yacron2 1.0.9

A modern, rootless-container-friendly cron replacement.

yacron2 (Yet Another Cron 2)

A modern, container-friendly cron replacement.

yacron2 is a fork of yacron (byGustavo Carneiro), continuing development from version 0.19.

Features

• "Crontab" is in YAML format
• Builtin sending of Sentry and Mail outputs when cron jobs fail
• Flexible configuration: you decide how to determine if a cron job fails or not
• Designed for running in Docker, Kubernetes, or 12 factor environments:
  • Runs in the foreground
  • Logs everything to stdout/stderr
  • Production-ready for locked-down corporate container platforms: runs as a non-root user, under a restricted seccomp profile, with a read-only root filesystem, an fsGroup-mounted config, and all Linux capabilities dropped — no writable paths or elevated privileges required (see Production container deployment)
• Option to automatically retry failing cron jobs, with exponential backoff
• Optional HTTP REST API, to fetch status and start jobs on demand
• Arbitrary timezone support

Installation

Run with Docker

Prebuilt, multi-architecture (linux/amd64 + linux/arm64) images are published to the GitHub Container Registry on every release. Mount your crontab and go:

docker run --rm \
  -v "$PWD/yacron2tab.yaml:/etc/yacron2.d/yacron2tab.yaml:ro" \
  ghcr.io/ptweezy/yacron2:latest

The image runs as a non-root user and reads its configuration from /etc/yacron2.d by default. For production, pin a specific version instead of latest (e.g. ghcr.io/ptweezy/yacron2:1.0.4) and see Production container deployment for the hardened Kubernetes/Docker setup.

Install using pip

yacron2 requires Python >= 3.13 (for systems with older Python, use the binary instead). It is advisable to install it in a Python virtual environment, for example:

python3 -m venv yacron2env
. yacron2env/bin/activate
pip install yacron2

Install using pipx

pipx automates creating a virtualenv and installing a python program in the newly created virtualenv. It is as simple as:

pipx install yacron2

Install using binary

Alternatively, a self-contained binary can be downloaded from github: https://github.com/ptweezy/yacron2/releases. Every release automatically attaches a binary for both architectures in two libc flavors:

• yacron2-linux-amd64 / yacron2-linux-arm64 — glibc builds for the mainstream distros. They work on any Linux system post glibc 2.39 (e.g. Ubuntu 24.04) on the matching CPU.
• yacron2-linux-amd64-musl / yacron2-linux-arm64-musl — musl builds for Alpine and other musl-based systems.

Python is not required on the target system (it is embedded in the executable):

# pick the asset for your architecture and libc (glibc amd64 shown;
# append -musl on Alpine)
curl -fsSL -o yacron2 \
  https://github.com/ptweezy/yacron2/releases/latest/download/yacron2-linux-amd64
chmod +x yacron2
./yacron2 --version

The standalone binary is a self-extracting executable: on each start it unpacks its embedded Python runtime into a temporary directory and loads shared libraries from there. It therefore needs a temporary directory that is both writable and executable. On an ordinary system the default /tmp already satisfies this, so no extra setup is required.

This only matters when you run the binary under a read-only root filesystem (for example, a hardened container). With the root filesystem read-only, /tmp is read-only too, and the binary aborts at startup — Could not create temporary directory, or Error loading shared library …: Operation not permitted. Give it a small writable and executable temp mount and it runs fine:

# Note `exec`: Docker's --tmpfs defaults to `noexec`, but the binary must be
# able to execute the libraries it unpacks.
docker run --rm --read-only \
  --tmpfs /tmp:rw,exec,nosuid,nodev,size=64m \
  -v "$PWD/yacron2tab.yaml:/etc/yacron2.d/yacron2tab.yaml:ro" \
  your-image-with-the-binary -c /etc/yacron2.d

On Kubernetes, mount an emptyDir at /tmp (an emptyDir is writable and executable by default; use medium: Memory for a tmpfs). Alternatively, point the binary at another writable, executable directory with TMPDIR=/path.

