cron is a tool for automation job on linux.
installation
#check installation, if not exist it can be installed from distro's software repository
$ which anacron
/usr/sbin/anacron
usage
#create example task script with content: #!/bin/sh touch /tmp/hello
#create cron directory $ mkdir -p ~/.local/etc/cron.daily ~/.var/spool/anacron #put example task script in cron.daily directory. you can add weekly, fortnightly, or even monthly directories to ~/.local/etc to schedule a wide variety of intervals, the configuration in ~/.local/etc/anacrontab should be changed accordingly. $ cp example ~/.local/etc/cron.daily #chmod +x ~/.local/etc/cron.daily/example
#To configure anacron to run your cron jobs, create a configuration file at ~/.local/etc/anacrontab: SHELL=/bin/sh PATH=/sbin:/bin:/usr/sbin:/usr/bin 1 0 cron.mine run-parts /home/tux/.local/etc/cron.daily/
#Verify your anacrontab file’s syntax:
$ anacron -T -t ~/.local/etc/anacrontab
-S /home/tux/.var/spool/anacron
#Adding anacron to .profile, The -fn options tell anacron to ignore timestamps for test purpose, afterward you should remove that option
anacron -fn -t /home/tux/.local/etc/anacrontab
-S /home/tux/.var/spool/anacron
tips
use cron with docker
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Using the Host’s Crontab
#start a docker container to execuate task.sh every 5 mins */5 * * * * docker run –rm example_app_image:latest /example-scheduled-task.sh
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Using Cron Within Your Containers
#create a file named crontab */5 * * * * /usr/bin/sh /example-scheduled-task.sh #create a docker image with this cron file RUN apt-get update && apt-get install -y cron COPY example-crontab /etc/cron.d/example-crontab RUN chmod 0644 /etc/cron.d/example-crontab &&
crontab /etc/cron.d/example-crontab -
Separating Cron From Application’s Services with a docker-compose file it is possible to start two docker containers: one for cron, one for application service.
version: “3”
services: app: image: demo-image:latest volumes: - data:/app-data cron: image: demo-image:latest entrypoint: /bin/bash command: [“cron”, “-f”] volumes: - data:/app-data
volumes: data:
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run cron jobs on kubernetes
apiVersion: batch/v1beta1 kind: CronJob metadata: name: my-cron namespace: my-namespace spec: schedule: “*/5 * * * *” concurrencyPolicy: Forbid jobTemplate: spec: template: spec: containers: - name: my-container image: my-image:latest command: [“/bin/bash”, “/my-cron-script.sh”] restartPolicy: OnFailure
