Editing files from dockerfile

Question

I need to add several lines to /etc/sysctl.conf in a Docker image.

Is there an idempotent way to do this via a Dockerfile rather than editing manually and using the docker commit approach?

Answer 1

I would use the following approach in the Dockerfile

RUN   echo "Some line to add to a file" >> /etc/sysctl.conf 

That should do the trick. If you wish to replace some characters or similar you can work this out with sed by using e.g. the following:

RUN   sed -i "s|some-original-string|the-new-string |g" /etc/sysctl.conf 

However, if your problem lies in simply getting the settings to "bite" this question might be of help.

Answer 2

sed work pretty well to replace stuff, if you need to append, you can user double redirect

sed -i 's/origin text/new text/g' /etc/sysctl.conf bash -c 'echo hello world' >> /etc/sysctl.conf 

-i is a non-standard option of GNU sed for inline editing (alleviating the need for dealing with temporary files).

The s is the substitute command of sed for find and replace

The g means global replace i.e. find all occurrences of origin text and replace with new text using sed