Sandbox apps fail to run if data-dir is on a non-shared mountpoint

[euank]

Environment

rkt master on semaphore, any other environment with "/" not mounted shared.

$ cat /etc/os-release
NAME="Ubuntu"
VERSION="14.04.5 LTS, Trusty Tahr"
ID=ubuntu
ID_LIKE=debian
PRETTY_NAME="Ubuntu 14.04.5 LTS"
VERSION_ID="14.04"
HOME_URL="http://www.ubuntu.com/"
SUPPORT_URL="http://help.ubuntu.com/"
BUG_REPORT_URL="http://bugs.launchpad.net/ubuntu/"

$ systemctl --version
systemctl: command not found

What did you do?

# terminal 1
$ sudo RKT_EXPERIMENT_APP=true rkt app sandbox --debug

# terminal 2
$ sudo rkt image fetch --insecure-options=image docker://busybox
$ sudo RKT_EXPERIMENT_APP=true rkt app add $uuid docker://busybox --name=test
$ sudo RKT_EXPERIMENT_APP=true rkt app start --app test

What did you expect to see?

"/bin/sh" should run and then exit.

What did you see instead?

The sandbox terminal prints Error: Unable to open "/bin/sh": No such file or directory

Possible Solutions

There's two main paths we can go down to improve this:

1. Explicitly denounce support for non-shared locations for the datadir
2. Remount the datadirectory as shared to avoid this

If we go with 1. then the resolution of this issue would be detecting and giving a useful error in that scenario.

Note that docker goes with 2 these days, their code is here.