# OpenZFS zfs-2.3.9

- Product: OpenZFS (https://whatsnew.fyi/product/openzfs)
- Vendor: OpenZFS
- Date: 2026-08-21
- Version: zfs-2.3.9
- Original notes: https://github.com/openzfs/zfs/releases/tag/zfs-2.3.9
- Permalink: https://whatsnew.fyi/product/openzfs/releases/zfs-2.3.9
- Labels: Platforms: Linux

What's New is an index, not a publisher: every entry below links to the vendor's own release notes, which are the authoritative source. Entries are labelled where they are hand-curated sample data, pre-releases, or drawn from a secondary source such as a developer blog.

Reuse: the summaries, labels and curation here are © What's New. Quote freely with attribution and a link back; wholesale republication of the corpus is not permitted — terms: https://whatsnew.fyi/terms. The vendors' own release notes remain their publishers'.

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- **added** — Add workaround for device_access ZTS test
- **added** — Add 'capsh' to commands.cfg
- **added** — zhack: add "mmp reclaim" to recover a pool stranded by MMP
- **added** — Add missing checks to zfs_clone_range_replay()
- **added** — libspl: Implement VERIFY_IMPLY and VERIFY_EQUIV
- **added** — Add SECURITY.md policy file
- **changed** — vdev_disk: use calling cred to check for device access
- **changed** — vdev_file: use calling cred to check for device access
- **changed** — zfs_file_open: add cred arg, use it to check access
- **changed** — vdev_open: pass credential to check for permission to open device
- **changed** — secpolicy_sys_config: only permit a global zone credential
- **changed** — secpolicy_zinject: only permit a global zone credential
- **changed** — config: detect idmap method via generic_permission test
- **changed** — mmp: tell a failed uberblock claim apart from remote activity
- **changed** — Make systemd-udev-settle optional for the import units
- **changed** — nvpair: i_get_value_size() string array handling tweak
- **changed** — nvpair: Improve native handling of unterminated strings
- **changed** — Linux 5.19/6.17: handle differences in how to flush delay workqueue
- **changed** — Linux 6.3: follow_down() gains flags arg
- **changed** — Linux 6.18 compat: vfs_parse_fs_string() takes 3 args
- **fixed** — Fix ddtprune causing space leak
- **fixed** — nvpair: Fix operator precedence
- **fixed** — build: Fix release detection when build dir is not source dir
- **fixed** — man: zvol_request_sync is not ignored under blk-mq
- **fixed** — libzfs: don't read a dataset handle after closing it in resume send
- **fixed** — mmp: do not require writes to mirror legs the config marks absent
- **fixed** — libzfs: String trimming should not operate out of bounds
- **fixed** — libzfs: don't truncate a resolved vdev path in zpool_vdev_name()
- **fixed** — libzfs: Do not call munmap() when mmap() fails
- **fixed** — zfs: fix stale POSIX ACL cache after rollback
- **fixed** — zed: let autoexpand see capacity changes on partitioned disks
- **fixed** — dmu_recv: Avoid potential null deref
- **fixed** — DDT: Fix several bugs in pruning
- **fixed** — mmp: skip non-writeable vdevs during activity check
- **fixed** — L2ARC: bound the rebuild by the write hand on a first sweep
- **fixed** — libzfs: fallback VDEV_UPATH to VDEV_PATH for non-DM devices
- **fixed** — Fix reads for blocks freed after being cloned
- **fixed** — Rate limit Direct I/O verify zevents
- **fixed** — zpl_inode: remove zpl_rename no-flags variants
- **fixed** — Fix receive -x according to comment
- **fixed** — linux: batch DMU reads of non-resident pages in mappedread()
- **fixed** — Linux: fix zfs_write() infinite loop on unfaultable buffer
- **fixed** — build: Fix for building dist target outside of project root
- **fixed** — libzfs: fix MS_CRYPT/MS_OVERLAY collision with umount2(2) flags
- **fixed** — linux: handle mmap read beyond file size
- **fixed** — Fix race between device removal completion and pool export
- **fixed** — ddt_log: Fix refcount tagging for begin/commit
- **fixed** — Update mtime/ctime when fallocate grows a file
- **fixed** — Clean up embedded slog metaslab across txgs
- **fixed** — zbookmark_compare: handle "marker" bookmarks with negative levels
- **removed** — secpolicy_nfs: remove, not used

