The "remount" option to the "zfs mount" subcommand is not documented in the man page, but it is supported by Illumos. It is used to temporarily change a filesystem's properties while the fs is mounted. # On Illumos $ mount | grep foo /foo on foo read/write/setuid/devices/nonbmand/exec/xattr/atime/dev=4350004 on Fri Sep 1 15:09:49 2017 $ sudo zfs mount -o remount,noatime foo $ mount | grep foo /foo on foo read/write/setuid/devices/nonbmand/exec/xattr/noatime/dev=4350004 on Fri Sep 1 15:10:06 2017 # On FreeBSD > zfs mount -o remount,atime testpool cannot mount 'testpool': mountpoint or dataset is busy
(In reply to Alan Somers from comment #0) I wonder if -o update would do what you want... I believe that there is nothing ZFS-specific about 'remount', I think that it's just an illumos mount option equivalent to FreeBSD 'update' option.
A commit references this bug: Author: asomers Date: Tue Sep 5 19:40:04 UTC 2017 New revision: 323194 URL: https://svnweb.freebsd.org/changeset/base/323194 Log: Fix remounting ZFS filesystem with "zfs mount" "zfs mount -o" passes a list of mount options directly to nmount(2) after sanity checking them. In particular, zfs(8) will refuse to mount an already existing file system unless "remount" is specified in the option list. However, the "remount" option only exists in Illumos. FreeBSD's equivalent is "update". PR: 221985 Reviewed by: avg MFC after: 3 weeks Sponsored by: Spectra Logic Corp Differential Revision: https://reviews.freebsd.org/D12233 Changes: head/sys/cddl/compat/opensolaris/sys/mntent.h
A commit references this bug: Author: asomers Date: Wed Sep 27 15:07:42 UTC 2017 New revision: 324062 URL: https://svnweb.freebsd.org/changeset/base/324062 Log: MFC r323194: Fix remounting ZFS filesystem with "zfs mount" "zfs mount -o" passes a list of mount options directly to nmount(2) after sanity checking them. In particular, zfs(8) will refuse to mount an already existing file system unless "remount" is specified in the option list. However, the "remount" option only exists in Illumos. FreeBSD's equivalent is "update". PR: 221985 Reviewed by: avg Sponsored by: Spectra Logic Corp Differential Revision: https://reviews.freebsd.org/D12233 Changes: _U stable/11/ stable/11/sys/cddl/compat/opensolaris/sys/mntent.h
A commit references this bug: Author: asomers Date: Tue Nov 28 17:33:11 UTC 2017 New revision: 326328 URL: https://svnweb.freebsd.org/changeset/base/326328 Log: MFC r323194: Fix remounting ZFS filesystem with "zfs mount" "zfs mount -o" passes a list of mount options directly to nmount(2) after sanity checking them. In particular, zfs(8) will refuse to mount an already existing file system unless "remount" is specified in the option list. However, the "remount" option only exists in Illumos. FreeBSD's equivalent is "update". PR: 221985 Reviewed by: avg Sponsored by: Spectra Logic Corp Differential Revision: https://reviews.freebsd.org/D12233 Changes: _U stable/10/ stable/10/sys/cddl/compat/opensolaris/sys/mntent.h
A commit references this bug: Author: asomers Date: Tue Feb 20 18:42:09 UTC 2018 New revision: 329652 URL: https://svnweb.freebsd.org/changeset/base/329652 Log: Update ZFS tests now that PR 221985 is fixed tests/sys/cddl/zfs/tests/cli_root/zfs_get/zfs_get_003_pos.ksh tests/sys/cddl/zfs/tests/cli_root/zfs_mount/zfs_mount_007_pos.ksh Convert Illumos syntax => FreeBSD syntax tests/sys/cddl/zfs/tests/cli_root/zfs_get/zfs_get_test.sh Clear expected failure for zfs_get_003_pos tests/sys/cddl/zfs/tests/cli_root/zfs_mount/zfs_mount_007_pos.ksh Remove the "devices" property. Unlike on Illumos, on FreeBSD it can't be changed temporarily (or at all). tests/sys/cddl/zfs/tests/cli_root/zfs_mount/zfs_mount_test.sh Remove the expected failure for zfs_mount_007_pos due to 221985, but add a new expected failure due to PR 115361. PR: 221985 PR: 115361 Sponsored by: Spectra Logic Corp Changes: projects/zfsd/head/tests/sys/cddl/zfs/tests/cli_root/zfs_get/zfs_get_003_pos.ksh projects/zfsd/head/tests/sys/cddl/zfs/tests/cli_root/zfs_get/zfs_get_test.sh projects/zfsd/head/tests/sys/cddl/zfs/tests/cli_root/zfs_mount/zfs_mount_007_pos.ksh projects/zfsd/head/tests/sys/cddl/zfs/tests/cli_root/zfs_mount/zfs_mount_test.sh