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udftools
===================
Kernel support for packet writing
---------------------------------
Packet writing is a technique by which a writable medium (typically a
CD or DVD) can be used just like a USB stick or a directory on the
hard disc: Files and directories can be created/renamed/removed
freely, and no separate "burning" step is necessary to write the data
to the medium. Packet writing is possible both with write-once media
(CD-R, DVD+R, DVD-R) and rewritable media (CD-RW, DVD+RW,
DVD-RW). Obviously, with write-once media the free space on the
filesystem will not increase if you delete files.
In order to do packet writing under Linux, your kernel needs
both support for UDF (Universal Disc Format) filesystems and for
packet writing. This is the case for kernels later than about 2.6.10.
This package tries to support both old-style packet writing
(kernel <2.6.8), and the newer variant (>=2.6.10), with and without
udev. Use a recent 2.6 kernel for optimum results!
Formatting and using a UDF DVD-RW or CD-RW for packet writing
-------------------------------------------------------------
The commands differ depending on whether you are using DVD or CD
media.
1) Edit /etc/udftools.conf and add your drive for packet writing.
For example, if your CD/DVD writer is /dev/hdc and you want it
available as the default /dev/pktcdvd/0, then use the setting
"DEVICES=/dev/hdc". Execute "/etc/rc.d/rc.udftools start" afterwards to
register the device.
If the device name /dev/hdc differs on your system, adjust the
following commands as appropriate.
2) Prepare the medium in restricted overwrite mode:
DVD-RW: dvd+rw-format -force /dev/hdc
CD-RW: Do nothing, skip this step!
3) Write an empty session spanning the whole medium. It seems that
without this step, any attempt to create the UDF filesystem will fail.
DVD-RW: growisofs -Z /dev/hdc=/dev/zero
CD-RW: cdrwtool -d /dev/hdc -q
4) Format the packet device in UDF format.
DVD-RW: mkudffs --udfrev=0x0150 --spartable=2 --media-type=dvdrw /dev/pktcdvd/0
CD-RW: mkudffs --udfrev=0x0150 --spartable=2 --media-type=cdrw /dev/pktcdvd/0
The parameters require some more explanation: For --udfrev, use either
0x0150 for UDF version 1.50, or 0x0201 for UDF version 2.01. The
version decision has mostly to do with compatibility:
- Windows 98/ME can read up to v1.02
- Windows 2000, Mac OS 9, Linux 2.4 can read up to v1.50
- Windows 2003/XP can read up to v2.01
- Linux 2.6 can read up to v2.60
For normal data, UDF 1.50 is OK. UDF 2.00 and 2.01 introduce
additional functionality for streaming audio/video.
Possible values for --media-type are: hd dvdram dvdrw worm mo cdrw cdr.
Use the one appropriate for your medium/device.
5) Mount the disc. The "noatime" option is important: It will reduce
the amount of writes to the device and thus increase its lifetime. You
may first have to create the mount directory using "mkdir
/media/dvd0":
mount -t udf -o rw,noatime /dev/pktcdvd/0 /media/dvd0
The "sync" mount option might also be useful, but will typically cause
an increased number of write accesses to the medium. From now on, the
root user can access the filesystem under /media/dvd0 using read and
write operations.
6) If regular users should also have write access, modify the
permissions as follows _while the filesystem is mounted_:
chgrp plugdev /media/dvd0 # Set group ownership to "plugdev"
chmod g+rwx /media/dvd0 # Give full read/write access to group
Now all users who should have access to the disc need to be added to
the "plugdev" group using "adduser <username> plugdev".
To also allow these users to mount and unmount/eject the medium, you
can use either of these two routes:
- Install the "pmount" package and add the device to the list of
allowed devices using "echo /dev/pktcdvd/0 >>/etc/pmount.allow".
All members of the group "plugdev" will then be able to mount the
disc using "pmount /dev/pktcdvd/0 dvd0" and unmount it using
"pumount /media/dvd0".
- Add a line like the following to /etc/fstab:
/dev/pktcdvd/0 /media/dvd0 udf rw,noatime,users,noauto 0 0
This will enable _all_ users to mount the disc using
"mount /media/dvd0" and unmount it with
"umount /media/dvd0". However, with the permissions from step 5)
above, only the members of group "plugdev" ought to be able to
write to it.
Support for UDF filesystems
---------------------------
UDF (not packet writing) support in Linux 2.4 and later kernels is
sufficient to read from and write to UDF filesystems. For example, you
can create a regular file, "format" it using mkudffs, and then
loop-mount it. To do this, execute the following commands as root:
(After "count=", supply the required size in MB of the filesystem.)
dd if=/dev/zero of=udfimage bs=1M count=10
mkudffs udfimage
mkdir udfmnt
mount -o loop -t udf udfimage udfmnt
You need Linux 2.4+ with UDF read *and* write support enabled. Now you
can copy data to the "udfmnt" directory. After an "umount udfmnt", the
file "udfimage" could theoretically be written to a CD-R(W) or
DVD-R(W). In practice, you will not want to do that, as the whole
point of using UDF is to do packet writing.
"/dev/pktcdvd0" not present?
----------------------------
The "pktsetup" tool requires a device like /dev/pktcdvd0,
/dev/pktcdvd1 etc. If the device is not present on your system, this
means one of two things:
- You are using devfs (the file /dev/.devfsd is present). In this
case, just try to use the device, and the appropriate driver should
be loaded automatically.
- You are not using devfs now, but it was being used at the time the
udftools package was installed. In this case, you need to create
the devices as root now, using the command:
dpkg-reconfigure udftools
- You are using udev, and there is no packet writing support in your
kernel.
-- Richard Atterer <atterer@debian.org> Wed, 22 Nov 2006 23:38:16 +0100
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