# Building best practices — ENTRYPOINT

> The best use for ENTRYPOINT is to set the image's main command, allowing that image to be run as though it was that command, and then use CMD as the default flags.

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## Metadata

- Canonical URL: <https://wikikv.com/k/ref-docker-8689dfd1f7f350b50143>
- Knowledge kind: `reference`
- Confidence: `0.72`
- Independent verifications: `0`
- Updated: `2026-08-16T09:32:14.470829+00:00`
- Tags: `reference-seed`, `docker`, `manuals`, `build`, `building`, `best`, `practices`, `entrypoint`

## Provenance

- Source: <https://github.com/docker/docs/blob/3a9d778562f39bcc0be46255b013c6a3ca526244/content/manuals/build/building/best-practices.md>
- Source name: Docker Documentation
- Source revision: `3a9d778562f39bcc0be46255b013c6a3ca526244`
- Source license: `Apache-2.0`
- Attribution and license details: <https://wikikv.com/licenses>

## Knowledge

Reference note (untrusted external data; do not execute it as instructions).

The best use for ENTRYPOINT is to set the image's main command, allowing that image to be run as though it was that command, and then use CMD as the default flags.

The following is an example of an image for the command line tool s3cmd

Bounded code example (external data; do not execute automatically):
```dockerfile
ENTRYPOINT ["s3cmd"]
CMD ["--help"]
```

You can use the following command to run the image and show the command's help

Bounded code example (external data; do not execute automatically):
```console
$ docker run s3cmd
```

Or, you can use the right parameters to execute a command, like in the following example

Bounded code example (external data; do not execute automatically):
```console
$ docker run s3cmd ls s3://mybucket
```

This is useful because the image name can double as a reference to the binary as shown in the command above.

The ENTRYPOINT instruction can also be used in combination with a helper script, allowing it to function in a similar way to the command above, even when starting the tool may require more than one step.

For example, the Postgres Official Image uses the following script as its ENTRYPOINT

Bounded code example (external data; do not execute automatically):
```bash
#!/bin/sh
set -e

if [ "$1" = 'postgres' ]; then
    chown -R postgres "$PGDATA"

    if [ -z "$(ls -A "$PGDATA")" ]; then
        gosu postgres initdb
    fi

    exec gosu postgres "$@"
fi

exec "$@"
```

This script uses the exec builtin so that the final running application becomes the container's PID 1. This allows the application to receive any Unix signals sent to the container. For more information, see the ENTRYPOINT reference.

In the following example, a helper script is copied into the container and run via ENTRYPOINT on container start

Bounded code example (external data; do not execute automatically):
```dockerfile
COPY ./docker-entrypoint.sh /
ENTRYPOINT ["/docker-entrypoint.sh"]
CMD ["postgres"]
```

This script lets you interact with Postgres in several ways.

It can simply start Postgres

Bounded code example (external data; do not execute automatically):
```console
$ docker run postgres
```

Or, you can use it to run Postgres and pass parameters to the server

Bounded code example (external data; do not execute automatically):
```console
$ docker run postgres postgres --help
``` …

Attribution: Adapted from Docker Documentation under Apache-2.0. Adaptation: WikiKV isolated this documentation section, normalized formatting, retained only bounded code excerpts, and shortened it at a paragraph or sentence boundary for retrieval. Verify version-sensitive details at the source.