# exec 格式
ENTRYPOINT ["executable", "param1", "param2"]
# shell 格式
ENTRYPOINT command param1 param2
docker run --entrypoint
<ENTRYPOINT> "<CMD>"
那么有了 CMD 后,为什么还要有 ENTRYPOINT 呢?这种 <ENTRYPOINT> "<CMD>" 有什么好处么?
CMD # 指定这个容器启动的时候要运行的命令,不可以追加命令
ENTRYPOINT # 指定这个容器启动的时候要运行的命令,可以追加命令
啥意思?这其实也是 ENTRYPOINT 的应用场景之一,下面来看
FROM centos
CMD ["ls","-a"]
docker build -f CMD.dockerfile -t test .
> docker run test
.
..
.dockerenv
bin
dev
etc
home
lib
lib64
lost+found
media
mnt
opt
proc
root
run
sbin
srv
sys
tmp
usr
var
> docker run test -l
docker: Error response from daemon: OCI runtime create failed: container_linux.go:380: starting container process caused: exec: "-l": executable file not found in $PATH: unknown.
> docker run test ls -a -l
total 56
drwxr-xr-x 1 root root 4096 Oct 28 09:36 .
drwxr-xr-x 1 root root 4096 Oct 28 09:36 ..
-rwxr-xr-x 1 root root 0 Oct 28 09:36 .dockerenv
lrwxrwxrwx 1 root root 7 Nov 3 2020 bin -> usr/bin
drwxr-xr-x 5 root root 340 Oct 28 09:36 dev
drwxr-xr-x 1 root root 4096 Oct 28 09:36 etc
drwxr-xr-x 2 root root 4096 Nov 3 2020 home
lrwxrwxrwx 1 root root 7 Nov 3 2020 lib -> usr/lib
lrwxrwxrwx 1 root root 9 Nov 3 2020 lib64 -> usr/lib64
drwx------ 2 root root 4096 Sep 15 14:17 lost+found
drwxr-xr-x 2 root root 4096 Nov 3 2020 media
drwxr-xr-x 2 root root 4096 Nov 3 2020 mnt
drwxr-xr-x 2 root root 4096 Nov 3 2020 opt
dr-xr-xr-x 221 root root 0 Oct 28 09:36 proc
dr-xr-x--- 2 root root 4096 Sep 15 14:17 root
drwxr-xr-x 11 root root 4096 Sep 15 14:17 run
lrwxrwxrwx 1 root root 8 Nov 3 2020 sbin -> usr/sbin
drwxr-xr-x 2 root root 4096 Nov 3 2020 srv
dr-xr-xr-x 13 root root 0 Oct 28 09:36 sys
drwxrwxrwt 7 root root 4096 Sep 15 14:17 tmp
drwxr-xr-x 12 root root 4096 Sep 15 14:17 usr
drwxr-xr-x 20 root root 4096 Sep 15 14:17 var
可以了,但这明显不是最优选择,ENTRYPOINT 就可以解决这个问题
FROM centos
ENTRYPOINT ["ls","-a"]
docker build -f ENTRYPOINT.dockerfile -t test .
> docker run test -l
total 56
drwxr-xr-x 1 root root 4096 Oct 28 09:38 .
drwxr-xr-x 1 root root 4096 Oct 28 09:38 ..
-rwxr-xr-x 1 root root 0 Oct 28 09:38 .dockerenv
lrwxrwxrwx 1 root root 7 Nov 3 2020 bin -> usr/bin
drwxr-xr-x 5 root root 340 Oct 28 09:38 dev
drwxr-xr-x 1 root root 4096 Oct 28 09:38 etc
drwxr-xr-x 2 root root 4096 Nov 3 2020 home
lrwxrwxrwx 1 root root 7 Nov 3 2020 lib -> usr/lib
lrwxrwxrwx 1 root root 9 Nov 3 2020 lib64 -> usr/lib64
drwx------ 2 root root 4096 Sep 15 14:17 lost+found
drwxr-xr-x 2 root root 4096 Nov 3 2020 media
drwxr-xr-x 2 root root 4096 Nov 3 2020 mnt
drwxr-xr-x 2 root root 4096 Nov 3 2020 opt
dr-xr-xr-x 207 root root 0 Oct 28 09:38 proc
dr-xr-x--- 2 root root 4096 Sep 15 14:17 root
drwxr-xr-x 11 root root 4096 Sep 15 14:17 run
lrwxrwxrwx 1 root root 8 Nov 3 2020 sbin -> usr/sbin
drwxr-xr-x 2 root root 4096 Nov 3 2020 srv
dr-xr-xr-x 13 root root 0 Oct 28 09:38 sys
drwxrwxrwt 7 root root 4096 Sep 15 14:17 tmp
drwxr-xr-x 12 root root 4096 Sep 15 14:17 usr
drwxr-xr-x 20 root root 4096 Sep 15 14:17 var
FROM alpine:3.4
...
RUN addgroup -S redis && adduser -S -G redis redis
...
ENTRYPOINT ["docker-entrypoint.sh"]
EXPOSE 6379
CMD [ "redis-server" ]
#!/bin/sh
...
# allow the container to be started with `--user`
if [ "$1" = 'redis-server' -a "$(id -u)" = '0' ]; then
find . \! -user redis -exec chown redis '{}' +
exec gosu redis "$0" "$@"
fi
exec "$@"
该脚本的内容就是根据 CMD 的内容来判断,如果是 redis-server 的话,则切换到 redis 用户身份启动服务器,否则依旧使用 root 身份执行
[root@poloyy ~]# docker run -it redis id
uid=0(root) gid=0(root) groups=0(root)
# 直接进入容器内部
[root@poloyy ~]# docker run -it redis
root@565f89976d63:/#