This requirement is unique to the standalone binary. The published container image (and pip/pipx installs) run yacron2 as a normal Python package with the interpreter on disk, so they never self-extract and need no writable temp directory — see Production container deployment.

Production container deployment

yacron2 is built to run unmodified under the hardened security contexts that corporate and enterprise Kubernetes / container platforms enforce. At runtime the daemon only reads its configuration and secrets and writes its output to stdout/stderr — it never needs a writable working directory, temp files, or log files — so it slots cleanly into a locked-down pod:

• Non-root user — yacron2 needs no special privileges to run, so the whole daemon can run as an unprivileged UID. Only the optional per-job user/group switching (see Change to another user/group) requires running as root; if you don't use that feature, drop root entirely.
• Seccomp profile — yacron2 makes no exotic syscalls, so the RuntimeDefault seccomp profile (or an equivalently strict custom profile) works out of the box.
• Read-only root filesystem — no runtime writes are required by the published image (or a pip/pipx install). Mount your crontab config read-only. (If you enable the optional HTTP interface on a Unix socket, point the socket at a small writable emptyDir volume rather than the root filesystem. And if you deploy the standalone binary instead of the image, it additionally needs a small writable, executable temp mount — see Install using binary.)
• fsGroup and dropped capabilities — config and secret volumes can be mounted with an fsGroup so the non-root process can read them, and you can drop all Linux capabilities and forbid privilege escalation.

The published image (ghcr.io/ptweezy/yacron2) is already built this way — non-root, with yacron2 -c /etc/yacron2.d as its entrypoint and no writable paths required — so for most deployments you can use it directly and mount your crontab read-only. If you would rather bake the configuration into your own image, base it on the published image:

FROM ghcr.io/ptweezy/yacron2:latest

# The base image already runs as the non-root user 65534.
COPY yacron2tab.yaml /etc/yacron2.d/yacron2tab.yaml

And a corresponding Kubernetes Deployment with a fully restricted security context:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: yacron2
spec:
  replicas: 1
  selector:
    matchLabels:
      app: yacron2
  template:
    metadata:
      labels:
        app: yacron2
    spec:
      securityContext:           # pod-level
        runAsNonRoot: true
        runAsUser: 65534
        runAsGroup: 65534
        fsGroup: 65534           # lets the non-root process read mounted volumes
        seccompProfile:
          type: RuntimeDefault
      containers:
        - name: yacron2
          image: ghcr.io/ptweezy/yacron2:latest
          args: ["-c", "/etc/yacron2.d"]
          securityContext:       # container-level
            allowPrivilegeEscalation: false
            readOnlyRootFilesystem: true
            capabilities:
              drop:
                - ALL
          resources:
            limits:
              cpu: 200m
              memory: 128Mi
            requests:
              cpu: 10m
              memory: 64Mi
          volumeMounts:
            - name: crontab
              mountPath: /etc/yacron2.d
              readOnly: true
      volumes:
        - name: crontab
          configMap:
            name: yacron2tab

Usage

Configuration is in YAML format. To start yacron2, give it a configuration file or directory path as the -c argument. For example:

yacron2 -c /tmp/my-crontab.yaml

This starts yacron2 (always in the foreground!), reading /tmp/my-crontab.yaml as configuration file. If the path is a directory, any *.yaml or *.yml files inside this directory are taken as configuration files.

Configuration basics

This configuration runs a command every 5 minutes:

jobs:
  - name: test-01
    command: echo "foobar"
    shell: /bin/bash
    schedule: "*/5 * * * *"

The command can be a string or a list of strings. If command is a string, yacron2 runs it through a shell, which is /bin/bash in the above example, but is /bin/sh by default.

