Why dockered centos doesn't recognize pip? - docker

Question

I want to create a container with python and few packages over centos. I've tried to run several commands inside raw centos container. Everything worked fine I've installed everything I want. Then I created Dockerfile with the same commands executed via RUN and I'm getting /bin/sh: pip: command not found What could be wrong? I mean the situation at all. Why everything could be executed in the command line but not be executed with RUN? I've tried both variants:
RUN command
RUN command
RUN pip install ...
and
RUN command\
&& command\
&& pip install ...
Commands that I execute:
from centos
run yum install -y centos-release-scl\
&& yum install -y rh-python36\
&& scl enable rh-python36 bash\
&& pip install django
UPD: Full path to the pip helped. What's wrong?

Answer 1

You need to install pip first using
yum install python-pip
or if you need python3 (from epel)
yum install python36-pip
When not sure, ask yum:
yum whatprovides /usr/bin/pip
python2-pip-18.1-1.fc29.noarch : A tool for installing and managing Python 2 packages
Repo : #System
Matched from:
Filename : /usr/bin/pip
python2-pip-18.1-1.fc29.noarch : A tool for installing and managing Python 2 packages
Repo : updates
Matched from:
Filename : /usr/bin/pip
python2-pip-18.0-4.fc29.noarch : A tool for installing and managing Python 2 packages
Repo : fedora
Matched from:
Filename : /usr/bin/pip
This output is from Fedora29, but you should get similar result in Centos/RHEL
UPDATE
From comment
But when I execute same commands from docker run -ti centos everything
is fine. What's the problem?
Maybe your PATH is broken somehow? Can you try full path to pip?

Answer 2

As it has already been mentioned by #rkosegi, it must be a PATH issue. The following seems to work:
FROM centos
ENV PATH /opt/rh/rh-python36/root/usr/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
RUN yum install -y centos-release-scl
RUN yum install -y rh-python36
RUN scl enable rh-python36 bash
RUN pip install django
I "found" the above PATH by starting a centos container and typing the commands one-by-one (since you've mentioned that it is working).
There is a nice explanation on this, in the slides of BMitch which can be found here: sudo-bmitch.github.io/presentations/dc2018/faq-stackoverflow.html#24
Q: Why doesn't RUN work?
Why am I getting ./build.sh is not found?
RUN cd /app/srcRUN ./build.sh
The only part saved from a RUN is the filesystem (as a new layer).
Environment variables, launched daemons, and the shell state are all discarded with the temporary container when pid 1 exits.
Solution: merge multiple lines with &&:
RUN cd /app/src && ./build.sh

Answer 3

I know this was asked a while ago, but I just had this issue when building a Docker image, and wasn't able to find a good answer quickly, so I'll leave it here for posterity.
Adding the scl enable command wouldn't work for me in my Dockerfile, so I found that you can enable scl packages without the scl command by running:
source /opt/rh/<package-name>/enable.
If I remember correctly, you won't be able to do:
RUN source /opt/rh/<package-name>/enable
RUN pip install <package>
Because each RUN command creates a different layer, and shell sessions aren't preserved, so I just ran the commands together like this:
RUN source /opt/rh/rh-python36/enable && pip install <package>
I think the scl command has issues running in Dockerfiles because scl enable <package> bash will open a new shell inside your current one, rather than adding the package to the path in your current shell.
Edit:
Found that you can add packages to your current shell by running:
source scl_source enable <package>