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After a ZFS send to a UFS mount, 'umount(1M)' of same UFS mount will hang (Doc ID 2778775.1)

Last updated on MAY 24, 2021

Applies to:

Solaris Operating System - Version 11.4 and later
Information in this document applies to any platform.


A ZFS shapshot sent via "zfs send" command to a UFS filesystem will render the file system un-mountable.

Any attempt to umount(1M) or umount -f (force) will cause the process to hang in the shell, and any attempt to attach to the hung process will also "hang", e.g. via 'truss' or dtrace.

How to replicate:

1. Create a UFS filesystem, then mount it. (e.g. /test)
2. Run "zfs send data/u01@NOW > /test/u01.out"
3. Try to umount /test - it will hang



Don not try this in any critical production environment. Recovery from this requires one to actually reboot the Solaris node. There is no other way to kill or remove the hung process.


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