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I am trying to run a cronjob inside a docker container that invokes a shell script.
Yesterday I have been searching all over the web and stack overflow, but I could not really find a solution that works.
How can I do this?
You can copy your crontab into an image, in order for the container launched from said image to run the job.
Important: as noted in docker-cron issue 3: use LF, not CRLF for your cron file.
See "Run a cron job with Docker" from Julien Boulay in his Ekito/docker-cron:
Let’s create a new file called "hello-cron" to describe our job.
# must be ended with a new line "LF" (Unix) and not "CRLF" (Windows)
* * * * * echo "Hello world" >> /var/log/cron.log 2>&1
# An empty line is required at the end of this file for a valid cron file.
If you are wondering what is 2>&1, Ayman Hourieh explains.
The following Dockerfile describes all the steps to build your image
FROM ubuntu:latest
MAINTAINER docker#ekito.fr
RUN apt-get update && apt-get -y install cron
# Copy hello-cron file to the cron.d directory
COPY hello-cron /etc/cron.d/hello-cron
# Give execution rights on the cron job
RUN chmod 0644 /etc/cron.d/hello-cron
# Apply cron job
RUN crontab /etc/cron.d/hello-cron
# Create the log file to be able to run tail
RUN touch /var/log/cron.log
# Run the command on container startup
CMD cron && tail -f /var/log/cron.log
But: if cron dies, the container keeps running.
(see Gaafar's comment and How do I make apt-get install less noisy?:
apt-get -y install -qq --force-yes cron can work too)
As noted by Nathan Lloyd in the comments:
Quick note about a gotcha:
If you're adding a script file and telling cron to run it, remember to
RUN chmod 0744 /the_script
Cron fails silently if you forget.
OR, make sure your job itself redirect directly to stdout/stderr instead of a log file, as described in hugoShaka's answer:
* * * * * root echo hello > /proc/1/fd/1 2>/proc/1/fd/2
Replace the last Dockerfile line with
CMD ["cron", "-f"]
But: it doesn't work if you want to run tasks as a non-root.
See also (about cron -f, which is to say cron "foreground") "docker ubuntu cron -f is not working"
Build and run it:
sudo docker build --rm -t ekito/cron-example .
sudo docker run -t -i ekito/cron-example
Be patient, wait for 2 minutes and your command-line should display:
Hello world
Hello world
Eric adds in the comments:
Do note that tail may not display the correct file if it is created during image build.
If that is the case, you need to create or touch the file during container runtime in order for tail to pick up the correct file.
See "Output of tail -f at the end of a docker CMD is not showing".
See more in "Running Cron in Docker" (Apr. 2021) from Jason Kulatunga, as he commented below
See Jason's image AnalogJ/docker-cron based on:
Dockerfile installing cronie/crond, depending on distribution.
an entrypoint initializing /etc/environment and then calling
cron -f -l 2
The accepted answer may be dangerous in a production environment.
In docker you should only execute one process per container because if you don't, the process that forked and went background is not monitored and may stop without you knowing it.
When you use CMD cron && tail -f /var/log/cron.log the cron process basically fork in order to execute cron in background, the main process exits and let you execute tailf in foreground. The background cron process could stop or fail you won't notice, your container will still run silently and your orchestration tool will not restart it.
You can avoid such a thing by redirecting directly the cron's commands output into your docker stdout and stderr which are located respectively in /proc/1/fd/1 and /proc/1/fd/2.
Using basic shell redirects you may want to do something like this :
* * * * * root echo hello > /proc/1/fd/1 2>/proc/1/fd/2
And your CMD will be : CMD ["cron", "-f"]
But: this doesn't work if you want to run tasks as a non-root.
For those who wants to use a simple and lightweight image:
FROM alpine:3.6
# copy crontabs for root user
COPY config/cronjobs /etc/crontabs/root
# start crond with log level 8 in foreground, output to stderr
CMD ["crond", "-f", "-d", "8"]
Where cronjobs is the file that contains your cronjobs, in this form:
* * * * * echo "hello stackoverflow" >> /test_file 2>&1
# remember to end this file with an empty new line
But apparently you won't see hello stackoverflow in docker logs.
What #VonC has suggested is nice but I prefer doing all cron job configuration in one line. This would avoid cross platform issues like cronjob location and you don't need a separate cron file.
FROM ubuntu:latest
# Install cron
RUN apt-get -y install cron
# Create the log file to be able to run tail
RUN touch /var/log/cron.log
# Setup cron job
RUN (crontab -l ; echo "* * * * * echo "Hello world" >> /var/log/cron.log") | crontab
# Run the command on container startup
CMD cron && tail -f /var/log/cron.log
After running your docker container, you can make sure if cron service is working by:
# To check if the job is scheduled
docker exec -ti <your-container-id> bash -c "crontab -l"
# To check if the cron service is running
docker exec -ti <your-container-id> bash -c "pgrep cron"
If you prefer to have ENTRYPOINT instead of CMD, then you can substitute the CMD above with
ENTRYPOINT cron start && tail -f /var/log/cron.log
But: if cron dies, the container keeps running.
There is another way to do it, is to use Tasker, a task runner that has cron (a scheduler) support.
Why ? Sometimes to run a cron job, you have to mix, your base image (python, java, nodejs, ruby) with the crond. That means another image to maintain. Tasker avoid that by decoupling the crond and you container. You can just focus on the image that you want to execute your commands, and configure Tasker to use it.
Here an docker-compose.yml file, that will run some tasks for you
version: "2"
services:
tasker:
image: strm/tasker
volumes:
- "/var/run/docker.sock:/var/run/docker.sock"
environment:
configuration: |
logging:
level:
ROOT: WARN
org.springframework.web: WARN
sh.strm: DEBUG
schedule:
- every: minute
task: hello
- every: minute
task: helloFromPython
- every: minute
task: helloFromNode
tasks:
docker:
- name: hello
image: debian:jessie
script:
- echo Hello world from Tasker
- name: helloFromPython
image: python:3-slim
script:
- python -c 'print("Hello world from python")'
- name: helloFromNode
image: node:8
script:
- node -e 'console.log("Hello from node")'
There are 3 tasks there, all of them will run every minute (every: minute), and each of them will execute the script code, inside the image defined in image section.
Just run docker-compose up, and see it working. Here is the Tasker repo with the full documentation:
http://github.com/opsxcq/tasker
Though this aims to run jobs beside a running process in a container via Docker's exec interface, this may be of interest for you.
I've written a daemon that observes containers and schedules jobs, defined in their metadata, on them. Example:
version: '2'
services:
wordpress:
image: wordpress
mysql:
image: mariadb
volumes:
- ./database_dumps:/dumps
labels:
deck-chores.dump.command: sh -c "mysqldump --all-databases > /dumps/dump-$$(date -Idate)"
deck-chores.dump.interval: daily
'Classic', cron-like configuration is also possible.
Here are the docs, here's the image repository.
VonC's answer is pretty thorough. In addition I'd like to add one thing that helped me. If you just want to run a cron job without tailing a file, you'd be tempted to just remove the && tail -f /var/log/cron.log from the cron command.
However this will cause the Docker container to exit shortly after running because when the cron command completes, Docker thinks the last command has exited and hence kills the container. This can be avoided by running cron in the foreground via cron -f.
