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https://github.com/krallin/tini

A tiny but valid `init` for containers
https://github.com/krallin/tini

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A tiny but valid `init` for containers

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Tini - A tiny but valid `init` for containers

=============================================



[![Build Status](https://travis-ci.org/krallin/tini.svg?branch=master)](https://travis-ci.org/krallin/tini)



Tini is the simplest `init` you could think of.



All Tini does is spawn a single child (Tini is meant to be run in a container),

and wait for it to exit all the while reaping zombies and performing

signal forwarding.



Why Tini?

---------



Using Tini has several benefits:



- It protects you from software that accidentally creates zombie processes,

  which can (over time!) starve your entire system for PIDs (and make it

  unusable).

- It ensures that the *default signal handlers* work for the software you run

  in your Docker image. For example, with Tini, `SIGTERM` properly terminates

  your process even if you didn't explicitly install a signal handler for it.

- It does so completely transparently! Docker images that work without Tini

  will work with Tini without any changes.



If you'd like more detail on why this is useful, review this issue discussion:

[What is advantage of Tini?][0].



Using Tini

----------



*NOTE: If you are using Docker 1.13 or greater, Tini is included in Docker

itself. This includes all versions of Docker CE. To enable Tini, just [pass the

`--init` flag to `docker run`][5].*



*NOTE: There are [pre-built Docker images available for Tini][10]. If

you're currently using an Ubuntu or CentOS image as your base, you can use

one of those as a drop-in replacement.*



*NOTE: There are Tini packages for Alpine Linux and NixOS. See below for

installation instructions.*



Add Tini to your container, and make it executable. Then, just invoke Tini

and pass your program and its arguments as arguments to Tini.



In Docker, you will want to use an entrypoint so you don't have to remember

to manually invoke Tini:



    # Add Tini

    ENV TINI_VERSION v0.19.0

    ADD https://github.com/krallin/tini/releases/download/${TINI_VERSION}/tini /tini

    RUN chmod +x /tini

    ENTRYPOINT ["/tini", "--"]



    # Run your program under Tini

    CMD ["/your/program", "-and", "-its", "arguments"]

    # or docker run your-image /your/program ...



Note that you *can* skip the `--` under certain conditions, but you might

as well always include it to be safe. If you see an error message that

looks like `tini: invalid option -- 'c'`, then you *need* to add the `--`.



Arguments for Tini itself should be passed like `-v` in the following example:

`/tini -v -- /your/program`.



*NOTE: The binary linked above is a 64-bit dynamically-linked binary.*



### Signed binaries ###



The `tini` and `tini-static` binaries are signed using the key `595E85A6B1B4779EA4DAAEC70B588DFF0527A9B7`.



You can verify their signatures using `gpg` (which you may install using

your package manager):



    ENV TINI_VERSION v0.19.0

    ADD https://github.com/krallin/tini/releases/download/${TINI_VERSION}/tini /tini

    ADD https://github.com/krallin/tini/releases/download/${TINI_VERSION}/tini.asc /tini.asc

    RUN gpg --batch --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys 595E85A6B1B4779EA4DAAEC70B588DFF0527A9B7 \

     && gpg --batch --verify /tini.asc /tini

    RUN chmod +x /tini



### Verifying binaries via checksum ###



The `tini` and `tini-static` binaries have generated checksums (`SHA1` and `SHA256`).



You can verify their checksums using `sha1sum` and `sha256sum` (which you may install using

your package manager):



    ENV TINI_VERSION v0.19.0

    RUN wget --no-check-certificate --no-cookies --quiet https://github.com/krallin/tini/releases/download/${TINI_VERSION}/tini-amd64 \

        && wget --no-check-certificate --no-cookies --quiet https://github.com/krallin/tini/releases/download/${TINI_VERSION}/tini-amd64.sha256sum \

        && echo "$(cat tini-amd64.sha256sum)" | sha256sum -c



### Alpine Linux Package ###



On Alpine Linux, you can use the following command to install Tini:



    RUN apk add --no-cache tini

    # Tini is now available at /sbin/tini

    ENTRYPOINT ["/sbin/tini", "--"]



### NixOS ###



Using Nix, you can use the following command to install Tini:



    nix-env --install tini



### Debian ###



On Debian (Buster or newer), you can use the following command to install Tini:



    apt-get install tini



Note that this installs `/usr/bin/tini` (and `/usr/bin/tini-static`), not `/tini`.



### Arch Linux ###



On Arch Linux, there is a package available on the [AUR](https://wiki.archlinux.org/index.php/Arch_User_Repository).

Install using the [official instructions](https://wiki.archlinux.org/index.php/Arch_User_Repository#Installing_packages)

or use an [AUR helper](https://wiki.archlinux.org/index.php/AUR_helpers):



    pacaur -S tini



### Other Platforms ###



ARM and 32-bit binaries are available! You can find the complete list of

available binaries under [the releases tab][11].



Options

-------



### Verbosity ###



The `-v` argument can be used for extra verbose output (you can pass it up to

3 times, e.g. `-vvv`).



