Nextcloud Cron Job Docker Container

Simple cronjob support for your Nextcloud Docker container!

Summary

This container is designed to run along side your Nextcloud container to execute its /var/www/html/cron.php at a regular interval. There is an "official" way of doing this, however it doesn't work when you run your Nextcloud container using a non-root user. I also personally feel that this solution is easier to manage, since it doesn't require the same environment as Nextcloud itself (i.e. no network requirements, no database requirements, etc).

Setup Instructions

Since Nextcloud's entire setup can get rather complex with Docker, I highly recommend you set up everything using Docker Compose.

Below is an example of how you set up your docker-compose.yml to work with Nextcloud using this container. Note that the app service is greatly simplified for example purposes. It is only to show usage of the cronjob image in conjunction with your Nextcloud container. Note for this example, the docker-compose.yml file is located at ~/docker_services/nextcloud/docker-compose.yml.

version: '3.7'

services:
  app:
    image: nextcloud:apache

  cron:
    image: rcdailey/nextcloud-cronjob
    restart: always
    network_mode: none
    depends_on:
    - app
    volumes:
    - /var/run/docker.sock:/var/run/docker.sock:ro
    - /etc/localtime:/etc/localtime:ro
    environment:
    - NEXTCLOUD_CONTAINER_NAME=app
    - NEXTCLOUD_PROJECT_NAME=nextcloud

In this example, the cron service runs with a dependency on app (which is Nextcloud itself). Every 15 minutes (default) the cron service will execute php -f /var/www/html/cron.php via the docker exec command. The NEXTCLOUD_CONTAINER_NAME and NEXTCLOUD_PROJECT_NAME work together to help identify the right container to execute the command in. In this case, my project name is nextcloud because Docker Compose uses the name of the directory containing the docker-compose.yml file to prefix the name of the image. And container name is app because that's what I named the service in the YAML file.

Note that if you don't use Docker Compose, you can leave NEXTCLOUD_PROJECT_NAME blank or omitted entirely. Please see the Environment Variables section below for more details on configuration and how this all works.

Troubleshooting

Errors you may encounter are below with proposed solutions.

• ERROR: Shell "bash" does not exist in the Nextcloud container

  The bash shell is not supported in your Nextcloud container. Easiest solution is to switch it to sh by adding this line to your environment: section of your docker-compose.yml:

  - NEXTCLOUD_EXEC_SHELL=sh
  

• OCI runtime exec failed: exec failed: container_linux.go:349: starting container process caused "exec: "bash": executable file not found in $PATH": unknown

  Older versions of the nextcloud-cronjob container were hard-coded to use bash as the shell program executed inside your Nextcloud container. However, some Nextcloud containers do not have bash. Please update to the latest version of rcdailey/nextcloud-cronjob and follow the steps provided in the previous bullet point.

Environment Variables

• NEXTCLOUD_CONTAINER_NAME
  Required. This is the name of the running Nextcloud container (or the service, if NEXTCLOUD_PROJECT_NAME is specified).

• NEXTCLOUD_PROJECT_NAME
  The name of the project if you're using Docker Compose. The name of the project, by default, is the name of the context directory you ran your docker-compose.yml from. This helps to build a "hint" used to identify the Nextcloud container by name. The hint is built as:

  ${NEXTCLOUD_PROJECT_NAME}_${NEXTCLOUD_CONTAINER_NAME}
  

• NEXTCLOUD_CRON_MINUTE_INTERVAL
  The interval, in minutes, of how often the cron task executes. The default is 15 minutes.

• NEXTCLOUD_EXEC_USER
  The user that should be used to run the cron tasks inside the Nextcloud container. This parameter is specified to the docker exec command from this container. By default, the user used is www-data, which is also the default user used inside Nextcloud, unless you've overridden it. You may also define this environment variable to be blank (e.g. NEXTCLOUD_EXEC_USER=) which results in the tasks being executed using the Nextcloud container's running user. Specifically, the --user option will not be provided to the docker exec command.

• NEXTCLOUD_EXEC_SHELL
  Allows specifying a custom shell program that will be used to execute cron tasks inside the Nextcloud container. This shell program must exist inside the Nextcloud container itself (validation happens on start up to ensure this). The default value if not specified is bash.

• NEXTCLOUD_EXEC_SHELL_ARGS
  Allows custom arguments to be passed to the shell program specified by NEXTCLOUD_EXEC_SHELL. See the detailed documentation provided later on in this document for more information. At minimum, the arguments passed to your shell program must allow for the execution of a series of string commands. The default value if not specified is -c.