If you're using docker for windows, remember that you have to change your line-ending format from CRLF to LF (i.e. from dos to unix) if you intend on importing your crontab file from windows to your ubuntu container. If not, your cron-job won't work. Here's a working example:
FROM ubuntu:latest
RUN apt-get update && apt-get -y install cron
RUN apt-get update && apt-get install -y dos2unix
# Add crontab file (from your windows host) to the cron directory
ADD cron/hello-cron /etc/cron.d/hello-cron
# Change line ending format to LF
RUN dos2unix /etc/cron.d/hello-cron
# Give execution rights on the cron job
RUN chmod 0644 /etc/cron.d/hello-cron
# Apply cron job
RUN crontab /etc/cron.d/hello-cron
# Create the log file to be able to run tail
RUN touch /var/log/hello-cron.log
# Run the command on container startup
CMD cron && tail -f /var/log/hello-cron.log
This actually took me hours to figure out, as debugging cron jobs in docker containers is a tedious task. Hope it helps anyone else out there that can't get their code to work!
But: if cron dies, the container keeps running.
I created a Docker image based on the other answers, which can be used like
docker run -v "/path/to/cron:/etc/cron.d/crontab" gaafar/cron
where /path/to/cron: absolute path to crontab file, or you can use it as a base in a Dockerfile:
FROM gaafar/cron
# COPY crontab file in the cron directory
COPY crontab /etc/cron.d/crontab
# Add your commands here
For reference, the image is here.
Unfortunately, none of the above answers worked for me, although all answers lead to the solution and eventually to my solution, here is the snippet if it helps someone. Thanks
This can be solved with the bash file, due to the layered architecture of the Docker, cron service doesn't get initiated with RUN/CMD/ENTRYPOINT commands.
Simply add a bash file which will initiate the cron and other services (if required)
DockerFile
FROM gradle:6.5.1-jdk11 AS build
# apt
RUN apt-get update
RUN apt-get -y install cron
# Setup cron to run every minute to print (you can add/update your cron here)
RUN touch /var/log/cron-1.log
RUN (crontab -l ; echo "* * * * * echo testing cron.... >> /var/log/cron-1.log 2>&1") | crontab
# entrypoint.sh
RUN chmod +x entrypoint.sh
CMD ["bash","entrypoint.sh"]
entrypoint.sh
#!/bin/sh
service cron start & tail -f /var/log/cron-2.log
If any other service is also required to run along with cron then add that service with & in the same command, for example: /opt/wildfly/bin/standalone.sh & service cron start & tail -f /var/log/cron-2.log
Once you will get into the docker container there you can see that testing cron.... will be getting printed every minute in file: /var/log/cron-1.log
But, if cron dies, the container keeps running.
Define the cronjob in a dedicated container which runs the command via docker exec to your service.
This is higher cohesion and the running script will have access to the environment variables you have defined for your service.
#docker-compose.yml
version: "3.3"
services:
myservice:
environment:
MSG: i'm being cronjobbed, every minute!
image: alpine
container_name: myservice
command: tail -f /dev/null
cronjobber:
image: docker:edge
volumes:
- /var/run/docker.sock:/var/run/docker.sock
container_name: cronjobber
command: >
sh -c "
echo '* * * * * docker exec myservice printenv | grep MSG' > /etc/crontabs/root
&& crond -f"
I decided to use busybox, as it is one of the smallest images.
crond is executed in foreground (-f), logging is send to stderr (-d), I didn't choose to change the loglevel.
crontab file is copied to the default path: /var/spool/cron/crontabs
FROM busybox:1.33.1
# Usage: crond [-fbS] [-l N] [-d N] [-L LOGFILE] [-c DIR]
#
# -f Foreground
# -b Background (default)
# -S Log to syslog (default)
# -l N Set log level. Most verbose 0, default 8
# -d N Set log level, log to stderr
# -L FILE Log to FILE
# -c DIR Cron dir. Default:/var/spool/cron/crontabs
COPY crontab /var/spool/cron/crontabs/root
CMD [ "crond", "-f", "-d" ]
But output of the tasks apparently can't be seen in docker logs.
When you deploy your container on another host, just note that it won't start any processes automatically. You need to make sure that 'cron' service is running inside your container.
In our case, I am using Supervisord with other services to start cron service.
[program:misc]
command=/etc/init.d/cron restart
user=root
autostart=true
autorestart=true
stderr_logfile=/var/log/misc-cron.err.log
stdout_logfile=/var/log/misc-cron.out.log
priority=998
From above examples I created this combination:
Alpine Image & Edit Using Crontab in Nano (I hate vi)
FROM alpine
RUN apk update
RUN apk add curl nano
ENV EDITOR=/usr/bin/nano
# start crond with log level 8 in foreground, output to stderr
CMD ["crond", "-f", "-d", "8"]
# Shell Access
# docker exec -it <CONTAINERID> /bin/sh
# Example Cron Entry
# crontab -e
# * * * * * echo hello > /proc/1/fd/1 2>/proc/1/fd/2
# DATE/TIME WILL BE IN UTC
Setup a cron in parallel to a one-time job
Create a script file, say run.sh, with the job that is supposed to run periodically.
#!/bin/bash
timestamp=`date +%Y/%m/%d-%H:%M:%S`
echo "System path is $PATH at $timestamp"
Save and exit.
Use Entrypoint instead of CMD
f you have multiple jobs to kick in during docker containerization, use the entrypoint file to run them all.
Entrypoint file is a script file that comes into action when a docker run command is issued. So, all the steps that we want to run can be put in this script file.
For instance, we have 2 jobs to run:
Run once job: echo “Docker container has been started”
Run periodic job: run.sh
Create entrypoint.sh
#!/bin/bash
# Start the run once job.
echo "Docker container has been started"
# Setup a cron schedule
echo "* * * * * /run.sh >> /var/log/cron.log 2>&1
# This extra line makes it a valid cron" > scheduler.txt
crontab scheduler.txt
cron -f
Let’s understand the crontab that has been set up in the file
* * * * *: Cron schedule; the job must run every minute. You can update the schedule based on your requirement.
/run.sh: The path to the script file which is to be run periodically
/var/log/cron.log: The filename to save the output of the scheduled cron job.
2>&1: The error logs(if any) also will be redirected to the same output file used above.
Note: Do not forget to add an extra new line, as it makes it a valid cron.
Scheduler.txt: the complete cron setup will be redirected to a file.
Using System/User specific environment variables in cron
My actual cron job was expecting most of the arguments as the environment variables passed to the docker run command. But, with bash, I was not able to use any of the environment variables that belongs to the system or the docker container.
Then, this came up as a walkaround to this problem:
Add the following line in the entrypoint.sh
declare -p | grep -Ev 'BASHOPTS|BASH_VERSINFO|EUID|PPID|SHELLOPTS|UID' > /container.env
Update the cron setup and specify-
SHELL=/bin/bash
BASH_ENV=/container.env
At last, your entrypoint.sh should look like
#!/bin/bash
# Start the run once job.
echo "Docker container has been started"
declare -p | grep -Ev 'BASHOPTS|BASH_VERSINFO|EUID|PPID|SHELLOPTS|UID' > /container.env
# Setup a cron schedule
echo "SHELL=/bin/bash
BASH_ENV=/container.env
* * * * * /run.sh >> /var/log/cron.log 2>&1
# This extra line makes it a valid cron" > scheduler.txt
crontab scheduler.txt
cron -f
Last but not the least: Create a Dockerfile
FROM ubuntu:16.04
MAINTAINER Himanshu Gupta
# Install cron
RUN apt-get update && apt-get install -y cron
# Add files
ADD run.sh /run.sh
ADD entrypoint.sh /entrypoint.sh
RUN chmod +x /run.sh /entrypoint.sh
ENTRYPOINT /entrypoint.sh
That’s it. Build and run the Docker image!
