Public bug reported:
Description
When mounting an NFSv3 filesystem on Ubuntu 24.04 LTS, specifying the option
lookupcache=pos (or lookupcache=positive) causes the mount to ignore both ro
and rw
mount flags. Even when rw is explicitly requested, the resulting mount is
read-only.
This behaviour does not occur on Ubuntu 22.04 LTS using the same server, export,
and mount options. The issue has been reproduced on a clean Ubuntu 24.04
installation and tested against multiple independent NFS servers.
Steps to Reproduce
# Ubuntu 24.04
mkdir -p /mnt/nfstest
mount -t nfs -o rw,vers=3,lookupcache=pos server:/export /mnt/nfstest
Expected Result
The NFS filesystem is mounted read-write (rw).
Actual Result
The filesystem is mounted read-only (ro).
Both nfsstat -m and /proc/mounts show the mount as ro.
Verification
nfsstat -m
grep ' /mnt/nfstest ' /proc/mounts
Control Test (works correctly)
mount -t nfs -o rw,vers=3 server:/export /mnt/nfstest
This results in a correct rw mount.
Regression Confirmation
The issue is a regression between Ubuntu 22.04 and Ubuntu 24.04.
Ubuntu 22.04 LTS:
- Kernel: 5.15
- util-linux / libmount: 2.37.2
- nfs-common: 2.6.1
Result:
Mounting with lookupcache=pos results in a correct rw mount.
Ubuntu 24.04 LTS:
- Kernel: 6.8
- util-linux / libmount: 2.39.3
- nfs-common: 2.6.4
Result:
Mounting with lookupcache=pos always results in a ro mount.
Test Environment
The issue was reproduced on:
- A fresh Ubuntu 24.04 LTS installation
- Two different NFS servers:
- Dell EMC Unity
- Synology NAS
The same behaviour occurs with both servers.
Additional Observations
- mount -vvv shows that rw/ro flags are not passed as mount flags when
lookupcache=pos is specified.
- No relevant kernel messages appear in dmesg.
- The problem occurs with manual mounts and is not related to systemd or fstab.
System Information (Ubuntu 24.04)
Ubuntu 24.04.3 LTS
Kernel: 6.8.0-90-generic
util-linux: 2.39.3-9ubuntu6.4
libmount: 2.39.3
nfs-common: 2.6.4-3ubuntu5.1
ProblemType: Bug
DistroRelease: Ubuntu 24.04
Package: util-linux 2.39.3-9ubuntu6.4
ProcVersionSignature: Ubuntu 6.8.0-90.91-generic 6.8.12
Uname: Linux 6.8.0-90-generic x86_64
NonfreeKernelModules: zfs
ApportVersion: 2.28.1-0ubuntu3.8
Architecture: amd64
CasperMD5json:
{
"result": "skip"
}
Date: Thu Jan 15 12:20:10 2026
InstallationDate: Installed on 2026-01-15 (0 days ago)
InstallationMedia: Ubuntu-Server 24.04 LTS "Noble Numbat" - Release amd64
(20240423)
ProcEnviron:
LANG=C.UTF-8
PATH=(custom, no user)
SHELL=/bin/bash
TERM=xterm-256color
SourcePackage: util-linux
UpgradeStatus: No upgrade log present (probably fresh install)
** Affects: util-linux (Ubuntu)
Importance: Undecided
Status: New
** Tags: amd64 apport-bug noble
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https://bugs.launchpad.net/bugs/2138438
Title:
Ubuntu 24.04: NFS mounts with lookupcache=pos become read-only
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