Questions[docker](server)

I have the following line in the Dockerfile.

RUN apt-get install -y tzdata

When I run it, it asks for my input. After I provided my input, it hung there. Does anybody know how to solve this problem?

Step 25/25 : RUN apt-get install -y tzdata
 ---> Running in ee47a1beff84
Reading package lists...
Building dependency tree...
Reading state information...
The following NEW packages will be installed:
  tzdata
0 upgraded, 1 newly installed, 0 to remove and 0 not upgraded.
Need to get 189 kB of archives.
After this operation, 3104 kB of additional disk space will be used.
Get:1 http://archive.ubuntu.com/ubuntu bionic-updates/main amd64 tzdata all 2018i-0ubuntu0.18.04 [189 kB]
debconf: unable to initialize frontend: Dialog
debconf: (TERM is not set, so the dialog frontend is not usable.)
debconf: falling back to frontend: Readline
debconf: unable to initialize frontend: Readline
debconf: (This frontend requires a controlling tty.)
debconf: falling back to frontend: Teletype
dpkg-preconfigure: unable to re-open stdin: 
Fetched 189 kB in 1s (219 kB/s)
Selecting previously unselected package tzdata.
(Reading database ... 25194 files and directories currently installed.)
Preparing to unpack .../tzdata_2018i-0ubuntu0.18.04_all.deb ...
Unpacking tzdata (2018i-0ubuntu0.18.04) ...
Setting up tzdata (2018i-0ubuntu0.18.04) ...
debconf: unable to initialize frontend: Dialog
debconf: (TERM is not set, so the dialog frontend is not usable.)
debconf: falling back to frontend: Readline
Configuring tzdata
------------------

Please select the geographic area in which you live. Subsequent configuration
questions will narrow this down by presenting a list of cities, representing
the time zones in which they are located.

  1. Africa      4. Australia  7. Atlantic  10. Pacific  13. Etc
  2. America     5. Arctic     8. Europe    11. SystemV
  3. Antarctica  6. Asia       9. Indian    12. US
Geographic area:
``

Let's say I want to tag a Docker image, and make a typo. How do I remove the tag without removing the image itself? Neither the manpages nor the Docker documentation mention removing tags.

docker tag 0e5574283393 my-imaj
docker tag 0e5574283393 my-image
# docker untag my-imaj # There is no "docker untag"!

Not understanding what is happening when I try to execute two commands at runtime via CMD directive in `Dockerfile. I assumed that this should work:

CMD ["/etc/init.d/nullmailer", "start", ";", "/usr/sbin/php5-fpm"]

But it's not working. Container has not started. So I had to do it like this:

CMD ["sh", "-c", "/etc/init.d/nullmailer start ; /usr/sbin/php5-fpm"]

I don't understand. Why is that? Why first line is not the right way? Can somebody explain me these "CMD shell format vs JSON format, etc" stuff. In simple words.

Just to note - the same was with command: directive in docker-compose.yml, as expected.

I had an issue with a container, even though it builds perfectly it does not properly start. The cause is a workaround I've added to the Dockerfile (for having a self-configured /etc/hosts routing)

RUN mkdir -p -- /lib-override /etc-override && cp /lib/libnss_files.so.2 /lib-override
ADD hosts.template /etc-override/hosts
RUN perl -pi -e 's:/etc/hosts:/etc-override/hosts:g' /lib-override/libnss_files.so.2
ENV LD_LIBRARY_PATH /lib-override

Obviously there's some error in there, but I wonder how can I get more info on what docker is doing while running. for example, this works:

$ docker run image ls
usr bin ...

But this doesn't:

$ docker run image ls -l
$

There is nothing in the logs and I can't call an interactive shell either. I can use strace to see what's happening but I was hoping theres a better way.

Is there any way I can set docker to be more verbose?

EDIT: Thanks to Andrew D. I now know what's wrong with the code above (I left it so his answer can be understood). Now the issue is still how might I debug something like this or get some insides at why ls -l failed why ls did not.

EDIT: The -D=true might give more output, though not in my case...

I want to inspect a docker image created by someone else with both an entrypoint and cmd specified, for example:

ENTRYPOINT ["/usr/sbin/apache2ctl"]
CMD ["-D", "FOREGROUND"]

I currently do:

docker run --interactive --tty --entrypoint=/bin/bash $IMAGE --login

Is there a way to override CMD to be empty (so I don't have to use "--login") ?