基于centos的rootfs 创建自己的base image

[root@localhost ~]# cat welcome.sh
#!/bin/bash
echo -e "\033[1;32;40mUSAGE:\nYou can override the environment 'USERNAME' with your favorite name.\nAlso,you can override the instruction value of 'CMD' with any available commands in the system by format '-c COMMAND'.\033[0m"
export USERNAME
if [[ -z $USERNAME ]];then
        export USERNAME="Private_PandaEye"
fi
echo -e "\nWelcome to the Docker World,$USERNAME.\n"
[root@localhost ~]#

[root@localhost ~]# cat dockerfile
#This is the 1st dockerfile for study dockerfile syntax.
FROM scratch
MAINTAINER  PandaEye
#Add the archive tar.gz file to the / of the docker images. The image generated after this instuctions.
ADD ./my_rootfs.tar.gz  /

#Install the package so that the "useradd" commands is available.
#Here, while we use the exec format for RUN instructions,environment variable can not be parsed,because no shell will be used.
#So we need use the sh or bash in exec format to make the environment variable can be parsed.
#"/bin/bash -c yum install $PKGNAME -y" inlcude 3 parts： command "/bin/bash", option "-c" , option value "yum install $PKGNAME -y"
#This 3 part can not be change. otherwise, it report error.
ARG PKGNAME="shadow-utils"
RUN ["/bin/bash","-c","yum install $PKGNAME -y"]

#Create the user,the default username is 'PandaEye', it can be override by:"docker build  --build-arg=USERNAME=WANTED_NAME".
ARG USERNAME=PandaEye
RUN useradd -c "$USERNAME's ID" -b /bin/bash -m -d /home/$USERNAME $USERNAME
WORKDIR /home/$USERNAME

#In the file : welcome.sh , it try to use the ENV parameter: USERNAME,if not defined, it will define in the welcome.sh
COPY ./welcome.sh  ./
#Below environment USERNAME value is ARG's USERNAME value. If no this line, the docker images has no environment USERNAME.
#The USERNAME environment parameter can be override by: "docker run --env USERNAME=value".
ENV USERNAME $USERNAME
#The CMD can be override while using: docker run IMAGNAME DEFINED_CMD , the DEFINED_CMD must have the similar format: -c CMD_VALUE
#Both CMD and ENTRYPOINT using the exec-format required for make CMD as parameter of ENTRYPOINT.
CMD ["-c","./welcome.sh"]
ENTRYPOINT ["/bin/bash"]

#ONBUILD instruction used to set the info for new image which based on this image.
ONBUILD ARG BASEIMG_RD="The base image build by auth: PandaEye. This is not official base image. "
ONBUILD RUN  ["/bin/bash","-c","echo $BASEIMG_RD"]
[root@localhost ~]#

[root@localhost ~]# docker build -t my_baseimage  --build-arg=USERNAME="ZHANGFEI"   .
Sending build context to Docker daemon 725.3 MB
Step 1/14 : FROM scratch
 --->
Step 2/14 : MAINTAINER PandaEye
 ---> Running in fa6cd58beed7
......
Removing intermediate container 9386d4f58307
Step 14/14 : ONBUILD run /bin/bash -c echo $BASEIMG_RD
 ---> Running in c367b9387a11
 ---> e64162ad76f3
Removing intermediate container c367b9387a11
Successfully built e64162ad76f3
[root@localhost ~]#

[root@localhost ~]# docker run my_baseimage
USAGE:
You can override the environment 'USERNAME' with your favorite name.
Also,you can override the instruction value of 'CMD' with any available commands in the system by format '-c COMMAND'.

Welcome to the Docker World,ZHANGFEI.

[root@localhost ~]# docker run -e USERNAME=GuanYu my_baseimage
USAGE:
You can override the environment 'USERNAME' with your favorite name.
Also,you can override the instruction value of 'CMD' with any available commands in the system by format '-c COMMAND'.

Welcome to the Docker World,GuanYu.

[root@localhost ~]# docker run -it my_baseimage -c /bin/bash
bash-4.2# ls
welcome.sh
bash-4.2# echo $USERNAME
ZHANGFEI
bash-4.2# exit
exit
[root@localhost ~]# docker run -it -e USERNAME=LIUBEI my_baseimage -c /bin/bash
bash-4.2# echo $USERNAME
LIUBEI
bash-4.2#