If the command is a list of strings, the command is executed directly, without a shell. The ARGV of the command to execute is extracted directly from the configuration:

jobs:
  - name: test-01
    command:
      - echo
      - foobar
    schedule: "*/5 * * * *"

The schedule option can be a string in a crontab format specified by https://github.com/josiahcarlson/parse-crontab (this module is used by yacron2). Additionally @reboot can be included , which will only run the job when yacron2 is initially executed. Further schedule can be an object with properties. The following configuration runs a command every 5 minutes, but only on the specific date 2017-07-19, and doesn't run it in any other date:

jobs:
  - name: test-01
    command: echo "foobar"
    schedule:
      minute: "*/5"
      dayOfMonth: 19
      month: 7
      year: 2017
      dayOfWeek: "*"

Important: by default all time is interpreted to be in UTC, but you can request to use local time instead. For instance, the cron job below runs every day at 19h27 local time because of the utc: false option:

jobs:
  - name: test-01
    command: echo "hello"
    schedule: "27 19 * * *"
    utc: false
    captureStdout: true

Since Yacron2 version 0.11, you can also request that the schedule be interpreted in an arbitrary timezone, using the timezone attribute:

jobs:
  - name: test-01
    command: echo "hello"
    schedule: "27 19 * * *"
    timezone: America/Los_Angeles
    captureStdout: true

You can ask for environment variables to be defined for command execution:

jobs:
  - name: test-01
    command: echo "foobar"
    shell: /bin/bash
    schedule: "*/5 * * * *"
    environment:
      - key: PATH
        value: /bin:/usr/bin

You can also provide an environment file to define environments for command execution:

jobs:
  - name: test-01
    command: echo "foobar"
    shell: /bin/bash
    schedule: "*/5 * * * *"
    env_file: .env

The env file must be a list of KEY=VALUE pairs. Empty lines and lines starting with # will be ignored.

Variables declared in the environment option will override those found in the env_file.

Specifying defaults

There can be a special defaults section in the config. Any attributes defined in this section provide default values for cron jobs to inherit. Although cron jobs can still override the defaults, as needed:

defaults:
    environment:
      - key: PATH
        value: /bin:/usr/bin
    shell: /bin/bash
    utc: false
jobs:
  - name: test-01
    command: echo "foobar"  # runs with /bin/bash as shell
    schedule: "*/5 * * * *"
  - name: test-02  # runs with /bin/sh as shell
    command: echo "zbr"
    shell: /bin/sh
    schedule: "*/5 * * * *"

Note: if the configuration option is a directory and there are multiple configuration files in that directory, then the defaults section in each configuration file provides default options only for cron jobs inside that same file; the defaults have no effect beyond any individual YAML file.

Reporting

Yacron2 has builtin support for reporting jobs failure (more on that below) by email, Sentry and shell command (additional reporting methods might be added in the future):

- name: test-01
  command: |
    echo "hello" 1>&2
    sleep 1
    exit 10
  schedule:
    minute: "*/2"
  captureStderr: true
  onFailure:
    report:
      sentry:
        dsn:
          value: example
          # Alternatively:
          # fromFile: /etc/secrets/my-secret-dsn
          # fromEnvVar: SENTRY_DSN
        fingerprint:  # optional, since yacron2 0.6
          - yacron2
          - "{{ environment.HOSTNAME }}"
          - "{{ name }}"
        extra:
          foo: bar
          zbr: 123
        level: warning
        environment: production
      mail:
        from: [e-mail]
        to: [e-mail]
        smtpHost: 127.0.0.1
        # optional fields:
        username: "username1"  # set username and password to enable login
        password:
          value: example
          # Alternatively:
          # fromFile: /etc/secrets/my-secret-password
          # fromEnvVar: MAIL_PASSWORD
        tls: false  # set to true to enable TLS
        starttls: false  # set to true to enable StartTLS
      shell:
        shell: /bin/bash
        command: ...

Here, the onFailure object indicates that what to do when a job failure is detected. In this case we ask for it to be reported both to sentry and by sending an email.

The captureStderr: true part instructs yacron2 to capture output from the the program's standard error, so that it can be included in the report. We could also turn on standard output capturing via the captureStdout: true option. By default, yacron2 captures only standard error. If a cron job's standard error or standard output capturing is not enabled, these streams will simply write to the same standard output and standard error as yacron2 itself.

Both stdout and stderr stream lines are by default prefixed with [{job_name} {stream_name}], i.e. [test-01 stdout], if for any reason you need to change this, provide the option streamPrefix (new in version 0.16) with your own custom string.

