Docker PHP映像助手和构建依赖项

Question

This directive is from the description of the official docker php image :

RUN apt-get update && apt-get install -y \
        libfreetype6-dev \
        libjpeg62-turbo-dev \
        libmcrypt-dev \
        libpng12-dev \
    && docker-php-ext-install -j$(nproc) iconv mcrypt \
    && docker-php-ext-configure gd --with-freetype-dir=/usr/include/ --with-jpeg-dir=/usr/include/ \
    && docker-php-ext-install -j$(nproc) gd

I have two questions:

1. What are the packages with the -dev suffix for? How do I know I need them and which ones in particular?
2. What is -j$(nproc) ?

Answer 1

The -dev indicates that the package contains headers and libraries that you can use to link and then compile in another application or library in this case it would be iconv using mcrypt and gd using freetype , jpeg62-turbo , and png12 .

The -j$(nproc) command is letting the installer know how many processors make has available in the build cycle.

Answer 2

1. The packages with the -dev suffix are development files for different libraries. These are likely required to build one or more PHP extensions. For example, Googleing for libjpeg62-turbo-dev shows that it's "development files for the libjpeg-turbo library." PHP will use this library in some of it's image handling functions: http://php.net/manual/en/image.installation.php . You should keep them if you want the functions that require them to work properly. I'd just leave all of them, unless you're really trying to optimize for small size or something.

2. -j$(nproc) is asking it to install extensions in parallel according to the number of processors available.