minit

The missing init daemon for container

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1. Installation

You can install minit to your own container image by a multi-stage Dockerfile

FROM guoyk/minit:VERSION AS minit
# Or using Github Packages
# FROM ghcr.io/guoyk93/minit:VERSION AS minit

# Your own build stage
FROM ubuntu:22.04

# ...

# Copy minit binary
COPY --from=minit /minit /minit

# Set ENTRYPOINT to minit
ENTRYPOINT ["/minit"]

# Add a unit file to /etc/minit.d
ADD my-service.yml /etc/minit.d/my-service.yml

2. Unit Loading

2.1 From Files

Add Unit YAML files to /etc/minit.d

Override default directory by environment variable MINIT_UNIT_DIR

Use --- to separate multiple units in single YAML file

2.2 From Environment Variable

Example:

ENV MINIT_MAIN="redis-server /etc/redis.conf"
ENV MINIT_MAIN_DIR="/work"
ENV MINIT_MAIN_NAME="main-program"
ENV MINIT_MAIN_GROUP="super-main"
ENV MINIT_MAIN_KIND="cron"
ENV MINIT_MAIN_IMMEDIATE=true
ENV MINIT_MAIN_CRON="* * * * *"
ENV MINIT_MAIN_CHARSET=gbk18030

2.3 From Command Arguments

Example:

ENTRYPOINT ["/minit"]
CMD ["redis-server", "/etc/redis.conf"]

3. Unit Types

3.1 Type: render

render units execute at the very first stage. It renders template files.

See pkg/mtmpl/funcs.go for available functions.

Example:

• /etc/minit.d/render-demo.yaml

kind: render
name: render-demo
files:
  - /opt/*.txt

• /opt/demo.txt

Hello, {{stringsToUpper .Evn.HOME}}

Upon startup, minit will render file /opt/demo.txt

Since default user for container is root, the content of file /opt/demo.txt will become:

Hello, ROOT

3.2 Type: once

once units execute after render units. It runs command once.

Example:

kind: once
name: once-demo
command:
  - echo
  - once

3.3 Type: daemon

daemon units execute after render and once. It runs long-running command.

Example:

kind: daemon
name: daemon-demo
command:
  - sleep
  - 9999

3.4 Type: cron

cron units execute after render and once. It runs command at cron basis.

Example:

kind: cron
name: cron-demo
cron: "* * * * *" # cron expression, support extended syntax by https://github.com/robfig/cron
immediate: true # execute once on started
command:
  - echo
  - cron

4. Unit Features

4.1 Replicas

If count field is set, minit will replicate this unit with sequence number suffixed

Example:

kind: once
name: once-demo-replicas
count: 2
command:
  - echo
  - $MINIT_UNIT_SUB_ID

Is equal to:

kind: once
name: once-demo-replicas-1
command:
  - echo
  - 1
---
kind: once
name: once-demo-replicas-2
command:
  - echo
  - 2

4.2 Logging

Log Files

minit write console logs of every command unit into /var/log/minit

This directory can be overridden by environment MINIT_LOG_DIR

Set MINIT_LOG_DIR=none to disable file logging and optimize performance of minit

Console Encoding

If charset field is set, minit will transcode command console output from other encodings to utf8

Example:

kind: once
name: once-demo-transcode
charset: gbk # supports gbk, gb18030 only
command:
  - command-that-produces-gbk-logs

4.3 Extra Environment Variables

If env field is set, minit will append extra environment variables while launching command.

Example:

kind: daemon
name: daemon-demo-env
env:
  AAA: BBB
command:
  - echo
  - $AAA

4.4 Render Environment Variables

Any environment with prefix MINIT_ENV_ will be rendered before passing to command.

Example:

kind: daemon
name: daemon-demo-render-env
env:
  MINIT_ENV_MY_IP: '{{netResolveIP "google.com"}}'
command:
  - echo
  - $MY_IP

4.5 Using shell in command units

By default, command field will be passed to exec syscall, minit won't modify ti, except simple environment variable substitution.