Here's my docker-compose based solution:
cron:
image: alpine:3.10
command: crond -f -d 8
depends_on:
- servicename
volumes:
- './conf/cron:/etc/crontabs/root:z'
restart: unless-stopped
the lines with cron entries are on the ./conf/cron file.
Note: this won't run commands that aren't in the alpine image.
Also, output of the tasks apparently won't appear in docker logs.
This question have a lot of answers, but some are complicated and another has some drawbacks. I try to explain the problems and try to deliver a solution.
cron-entrypoint.sh:
#!/bin/bash
# copy machine environment variables to cron environment
printenv | cat - /etc/crontab > temp && mv temp /etc/crontab
## validate cron file
crontab /etc/crontab
# cron service with SIGTERM support
service cron start
trap "service cron stop; exit" SIGINT SIGTERM
# just dump your logs to std output
tail -f \
/app/storage/logs/laravel.log \
/var/log/cron.log \
& wait $!
Problems solved
environment variables are not available on cron environment (like env vars or kubernetes secrets)
stop when crontab file is not valid
stop gracefully cron jobs when machine receive an SIGTERM signal
For context, I use previous script on Kubernetes with Laravel app.
this line was the one that helped me run my pre-scheduled task.
ADD mycron/root /etc/cron.d/root
RUN chmod 0644 /etc/cron.d/root
RUN crontab /etc/cron.d/root
RUN touch /var/log/cron.log
CMD ( cron -f -l 8 & ) && apache2-foreground # <-- run cron
--> My project run inside: FROM php:7.2-apache
But: if cron dies, the container keeps running.
When running on some trimmed down images that restrict root access, I had to add my user to the sudoers and run as sudo cron
FROM node:8.6.0
RUN apt-get update && apt-get install -y cron sudo
COPY crontab /etc/cron.d/my-cron
RUN chmod 0644 /etc/cron.d/my-cron
RUN touch /var/log/cron.log
# Allow node user to start cron daemon with sudo
RUN echo 'node ALL=NOPASSWD: /usr/sbin/cron' >>/etc/sudoers
ENTRYPOINT sudo cron && tail -f /var/log/cron.log
Maybe that helps someone
But: if cron dies, the container keeps running.
So, my problem was the same. The fix was to change the command section in the docker-compose.yml.
From
command: crontab /etc/crontab && tail -f /etc/crontab
To
command: crontab /etc/crontab
command: tail -f /etc/crontab
The problem was the '&&' between the commands. After deleting this, it was all fine.
Focusing on gracefully stopping the cronjobs when receiving SIGTERM or SIGQUIT signals (e.g. when running docker stop).
That's not too easy. By default, the cron process just got killed without paying attention to running cronjobs. I'm elaborating on pablorsk's answer:
Dockerfile:
FROM ubuntu:latest
RUN apt-get update \
&& apt-get -y install cron procps \
&& rm -rf /var/lib/apt/lists/*
# Copy cronjobs file to the cron.d directory
COPY cronjobs /etc/cron.d/cronjobs
# Give execution rights on the cron job
RUN chmod 0644 /etc/cron.d/cronjobs
# similarly prepare the default cronjob scripts
COPY run_cronjob.sh /root/run_cronjob.sh
RUN chmod +x /root/run_cronjob.sh
COPY run_cronjob_without_log.sh /root/run_cronjob_without_log.sh
RUN chmod +x /root/run_cronjob_without_log.sh
# Apply cron job
RUN crontab /etc/cron.d/cronjobs
# to gain access to environment variables, we need this additional entrypoint script
COPY entrypoint.sh /entrypoint.sh
RUN chmod +x /entrypoint.sh
# optionally, change received signal from SIGTERM TO SIGQUIT
#STOPSIGNAL SIGQUIT
# Run the command on container startup
ENTRYPOINT ["/entrypoint.sh"]
entrypoint.sh:
#!/bin/bash
# make global environment variables available within crond, too
printenv | grep -v "no_proxy" >> /etc/environment
# SIGQUIT/SIGTERM-handler
term_handler() {
echo 'stopping cron'
service cron stop
echo 'stopped'
echo 'waiting'
x=$(($(ps u -C run_cronjob.sh | wc -l)-1))
xold=0
while [ "$x" -gt 0 ]
do
if [ "$x" != "$xold" ]; then
echo "Waiting for $x running cronjob(s):"
ps u -C run_cronjob.sh
xold=$x
sleep 1
fi
x=$(($(ps u -C run_cronjob.sh | wc -l)-1))
done
echo 'done waiting'
exit 143; # 128 + 15 -- SIGTERM
}
# cron service with SIGTERM and SIGQUIT support
service cron start
trap "term_handler" QUIT TERM
# endless loop
while true
do
tail -f /dev/null & wait ${!}
done
cronjobs
* * * * * ./run_cronjob.sh cron1
*/2 * * * * ./run_cronjob.sh cron2
*/3 * * * * ./run_cronjob.sh cron3
Assuming you wrap all your cronjobs in a run_cronjob.sh script. That way, you can execute arbitrary code for which shutdown will wait gracefully.
run_cronjobs.sh (optional helper script to keep cronjob definitions clean)
#!/bin/bash
DIR_INCL="${BASH_SOURCE%/*}"
if [[ ! -d "$DIR_INCL" ]]; then DIR_INCL="$PWD"; fi
cd "$DIR_INCL"
# redirect all cronjob output to docker
./run_cronjob_without_log.sh "$#" > /proc/1/fd/1 2>/proc/1/fd/2
run_cronjob_without_log.sh
your_actual_cronjob_src()
Btw, when receiving a SIGKILL the container still shut downs immediately. That way you can use a command like docker-compose stop -t 60 cron-container to wait 60s for cronjobs to finish gracefully, but still terminate them for sure after the timeout.
All the answers require root access inside the container because 'cron' itself requests for UID 0.
To request root acces (e.g. via sudo) is against docker best practices.
I used https://github.com/gjcarneiro/yacron to manage scheduled tasks.
I occasionally tried to find a docker-friendly cron implementation. And this last time I tried, I've found a couple.
By docker-friendly I mean, "output of the tasks can be seen in docker logs w/o resorting to tricks."
The most promising I see at the moment is supercronic. It can be fed a crontab file, all while being docker-friendly. To make use of it:
docker-compose.yml:
services:
supercronic:
build: .
command: supercronic crontab
Dockerfile:
FROM alpine:3.17
RUN set -x \
&& apk add --no-cache supercronic shadow \
&& useradd -m app
USER app
COPY crontab .
crontab:
* * * * * date
A gist with a bit more info.
Another good one is yacron, but it uses YAML.
ofelia can be used, but they seem to focus on running tasks in separate containers. Which is probably not a downside, but I'm not sure why I'd want to do that.
And there's also a number of traditional cron implementations: dcron, fcron, cronie. But they come with "no easy way to see output of the tasks."
Just adding to the list of answers that you can also use this image:
https://hub.docker.com/repository/docker/cronit/simple-cron
And use it as a basis to start cron jobs, using it like this:
FROM cronit/simple-cron # Inherit from the base image
#Set up all your dependencies
COPY jobs.cron ./ # Copy your local config
Evidently, it is possible to run cron as a process inside the container (under root user) alongside other processes , using ENTRYPOINT statement in Dockerfile with start.sh script what includes line process cron start. More info here
#!/bin/bash
# copy environment variables for local use
env >> etc/environment
# start cron service
service cron start
# start other service
service other start
#...
