[5.8]alexander@MacBook-Air-Alexander:~/Dockerfiles> docker build -t dockerfile .
[+] Building 0.3s (6/8)
 => [internal] load build definition from Dockerfile                                                                                                                               0.0s
 => => transferring dockerfile: 84B                                                                                                                                                0.0s
 => [internal] load .dockerignore                                                                                                                                                  0.0s
 => => transferring context: 2B                                                                                                                                                    0.0s
 => [internal] load metadata for docker.io/library/ubuntu:latest                                                                                                                   0.0s
 => [1/5] FROM docker.io/library/ubuntu:latest                                                                                                                                     0.0s
 => CACHED [2/5] RUN apt update &&     apt install -y openjdk-8-jdk &&     apt install -y openssh-server sudo -y                                                                   0.0s
 => ERROR [3/5] RUN useradd -rm -d /home/ubuntu -s /bin/bash -g root -G sudo -u 1000 test1                                                                                         0.2s
------
 > [3/5] RUN useradd -rm -d /home/ubuntu -s /bin/bash -g root -G sudo -u 1000 test1:
#6 0.178 useradd: UID 1000 is not unique
------
executor failed running [/bin/sh -c useradd -rm -d /home/ubuntu -s /bin/bash -g root -G sudo -u 1000 test1]: exit code: 4
[5.8]{1}alexander@MacBook-Air-Alexander:~/Dockerfiles> nano Dockerfile
[5.8]alexander@MacBook-Air-Alexander:~/Dockerfiles> docker build -t dockerfile .
[+] Building 0.2s (6/8)
 => [internal] load build definition from Dockerfile                                                                                                                               0.0s
 => => transferring dockerfile: 538B                                                                                                                                               0.0s
 => [internal] load .dockerignore                                                                                                                                                  0.0s
 => => transferring context: 2B                                                                                                                                                    0.0s
 => [internal] load metadata for docker.io/library/ubuntu:latest                                                                                                                   0.0s
 => [1/5] FROM docker.io/library/ubuntu:latest                                                                                                                                     0.0s
 => CACHED [2/5] RUN apt update &&     apt install -y openjdk-8-jdk &&     apt install -y openssh-server sudo -y                                                                   0.0s
 => ERROR [3/5] RUN useradd -rm -d /home/ubuntu -s /bin/bash -g root -G sudo -u 1000 test                                                                                          0.2s
------
 > [3/5] RUN useradd -rm -d /home/ubuntu -s /bin/bash -g root -G sudo -u 1000 test:
#6 0.174 useradd: user 'test' already exists
------
executor failed running [/bin/sh -c useradd -rm -d /home/ubuntu -s /bin/bash -g root -G sudo -u 1000 test]: exit code: 9