I've been interested in this question since Nov 2012 and even set up a FreeNAS VM to reproduce the issue.
I eventually gave up but since the question has been resuscitated I will share what I found out back then and in the last hours (luckily I didn't delete the VM) and what I think the cause for this issue is. I have also found a workaround.
My setup
First of all, this is my test setup:
OS X 10.8.2 (sorry, no 10.7.5 around).
FreeNAS (FreeBSD 8.2-RELEASE-p1)
(The OP's version is FreeBSD 8.2-RELEASE-p7 - I couldn't find the same version.)
A NAS filesystem in /mnt/raid:
A user named netboot:
An AFP filesystem (/mnt/raid/netboot) exported as netboot:
(Note that it is configured read-only).
An NFS filesystem (same path as AFP filesystem, to match the OP's configuration: /mnt/raid/netboot):
AFP works, NFS doesn't
I mounted the AFP read-only filesystem as user netboot using the Finder with ⌘K:
and mounted a DMG image file without any problems:
$ sudo rm /private/var/netboot/Library-Shadow
$ sudo /usr/bin/hdiutil attach /Volumes/netboot/p7zip-9.04-0.i386.dmg -notremovable -shadow /private/var/netboot/Library-Shadow -owners on -noverify -noautofsck -nobrowse
Password:
/dev/disk3 Apple_partition_scheme
/dev/disk3s1 Apple_partition_map
/dev/disk3s2 Apple_HFS /Volumes/p7zip.pkg
Then I unmounted it and mounted the read-only NFS filesystem (I also used ⌘K) and couldn't mount the DMG image file.
I think the problem is logged here:
CBSDBackingStore::setPermission: opening /Volumes/netboot/Lion.nbi/Library.dmg
CBSDBackingStore::OpenLockFriendly: mapping flags 0x00000000 -> 0x00000014 (locks are MANDATORY)
CBSDBackingStore:OpenLockFriendly: could not open with lock 30
Error 30 means (see man 2 intro):
30 EROFS Read-only file system. An attempt was made to modify a file
or directory was made on a file system that was read-only at the time.
No surprise here, it is indeed a read-only filesystem, but... when mounted over AFP it works, why?
Because Apple's NFS implementation has some problems with locking. As stated in this post at gluster.org:
OS X does a phenominal amount of file locking (some would say,
needlessly so) and has always been really sensitive to the
configuration of locking on the NFS servers. So much so that if you
randomly pick an NFS server in a large enterprise, true success is
pretty unlikely.
In my setup, the NFS server (that is, the FreeNAS VM) was suddenly irresponsive (from my Mac's /var/log/system.log):
Mar 15 15:35:04 avallone.local rpc.lockd[8119]: Lockd got unexpected signal 20
Mar 15 15:35:04 avallone com.apple.launchd[1] (com.apple.lockd[8119]): Exited with code: 1
Mar 15 15:35:04 avallone com.apple.launchd[1] (com.apple.lockd): Throttling respawn: Will start in 10 seconds
(...)
Mar 15 15:35:07 avallone com.apple.launchd[1] (com.apple.statd[8121]): Exited with code: 1
Mar 15 15:35:07 avallone com.apple.launchd[1] (com.apple.statd): Throttling respawn: Will start in 10 seconds
Mar 15 15:35:13 avallone kernel[0]: nfs server 172.16.54.186:/mnt/raid/netboot: lockd not responding
Mar 15 15:35:13 avallone.local KernelEventAgent[72]: tid 00000000 received event(s) VQ_NOTRESP (1)
Mar 15 15:35:13 avallone.local KernelEventAgent[72]: tid 00000000 type 'nfs', mounted on '/Volumes/netboot', from '172.16.54.186:/mnt/raid/netboot', not responding
(...)