If your image doesn't contain any daemon (so it's only the short-running script or process), you may also consider starting your cron from outside, by simply defining a LABEL with the cron information, plus the scheduler itself. This way, your default container state is "exited". If you have multiple scripts, this may result in a lower footprint on your system than having multiple parallel-running cron instances.
See: https://github.com/JaciBrunning/docker-cron-label
Example docker-compose.yaml:
version: '3.8'
# Example application of the cron image
services:
cron:
image: jaci/cron-label:latest
volumes:
- "/var/run/docker.sock:/var/run/docker.sock"
- "/etc/localtime:/etc/localtime:ro"
hello:
image: hello-world
restart: "no"
labels:
- "cron.schedule=* * * * * "
I wanted to share a modification to the typical off of some of these other suggestions that I found more flexible. I wanted to enable changing the cron time with an environment variable and ended up adding an additional script that runs within my entrypoint.sh, but before the call to cron -f
*updatecron.sh*
#!/bin/sh
#remove old cron files
rm -rf /etc/cron.*/*
#create a new formatted cron definition
echo "$crondef [appname] >/proc/1/fd/1 2>/proc/1/fd/2" >> /etc/cron.d/restart-cron
echo \ >> /etc/cron.d/restart-cron
chmod 0644 /etc/cron.d/restart-cron
crontab /etc/cron.d/restart-cron
This removes any existing cron files, creates a new cronfile using an ENV variable of crondef, and then loads it.
Our's was a nodejs application to be run as cron job and it was also dependent on environment variables.
The below solution worked for us.
Docker file:
# syntax=docker/dockerfile:1
FROM node:12.18.1
ENV NODE_ENV=production
COPY ["startup.sh", "./"]
# Removed steps to build the node js application
#--------------- Setup cron ------------------
# Install Cron
RUN apt-get update
RUN apt-get -y install cron
# Run every day at 1AM
#/proc/1/fd/1 2>/proc/1/fd/2 is used to redirect cron logs to standard output and standard error
RUN (crontab -l ; echo "0 1 * * * /usr/local/bin/node /app/dist/index.js > /proc/1/fd/1 2>/proc/1/fd/2") | crontab
#--------------- Start Cron ------------------
# Grant execution rights
RUN chmod 755 startup.sh
CMD ["./startup.sh"]
startup.sh:
!/bin/bash
echo "Copying env variables to /etc/environment so that it is available for cron jobs"
printenv >> /etc/environment
echo "Starting cron"
cron -f
With multiple jobs and various dependencies like zsh and curl, this is a good approach while also combining the best practices from other answers. Bonus: This does NOT require you to set +x execution permissions on myScript.sh, which can be easy to miss in a new environment.
cron.dockerfile
FROM ubuntu:latest
# Install dependencies
RUN apt-get update && apt-get -y install \
cron \
zsh \
curl;
# Setup multiple jobs with zsh and redirect outputs to docker logs
RUN (echo "\
* * * * * zsh -c 'echo "Hello World"' 1> /proc/1/fd/1 2>/proc/1/fd/2 \n\
* * * * * zsh /myScript.sh 1> /proc/1/fd/1 2>/proc/1/fd/2 \n\
") | crontab
# Run cron in forground, so docker knows the task is running
CMD ["cron", "-f"]
Integrate this with docker compose like so:
docker-compose.yml
services:
cron:
build:
context: .
dockerfile: ./cron.dockerfile
volumes:
- ./myScript.sh:/myScript.sh
Keep in mind that you need to docker compose build cron when you change contents of the cron.dockerfile, but changes to myScript.sh will be reflected right away as it's mounted in compose.
Okay so firstly I read some posts on this topic. That is how I ended up with my solution. Still I don’t find my mistake. Also I am more of a beginner.
So this is my docker file:
FROM conda/miniconda3
WORKDIR /app
RUN apt-get update -y
RUN apt-get install cron -y
RUN apt-get install curl -y
RUN conda update -n base -c defaults conda
RUN conda install mamba -n base -c conda-forge
COPY ./environment.yml ./environment.yml
RUN mamba env create -f environment.yml
# Make RUN commands use the new environment:
SHELL ["conda", "run", "--no-capture-output", "-n", "d2", "/bin/bash", "-c"]
#Setup cron
COPY ./cronjob /etc/cron.d/cronjob
RUN crontab /etc/cron.d/cronjob
RUN chmod 0600 /etc/cron.d/cronjob
RUN touch ./cron.log
COPY ./ ./
RUN ["chmod", "+x", "run.sh"]
ENTRYPOINT ["sh", "run.sh"]
CMD ["cron", "-f"]
What I want to do:
Run my run.sh (I managed to do that.)
Setup a cronjob inside my container which is defined in a file called cronjob (see content below)
My cronjob is not working. Why?
Note that cron.log is empty. It is never triggered.
Also the output of crontab -l (run inside of the container) is:
$ crontab -l
# Updates every 15 minutes.
*/15 * * * * /bin/sh /app/cron.sh >> /app/cron.log 2&>1
cronjob
# Updates every 15 minutes.
*/15 * * * * /bin/sh /app/cron.sh >> /app/cron.log 2&>1
As Saeed pointed out already, there is reason to believe you did not place your cron.sh script inside the container.
On top of that cron is programmed such that it does not log failed invocations anywhere. You can try to turn on some debug logging (I almost had to search cron's source to find the right settings years ago). Finally cron will send it's debug output to syslog - but in your container only cron is running, so the log entries are probably lost on that stage again.
That ultimately means you are in the dark and need to find the needle. But installing the script is a first good attempt.
As Saeed said in this comment
First of all, your cronjob command is wrong. You should have 2>&1 instead of 2&>1. Second. run ls -lh /app/cron.sh to see if your file is copied. Also be sure cron.sh is in the directory where your Dockerfile is.
2&>1 was the mistake that I had made.
I had a similar issue with the crontab not being read
I was also using something like:
COPY ./cronjob /etc/cron.d/cronjob
Locally the cronjob file had permissions of 664 instead of 644. This was causing cron to log Sep 29 16:21:01 0f2c2e0ddbfd cron[389]: (*system*crontab) INSECURE MODE (group/other writable) (/etc/cron.d/crontab) (I actually had to install syslog-ng to see this happen).
Turns out cron will refuse to read cron configurations if they are writeable by others. I guess it makes sense in hindsight but I was completely oblivious to this.
Changing my cronjob file permissions to 644 fixed this for me (I did this on my local filesystem, the Dockerfile copies permissions over)
only you need to root right then it will solve issuse
*/15 * * * * root /bin/sh /app/cron.sh >> /app/cron.log 2&>1
I am trying to run a cronjob inside a docker container that invokes a shell script.
Yesterday I have been searching all over the web and stack overflow, but I could not really find a solution that works.
How can I do this?
You can copy your crontab into an image, in order for the container launched from said image to run the job.
Important: as noted in docker-cron issue 3: use LF, not CRLF for your cron file.
See "Run a cron job with Docker" from Julien Boulay in his Ekito/docker-cron:
Let’s create a new file called "hello-cron" to describe our job.
# must be ended with a new line "LF" (Unix) and not "CRLF" (Windows)
* * * * * echo "Hello world" >> /var/log/cron.log 2>&1
# An empty line is required at the end of this file for a valid cron file.
If you are wondering what is 2>&1, Ayman Hourieh explains.
