使用docker-enter来进入docker容器
docker容器没起sshd服务的时候，还想进入docker怎么办，我们可以使用nsenter进入docker容器的命名空间namespace来虚拟登入docker容器。
nsenter一般默认自带了，没有的话，安装下。然后把如下这个脚本命名成docker-enter或者别的名字，赋执行权限，放入$PATH下即可，使用方式：docker-enter <container-id>
#!/bin/sh
if [ -e $(dirname "$0")/nsenter ]; then
# with boot2docker, nsenter is not in the PATH but it is in the same folder
NSENTER=$(dirname "$0")/nsenter
else
NSENTER=nsenter
fi
if [ -z "$1" ]; then
echo "Usage: `basename "$0"` CONTAINER [COMMAND [ARG]...]"
echo ""
echo "Enters the Docker CONTAINER and executes the specified COMMAND."
echo "If COMMAND is not specified, runs an interactive shell in CONTAINER."
else
PID=$(docker inspect --format "{{.State.Pid}}" "$1")
if [ -z "$PID" ]; then
exit 1
fi
shift
OPTS="--target $PID --mount --uts --ipc --net --pid --"
if [ -z "$1" ]; then
# No command given.
# Use su to clear all host environment variables except for TERM,
# initialize the environment variables HOME, SHELL, USER, LOGNAME, PATH,
# and start a login shell.
"$NSENTER" $OPTS su - root
else
# Use env to clear all host environment variables.
"$NSENTER" $OPTS env --ignore-environment -- "$@"
fi
fi
使用nsenter进入Docker容器
Docker容器运行后，如何进入容器进行操作呢？起初我是用SSH。如果只启动一个容器，用SSH还能应付，只需要将容器的22端口映射到本机的一个端口即可。当我启动了五个容器后，每个容器默认是没有配置SSH Server的，安装配置SSHD，映射容器SSH端口，实在是麻烦。
我发现很多Docker镜像都是没有安装SSHD服务的，难道有其他方法进入Docker容器？
浏览了Docker的文档，我没有找到答案。还是要求助于无所不能的Google，万能的Google告诉我用nsenter吧。
在大多数Linux发行版中，util-linux包中含有nsenter.如果没有，你需要安装它.
cd /tmp
curl https://www.kernel.org/pub/linux/utils/util-linux/v2.24/util-linux-2.24.tar.gz \
| tar -zxf-
cd util-linux-2.24
./configure --without-ncurses
make nsenter
cp nsenter /usr/local/bin
使用shell脚本 docker-enter，将如下代码保存为docker-enter, chomod +x docker-enter
#!/bin/sh
if [ -e $(dirname "$0")/nsenter ]; then
# with boot2docker, nsenter is not in the PATH but it is in the same folder
NSENTER=$(dirname "$0")/nsenter
else
NSENTER=nsenter
fi
if [ -z "$1" ]; then
echo "Usage: `basename "$0"` CONTAINER [COMMAND [ARG]...]"
echo ""
echo "Enters the Docker CONTAINER and executes the specified COMMAND."
echo "If COMMAND is not specified, runs an interactive shell in CONTAINER."
else
PID=$(docker inspect --format "{{.State.Pid}}" "$1")
if [ -z "$PID" ]; then
exit 1
fi
shift
OPTS="--target $PID --mount --uts --ipc --net --pid --"
if [ -z "$1" ]; then
# No command given.
# Use su to clear all host environment variables except for TERM,
# initialize the environment variables HOME, SHELL, USER, LOGNAME, PATH,
# and start a login shell.
"$NSENTER" $OPTS su - root
else
# Use env to clear all host environment variables.
"$NSENTER" $OPTS env --ignore-environment -- "$@"
fi
fi
运行 docker-enter <container id> ，这样就进入到指定的容器中