这样的错误，原因是有另外的 image FROM 了这个 image，
可以使用下面的命令列出所有在指定 image 之后创建的 image 的父 image
docker image inspect --format='{{.RepoTags}} {{.Id}} {{.Parent}}' $(docker image ls -q --filter since=d13c942271d6)
下面是操作过程
➜ ~ docker rmi d1 #删除失败
Error response from daemon: conflict: unable to delete d13c942271d6 (cannot be forced) - image has dependent child images
➜ ~ docker images -a #查看所有镜像
REPOSITORY TAG IMAGE ID CREATED SIZE
auto latest aaaad2136cee 31 minutes ago 1.39 GB
<none> <none> a855a23d8f8a 31 minutes ago 1.39 GB
<none> <none> a92d51f5b441 33 minutes ago 346 MB
<none> <none> a044cd3dbeaa 33 minutes ago 357 MB
<none> <none> 6a197e155f6c 33 minutes ago 346 MB
<none> <none> 917576287796 42 minutes ago 137 MB
<none> <none> 38c89b17d46b 42 minutes ago 72.8 MB
<none> <none> 13811273b8c8 42 minutes ago 72.8 MB
<none> <none> e4f91dddb373 42 minutes ago 72.8 MB
docker.io/ubuntu 20.04 d13c942271d6 2 weeks ago 72.8 MB
➜ ~ docker rmi d1 #删除存在image的镜像（无法删除）
Error response from daemon: conflict: unable to delete d13c942271d6 (cannot be forced) - image has dependent child images
➜ ~ docker image inspect --format='{{.RepoTags}} {{.Id}} {{.Parent}}' $(docker image ls -q --filter since=d13c942271d6)
[auto:latest] sha256:aaaad2136cee268449e335eda580f20bcd772edb8e0367a8022e161d367a3731 sha256:a855a23d8f8a187484f4a2e6d41c313ccede92b384fbe7a3f014f0d0b7bcf4d5
➜ ~ docker rmi aa #查找出所有在指定 image 之后创建的 image 的父 image，可看到是同一个依赖镜像，删除关联的依赖镜像，关联的none镜像也会被删除
Untagged: auto:latest
Deleted: sha256:aaaad2136cee268449e335eda580f20bcd772edb8e0367a8022e161d367a3731
Deleted: sha256:a855a23d8f8a187484f4a2e6d41c313ccede92b384fbe7a3f014f0d0b7bcf4d5
Deleted: sha256:f861416f8e6afedcb19aac097d12ef93da4f6fb8e1ce9fd8dd80194102dfa7af
Deleted: sha256:a044cd3dbeaa603ba9339aee3b9061c233aaf1aad23f3dbb7ad3eeff7774631b
Deleted: sha256:28d3b1bbfbc35ccd9f603e7f13da383d3672db44fa2b13378dec9c4ac605db09
Deleted: sha256:a92d51f5b441f2d3432e9d96a79cd09a66f81b450125ccde70d0797d9ab84278
Deleted: sha256:6a197e155f6c08986187271e9530922b5970c89b276b2cdc30323cc7837d9a19
Deleted: sha256:4ba15559469dd758f2fe5ca39d4d279f52c863371ee506829193fc6f0ddd21be
Deleted: sha256:91757628779692545c1dca515a6625bd75e8b3e0735400722e1865b0602fd54f
Deleted: sha256:1f24416adf6beac08ede0b89e22e24c4333d90430240b7e717b1265bea78e85f
Deleted: sha256:38c89b17d46bc441a9942c025d77bd88e947bb156edc9696cd55af98dfda9f7e
Deleted: sha256:13811273b8c89bcf33b1f0c92f933fe0bbfd21100d4c55e5c0c056194f594052
Deleted: sha256:e4f91dddb37307ed30e844afa9f7f07c0e38623e7591d68946eba018ec48b6b5
➜ ~ docker images -a #再次查看镜像列表，相关镜像已经删除
REPOSITORY TAG IMAGE ID CREATED SIZE
docker.io/ubuntu 20.04 d13c942271d6 2 weeks ago 72.8 MB