The following Dockerfile describes all the steps to build your image
FROM ubuntu:latest
MAINTAINER docker#ekito.fr
RUN apt-get update && apt-get -y install cron
# Copy hello-cron file to the cron.d directory
COPY hello-cron /etc/cron.d/hello-cron
# Give execution rights on the cron job
RUN chmod 0644 /etc/cron.d/hello-cron
# Apply cron job
RUN crontab /etc/cron.d/hello-cron
# Create the log file to be able to run tail
RUN touch /var/log/cron.log
# Run the command on container startup
CMD cron && tail -f /var/log/cron.log
But: if cron dies, the container keeps running.
(see Gaafar's comment and How do I make apt-get install less noisy?:
apt-get -y install -qq --force-yes cron can work too)
As noted by Nathan Lloyd in the comments:
Quick note about a gotcha:
If you're adding a script file and telling cron to run it, remember to
RUN chmod 0744 /the_script
Cron fails silently if you forget.
OR, make sure your job itself redirect directly to stdout/stderr instead of a log file, as described in hugoShaka's answer:
* * * * * root echo hello > /proc/1/fd/1 2>/proc/1/fd/2
Replace the last Dockerfile line with
CMD ["cron", "-f"]
But: it doesn't work if you want to run tasks as a non-root.
See also (about cron -f, which is to say cron "foreground") "docker ubuntu cron -f is not working"
Build and run it:
sudo docker build --rm -t ekito/cron-example .
sudo docker run -t -i ekito/cron-example
Be patient, wait for 2 minutes and your command-line should display:
Hello world
Hello world
Eric adds in the comments:
Do note that tail may not display the correct file if it is created during image build.
If that is the case, you need to create or touch the file during container runtime in order for tail to pick up the correct file.
See "Output of tail -f at the end of a docker CMD is not showing".
See more in "Running Cron in Docker" (Apr. 2021) from Jason Kulatunga, as he commented below
See Jason's image AnalogJ/docker-cron based on:
Dockerfile installing cronie/crond, depending on distribution.
an entrypoint initializing /etc/environment and then calling
cron -f -l 2
The accepted answer may be dangerous in a production environment.
In docker you should only execute one process per container because if you don't, the process that forked and went background is not monitored and may stop without you knowing it.
When you use CMD cron && tail -f /var/log/cron.log the cron process basically fork in order to execute cron in background, the main process exits and let you execute tailf in foreground. The background cron process could stop or fail you won't notice, your container will still run silently and your orchestration tool will not restart it.
You can avoid such a thing by redirecting directly the cron's commands output into your docker stdout and stderr which are located respectively in /proc/1/fd/1 and /proc/1/fd/2.
Using basic shell redirects you may want to do something like this :
* * * * * root echo hello > /proc/1/fd/1 2>/proc/1/fd/2
And your CMD will be : CMD ["cron", "-f"]
But: this doesn't work if you want to run tasks as a non-root.
For those who wants to use a simple and lightweight image:
FROM alpine:3.6
# copy crontabs for root user
COPY config/cronjobs /etc/crontabs/root
# start crond with log level 8 in foreground, output to stderr
CMD ["crond", "-f", "-d", "8"]
Where cronjobs is the file that contains your cronjobs, in this form:
* * * * * echo "hello stackoverflow" >> /test_file 2>&1
# remember to end this file with an empty new line
But apparently you won't see hello stackoverflow in docker logs.
What #VonC has suggested is nice but I prefer doing all cron job configuration in one line. This would avoid cross platform issues like cronjob location and you don't need a separate cron file.
FROM ubuntu:latest
# Install cron
RUN apt-get -y install cron
# Create the log file to be able to run tail
RUN touch /var/log/cron.log
# Setup cron job
RUN (crontab -l ; echo "* * * * * echo "Hello world" >> /var/log/cron.log") | crontab
# Run the command on container startup
CMD cron && tail -f /var/log/cron.log
After running your docker container, you can make sure if cron service is working by:
# To check if the job is scheduled
docker exec -ti <your-container-id> bash -c "crontab -l"
# To check if the cron service is running
docker exec -ti <your-container-id> bash -c "pgrep cron"
If you prefer to have ENTRYPOINT instead of CMD, then you can substitute the CMD above with
ENTRYPOINT cron start && tail -f /var/log/cron.log
But: if cron dies, the container keeps running.
There is another way to do it, is to use Tasker, a task runner that has cron (a scheduler) support.
Why ? Sometimes to run a cron job, you have to mix, your base image (python, java, nodejs, ruby) with the crond. That means another image to maintain. Tasker avoid that by decoupling the crond and you container. You can just focus on the image that you want to execute your commands, and configure Tasker to use it.
Here an docker-compose.yml file, that will run some tasks for you
version: "2"
services:
tasker:
image: strm/tasker
volumes:
- "/var/run/docker.sock:/var/run/docker.sock"
environment:
configuration: |
logging:
level:
ROOT: WARN
org.springframework.web: WARN
sh.strm: DEBUG
schedule:
- every: minute
task: hello
- every: minute
task: helloFromPython
- every: minute
task: helloFromNode
tasks:
docker:
- name: hello
image: debian:jessie
script:
- echo Hello world from Tasker
- name: helloFromPython
image: python:3-slim
script:
- python -c 'print("Hello world from python")'
- name: helloFromNode
image: node:8
script:
- node -e 'console.log("Hello from node")'
There are 3 tasks there, all of them will run every minute (every: minute), and each of them will execute the script code, inside the image defined in image section.
Just run docker-compose up, and see it working. Here is the Tasker repo with the full documentation:
http://github.com/opsxcq/tasker
Though this aims to run jobs beside a running process in a container via Docker's exec interface, this may be of interest for you.
I've written a daemon that observes containers and schedules jobs, defined in their metadata, on them. Example:
version: '2'
services:
wordpress:
image: wordpress
mysql:
image: mariadb
volumes:
- ./database_dumps:/dumps
labels:
deck-chores.dump.command: sh -c "mysqldump --all-databases > /dumps/dump-$$(date -Idate)"
deck-chores.dump.interval: daily
'Classic', cron-like configuration is also possible.
Here are the docs, here's the image repository.
VonC's answer is pretty thorough. In addition I'd like to add one thing that helped me. If you just want to run a cron job without tailing a file, you'd be tempted to just remove the && tail -f /var/log/cron.log from the cron command.
However this will cause the Docker container to exit shortly after running because when the cron command completes, Docker thinks the last command has exited and hence kills the container. This can be avoided by running cron in the foreground via cron -f.
If you're using docker for windows, remember that you have to change your line-ending format from CRLF to LF (i.e. from dos to unix) if you intend on importing your crontab file from windows to your ubuntu container. If not, your cron-job won't work. Here's a working example:
FROM ubuntu:latest
RUN apt-get update && apt-get -y install cron
RUN apt-get update && apt-get install -y dos2unix
# Add crontab file (from your windows host) to the cron directory
ADD cron/hello-cron /etc/cron.d/hello-cron
# Change line ending format to LF
RUN dos2unix /etc/cron.d/hello-cron
# Give execution rights on the cron job
RUN chmod 0644 /etc/cron.d/hello-cron
# Apply cron job
RUN crontab /etc/cron.d/hello-cron
# Create the log file to be able to run tail
RUN touch /var/log/hello-cron.log
# Run the command on container startup
CMD cron && tail -f /var/log/hello-cron.log
This actually took me hours to figure out, as debugging cron jobs in docker containers is a tedious task. Hope it helps anyone else out there that can't get their code to work!
But: if cron dies, the container keeps running.
I created a Docker image based on the other answers, which can be used like
docker run -v "/path/to/cron:/etc/cron.d/crontab" gaafar/cron
where /path/to/cron: absolute path to crontab file, or you can use it as a base in a Dockerfile:
FROM gaafar/cron
# COPY crontab file in the cron directory
COPY crontab /etc/cron.d/crontab
# Add your commands here
For reference, the image is here.