###### Supported Platforms
- **Linux**: compatible with 4.18 - 7.2 kernels
- **FreeBSD**: compatible with releases starting from 13.3+, 14.0+

###### Changes
- [zfs-2.3.9] Add workaround for device_access ZTS test
- [zfs-2.3.9] Add 'capsh' to commands.cfg
- ZTS: device access tests #18960
- vdev_disk: use calling cred to check for device access #18960
- vdev_file: use calling cred to check for device access #18960
- zfs_file_open: add cred arg, use it to check access #18960
- vdev_open: pass credential to check for permission to open device #18960
- secpolicy_zfs: add a note about the power of CAP_SYS_ADMIN #18959
- secpolicy_sys_config: only permit a global zone credential #18959
- secpolicy_zinject: only permit a global zone credential #18959
- secpolicy_nfs: remove, not used #18959
- ZTS: test secpolicy_zinject correctly limits namespace access #18959
- ZTS: test secpolicy_sys_config correctly limits namespace access #18959
- config: detect idmap method via generic_permission test #18769
- mmp: tell a failed uberblock claim apart from remote activity #18892
- ZTS: add coverage for zhack mmp reclaim #18892
- zhack: add "mmp reclaim" to recover a pool stranded by MMP #18892
- Make systemd-udev-settle optional for the import units #18832
- Fix ddtprune causing space leak #17982 #17983
- Linux 7.2 compat: META #18941
- nvpair: i_get_value_size() string array handling tweak #18877
- nvpair: Improve native handling of unterminated strings #18876
- CodeQL: Flag implicit compare-then-assign in branch conditions #18899
- Linux 5.19/6.17: handle differences in how to flush delay workqueue #18847
- Linux 6.3: follow_down() gains flags arg #18847
- Linux 6.18 compat: vfs_parse_fs_string() takes 3 args #18847
- nvpair: Fix operator precedence #18874
- ZTS: don't read a command's exit status as a missing binary #18726 #18882
- build: Fix release detection when build dir is not source dir #18891
- CI: don't fail a passing job when a log reader has already exited #18885
- CI: publish the per-VM test counter atomically #18885
- man: zvol_request_sync is not ignored under blk-mq #18887
- libzfs: don't read a dataset handle after closing it in resume send #18870 #18883
- ZTS: add coverage for the MMP claim on a degraded mirror #18855
- mmp: do not require writes to mirror legs the config marks absent #18855
- libzfs: String trimming should not operate out of bounds #18868
- libzfs: don't truncate a resolved vdev path in zpool_vdev_name() #18851 #18871
- libzfs: Do not call munmap() when mmap() fails #18869
- Add missing checks to zfs_clone_range_replay() #18867
- zfs: fix stale POSIX ACL cache after rollback #18837
- zed: let autoexpand see capacity changes on partitioned disks #12505 #18833
- ZTS: make file_check actually compare the resume test results #18834
- dmu_recv: Avoid potential null deref #18848
- DDT: Fix several bugs in pruning #18838
- cstyle: better tolerance for struct literals
- libspl: Implement VERIFY_IMPLY and VERIFY_EQUIV #18822
- mmp: skip non-writeable vdevs during activity check #18823 #18835
- zdb: output refcounts from verify_spacemap_refcounts() #18809
- L2ARC: bound the rebuild by the write hand on a first sweep #3114 #3400 #5583 #10224 #12779 #18827
- libzfs: fallback VDEV_UPATH to VDEV_PATH for non-DM devices #18439 #18802
- Fix reads for blocks freed after being cloned #18421 #18724
- Rate limit Direct I/O verify zevents #18795
- CI: Update Alpine Linux runner to 3.24.1 #18790
- Remove libuutil from the pull request template and fix headings #18791
- CI: Fix race caused by shared ctr file updates #18778
- zpl_inode: remove zpl_rename no-flags variants #18769
- ZTS: migration/setup: clear stale zfs_member label before new_fs #18492 #18753
- Fix receive -x according to comment #18737 #18738
- Add SECURITY.md policy file #18766
- linux: batch DMU reads of non-resident pages in mappedread() #16031 #18741
- Linux: fix zfs_write() infinite loop on unfaul

_[Truncated at 4000 characters — full notes: https://github.com/openzfs/zfs/releases/tag/zfs-2.3.9]_