This is my reply for a support-request on SourceForge. I have experienced that my reply to <bra...@support-requests.aufs.p.re.sf.net> was ignored and I had to forward to aufs-users ML. This time, I wrote to both.
"MasterQ": > Hello, > i have a box with a linux installation on a sdcard. To protect the box from > changes and to protect the sd-card (without wear-leveling) from many > write-cycles I use aufs with to branches: > 1. ext4 ro mounted partition /ro > 2. ramfs partion on /rw. > I have mounted both and merged them with aufs that works fine. > > I want to give this box away. But it is possibile that i have to give support > and need /ro branch to be writeable. > For example for keeping log files after system crash or make a system update. > I see, the second example could be made in chroot enviorment. > > Teoriticaly something like: > 1. remount the /ro with -o remount,rw > 2. mount -o remount,mod:/ro=rw / > 4. mount -o remount,mod:/rw=ro / > > Should solve the problem, but of cause /rw will be allways busy. > > So what i like to ask is... > Is there something like: > 1. remount the /ro with -o remount,rw > 2. mount -o remount,mod:/ro=rw / > 3. Tell aufs so save new files to /ro Hello MasterQ, Unfortunately I cannot fully understand what you wrote. What you want to do looks like as making the root dir readonly because your first writable branch /rw is already busy. Generally you can make the root dir readonly only when shutting down the system. In this case, you can use "aubrsync" script to reflect the contents of /rw to /ro (which should be writable). "aubrsync" script is available the system shutdown time only. So it may not be your solution. Another option is a rather new feature called "move-down" (oppsite of copy-up). Try a utility called "aumvdown" in aufs-util.git. - remount the /ro with -o remount,rw - mount -o remount,mod:/ro=rw / - run aumvdown until "remount,mod:/rw=ro" succeeds But I am not sure when the third step succeeds. Additionally when it succeeds, errors may happen because the file becomes "readonly" for some applications. Inserting a new writable branch before your /rw may make the problem smaller. But I don't think it can be a solution for you. Hope this helps J. R. Okajima ------------------------------------------------------------------------------ Put Bad Developers to Shame Dominate Development with Jenkins Continuous Integration Continuously Automate Build, Test & Deployment Start a new project now. Try Jenkins in the cloud. http://p.sf.net/sfu/13600_Cloudbees