- name: test-01
  command: echo "hello world"
  schedule:
    minute: "*/2"
  captureStdout: true
  streamPrefix: "[{job_name} job]"

In some cases, for instance when you're logging JSON objects you might want to completely get rid of the prefix altogether:

- name: test-01
  command: echo "hello world"
  schedule:
    minute: "*/2"
  captureStdout: true
  streamPrefix: ""

It is possible also to report job success, as well as failure, via the onSuccess option.

- name: test-01
  command: echo "hello world"
  schedule:
    minute: "*/2"
  captureStdout: true
  onSuccess:
    report:
      mail:
        from: [e-mail]
        to: [e-mail]
        smtpHost: 127.0.0.1

Since yacron2 0.5, it is possible to customise the format of the report. For mail reporting, the option subject indicates what is the subject of the email, while body formats the email body. For Sentry reporting, there is only body. In all cases, the values of those options are strings that are processed by the jinja2 templating engine. The following variables are available in templating:

• name(str): name of the cron job
• success(bool): whether or not the cron job succeeded
• stdout(str): standard output of the process
• stderr(str): standard error of the process
• exit_code(int): process exit code
• command(str): cron job command
• shell(str): cron job shell
• environment(dict): subprocess environment variables

Example:

- name: test-01
  command: |
    echo "hello" 1>&2
    sleep 1
    exit 10
  schedule:
    minute: "*/2"
  captureStderr: true
  onFailure:
    report:
      mail:
        from: [e-mail]
        to: [e-mail]
        smtpHost: 127.0.0.1
        subject: Cron job '{{name}}' {% if success %}completed{% else %}failed{% endif %}
        body: |
          {{stderr}}
          (exit code: {{exit_code}})

The shell reporter (since yacron2 0.13) executes a user given shell command in the specified shell. It passes all environment variables from the python executable and specifies some additional ones to inform about the state of the job:

• YACRON2_FAIL_REASON (str)
• YACRON2_FAILED ("1" or "0")
• YACRON2_JOB_NAME (str)
• YACRON2_JOB_COMMAND (str)
• YACRON2_JOB_SCHEDULE (str)
• YACRON2_RETCODE (str)
• YACRON2_STDERR (str)
• YACRON2_STDOUT (str)

A simple example configuration:

- name: test-01
  command: echo "foobar" && exit 123
  shell: /bin/bash
  schedule: "* * * * *"
  onFailure:
    report:
      shell:
        shell: /bin/bash
        command: echo "Error code $YACRON2_RETCODE"

Since yacron2 0.15, it is possible to send emails formatted as html, by adding the html: true property. For example, here the standard output of a shell command is captured and interpreted as html and placed in the email message:

- name: test-01
  command: echo "hello <b>world</b>"
  schedule: "@reboot"
  captureStdout: true
  onSuccess:
    report:
      mail:
        from: [e-mail]
        to: [e-mail], [e-mail]
        html: true
        smtpHost: 127.0.0.1
        smtpPort: 1025
        subject: This is a cron job with html body

Metrics

Yacron2 has builtin support for writing job metrics to Statsd:

jobs:
  - name: test01
    command: echo "hello"
    schedule: "* * * * *"
    statsd:
      host: my-statsd.example.com
      port: 8125
      prefix: my.cron.jobs.prefix.test01

With this config Yacron2 will write the following metrics over UDP to the Statsd listening on my-statsd.example.com:8125:

my.cron.jobs.prefix.test01.start:1|g  # this one is sent when the job starts
my.cron.jobs.prefix.test01.stop:1|g   # the rest are sent when the job stops
my.cron.jobs.prefix.test01.success:1|g
my.cron.jobs.prefix.test01.duration:3|ms|@0.1

Handling failure

By default, yacron2 considers that a job has failed if either the process returns a non-zero code or if it generates output to standard error (and standard error capturing is enabled, of course).

You can instruct yacron2 how to determine if a job has failed or not via the failsWhen option:

failsWhen:
  producesStdout: false
  producesStderr: true
  nonzeroReturn: true
  always: false

producesStdout : If true, any captured standard output causes yacron2 to consider the job as failed. This is false by default.

producesStderr : If true, any captured standard error causes yacron2 to consider the job as failed. This is true by default.

nonzeroReturn : If true, if the job process returns a code other than zero causes yacron2 to consider the job as failed. This is true by default.

always : If true, if the job process exits that causes yacron2 to consider the job as failed. This is false by default.

