The Linux NFS4 kernel client implementation is not free of bugs. Below we list the bugs we know and which distros are known to be affected and what the fix is (if existent).
NFS4 Mount Point Hangs after Server or Network Downtime
After a file server reboot or fail-over in case of high-availabile file services, or after the network at ETH experiences problems, it happens that access to any path on NFS4 mounted shares hangs on the client.
Known Affected Distros
- RHEL 7.5, 7.6 (3.10.0-957.5.1.el7.x86_64 and 4.20.12-1.el7.elrepo.x86_64)
- Ubuntu 18.04 (4.15.0-45-generic), 18.10 (4.18.0-15-generic and 4.20.13-042013-generic)
Known Unaffected Distros
- RHEL 6
- Ubuntu 16.04
- Fedora 29
Currently only a client reboot solves the issue. Temporarily
umount -l -f
can be used to unmount the mounted share forcibly and make the system usable again but the data can only be accessed again after a reboot.