[Bug 1379441] [NEW] installation fails when /var/cache/lxc is read-only

[Nobuto MURATA]

Public bug reported:

I'm following this guide:
https://www.stgraber.org/2013/12/21/lxc-1-0-advanced-container-usage/
[quote]
Now restart “p1″ and you’ll see /var/cache/lxc in there, showing the same thing as you have on the host. Note that if you want the container to only be able to read the data, you can simply add “ro” as a mount flag in the fstab.
[/quote]

However lxc package installation fails when /var/cache/lxc is read-only.
Is it possible to mark "chmod 700 /var/cache/lxc" in postinst as
optional to allow read-only filesystem on /var/cache/lxc?

Steps to reproduce:
$ sudo lxc-create -t ubuntu-cloud -n bind-mount-ro-test -- --release trusty -S ~/.ssh/id_rsa.pub

$ echo 'lxc.aa_profile = lxc-container-default-with-nesting' | sudo tee -a /var/lib/lxc/bind-mount-ro-test/config
$ echo 'lxc.mount.entry = /var/cache/lxc var/cache/lxc none bind,create=dir,ro' | sudo tee -a /var/lib/lxc/bind-mount-ro-test/config

[login to the container]
$ sudo apt-get install lxc
<snip>
Setting up lxc (1.0.5-0ubuntu0.1) ...
Setting up lxc dnsmasq configuration.
chmod: changing permissions of '/var/cache/lxc': Read-only file system
dpkg: error processing package lxc (--configure):
 subprocess installed post-installation script returned error exit status 1
dpkg: dependency problems prevent configuration of lxc-templates:
 lxc-templates depends on lxc (>= 0.8.0~rc1-4ubuntu43); however:
  Package lxc is not configured yet.

dpkg: error processing package lxc-templates (--configure):
 dependency problems - leaving unconfigured
Errors were encountered while processing:
 lxc
 lxc-templates

[lxc.postinst]
    # Up to version 1.0.0~alpha2-0ubuntu4 lxc was installed world
    # readable.  After that version if users want it that way for
    # convenience, then that's fine.  But one time go ahead and
    # forcibly change the permissions.
    if dpkg --compare-versions "$2" lt "1.0.0~alpha2-0ubuntu5"; then
        chmod 700 /var/lib/lxc
        chmod 700 /var/cache/lxc
    fi

ProblemType: Bug
DistroRelease: Ubuntu 14.10
Package: lxc 1.1.0~alpha1-0ubuntu5
ProcVersionSignature: Ubuntu 3.16.0-18.25-generic 3.16.3
Uname: Linux 3.16.0-18-generic x86_64
ApportVersion: 2.14.7-0ubuntu2
Architecture: amd64
CurrentDesktop: Unity
Date: Fri Oct 10 02:04:01 2014
EcryptfsInUse: Yes
InstallationDate: Installed on 2014-05-19 (143 days ago)
InstallationMedia: Ubuntu 14.10 "Utopic Unicorn" - Alpha amd64 (20140518)
SourcePackage: lxc
UpgradeStatus: No upgrade log present (probably fresh install)
defaults.conf:
 lxc.network.type = veth
 lxc.network.link = lxcbr0
 lxc.network.flags = up
 lxc.network.hwaddr = 00:16:3e:xx:xx:xx

** Affects: lxc (Ubuntu)
     Importance: Undecided
         Status: New


** Tags: amd64 apparmor apport-bug utopic

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Title:
  installation fails when /var/cache/lxc is read-only

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