Unfortunately, none of the above answers worked for me, although all answers lead to the solution and eventually to my solution, here is the snippet if it helps someone. Thanks
This can be solved with the bash file, due to the layered architecture of the Docker, cron service doesn't get initiated with RUN/CMD/ENTRYPOINT commands.
Simply add a bash file which will initiate the cron and other services (if required)
DockerFile
FROM gradle:6.5.1-jdk11 AS build
# apt
RUN apt-get update
RUN apt-get -y install cron
# Setup cron to run every minute to print (you can add/update your cron here)
RUN touch /var/log/cron-1.log
RUN (crontab -l ; echo "* * * * * echo testing cron.... >> /var/log/cron-1.log 2>&1") | crontab
# entrypoint.sh
RUN chmod +x entrypoint.sh
CMD ["bash","entrypoint.sh"]
entrypoint.sh
#!/bin/sh
service cron start & tail -f /var/log/cron-2.log
If any other service is also required to run along with cron then add that service with & in the same command, for example: /opt/wildfly/bin/standalone.sh & service cron start & tail -f /var/log/cron-2.log
Once you will get into the docker container there you can see that testing cron.... will be getting printed every minute in file: /var/log/cron-1.log
But, if cron dies, the container keeps running.
Define the cronjob in a dedicated container which runs the command via docker exec to your service.
This is higher cohesion and the running script will have access to the environment variables you have defined for your service.
#docker-compose.yml
version: "3.3"
services:
myservice:
environment:
MSG: i'm being cronjobbed, every minute!
image: alpine
container_name: myservice
command: tail -f /dev/null
cronjobber:
image: docker:edge
volumes:
- /var/run/docker.sock:/var/run/docker.sock
container_name: cronjobber
command: >
sh -c "
echo '* * * * * docker exec myservice printenv | grep MSG' > /etc/crontabs/root
&& crond -f"
I decided to use busybox, as it is one of the smallest images.
crond is executed in foreground (-f), logging is send to stderr (-d), I didn't choose to change the loglevel.
crontab file is copied to the default path: /var/spool/cron/crontabs
FROM busybox:1.33.1
# Usage: crond [-fbS] [-l N] [-d N] [-L LOGFILE] [-c DIR]
#
# -f Foreground
# -b Background (default)
# -S Log to syslog (default)
# -l N Set log level. Most verbose 0, default 8
# -d N Set log level, log to stderr
# -L FILE Log to FILE
# -c DIR Cron dir. Default:/var/spool/cron/crontabs
COPY crontab /var/spool/cron/crontabs/root
CMD [ "crond", "-f", "-d" ]
But output of the tasks apparently can't be seen in docker logs.
When you deploy your container on another host, just note that it won't start any processes automatically. You need to make sure that 'cron' service is running inside your container.
In our case, I am using Supervisord with other services to start cron service.
[program:misc]
command=/etc/init.d/cron restart
user=root
autostart=true
autorestart=true
stderr_logfile=/var/log/misc-cron.err.log
stdout_logfile=/var/log/misc-cron.out.log
priority=998
From above examples I created this combination:
Alpine Image & Edit Using Crontab in Nano (I hate vi)
FROM alpine
RUN apk update
RUN apk add curl nano
ENV EDITOR=/usr/bin/nano
# start crond with log level 8 in foreground, output to stderr
CMD ["crond", "-f", "-d", "8"]
# Shell Access
# docker exec -it <CONTAINERID> /bin/sh
# Example Cron Entry
# crontab -e
# * * * * * echo hello > /proc/1/fd/1 2>/proc/1/fd/2
# DATE/TIME WILL BE IN UTC
Setup a cron in parallel to a one-time job
Create a script file, say run.sh, with the job that is supposed to run periodically.
#!/bin/bash
timestamp=`date +%Y/%m/%d-%H:%M:%S`
echo "System path is $PATH at $timestamp"
Save and exit.
Use Entrypoint instead of CMD
f you have multiple jobs to kick in during docker containerization, use the entrypoint file to run them all.
Entrypoint file is a script file that comes into action when a docker run command is issued. So, all the steps that we want to run can be put in this script file.
For instance, we have 2 jobs to run:
Run once job: echo “Docker container has been started”
Run periodic job: run.sh
Create entrypoint.sh
#!/bin/bash
# Start the run once job.
echo "Docker container has been started"
# Setup a cron schedule
echo "* * * * * /run.sh >> /var/log/cron.log 2>&1
# This extra line makes it a valid cron" > scheduler.txt
crontab scheduler.txt
cron -f
Let’s understand the crontab that has been set up in the file
* * * * *: Cron schedule; the job must run every minute. You can update the schedule based on your requirement.
/run.sh: The path to the script file which is to be run periodically
/var/log/cron.log: The filename to save the output of the scheduled cron job.
2>&1: The error logs(if any) also will be redirected to the same output file used above.
Note: Do not forget to add an extra new line, as it makes it a valid cron.
Scheduler.txt: the complete cron setup will be redirected to a file.
Using System/User specific environment variables in cron
My actual cron job was expecting most of the arguments as the environment variables passed to the docker run command. But, with bash, I was not able to use any of the environment variables that belongs to the system or the docker container.
Then, this came up as a walkaround to this problem:
Add the following line in the entrypoint.sh
declare -p | grep -Ev 'BASHOPTS|BASH_VERSINFO|EUID|PPID|SHELLOPTS|UID' > /container.env
Update the cron setup and specify-
SHELL=/bin/bash
BASH_ENV=/container.env
At last, your entrypoint.sh should look like
#!/bin/bash
# Start the run once job.
echo "Docker container has been started"
declare -p | grep -Ev 'BASHOPTS|BASH_VERSINFO|EUID|PPID|SHELLOPTS|UID' > /container.env
# Setup a cron schedule
echo "SHELL=/bin/bash
BASH_ENV=/container.env
* * * * * /run.sh >> /var/log/cron.log 2>&1
# This extra line makes it a valid cron" > scheduler.txt
crontab scheduler.txt
cron -f
Last but not the least: Create a Dockerfile
FROM ubuntu:16.04
MAINTAINER Himanshu Gupta
# Install cron
RUN apt-get update && apt-get install -y cron
# Add files
ADD run.sh /run.sh
ADD entrypoint.sh /entrypoint.sh
RUN chmod +x /run.sh /entrypoint.sh
ENTRYPOINT /entrypoint.sh
That’s it. Build and run the Docker image!
Here's my docker-compose based solution:
cron:
image: alpine:3.10
command: crond -f -d 8
depends_on:
- servicename
volumes:
- './conf/cron:/etc/crontabs/root:z'
restart: unless-stopped
the lines with cron entries are on the ./conf/cron file.
Note: this won't run commands that aren't in the alpine image.
Also, output of the tasks apparently won't appear in docker logs.
This question have a lot of answers, but some are complicated and another has some drawbacks. I try to explain the problems and try to deliver a solution.
cron-entrypoint.sh:
#!/bin/bash
# copy machine environment variables to cron environment
printenv | cat - /etc/crontab > temp && mv temp /etc/crontab
## validate cron file
crontab /etc/crontab
# cron service with SIGTERM support
service cron start
trap "service cron stop; exit" SIGINT SIGTERM
# just dump your logs to std output
tail -f \
/app/storage/logs/laravel.log \
/var/log/cron.log \
& wait $!
