CODEWITHSUNDEEP
gitdockergitlab
Nan Xiao
Nan Xiao

Reputation: 17467

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

I use the docker run genezys/gitlab:7.5.2 command to create and start a container: 

[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...
......

I can see there are logs outputted in terminal.

But when I use docker run genezys/gitlab:7.5.2 /bin/true command:

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

There is no logs outputted.

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

Upvotes: 2

Views: 376

Answers (1)

VonC
VonC

Reputation: 1323973

That would be because the /bin/true CMD (from docker run genezys/gitlab:7.5.2 /bin/true) overwrites the original CMD defined in the Dockerfile:

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

Since GitLab is never run (with /bin/true), it never outputs any log.

The docker run has a COMMAND parameter:

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

The docker run "Overriding Dockerfile image defaults" mentions:

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

That includes 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.

Upvotes: 3

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