unit and then an additional timer unit  A single timer unit can include multiple schedules  so you normally wouldn t need more than one timer and one service   Here is a simple example that logs  Hello World  every 10 seconds    etc systemd system helloworld service    Unit  Description Say Hello  Service  ExecStart  usr bin logger -i Hello World    etc systemd system helloworld timer    Unit  Description Say Hello every 10 seconds  Timer  OnBootSec 10 OnUnitActiveSec 10 AccuracySec 1ms  Install  WantedBy timers target   After setting up these units  in  etc systemd system  as described above  for a system-wide setting  or at    config systemd user for a user-specific setup   you need to enable the timer  not the service though  by running systemctl enable --now helloworld timer  the --now flag also starts the timer immediately  otherwise  it will only start after the next boot  or user login    The  Timer  section fields used here are as follows    OnBootSec - start the service this many seconds after each boot  OnUnitActiveSec - start the service this many seconds after the last time the service was started  This is what causes the timer to repeat itself and behave like a cron job  AccuracySec - sets the accuracy of the timer  Timers are only as accurate as this field sets  and the default is 1 minute  emulates cron   The main reason to not demand the best accuracy is to improve power consumption - if SystemD can schedule the next run to coincide with other events  it needs to wake the CPU less often  The 1ms in the example above is not ideal - I usually set accuracy to 1  1 second  in my sub-minute scheduled jobs  but that would mean that if you look at the log showing the  Hello World  messages  you d see that it is often late by 1 second  If you re OK with that  I suggest setting the accuracy to 1 second or more    As you may have noticed  this timer doesn t mimic Cron all that well - in the sense that the command doesn t start at the beginning of every wall clock period  i e  it doesn t start on the 10th second on the clock  then the 20th and so on   Instead is just happens when the timer ellapses  If the system booted at 12 05 37  then the next time the command runs will be at 12 05 47  then at 12 05 57  etc  If you are interested in actual wall clock accuracy  then you may want to replace the OnBootSec and OnUnitActiveSec fields and instead set an OnCalendar rule with the schedule that you want  which as far as I understand can t be faster than 1 second  using the calendar format   The above example can also be written as   OnCalendar  - -      00 10 20 30 40 50   Last note  as you probably guessed  the helloworld timer unit starts the helloworld service unit because they have the same name  minus the unit type suffix   This is the default  but you can override that by setting the Unit field for the  Timer  section   More gory details can be found at    Arch Linux Wiki page about SystemD timers which gives a very good overview of the topic  with examples  man systemd timer man systemd time man systemd service man system exec

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Currently i m using the below method  Works with no issues             bin bash -c   for i in  1  X   do YOUR COMMANDS   sleep Y   done    If you want to run every N seconds then X will be 60 N and Y will be N

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Thanks for all the good answers  To make it simple I liked the mixed solution  with the control on crontab and the time division on the script  So this is what I did to run a script every 20 seconds  three times per minute   Crontab line             1-6   a b checkAgendaScript  gt  gt   home a b cronlogs checkAgenda log   Script    cd  home a b checkAgenda  java -jar checkAgenda jar sleep 20 java -jar checkAgenda jar  sleep 20 java -jar checkAgenda jar

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Use watch     watch --interval  30 script to run every 30 sec sh

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No need for two cron entries  you can put it into one with              bin bash -l -c   path to executable  sleep 30    path to executable    so in your case              bin bash -l -c  cd  srv last song releases 20120308133159  amp  amp  script rails runner -e production     Song insert latest       sleep 30   cd  srv last song releases 20120308133159  amp  amp  script rails runner -e production     Song insert latest

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I just had a similar task to do and use the following approach     nohup watch -n30  kill -3 NODE PID   amp    I needed to have a periodic kill -3  to get the stack trace of a program  every 30 seconds for several hours   nohup      amp     This is here to be sure that I don t lose the execution of watch if I loose the shell  network issue  windows crash etc

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Run in a shell loop  example      bin sh     counter 1 while true   do  echo  counter  counter    counter 1    if      counter  -eq 60     then   counter 0  fi  wget -q http   localhost tool heartbeat  -O -  gt   dev null 2 gt  amp 1  amp   sleep 1 done

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Crontab job can be used to schedule a job in minutes hours days  but not in seconds  The alternative    Create a script to execute every 30 seconds      bin bash   30sec sh  for COUNT in  seq 29    do   cp  application tmp    home test   sleep 30 done   Use crontab -e and a crontab to execute this script              home test 30sec sh  gt   dev null

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You can check out my answer to this similar question  Basically  I ve included there a bash script named  runEvery sh  which you can run with cron every 1 minute and pass as arguments the real command you wish to run and the frequency in seconds in which you want to run it   something like this              bin runEvery sh 5 myScript sh

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in dir  etc cron d   new create a file excute per 30s            yourusername   bin date  gt  gt   home yourusername temp date txt           yourusername sleep 30   bin date  gt  gt   home yourusername temp date txt   will run cron every 30 seconds

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Cron s granularity is in minutes and was not designed to wake up every x seconds to run something  Run your repeating task within a loop and it should do what you need      bin env bash while   true    do  sleep 30    do what you need to here done

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Have a look at frequent-cron - it s old but very stable and you can step down to micro-seconds  At this point in time  the only thing that I would say against it is that I m still trying to work out how to install it outside of init d but as a native systemd service  but certainly up to Ubuntu 18 it s running just fine still using init d  distance may vary on latter versions   It has the added advantage     of ensuring that it won t spawn another instance of the PHP script unless a prior one has completed  which reduces potential memory leakage issues

