Is it possible to add instructions like RUN in Dockerfile that, instead of run on docker build command, execute when a new container is created with docker run? I think this can be useful to initialize a volume attached to host file system.
2 Answers
Take a look at the ENTRYPOINT command. This specifies a command to run when the container starts, regardless of what someone provides as a command on the docker run command line. In fact, it is the job of the ENTRYPOINT script to interpret any command passed to docker run.
2 Comments
larsks
An
ENTRYPOINT script will run on docker start, but you could easily include logic in the script such that it could check if it had previously run.
Tasso Evangelista
Although I don't think this is a good way to do this, it's a Docker problem. The
ENTRYPOINT seems to be a proper workaround.I think you are looking for the CMD
https://docs.docker.com/reference/builder/#cmd
The main purpose of a
CMDis to provide defaults for an executing container. These defaults can include an executable, or they can omit the executable, in which case you must specify anENTRYPOINTinstruction as well.Note: don't confuse
RUNwithCMD.RUNactually runs a command and commits the result;CMDdoes not execute anything at build time, but specifies the intended command for the image.
You should also look into using Data Containers see this excellent Blog post.
Persistent volumes with Docker - Data-only container pattern http://container42.com/2013/12/16/persistent-volumes-with-docker-container-as-volume-pattern/
1 Comment
Tasso Evangelista
There is a downside using
CMD: a Dockerfile can have many of it, but only the last one will run.
docker run, but it can also be created withdocker create. AFAIK there is no command that can be run when justdocker createis run.