10
7
mount(8) OS X Manual Page describes the nodev
option:
Do not interpret character or block special devices on the file system. This option is useful for a server that has file systems containing special devices for architectures other than its own.
That alone, I don't fully understand …
… for me, the more important part of this question – which may help me to understand the option – is:
Why are USB flash drives mounted with the nodev option?
Example:
sh-3.2$ mount
/dev/disk1 on / (hfs, local, journaled)
devfs on /dev (devfs, local, nobrowse)
/dev/disk0s2 on /Volumes/swap (hfs, local, journaled)
/dev/disk0s4 on /Volumes/spare (hfs, local, journaled)
map -hosts on /net (autofs, nosuid, automounted, nobrowse)
map auto_home on /home (autofs, automounted, nobrowse)
localhost:/Eiu9XWYlwq4E8x9l_bQTiX on /Volumes/MobileBackups (mtmfs, nosuid, read-only, nobrowse)
/dev/disk3 on /Volumes/gjp22 (zfs, local, journaled, noatime)
/dev/disk3s1 on /opt (zfs, local, journaled, noatime)
/dev/disk6 on /Volumes/zhandy (zfs, local, journaled, noatime)
/dev/disk8s1 on /Volumes/experiment (hfs, local, nodev, nosuid, journaled, noowners)
/dev/disk10 on /Volumes/tall (zfs, local, journaled, noatime)
/dev/disk11s2 on /Volumes/LaCie Little Big Disk (hfs, local, nodev, nosuid, journaled, noowners)
/dev/disk12 on /Volumes/twoz (zfs, local, journaled, noatime)
Wuala on /Volumes/WualaDrive (osxfusefs, local, nodev, nosuid, synchronous, mounted by gjp22)
/dev/disk14s2 on /Volumes/Time Machine Backups (hfs, local, nodev, nosuid, journaled)
In that example, the four volumes with nodev
are:
- experiment – on a USB flash drive
- LaCie Little Big Disk – on a hard disk drive on FireWire 400, this volume includes a Time Machine
Backups.backupdb
- Wuala – file system integration uses FUSE for OS X
- Time Machine Backups
Loosely speaking, I can understand that 2, 3, and 4 are special. However:
- I can't understand the relevance of
nodev
to a USB flash drive.
Other references
Mounting USB disks automatically (How it works) – Unix and Linux
Background
Wishing to understand why Time Machine in Lion and Mountain Lion can not back up from USB flash drives. But this question is more generally about the nodev
option.
@grawity : Wrong,
nodev
option tells to reject reads and writes to device files so that existing one are concerned too. You can still create them. – user2284570 – 2016-04-12T10:05:29.783This is a great answer – thanks. If I understand things correctly, another question arises … in the ZEVO support forum: Why are ZEVO ZFS mounts without the nodev option? (At the moment I have no spare USB hard disk drive to give to HFS Plus alone.)
– Graham Perrin – 2013-01-19T14:08:34.973@GrahamPerrin: Such options as
nodev
are disabled by default, and have to be explicitly set when mounting. The OS X removable disk auto-mounter sets them, the equivalent programs on Linux do too, but they will not be set when runningmount
from terminal unless you manually add-o nodev
. (This does not hurt security sincemount
itself requires root privileges.) So it depends on how your ZEVO ZFS disk is mounted. – user1686 – 2013-01-19T14:18:14.223With ZEVO Community Edition 1.1.1, import is dynamic (automatic) and it seems that the default is to mount automatically without
nodev
. Neither the import nor the ZFS mount requires authentication … let's see how things fan out in the ZEVO area. – Graham Perrin – 2013-01-19T14:32:43.323