Problems solved
environment variables are not available on cron environment (like env vars or kubernetes secrets)
stop when crontab file is not valid
stop gracefully cron jobs when machine receive an SIGTERM signal
For context, I use previous script on Kubernetes with Laravel app.
this line was the one that helped me run my pre-scheduled task.
ADD mycron/root /etc/cron.d/root
RUN chmod 0644 /etc/cron.d/root
RUN crontab /etc/cron.d/root
RUN touch /var/log/cron.log
CMD ( cron -f -l 8 & ) && apache2-foreground # <-- run cron
--> My project run inside: FROM php:7.2-apache
But: if cron dies, the container keeps running.
When running on some trimmed down images that restrict root access, I had to add my user to the sudoers and run as sudo cron
FROM node:8.6.0
RUN apt-get update && apt-get install -y cron sudo
COPY crontab /etc/cron.d/my-cron
RUN chmod 0644 /etc/cron.d/my-cron
RUN touch /var/log/cron.log
# Allow node user to start cron daemon with sudo
RUN echo 'node ALL=NOPASSWD: /usr/sbin/cron' >>/etc/sudoers
ENTRYPOINT sudo cron && tail -f /var/log/cron.log
Maybe that helps someone
But: if cron dies, the container keeps running.
So, my problem was the same. The fix was to change the command section in the docker-compose.yml.
From
command: crontab /etc/crontab && tail -f /etc/crontab
To
command: crontab /etc/crontab
command: tail -f /etc/crontab
The problem was the '&&' between the commands. After deleting this, it was all fine.
Focusing on gracefully stopping the cronjobs when receiving SIGTERM or SIGQUIT signals (e.g. when running docker stop).
That's not too easy. By default, the cron process just got killed without paying attention to running cronjobs. I'm elaborating on pablorsk's answer:
Dockerfile:
FROM ubuntu:latest
RUN apt-get update \
&& apt-get -y install cron procps \
&& rm -rf /var/lib/apt/lists/*
# Copy cronjobs file to the cron.d directory
COPY cronjobs /etc/cron.d/cronjobs
# Give execution rights on the cron job
RUN chmod 0644 /etc/cron.d/cronjobs
# similarly prepare the default cronjob scripts
COPY run_cronjob.sh /root/run_cronjob.sh
RUN chmod +x /root/run_cronjob.sh
COPY run_cronjob_without_log.sh /root/run_cronjob_without_log.sh
RUN chmod +x /root/run_cronjob_without_log.sh
# Apply cron job
RUN crontab /etc/cron.d/cronjobs
# to gain access to environment variables, we need this additional entrypoint script
COPY entrypoint.sh /entrypoint.sh
RUN chmod +x /entrypoint.sh
# optionally, change received signal from SIGTERM TO SIGQUIT
#STOPSIGNAL SIGQUIT
# Run the command on container startup
ENTRYPOINT ["/entrypoint.sh"]
entrypoint.sh:
#!/bin/bash
# make global environment variables available within crond, too
printenv | grep -v "no_proxy" >> /etc/environment
# SIGQUIT/SIGTERM-handler
term_handler() {
echo 'stopping cron'
service cron stop
echo 'stopped'
echo 'waiting'
x=$(($(ps u -C run_cronjob.sh | wc -l)-1))
xold=0
while [ "$x" -gt 0 ]
do
if [ "$x" != "$xold" ]; then
echo "Waiting for $x running cronjob(s):"
ps u -C run_cronjob.sh
xold=$x
sleep 1
fi
x=$(($(ps u -C run_cronjob.sh | wc -l)-1))
done
echo 'done waiting'
exit 143; # 128 + 15 -- SIGTERM
}
# cron service with SIGTERM and SIGQUIT support
service cron start
trap "term_handler" QUIT TERM
# endless loop
while true
do
tail -f /dev/null & wait ${!}
done
cronjobs
* * * * * ./run_cronjob.sh cron1
*/2 * * * * ./run_cronjob.sh cron2
*/3 * * * * ./run_cronjob.sh cron3
Assuming you wrap all your cronjobs in a run_cronjob.sh script. That way, you can execute arbitrary code for which shutdown will wait gracefully.
run_cronjobs.sh (optional helper script to keep cronjob definitions clean)
#!/bin/bash
DIR_INCL="${BASH_SOURCE%/*}"
if [[ ! -d "$DIR_INCL" ]]; then DIR_INCL="$PWD"; fi
cd "$DIR_INCL"
# redirect all cronjob output to docker
./run_cronjob_without_log.sh "$#" > /proc/1/fd/1 2>/proc/1/fd/2
run_cronjob_without_log.sh
your_actual_cronjob_src()
Btw, when receiving a SIGKILL the container still shut downs immediately. That way you can use a command like docker-compose stop -t 60 cron-container to wait 60s for cronjobs to finish gracefully, but still terminate them for sure after the timeout.
All the answers require root access inside the container because 'cron' itself requests for UID 0.
To request root acces (e.g. via sudo) is against docker best practices.
I used https://github.com/gjcarneiro/yacron to manage scheduled tasks.
I occasionally tried to find a docker-friendly cron implementation. And this last time I tried, I've found a couple.
By docker-friendly I mean, "output of the tasks can be seen in docker logs w/o resorting to tricks."
The most promising I see at the moment is supercronic. It can be fed a crontab file, all while being docker-friendly. To make use of it:
docker-compose.yml:
services:
supercronic:
build: .
command: supercronic crontab
Dockerfile:
FROM alpine:3.17
RUN set -x \
&& apk add --no-cache supercronic shadow \
&& useradd -m app
USER app
COPY crontab .
crontab:
* * * * * date
A gist with a bit more info.
Another good one is yacron, but it uses YAML.
ofelia can be used, but they seem to focus on running tasks in separate containers. Which is probably not a downside, but I'm not sure why I'd want to do that.
And there's also a number of traditional cron implementations: dcron, fcron, cronie. But they come with "no easy way to see output of the tasks."
Just adding to the list of answers that you can also use this image:
https://hub.docker.com/repository/docker/cronit/simple-cron
And use it as a basis to start cron jobs, using it like this:
FROM cronit/simple-cron # Inherit from the base image
#Set up all your dependencies
COPY jobs.cron ./ # Copy your local config
Evidently, it is possible to run cron as a process inside the container (under root user) alongside other processes , using ENTRYPOINT statement in Dockerfile with start.sh script what includes line process cron start. More info here
#!/bin/bash
# copy environment variables for local use
env >> etc/environment
# start cron service
service cron start
# start other service
service other start
#...
If your image doesn't contain any daemon (so it's only the short-running script or process), you may also consider starting your cron from outside, by simply defining a LABEL with the cron information, plus the scheduler itself. This way, your default container state is "exited". If you have multiple scripts, this may result in a lower footprint on your system than having multiple parallel-running cron instances.
See: https://github.com/JaciBrunning/docker-cron-label
Example docker-compose.yaml:
version: '3.8'
# Example application of the cron image
services:
cron:
image: jaci/cron-label:latest
volumes:
- "/var/run/docker.sock:/var/run/docker.sock"
- "/etc/localtime:/etc/localtime:ro"
hello:
image: hello-world
restart: "no"
labels:
- "cron.schedule=* * * * * "
I wanted to share a modification to the typical off of some of these other suggestions that I found more flexible. I wanted to enable changing the cron time with an environment variable and ended up adding an additional script that runs within my entrypoint.sh, but before the call to cron -f
*updatecron.sh*
#!/bin/sh
#remove old cron files
rm -rf /etc/cron.*/*
#create a new formatted cron definition
echo "$crondef [appname] >/proc/1/fd/1 2>/proc/1/fd/2" >> /etc/cron.d/restart-cron
echo \ >> /etc/cron.d/restart-cron
chmod 0644 /etc/cron.d/restart-cron
crontab /etc/cron.d/restart-cron
This removes any existing cron files, creates a new cronfile using an ENV variable of crondef, and then loads it.
