Messages in this thread | | | From | Rob Landley <> | Subject | Re: /etc/mtab and per-process namespaces | Date | Sat, 29 Oct 2005 05:16:35 -0500 |
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On Friday 28 October 2005 19:06, Ram Pai wrote:
> > Mike's comments are very apt. The current situation with mount > > support is untenable. Even working on private development machines it > > gets confusing as to what is or is not mounted in various > > shells/processes. The basic infra-structure is there with process > > specific mount information (/proc/self/mounts) but mount and friends > > are a bit problematic with respect to supporting this.
I fairly extensively rewrote busybox mount, and one of my goals was doing the best job with /proc/mounts (only) support that I could. In some ways, busybox's mount is better (such as the fact it can autodetect when you're trying to mount a file and figure out it needs -o loop without being told).
If you want try the busybox version of mount/losetup/umount, I hope it does what you want and am willing to fix it if it doesn't. (P.S. To use /proc/mounts either configure it without /etc/mtab support or symlink /etc/mtab to /proc/mounts.)
> > I'm working on a namespace toolkit to address these issues. I've got > > a pretty basic tool, similar to sudo, which allows spawning processes > > with a protected namespace. I'm adding a configuration system which > > allow systems administrators to define a setup of bind mounts which > > are automatically executed before the user is given their shell. I'm > > also working up a PAM account module to go along with this. I would > > certainly be open to suggestions as to what else people would consider > > useful in such a toolkit. > > > > I've been pondering the best way to take on the mount problem. > > Current mount binaries seem to fall back to /proc/mounts if /etc/mtab > > is not present. All bets are off of course if the mount binary is > > used for the bind mount since a new /etc/mtab is created.
Have you tried having /etc/mtab be a symlink to /proc/mounts?
> > I'm willing to whack on the mount binary a bit as part of this. The > > obvious solution is to teach mount to act differently if it is running > > in a private namespace. If anybody knows of a good way to detect this > > I would be interested in knowing that. In newns (the namespace sudo > > tool) I'm setting an environment variable for mount to detect on but a > > system level approach would be more generic. > > actually there is a hackish way for a process to figure out if it is in > a different namespace than the system namespace. > > ls /proc/1/root > > in a system namespace it will allow you to see the content. > And in a per-process-namespace it will fail with permission denied. > > But I think we should figure out a cleaner way to decipher this, > and that would start with clearly defining the requirements, I think.
The big thing I've never figured out how to do is make umount -a work in the presence of multiple namespaces. (Should it just umount what it sees? I don't know how to umount everything because I can't find everything...)
> RP
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