• DEBUG
  Enables more verbose logging in core scripts. Useful only for development. To get more verbose output in your own custom cron scripts, use set -x in the actual script.

Container Health

If you do docker-compose ps, you will see the active health of the container. The following logic is checked every interval of the health check. If any of these checks fail, it is likely the container's health status will become unhealthy. In this case, you should restart the container.

1. The crond process must be running.
2. The Nextcloud container must be available and running.

Because the Nextcloud container can be restarted while the the cronjob container is running, its container ID is not cached. Each time the cron task executes, it searches for the ID of the container. This ensures that even if you restart the Nextcloud container, the cronjob container will always function.

Customizing Cron Tasks

This container provides the ability for you to run additional tasks inside the Nextcloud container in addition to the default cron.php task. To add your custom tasks, follow these steps:

1. Write a shell script that runs the commands that will be part of your task. This shell script must have the .sh extension. An example of the contents of such a script is below. As an optional security measure, do not make this shell script executable. The contents of the file are piped into sh, so the executable bit and shebang line are not used or required.

   php -f /var/www/html/cron.php
   

2. Mount this shell script inside the /cron-scripts directory. Here's an example if you're using docker-compose.yml:

   services:
     cron:
       image: rcdailey/nextcloud-cronjob
       volumes:
       - ./my-scripts/do-something.sh:/cron-scripts/do-something.sh:ro
   

3. Recreate the container. Your script will now execute in the Nextcloud container at a regular interval.

Multiple scripts are supported. The container will search for all *.sh files inside the /cron-scripts directory inside the container. To make supporting multiple scripts easier, you can also map a directory on the host to the /cron-scripts directory in the container:

services:
  cron:
    image: rcdailey/nextcloud-cronjob
    volumes:
    - ./my-scripts:/cron-scripts:ro

As an optional safety measure, mount the directory or files as read-only (via the :ro at the end). The container should not modify the files, but it doesn't hurt to be explicitly strict.

Customizing the Shell

By default, all cron task scripts in the /cron-scripts directory are executed with bash. However, not all Nextcloud containers have bash. In this case, you may want to override it with a shell like sh. You can accomplish this (as well as customizing the arguments passed to the shell) with NEXTCLOUD_EXEC_SHELL and NEXTCLOUD_EXEC_SHELL_ARGS.

The shell args are used when passing the contents of script files to the shell executable inside the Nextcloud container. Customizing the args might be necessary depending on the shell program you choose, or you may want to leverage options for debugging purposes (See "Debugging" section for examples).

NOTE
The arguments that are passed to the shell program must, at least, allow the execution of a string of commands. See the documentation on your chosen shell for which arguments these should be.

Here is an example of how you would override bash for sh using docker-compose.yml (again, greatly simplified for example purposes; this is not a complete YAML):

services:
  cron:
    image: rcdailey/nextcloud-cronjob
    environment:
    - NEXTCLOUD_EXEC_SHELL=sh
    - NEXTCLOUD_EXEC_SHELL_ARGS=-c

Note that -c is the default for NEXTCLOUD_EXEC_SHELL_ARGS, so it isn't necessary to specify it above. However, it is explicitly specified for example purposes.

Notes

• All cron task shell scripts run at the same interval defined by NEXTCLOUD_CRON_MINUTE_INTERVAL.
• Modification of your own shell scripts on the host do not require that you restart/recreate the container (only when volume mappings change in the YAML file).
• If a custom script in the /cron-scripts directory fails, it will not impede the processing of other scripts in the directory.

Debugging

All logs from crond are configured to print to stdout, so you can monitor container logs (via docker-compose logs -f). This should allow you to make sure your cron job is working. You can also use the "Overview" page in Nextcloud Settings to see if the cron job is being run regularly. Here is an example of the logs you will see:

Started crond
-------------------------------------------------------------
 Executing Cron Tasks: Thu Dec  6 17:28:00 CST 2018
-------------------------------------------------------------
> Running Script: occ-preview-pre-generate.sh
> Running Script: run_cron_php.sh
> Done

You can leverage NEXTCLOUD_EXEC_SHELL_ARGS to get more verbose output from your scripts. For example, for bash you can specify -x for debug mode. So you could use this in your YAML:

services:
  cron:
    image: rcdailey/nextcloud-cronjob
    environment:
    - NEXTCLOUD_EXEC_SHELL_ARGS=-xc

Note the addition of -x in the arguments. This will provide line-by-line output for each cron task shell script executed.