Tini - A tiny but valid init for containers

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 performingsignal 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 itunusable).
• It ensures that the default signal handlers work for the software you runin your Docker image. For example, with Tini, SIGTERM properly terminatesyour process even if you didn't explicitly install a signal handler for it.
• It does so completely transparently! Docker images that work without Tiniwill 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?.

Using Tini

NOTE: If you are using Docker 1.13 or greater, Tini is included in Dockeritself. This includes all versions of Docker CE. To enable Tini, just pass the--init flag to docker run.

NOTE: There are pre-built Docker images available for Tini. Ifyou're currently using an Ubuntu or CentOS image as your base, you can useone of those as a drop-in replacement.

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

Add Tini to your container, and make it executable. Then, just invoke Tiniand 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 rememberto 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 mightas well always include it to be safe. If you see an error message thatlooks 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 usingyour 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 usingyour 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.Install using the official instructionsor use an AUR helper:

pacaur -S tini

Other Platforms

ARM and 32-bit binaries are available! You can find the complete list ofavailable binaries under the releases tab.

Options

Verbosity

The -v argument can be used for extra verbose output (you can pass it up to3 times, e.g. -vvv).

Subreaping

By default, Tini needs to run as PID 1 so that it can reap zombies (byrunning as PID 1, zombies get re-parented to Tini).

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

NOTE: Tini will issue a warning if it detects that it isn't running as PID 1and 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 maynot be exactly what you want (e.g. if your child exits with 143 after receivingSIGTERM). 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 beinconvenient if sending a signal to that process does not have the desiredeffect. 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 thatevery process in the group gets the signal. This corresponds moreclosely to what happens when you do ctrl-C etc. in a terminal: Thesignal is sent to the foreground process group.

Parent Death Signal

Tini can set its parent death signal, which is the signal Tini should receivewhen its parent exits. To set the parent death signal, use the -p flag withthe name of the signal Tini should receive when its parent exits:

tini -p SIGTERM -- ...

NOTE: See this PR discussion to learn more about the parent death signaland 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 yourcontainer fails to start, you might want to consider using the statically-builtversion 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 weightto 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 runningcmake . && 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 Kernelheaders (< 3.4), Tini will be built with child subreaper support. This isusually what you want if you're going to use Tini with Docker (if your hostKernel supports Docker, it should also support child subreapers).

Understanding Tini

After spawning your process, Tini will wait for signals and forward thoseto the child process, and periodically reap zombie processes that may becreated 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 cancheck your container's exit code to know whether the child exitedsuccessfully).

Debugging

If something isn't working just like you expect, consider increasing theverbosity level (up to 3):

tini -v    -- bash -c 'exit 1'
tini -vv   -- true
tini -vvv  -- pwd

Authors

Maintainer:

• Thomas Orozco

Contributors:

• Tianon Gravi
• David Wragg
• Michael Crosby
• Wyatt Preul
• Patrick Steinhardt

Special thanks to:

• Danilo Bürger for packaging Tini for Alpine
• Asko Soukka for packaging Tini for Nix
• nfnty for packaging Tini for Arch Linux