为什么没有使用 "docker run image command" 启动容器的日志？

Question

我使用 docker run genezys/gitlab:7.5.2 命令创建并启动容器：

[root@localhost ~]# docker run genezys/gitlab:7.5.2
/opt/gitlab/embedded/bin/runsvdir-start: line 34: ulimit: max user processes: cannot modify limit: Operation not permitted
/opt/gitlab/embedded/bin/runsvdir-start: line 37: /proc/sys/fs/file-max: Read-only file system
[2015-05-05T05:43:02+00:00] INFO: Forking chef instance to converge...
......

我可以看到终端有日志输出。

但是当我使用 docker run genezys/gitlab:7.5.2 /bin/true 命令时：

[root@localhost ~]# docker run genezys/gitlab:7.5.2 /bin/true
[root@localhost ~]#

没有日志输出。

为什么没有使用 docker run image command 启动容器的日志？

Answer 1

那是因为 /bin/true CMD（来自 docker run genezys/gitlab:7.5.2 /bin/true）覆盖了定义的原始 CMD in the Dockerfile:

# Default is to run runit & reconfigure
CMD ["/usr/local/bin/gitlab.sh"]

因为 GitLab 永远不会运行（/bin/true），它从不输出任何日志。

docker run有一个COMMAND参数：

docker run [OPTIONS] IMAGE [COMMAND] [ARG...]

docker run "Overriding Dockerfile image defaults"提到：

Four of the Dockerfile commands cannot be overridden at runtime: FROM, MAINTAINER, RUN, and ADD.
Everything else has a corresponding override in docker run.

包括CMD:

Recall the optional COMMAND in the Docker commandline:

$ sudo docker run [OPTIONS] IMAGE[:TAG|@DIGEST] [COMMAND] [ARG...]

This command is optional because the person who created the IMAGE may have already provided a default COMMAND using the Dockerfile CMD instruction.
As the operator (the person running a container from the image), you can override that CMD instruction just by specifying a new COMMAND.

If the image also specifies an ENTRYPOINT then the CMD or COMMAND get appended as arguments to the ENTRYPOINT.

为什么没有使用 "docker run image command" 启动容器的日志？

Why is there no logs using "docker run image command" to start container?

git

docker

gitlab