Mar 15 15:35:34 avallone.local KernelEventAgent[72]: tid 00000000 unmounting 1 filesystems
The output of sudo /usr/bin/hdiutil attach -debug /Volumes/netboot/p7zip-9.04-0.i386.dmg -notremovable -shadow /private/var/netboot/Library-Shadow -owners on -noverify -noautofsck -nobrowse was:
CBSDBackingStore::setPermission: opening /Volumes/netboot/p7zip-9.04-0.i386.dmg
CBSDBackingStore::OpenLockFriendly: mapping flags 0x00000000 -> 0x00000014 (locks are MANDATORY)
CBSDBackingStore:OpenLockFriendly: could not open with lock 5
Error 5 means (again from man 2 intro):
5 EIO Input/output error. Some physical input or output error
occurred. This error will not be reported until a subsequent
operation on the same file descriptor and may be lost (over written)
by any subsequent errors.
which isn't suprising at all, the NFS filesystem was gone.
Workaround
A workaround (tested on OS X 10.8) is to mount NFS with options nolocks,locallocks. As explained in the post at gluster.org already mentioned:
Fortunately, there is a fix: just turn off network locking. You can do
it by adding the "nolocks,locallocks" options in the advanced options
field of the Disk Utility NFS mounting UI, but this is painful if you
do a lot of them, and doesn't help at all with /net. You can edit
/etc/auto_master to add these options to the /net entry, but it
doesn't affect other mounts - however I do recommend deleting the
hidefromfinder option in auto_master. If you want to fix every
automount, edit /etc/autofs.conf and search for the line that starts
with AUTOMOUNTD_MNTOPTS=. These options get applied on every mount.
Add nolocks,locallocks and your world will be faster and happier after
you reboot.
I manually mounted 172.16.54.186:/mnt/raid/netboot and it worked flawlessly:
$ sudo rm /private/var/netboot/Library-Shadow
$ sudo mount -o nolocks,locallocks,ro 172.16.54.186:/mnt/raid/netboot /tmp/mnt
$ sudo /usr/bin/hdiutil attach /tmp/mnt/p7zip-9.04-0.i386.dmg -notremovable -shadow /private/var/netboot/Library-Shadow -owners on -noverify -noautofsck -nobrowse
/dev/disk6 Apple_partition_scheme
/dev/disk6s1 Apple_partition_map
/dev/disk6s2 Apple_HFS /Volumes/p7zip.pkg
I also edited /etc/auto_master like this:
+auto_master # Use directory service
#/net -hosts -nobrowse,hidefromfinder,nosuid
/net -hosts -nosuid,nolocks,locallocks
/home auto_home -nobrowse,hidefromfinder
/Network/Servers -fstab
/- -static
stopped and started automountd and autofsd:
$ sudo launchctl unload /System/Library/LaunchDaemons/com.apple.automountd.plist
$ sudo launchctl unload /System/Library/LaunchDaemons/com.apple.autofsd.plist
$ sudo launchctl load /System/Library/LaunchDaemons/com.apple.autofsd.plist
$ sudo launchctl load /System/Library/LaunchDaemons/com.apple.automountd.plist
and worked like a charm:
$ cd /net/172.16.54.186/mnt/raid/netboot
$ ls
Network Trash Folder Temporary Items p7zip-9.04-0.i386.dmg
$ sudo rm /private/var/netboot/Library-Shadow
$ sudo /usr/bin/hdiutil attach p7zip-9.04-0.i386.dmg -notremovable -shadow /private/var/netboot/Library-Shadow -owners on -noverify -noautofsck -nobrowse
/dev/disk7 Apple_partition_scheme
/dev/disk7s1 Apple_partition_map
/dev/disk7s2 Apple_HFS /Volumes/p7zip.pkg
Best Answer
I had the same problem, and managed to open .dmg files by going into Disk Utility>File>Open Disk Image. Once opened in Disk Utility, Double Click (Right Click) the icon and click show in Finder. Then I could install what I wanted! Hop it works for you!