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man Dockerfile ADD/COPY/FROM clarify 

Signed-off-by: Sally O'Malley <somalley@redhat.com>
This commit is contained in:
Sally O'Malley 2015-09-03 05:49:19 -04:00 committed by Tibor Vass
parent c90013c460
commit 621debd575
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@ -58,6 +58,8 @@ A Dockerfile is similar to a Makefile.
`FROM image:tag` `FROM image:tag`
`FROM image@digest`
-- The **FROM** instruction sets the base image for subsequent instructions. A -- The **FROM** instruction sets the base image for subsequent instructions. A
valid Dockerfile must have **FROM** as its first instruction. The image can be any valid Dockerfile must have **FROM** as its first instruction. The image can be any
valid image. It is easy to start by pulling an image from the public valid image. It is easy to start by pulling an image from the public
@ -72,8 +74,12 @@ A Dockerfile is similar to a Makefile.
-- If no tag is given to the **FROM** instruction, Docker applies the -- If no tag is given to the **FROM** instruction, Docker applies the
`latest` tag. If the used tag does not exist, an error is returned. `latest` tag. If the used tag does not exist, an error is returned.
-- If no digest is given to the **FROM** instruction, Docker applies the
`latest` tag. If the used tag does not exist, an error is returned.
**MAINTAINER** **MAINTAINER**
-- **MAINTAINER** sets the Author field for the generated images. -- **MAINTAINER** sets the Author field for the generated images.
Useful for providing users with an email or url for support.
**RUN** **RUN**
-- **RUN** has two forms: -- **RUN** has two forms:
@ -114,7 +120,7 @@ A Dockerfile is similar to a Makefile.
CMD command param1 param2 CMD command param1 param2
``` ```
-- There can be only one **CMD** in a Dockerfile. If more than one **CMD** is listed, only -- There should be only one **CMD** in a Dockerfile. If more than one **CMD** is listed, only
the last **CMD** takes effect. the last **CMD** takes effect.
The main purpose of a **CMD** is to provide defaults for an executing container. The main purpose of a **CMD** is to provide defaults for an executing container.
These defaults may include an executable, or they can omit the executable. If These defaults may include an executable, or they can omit the executable. If
@ -150,13 +156,20 @@ A Dockerfile is similar to a Makefile.
the image. the image.
**LABEL** **LABEL**
-- `LABEL <key>[=<value>] [<key>[=<value>] ...]` -- `LABEL <key>[=<value>] [<key>[=<value>] ...]`or
```
LABEL <key>[ <value>]
LABEL <key>[ <value>]
...
```
The **LABEL** instruction adds metadata to an image. A **LABEL** is a The **LABEL** instruction adds metadata to an image. A **LABEL** is a
key-value pair. To include spaces within a **LABEL** value, use quotes and key-value pair. To include spaces within a **LABEL** value, use quotes and
backslashes as you would in command-line parsing. backslashes as you would in command-line parsing.
``` ```
LABEL "com.example.vendor"="ACME Incorporated" LABEL com.example.vendor="ACME Incorporated"
or
LABEL com.example.vendor "ACME Incorporated"
``` ```
An image can have more than one label. To specify multiple labels, separate An image can have more than one label. To specify multiple labels, separate
@ -179,7 +192,7 @@ A Dockerfile is similar to a Makefile.
-- `ENV <key> <value>` -- `ENV <key> <value>`
The **ENV** instruction sets the environment variable <key> to The **ENV** instruction sets the environment variable <key> to
the value `<value>`. This value is passed to all future the value `<value>`. This value is passed to all future
RUN, **ENTRYPOINT**, and **CMD** instructions. This is **RUN**, **ENTRYPOINT**, and **CMD** instructions. This is
functionally equivalent to prefixing the command with `<key>=<value>`. The functionally equivalent to prefixing the command with `<key>=<value>`. The
environment variables that are set with **ENV** persist when a container is run environment variables that are set with **ENV** persist when a container is run
from the resulting image. Use `docker inspect` to inspect these values, and from the resulting image. Use `docker inspect` to inspect these values, and
@ -205,8 +218,11 @@ A Dockerfile is similar to a Makefile.
then they must be relative to the source directory that is being built then they must be relative to the source directory that is being built
(the context of the build). The `<dest>` is the absolute path, or path relative (the context of the build). The `<dest>` is the absolute path, or path relative
to **WORKDIR**, into which the source is copied inside the target container. to **WORKDIR**, into which the source is copied inside the target container.
All new files and directories are created with mode 0755 and with the uid If the `<src>` argument is a local file in a recognized compression format
and gid of **0**. (tar, gzip, bzip2, etc) then it is unpacked at the specified `<dest>` in the
container's filesystem. Note that only local compressed files will be unpacked,
i.e., the URL download and archive unpacking features cannot be used together.
All new directories are created with mode 0755 and with the uid and gid of **0**.
**COPY** **COPY**
-- **COPY** has two forms: -- **COPY** has two forms:
@ -223,8 +239,10 @@ A Dockerfile is similar to a Makefile.
the path to a file or directory relative to the source directory that is the path to a file or directory relative to the source directory that is
being built (the context of the build) or a remote file URL. The `<dest>` is an being built (the context of the build) or a remote file URL. The `<dest>` is an
absolute path, or a path relative to **WORKDIR**, into which the source will absolute path, or a path relative to **WORKDIR**, into which the source will
be copied inside the target container. All new files and directories are be copied inside the target container. If you **COPY** an archive file it will
created with mode **0755** and with the uid and gid of **0**. land in the container exactly as it appears in the build context without any
attempt to unpack it. All new files and directories are created with mode **0755**
and with the uid and gid of **0**.
**ENTRYPOINT** **ENTRYPOINT**
-- **ENTRYPOINT** has two forms: -- **ENTRYPOINT** has two forms:
@ -241,7 +259,7 @@ A Dockerfile is similar to a Makefile.
container that can be run as an executable. When you specify an **ENTRYPOINT**, container that can be run as an executable. When you specify an **ENTRYPOINT**,
the whole container runs as if it was only that executable. The **ENTRYPOINT** the whole container runs as if it was only that executable. The **ENTRYPOINT**
instruction adds an entry command that is not overwritten when arguments are instruction adds an entry command that is not overwritten when arguments are
passed to docker run. This is different from the behavior of CMD. This allows passed to docker run. This is different from the behavior of **CMD**. This allows
arguments to be passed to the entrypoint, for instance `docker run <image> -d` arguments to be passed to the entrypoint, for instance `docker run <image> -d`
passes the -d argument to the **ENTRYPOINT**. Specify parameters either in the passes the -d argument to the **ENTRYPOINT**. Specify parameters either in the
**ENTRYPOINT** JSON array (as in the preferred exec form above), or by using a **CMD** **ENTRYPOINT** JSON array (as in the preferred exec form above), or by using a **CMD**
@ -327,3 +345,4 @@ A Dockerfile is similar to a Makefile.
# HISTORY # HISTORY
*May 2014, Compiled by Zac Dover (zdover at redhat dot com) based on docker.com Dockerfile documentation. *May 2014, Compiled by Zac Dover (zdover at redhat dot com) based on docker.com Dockerfile documentation.
*Feb 2015, updated by Brian Goff (cpuguy83@gmail.com) for readability *Feb 2015, updated by Brian Goff (cpuguy83@gmail.com) for readability
*Sept 2015, updated by Sally O'Malley (somalley@redhat.com)