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You can t  Cron has a 60 sec granularity             cd  srv last song releases 20120308133159  amp  amp  script rails runner -e production     Song insert latest               sleep 30  amp  amp  cd  srv last song releases 20120308133159  amp  amp  script rails runner -e production     Song insert latest

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You have   30 in the minutes specifier - that means every minute but with a step of 30  in other words  every half hour   Since cron does not go down to sub-minute resolutions  you will need to find another way  One possibility  though it s a bit of a kludge a   is to have two jobs  one offset by 30 seconds    Need these to run on 30-sec boundaries  keep commands in sync                          path to executable param1 param2             sleep 30    path to executable param1 param2    You ll see I ve added comments and formatted to ensure it s easy to keep them synchronised  Both cron jobs actually run every minute but the latter one will wait half a minute before executing the  quot meat quot  of the job   path to executable  For other  non-cron-based  options  see the other answers here  particularly the ones mentioning fcron and systemd  These are probably preferable assuming your system has the ability to use them  such as installing fcron or having a distro with systemd in it    If you don t want to use the kludgy solution  you can use a loop-based solution with a small modification  You ll still have to manage keeping your process running in some form but  once that s sorted  the following script should work     bin env bash    Debug code to start on minute boundary and to   gradually increase maximum payload duration to   see what happens when the payload exceeds 30 seconds     maxtime   20   while     quot   date   S  quot      quot 00 quot      do true  done  while true  do       Start a background timer BEFORE the payload runs       sleep 30  amp         Execute the payload  some random duration up to the limit        Extra blank line if excess payload         delay   RANDOM   maxtime   1         maxtime    1       echo  quot   date  Sleeping for   delay  seconds  max   maxtime    quot           delay  -gt 30     amp  amp  echo     sleep   delay         Wait for timer to finish before next cycle       wait done  The trick is to use a sleep 30 but to start it in the background before your payload runs  Then  after the payload is finished  just wait for the background sleep to finish  If the payload takes n seconds  where n  lt   30   the wait after the payload will then be 30 - n seconds  If it takes more than 30 seconds  then the next cycle will be delayed until the payload is finished  but no longer  You ll see that I have debug code in there to start on a one-minute boundary to make the output initially easier to follow  I also gradually increase the maximum payload time so you ll eventually see the payload exceed the 30-second cycle time  an extra blank line is output so the effect is obvious   A sample run follows  where cycles normally start 30 seconds after the previous cycle   Tue May 26 20 56 00 AWST 2020 Sleeping for 9 seconds  max 21   Tue May 26 20 56 30 AWST 2020 Sleeping for 19 seconds  max 22   Tue May 26 20 57 00 AWST 2020 Sleeping for 9 seconds  max 23   Tue May 26 20 57 30 AWST 2020 Sleeping for 7 seconds  max 24   Tue May 26 20 58 00 AWST 2020 Sleeping for 2 seconds  max 25   Tue May 26 20 58 30 AWST 2020 Sleeping for 8 seconds  max 26   Tue May 26 20 59 00 AWST 2020 Sleeping for 20 seconds  max 27   Tue May 26 20 59 30 AWST 2020 Sleeping for 25 seconds  max 28   Tue May 26 21 00 00 AWST 2020 Sleeping for 5 seconds  max 29   Tue May 26 21 00 30 AWST 2020 Sleeping for 6 seconds  max 30   Tue May 26 21 01 00 AWST 2020 Sleeping for 27 seconds  max 31   Tue May 26 21 01 30 AWST 2020 Sleeping for 25 seconds  max 32   Tue May 26 21 02 00 AWST 2020 Sleeping for 15 seconds  max 33   Tue May 26 21 02 30 AWST 2020 Sleeping for 10 seconds  max 34   Tue May 26 21 03 00 AWST 2020 Sleeping for 5 seconds  max 35   Tue May 26 21 03 30 AWST 2020 Sleeping for 35 seconds  max 36    Tue May 26 21 04 05 AWST 2020 Sleeping for 2 seconds  max 37   Tue May 26 21 04 35 AWST 2020 Sleeping for 20 seconds  max 38   Tue May 26 21 05 05 AWST 2020 Sleeping for 22 seconds  max 39   Tue May 26 21 05 35 AWST 2020 Sleeping for 18 seconds  max 40   Tue May 26 21 06 05 AWST 2020 Sleeping for 33 seconds  max 41    Tue May 26 21 06 38 AWST 2020 Sleeping for 31 seconds  max 42    Tue May 26 21 07 09 AWST 2020 Sleeping for 6 seconds  max 43    If you want to avoid the kludgy solution  this is probably better  You ll still need a cron job  or equivalent  to periodically detect if this script is running and  if not  start it  But the script itself then handles the timing    a  Some of my workmates would say that kludges are my specialty  -

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Use fcron  http   fcron free fr   - gives you granularity in seconds and way better and more feature rich than cron  vixie-cron  and stable too  I used to make stupid things like having about 60 php scripts running on one machine in very stupid settings and it still did its job

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Cron job cannot be used to schedule a job in seconds interval  i e You cannot schedule a cron job to run every 5 seconds  The alternative is to write a shell script that uses sleep 5 command in it   Create a shell script every-5-seconds sh using bash while loop as shown below     cat every-5-seconds sh    bin bash while true do   home ramesh backup sh  sleep 5 done   Now  execute this shell script in the background using nohup as shown below  This will keep executing the script even after you logout from your session  This will execute your backup sh shell script every 5 seconds     nohup   every-5-seconds sh  amp

[ubuntu] Running a cron every 30 seconds

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