### Subreaping ###



By default, Tini needs to run as PID 1 so that it can reap zombies (by

running as PID 1, zombies get re-parented to Tini).



If for some reason, you cannot run Tini as PID 1, you should register Tini as

a process subreaper instead (only in Linux >= 3.4), by either:



  + Passing the `-s` argument to Tini (`tini -s -- ...`)

  + Setting the environment variable `TINI_SUBREAPER`

    (e.g. `export TINI_SUBREAPER=`).



This will ensure that zombies get re-parented to Tini despite Tini not running

as PID 1.



*NOTE: Tini will issue a warning if it detects that it isn't running as PID 1

and isn't registered as a subreaper. If you don't see a warning, you're fine.*



### Remapping exit codes ###



Tini will reuse the child's exit code when exiting, but occasionally, this may

not be exactly what you want (e.g. if your child exits with 143 after receiving

SIGTERM). Notably, this can be an issue with Java apps.



In this case, you can use the `-e` flag to remap an arbitrary exit code to 0.

You can pass the flag multiple times if needed.



For example:



```

tini -e 143 -- ...

```



### Process group killing ###



By default, Tini only kills its immediate child process.  This can be

inconvenient if sending a signal to that process does not have the desired

effect.  For example, if you do



    docker run krallin/ubuntu-tini sh -c 'sleep 10'



and ctrl-C it, nothing happens: SIGINT is sent to the 'sh' process,

but that shell won't react to it while it is waiting for the 'sleep'

to finish.



With the `-g` option, Tini kills the child process group , so that

every process in the group gets the signal. This corresponds more

closely to what happens when you do ctrl-C etc. in a terminal: The

signal is sent to the foreground process group.



### Parent Death Signal ###



Tini can set its parent death signal, which is the signal Tini should receive

when *its* parent exits. To set the parent death signal, use the `-p` flag with

the name of the signal Tini should receive when its parent exits:



```

tini -p SIGTERM -- ...

```



*NOTE: See [this PR discussion][12] to learn more about the parent death signal

and use cases.*



More

----



### Existing Entrypoint ###



Tini can also be used with an existing entrypoint in your container!



Assuming your entrypoint was `/docker-entrypoint.sh`, then you would use:



    ENTRYPOINT ["/tini", "--", "/docker-entrypoint.sh"]



### Statically-Linked Version ###



Tini has very few dependencies (it only depends on libc), but if your

container fails to start, you might want to consider using the statically-built

version instead:



    ADD https://github.com/krallin/tini/releases/download/${TINI_VERSION}/tini-static /tini



### Size Considerations ###



Tini is a very small file (in the 10KB range), so it doesn't add much weight

to your container.



The statically-linked version is bigger, but still < 1M.



Building Tini

-------------



If you'd rather not download the binary, you can build Tini by running

`cmake . && make`.



Before building, you probably also want to run:



    export CFLAGS="-DPR_SET_CHILD_SUBREAPER=36 -DPR_GET_CHILD_SUBREAPER=37"



This ensure that even if you're building on a system that has old Linux Kernel

headers (< 3.4), Tini will be built with child subreaper support. This is

usually what you want if you're going to use Tini with Docker (if your host

Kernel supports Docker, it should also support child subreapers).



Understanding Tini

------------------



After spawning your process, Tini will wait for signals and forward those

to the child process, and periodically reap zombie processes that may be

created within your container.



When the "first" child process exits (`/your/program` in the examples above),

Tini exits as well, with the exit code of the child process (so you can

check your container's exit code to know whether the child exited

successfully).



Debugging

---------



If something isn't working just like you expect, consider increasing the

verbosity level (up to 3):



    tini -v    -- bash -c 'exit 1'

    tini -vv   -- true

    tini -vvv  -- pwd



Authors

=======



Maintainer:



  + [Thomas Orozco][20]



Contributors:



  + [Tianon Gravi][30]

  + [David Wragg][31]

  + [Michael Crosby][32]

  + [Wyatt Preul][33]

  + [Patrick Steinhardt][34]



Special thanks to:



  + [Danilo Bürger][40] for packaging Tini for Alpine

  + [Asko Soukka][41] for packaging Tini for Nix

  + [nfnty][42] for packaging Tini for Arch Linux



  [0]: https://github.com/krallin/tini/issues/8

  [5]: https://docs.docker.com/engine/reference/commandline/run/

  [10]: https://github.com/krallin/tini-images

  [11]: https://github.com/krallin/tini/releases

  [12]: https://github.com/krallin/tini/pull/114

  [20]: https://github.com/krallin/

  [30]: https://github.com/tianon

  [31]: https://github.com/dpw

  [32]: https://github.com/crosbymichael

  [33]: https://github.com/geek

  [34]: https://github.com/pks-t

  [40]: https://github.com/danilobuerger

  [41]: https://github.com/datakurre

  [42]: https://github.com/nfnty/pkgbuilds/tree/master/tini/tini