It is possible to instruct yacron2 to retry failing cron jobs by adding a retry option inside onFailure:

- name: test-01
  command: |
    echo "hello" 1>&2
    sleep 1
    exit 10
  schedule:
    minute: "*/10"
  captureStderr: true
  onFailure:
    report:
      mail:
        from: [e-mail]
        to: [e-mail]
        smtpHost: 127.0.0.1
    retry:
      maximumRetries: 10
      initialDelay: 1
      maximumDelay: 30
      backoffMultiplier: 2

The above settings tell yacron2 to retry the job up to 10 times, with the delay between retries defined by an exponential backoff process: initially 1 second, doubling for every retry up to a maximum of 30 seconds. A value of -1 for maximumRetries will mean yacron2 will keep retrying forever, this is mostly useful with a schedule of "@reboot" to restart a long running process when it has failed.

If the cron job is expected to fail sometimes, you may wish to report only in the case the cron job ultimately fails after all retries and we give up on it. For that situation, you can use the onPermanentFailure option:

- name: test-01
  command: |
    echo "hello" 1>&2
    sleep 1
    exit 10
  schedule:
    minute: "*/10"
  captureStderr: true
  onFailure:
    retry:
      maximumRetries: 10
      initialDelay: 1
      maximumDelay: 30
      backoffMultiplier: 2
  onPermanentFailure:
    report:
      mail:
        from: [e-mail]
        to: [e-mail]
        smtpHost: 127.0.0.1

Concurrency

Sometimes it may happen that a cron job takes so long to execute that when the moment its next scheduled execution is reached a previous instance may still be running. How yacron2 handles this situation is controlled by the option concurrencyPolicy, which takes one of the following values:

Allow : allows concurrently running jobs (default)

Forbid : forbids concurrent runs, skipping next run if previous hasn't finished yet

Replace : cancels currently running job and replaces it with a new one

Execution timeout

(new in version 0.4)

If you have a cron job that may possibly hang sometimes, you can instruct yacron2 to terminate the process after N seconds if it's still running by then, via the executionTimeout option. For example, the following cron job takes 2 seconds to complete, yacron2 will terminate it after 1 second:

- name: test-03
  command: |
    echo "starting..."
    sleep 2
    echo "all done."
  schedule:
    minute: "*"
  captureStderr: true
  executionTimeout: 1  # in seconds

When terminating a job, it is always a good idea to give that job process some time to terminate properly. For example, it may have opened a file, and even if you tell it to shutdown, the process may need a few seconds to flush buffers and avoid losing data.

On the other hand, there are times when programs are buggy and simply get stuck, refusing to terminate nicely no matter what. For this reason, yacron2 always checks if a process exited some time after being asked to do so. If it hasn't, it tries to forcefully kill the process. The option killTimeout option indicates how many seconds to wait for the process to gracefully terminate before killing it more forcefully. In Unix systems, we first send a SIGTERM, but if the process doesn't exit after killTimeout seconds (30 by default) then we send SIGKILL. For example, this cron job ignores SIGTERM, and so yacron2 will send it a SIGKILL after half a second:

- name: test-03
  command: |
    trap "echo '(ignoring SIGTERM)'" TERM
    echo "starting..."
    sleep 10
    echo "all done."
  schedule:
    minute: "*"
  captureStderr: true
  executionTimeout: 1
  killTimeout: 0.5

Change to another user/group

(new in version 0.11)

You can request that Yacron2 change to another user and/or group for a specific cron job. The field user indicates the user (uid or userame) under which the subprocess must be executed. The field group (gid or group name) indicates the group id. If only user is given, the group defaults to the main group of that user. Example:

- name: test-03
  command: id
  schedule:
    minute: "*"
  captureStderr: true
  user: www-data

Naturally, yacron2 must be running as root in order to have permissions to change to another user.

