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I need to access my "root" ZFS dataset to delete a file under "/var". But "/var" is overlayed by another ZFS dataset. Since these are system datasets I can't "umount" them while the machine is running. And I want to avoid to reboot the system in "failsafe" mode, since this is a production machine.
Teorically ZFS would refuse to mount "/var" dataset over the underlying "/var", because it is not empty. But it works, possibly because they are system datasets mounted early in the boot process.
But having the underlying "/var" not empty is preventing me to create an ABE (Alternate Boot Environment), so patching is risky, and I can't upgrade my system using Live Upgrade.
The machine is remote. I have an IP KVM, but I rather prefer to avoid booting this machine in "failsafe" mode, if I can.
I know there is a file in "/var/" because I can snapshot the "root" dataset and check it. But snapshots are read-only, so I can't get rid of the file.
I tried "mkdir /tmp/zzz; mount -F lofs / /tmp/zzz", but when I go to "/tmp/zzz/var", I see the "/var" dataset, not the underlying "root" dataset. That is, the LOFS is crossing mountpoints. I would usually like it, but not this time!.
Any suggestion, beside rebooting the machine in "failsafe" and mess with it thru the IP KVM?
jcea
Posted 2010-05-05T23:17:42.827
Reputation: 255
1Good suggestion!.
Too late to solve my immediate problem, but it should work. I know positively that NFS doesn't cross mount points. – jcea – 2010-05-19T18:12:08.490
I had the same issue with OTHER server.The NFS trick works if you export it via "share" instead of "zfs sharenfs", and if you import it especifying version 3. Version 4 does strange things with mountpoints, and doesn't work. I haven't experimented more. – jcea – 2010-09-30T00:39:10.737
Next problem, enable "root" access. To do so, export like "share -F nfs -o rw,root=127.0.0.1,anon=0 /". When done, stop the share with "unmount" and "unshare /". – jcea – 2010-09-30T00:52:18.057