I've just installed Docker on Ubuntu 14.04 (linode) but while it's being installed I saw this error:
modprobe: ERROR: ../libkmod/libkmod.c:556 kmod_search_moddep() could not open
moddep file '/lib/modules/4.1.0-x86_64-linode59/modules.dep.bin'
Warning: current kernel is not supported by the linux-image-extra-virtual package.
We have no AUFS support. Consider installing the packages
linux-image-virtual kernel and linux-image-extra-virtual for AUFS support.
After installing, it seems that Docker works.. sudo docker images and sudo docker ps are done without any errors. Should I worry on this error message? Should I install suggested packages (linux-image-virtual and linux-image-extra-virtual)?
There are several storage drivers in Docker, which are ranked in order of preference. The error message is telling you that Docker tried to the AUFS driver, but failed and fell back to the devicemapper driver.
Unless you have problems with devicemapper, I wouldn't worry about it.
You can find more info on the various drivers in this presentation: https://jpetazzo.github.io/assets/2015-03-03-not-so-deep-dive-into-docker-storage-drivers.html