If shell field is set, command field will act as a simple script file.

Example:

kind: once
name: once-demo-shell
shell: "/bin/bash -eu"
command: # this is merely a script file
  - if [ -n "${HELLO}" ]; then
  - echo "world"
  - fi

4.6 Unit Enabling / Disabling

Grouping

Use group field to set a group name to units.

Default unit group name is default

Allowlist Mode

If environment MINIT_ENABLE is set, minit will run in Allowlist Mode, only units with name existed in MINIT_ENABLE will be loaded.

Use format @group-name to enable a group of units

Use format &daemon to enable a kind of units

Example:

MINIT_ENABLE=once-demo,@demo

Denylist Mode

If environment MINIT_DISABLE is set, minit will run in Denylist Mode, units with name existed in MINIT_DISABLE will NOT be loaded.

Use format @group-name to disable a group of units

Example:

MINIT_DISABLE=once-demo,@demo

5. Extra Features

5.1 Zombie Processes Cleaning

When running as PID 1, minit will do zombie process cleaning

This is the responsibility of PID 1

5.2 Quick Exit

By default, minit will keep running even without daemon or cron units defined.

If you want to use minit in initContainers or outside of container, you can set envrionment variable MINIT_QUIT_EXIT=true to let minit exit as soon as possible

5.3 Resource limits (ulimit)

Warning: this feature need container running at Privileged mode

Use environment variable MINIT_RLIMIT_XXX to set resource limits

• unlimited means no limitation
• - means unchanged

Supported:

MINIT_RLIMIT_AS
MINIT_RLIMIT_CORE
MINIT_RLIMIT_CPU
MINIT_RLIMIT_DATA
MINIT_RLIMIT_FSIZE
MINIT_RLIMIT_LOCKS
MINIT_RLIMIT_MEMLOCK
MINIT_RLIMIT_MSGQUEUE
MINIT_RLIMIT_NICE
MINIT_RLIMIT_NOFILE
MINIT_RLIMIT_NPROC
MINIT_RLIMIT_RTPRIO
MINIT_RLIMIT_SIGPENDING
MINIT_RLIMIT_STACK

Example:

MINIT_RLIMIT_NOFILE=unlimited       # set soft limit and hard limit to 'unlimited'
MINIT_RLIMIT_NOFILE=128:unlimited   # set soft limit to 128，set hard limit to 'unlimited'
MINIT_RLIMIT_NOFILE=128:-           # set soft limit to 128，dont change hard limit
MINIT_RLIMIT_NOFILE=-:unlimited     # don't change soft limit，set hard limit to 'unlimited'

5.4 Kernel Parameters (sysctl)

Warning: this feature need container running at Privileged mode

Use environment variable MINIT_SYSCTL to set kernel parameters

Separate multiple entries with ,

Example:

MINIT_SYSCTL=vm.max_map_count=262144,vm.swappiness=60

5.5 Transparent Huge Page (THP)

Warning: this feature need container running at Privileged mode and host /sys mounted

Use environment variable MINIT_THP to set THP configuration.

Example:

# available values: never, madvise, always
MINIT_THP=madvise

5.6 Built-in WebDAV server

By setting environment variable MINIT_WEBDAV_ROOT, minit will start a built-in WebDAV server at port 7486

Environment Variables:

• MINIT_WEBDAV_ROOT, path to serve, /srv for example
• MINIT_WEBDAV_PORT, port of WebDAV server, default to 7486
• MINIT_WEBDAV_USERNAME and MINIT_WEBDAV_PASSWORD, optional basic auth for WebDAV server

5.7 Banner file

By putting a file at /etc/banner.minit.txt, minit will print it's content at startup

6. Donation

View https://guoyk.xyz/donation

7. Credits

GUO YANKE, MIT License