Remote web/HTTP interface

(new in version 0.10)

If you wish to remotely control yacron2, you can optionally enable an HTTP REST interface, with the following configuration (example):

web:
  listen:
     - http://127.0.0.1:8080
     - unix:///tmp/yacron2.sock

Now you have the following options to control it (using HTTPie as example):

Get the version of yacron2

$ http get http://127.0.0.1:8080/version
HTTP/1.1 200 OK
Content-Length: 22
Content-Type: text/plain; charset=utf-8
Date: Sun, 03 Nov 2019 19:48:15 GMT
Server: Python/3.7 aiohttp/3.6.2

0.10.0b3.dev7+g45bc4ce

Get the status of cron jobs

$ http get http://127.0.0.1:8080/status
HTTP/1.1 200 OK
Content-Length: 104
Content-Type: text/plain; charset=utf-8
Date: Sun, 03 Nov 2019 19:44:45 GMT
Server: Python/3.7 aiohttp/3.6.2

test-01: scheduled (in 14 seconds)
test-02: scheduled (in 74 seconds)
test-03: scheduled (in 14 seconds)

You may also get status info in json format:

$ http get http://127.0.0.1:8080/status Accept:application/json
HTTP/1.1 200 OK
Content-Length: 206
Content-Type: application/json; charset=utf-8
Date: Sun, 03 Nov 2019 19:45:53 GMT
Server: Python/3.7 aiohttp/3.6.2

[
    {
        "job": "test-01",
        "scheduled_in": 6.16588,
        "status": "scheduled"
    },
    {
        "job": "test-02",
        "scheduled_in": 6.165787,
        "status": "scheduled"
    },
    {
        "job": "test-03",
        "scheduled_in": 6.165757,
        "status": "scheduled"
    }
]

Start a job right now

Sometimes it's useful to start a cron job right now, even if it's not scheduled to run yet, for example for testing:

$ http post http://127.0.0.1:8080/jobs/test-02/start
HTTP/1.1 200 OK
Content-Length: 0
Content-Type: application/octet-stream
Date: Sun, 03 Nov 2019 19:50:20 GMT
Server: Python/3.7 aiohttp/3.6.2

Includes

(new in version 0.13)

You may have a use case where it's convenient to have multiple config files, and choose at runtime which one to use. In that case, it might be useful if you can put common definitions (such as defaults for reporting, shell, etc.) in a separate file, that is included by the other files.

To support this use case, it is possible to ask one config file to include another one, via the include directive. It takes a list of file names: those files will be parsed as configuration and merged in with this file.

Example, your main config file could be:

include:
  - _inc.yaml

jobs:

  - name: my job
    ...

And your included _inc.yaml file could contain some useful defaults:

defaults:
  shell: /bin/bash
  onPermanentFailure:
    report:
      sentry:
        ...

Custom logging

It's possible to provide a custom logging configuration, via the logging configuration section. For example, the following configuration displays log lines with an embedded timestamp for each message.

logging:
  # In the format of:
  # https://docs.python.org/3/library/logging.config.html#dictionary-schema-details
  version: 1
  disable_existing_loggers: false
  formatters:
    simple:
      format: '%(asctime)s [%(processName)s/%(threadName)s] %(levelname)s (%(name)s): %(message)s'
      datefmt: '%Y-%m-%d %H:%M:%S'
  handlers:
    console:
      class: logging.StreamHandler
      level: DEBUG
      formatter: simple
      stream: ext://sys.stdout
  root:
    level: INFO
    handlers:
      - console

Obscure configuration options

enabled: true|false (default true)

(new in yacron2 0.18)

It is possible to disable a specific cron job by adding a enabled: false option. Jobs with enabled: false will simply be skipped, as if they aren't there, apart from validating the configuration.

jobs:
  - name: test-01
    enabled: false  # this cron job will not run until you change this to `true`
    command: echo "foobar"
    shell: /bin/bash
    schedule: "* * * * *"

Contributing

Development setup, the test/lint/type-check workflow, and the automated release process (including the commit-message marker that triggers a PyPI release) are documented in CONTRIBUTING.md.