I have reduced the problem I described in my previous message to a much smaller test case. Here is an LXC config file that bind-mounts a single file, /other_file, from the host's root filesystem on top of another file, /empty, also from the host's root filesystem:
lxc.console = none lxc.rootfs = / lxc.mount.entry=/other_file empty none rw,bind 0 0 While the container is running, the host's /empty cannot be unlinked: host# rm /empty /other_file host# touch /empty /other_file host# lxc-execute -n test -f test.config -- sleep 30 & [1] 2419 host# strace -o rm.out rm /empty rm: cannot remove `/empty': Device or resource busy host# grep EBUSY rm.out unlinkat(AT_FDCWD, "/empty", 0) = -1 EBUSY (Device or resource busy) host# fg lxc-execute -n test -f test.config -- sleep 30 ^C host# rm /empty host# Can anyone explain why the host's /empty cannot be unlinked even though it is bind-mounted out of the running container? Why is it "busy"? Thanks, Barry On Mon, Dec 8, 2014 at 5:53 PM, Barry Jaspan <[email protected]> wrote: > > I'm using LXC on Ubuntu 12.04 (Precise) on EC2. I am creating a container > that uses the host's root filesystem. In the lxc config, I am bind-mounting > a different passwd file on top of /etc/passwd: > > lxc.mount.entry=/container/passwd etc/passwd none rw,bind 0 0 > > As expected, /etc/passwd on the host and /etc/passwd in the container are > different inodes: > > host# ls -i /etc/passwd > 58046 /etc/passwd > host# ls -i /container/passwd > 287145 /container/passwd > > container# ls -i /etc/passwd > 287145 /etc/passwd > > What I did not expect is that now it is not possible to unlink /etc/passwd > at the host level (or inside the container, although I don't care about > that): > > host# rm /etc/passwd > rm: cannot remove `/etc/passwd': Device or resource busy > host# chsh -s /bin/false root > chsh: failure while writing changes to /etc/passwd > > strace confirms that unlinkat() and rename() are returning EBUSY. (chsh > creates a replacement for /etc/passwd and then rename()'s it into place.) > > So, somehow, the fact that the host's /etc/passwd is *not* present in the > container marks its inode as busy. I do not think it is as simple as "an > inode that has been bind-mounted out of a namespace is busy" because a > simple bind-mount test case does not reproduce it: > > # echo foo > foo > # touch bar > # mount --bind ./foo ./bar > # cat bar > foo > # touch new > # mv new foo > # > > This seems related to http://lwn.net/Articles/570338/. However, in that > article, a file which is bind-mounted into another namespace causes EBUSY > from unlink/rename(). In my case, a file which is *not* bind-mounted into > another namespace is causing EBUSY. > > Can someone explain what is going on? > > Thanks, > > Barry > > -- > Barry Jaspan > Senior Architect | Acquia <http://acquia.com> > [email protected] | (c) 617.905.2208 | (w) 781-313-8298 > > Acquia Dev Cloud: You build killer websites. We do the rest. > <http://www.acquia.com/dev-cloud> <http://acquia.com/dev-cloud> > Acquia ranked #1 Software Vendor on the 2012 Inc 500 > <http://www.acquia.com/about-us/newsroom/press-releases/inc-magazine-unveils-31st-annual-list-america-s-fastest-growing> > > -- Barry Jaspan Senior Architect | Acquia <http://acquia.com> [email protected] | (c) 617.905.2208 | (w) 781-313-8298 Acquia Dev Cloud: You build killer websites. We do the rest. <http://www.acquia.com/dev-cloud> <http://acquia.com/dev-cloud> Acquia ranked #1 Software Vendor on the 2012 Inc 500 <http://www.acquia.com/about-us/newsroom/press-releases/inc-magazine-unveils-31st-annual-list-america-s-fastest-growing>
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