为什么docker无法将COPY文件构建到/dev文件夹? [英] Why can't docker build COPY files to the /dev folder?

问题描述

我想创建一个docker镜像，在其中将文件添加到/dev 文件夹.我正在使用这个 Dockerfile :

I want to create a docker image where I add a file to the /dev folder. I'm using this Dockerfile:

FROM ubuntu:bionic
COPY test.txt /dev/

使用以下方法构建此对象后:

After building this with:

docker build -t test .

我得到一个Docker映像，其中没有将任何内容添加到/dev 文件夹中. docker build 没有引发任何错误.

I get a docker image where nothing has been added to the /dev folder. No error has been thrown by docker build.

我发现这很奇怪，因为复制到其他文件夹可以正常工作.例如

I find this very strange because copying to different folders works fine. For example

• COPY test.txt/
• COPY test.txt/root/
• COPY test.txt/home/

一切正常.

/dev 文件夹是否具有某些特殊权限?如何将文件复制到/dev 文件夹?

Does the /dev folder have some special permissions? How do I copy a file to the /dev folder?

我正在使用 Windows上的Docker工具箱.

推荐答案

/dev 是linux系统上的一个特殊文件夹，保留用于维护与设备相关的资源(文件系统，磁盘等).并安装在特殊的文件系统上.在docker容器中，它将使用tmpfs专用文件系统重新安装，而不位于主容器文件系统(/)上.请参见以下示例:

/dev is a special folder on linux systems reserved to maintain the devices related ressources (filesystem, disks, etc...) and mounted on a special filesystem. In a docker container, it will be remounted with a tmpfs dedicated filesystem and is not on the main container filesystem (/). See the following example:

$ docker run -it --rm ubuntu:18.04
root@17b9ad96ccbc:/# df -h /dev/
Filesystem      Size  Used Avail Use% Mounted on
tmpfs            64M     0   64M   0% /dev

在您的情况下，您的文件实际上是在构建过程中复制的，但是在一个临时文件系统中，该文件系统在构建完成后就失效了.

In your case, your file was actually copied during the build but in a temporary filesystem that died as soon as the build was finished.

结论:不要将/dev 用作目标，请选择其他文件夹.

Conclusion: don't use /dev as a destination, choose an other folder.

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