Our's was a nodejs application to be run as cron job and it was also dependent on environment variables.
The below solution worked for us.
Docker file:
# syntax=docker/dockerfile:1
FROM node:12.18.1
ENV NODE_ENV=production
COPY ["startup.sh", "./"]
# Removed steps to build the node js application
#--------------- Setup cron ------------------
# Install Cron
RUN apt-get update
RUN apt-get -y install cron
# Run every day at 1AM
#/proc/1/fd/1 2>/proc/1/fd/2 is used to redirect cron logs to standard output and standard error
RUN (crontab -l ; echo "0 1 * * * /usr/local/bin/node /app/dist/index.js > /proc/1/fd/1 2>/proc/1/fd/2") | crontab
#--------------- Start Cron ------------------
# Grant execution rights
RUN chmod 755 startup.sh
CMD ["./startup.sh"]
startup.sh:
!/bin/bash
echo "Copying env variables to /etc/environment so that it is available for cron jobs"
printenv >> /etc/environment
echo "Starting cron"
cron -f
With multiple jobs and various dependencies like zsh and curl, this is a good approach while also combining the best practices from other answers. Bonus: This does NOT require you to set +x execution permissions on myScript.sh, which can be easy to miss in a new environment.
cron.dockerfile
FROM ubuntu:latest
# Install dependencies
RUN apt-get update && apt-get -y install \
cron \
zsh \
curl;
# Setup multiple jobs with zsh and redirect outputs to docker logs
RUN (echo "\
* * * * * zsh -c 'echo "Hello World"' 1> /proc/1/fd/1 2>/proc/1/fd/2 \n\
* * * * * zsh /myScript.sh 1> /proc/1/fd/1 2>/proc/1/fd/2 \n\
") | crontab
# Run cron in forground, so docker knows the task is running
CMD ["cron", "-f"]
Integrate this with docker compose like so:
docker-compose.yml
services:
cron:
build:
context: .
dockerfile: ./cron.dockerfile
volumes:
- ./myScript.sh:/myScript.sh
Keep in mind that you need to docker compose build cron when you change contents of the cron.dockerfile, but changes to myScript.sh will be reflected right away as it's mounted in compose.
I have a dockerfile image based on ubuntu. Iam trying to make a bash script run each day but the cron never runs. When the container is running, i check if cron is running and it is. the bash script works perfectly and the crontab command is well copied inside the container. i can't seem to find where the problem is coming from.
Here is the Dockerfile:
FROM snipe/snipe-it:latest
ENV TZ=America/Toronto
RUN apt-get update \
&& apt-get install awscli -y \
&& apt-get clean \
&& apt-get install cron -y \
&& rm -rf /var/lib/apt/lists/*
RUN mkdir /var/www/html/backups_scripts /var/www/html/config/scripts
COPY config/crontab.txt /var/www/html/backups_scripts
RUN /usr/bin/crontab /var/www/html/backups_scripts/crontab.txt
COPY config/scripts/backups.sh /var/www/html/config/scripts
CMD ["cron","-f"]
The last command CMD doesn't work. And as soon as i remove the cmd command i get this message when i check the cron task inside the container:
root#fcfb6052274a:/var/www/html# /etc/init.d/cron status
* cron is not running
Even if i start the cron process before the crontab, the crontab is still not launched
This dockerfile is called by a docker swarm file (compose file type). Maybe the cron must be activated with the compose file.
How can i tackle this problem ??? Thank you
You need to approach this differently, as you have to remember that container images and containers are not virtual machines. They're a single process that starts and is maintained through its lifecycle. As such, background processes (like cron) don't exist in a container.
What I've seen most people do is have the container just execute whatever you're looking for it to do on a job like do_the_thing.sh and then using the docker run command on on the host machine to call it via cron.
So for sake of argument, let's say you had an image called myrepo/task with a default entrypoint of do_the_thing.sh
On the host, you could add an entry to crontab:
# m h dom mon dow user command
0 */2 * * * root docker run --rm myrepo/task
Then it's down to a question of design. If the task needs files, you can pass them down via volume. If it needs to put something somewhere when it's done, maybe look at blob storage.
I think this question is a duplicate, with a detailed response with lots of upvotes here. I followed the top-most dockerfile example without issues.
Your CMD running cron in the foreground isn't the problem. I ran a quick version of your docker file and exec'ing into the container I could confirm cron was running. Recommend checking how your cron entries in the crontab file are re-directing their output.
Expanding on one of the other answers here a container is actually a lot like a virtual machine, and often they do run many processes concurrently. If you happen to have any other containers running you might be able to see this most easily by running docker stats and looking at the PID column.
Also, easy to examine interactively yourself like this:
$ # Create a simple ubuntu running container named my-ubuntu
$ docker run -it -h my-ubuntu ubuntu
root#my-ubuntu$ ps aw # Shows bash and ps processes running.
root#my-ubuntu$ # Launch a ten minute sleep in the background.
root#my-ubuntu$ sleep 600 &
root#my-ubuntu$ ps aw # Now shows sleep also running.
Im using the docker Mongo container and am attempting to take a backup via a bash script. The script, executed on its own, works fine. I can also see in syslog that cron is running but the command is not showing up. If I open my file with crontab -e, then save and quit (:wq), then restart cron, the job runs fine.
Here is the relevant section of my dockerfile:
ADD mongocron /etc/cron.d/
RUN tr -d '\015' < /etc/cron.d/mongocron > /etc/cron.d/mongocron
#RUN touch /etc/cron.d/mongocron
#RUN echo "* * * * * /db_scripts/MongoDBBackup.sh >> /db_scripts/logs/backup.log\n" > /etc/cron.d/mongocron
RUN crontab /etc/cron.d/mongocron
RUN chmod 0644 /etc/cron.d/mongocron
This is what is in the file mongocron:
* * * * * /db_scripts/MongoDBBackup.sh >> /db_scripts/logs/backup.log
This is the syslog output before resaving:
And here is a picture after:
Restarting cron on its own does not fix it. I have a feeling it has something to do with line endings, so thats why you see the commented out "echo" strategy in the dockerfile with a newline. I have also verified (before saving) that my command does show in when I crontab -l
I've faced this issue too and a missing newline in the end of file was the reason. #opHASnoNAME 's answer is right but when it starts working only after editing, new line is the reason. Your editor just adds it by default.
I was struggling with the same problem in the past.
Here is a working example, tested in the wild, taken from our DevBlog.
FROM ubuntu:latest
ADD start.sh /bin/start.sh
RUN chmod +x /bin/start.sh
# Add crontab file in the cron directory
ADD crontab /etc/cron.d/thecron
# Give execution rights on the cron job
RUN chmod 0644 /etc/cron.d/thecron
# Create the log file to be able to run tail
RUN touch /var/log/cron.log
# start script
CMD /bin/bash /bin/start.sh
The start.sh, think you don't need the part with export of env variables..
# export all environment variables to use in cron
env | sed 's/^\(.*\)$/export \1/g' > /root/envs.sh
chmod +x /root/envs.sh
# Run the command on container startup
cron && tail -f /var/log/cron.log
The Cron file, copied while building the image.
0 1 * * * root . /root/envs.sh;/bin/backup.sh >> /var/log/cron.log 2>&1