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Some broken fake cdrom drives return ID_CDROM_MEDIA_STATE=blank. $ /lib/udev/cdrom_id -d /dev/sr1 main: probing: '/dev/sr1' cd_inquiry: INQUIRY: [Nokia ][S60 ][1.0 ] cd_profiles: GET CONFIGURATION: number of profiles 76 cd_profiles: current profile 0x08 cd_media_toc: READ TOC: len: 12 cd_media_toc: last track 1 starts at block 0 cd_media_info: disk type 00 ID_CDROM=1 ID_CDROM_MRW=1 ID_CDROM_MRW_W=1 ID_CDROM_MEDIA=1 ID_CDROM_MEDIA_CD=1 ID_CDROM_MEDIA_STATE=blank Others work fine, but ID_CDROM_MEDIA_STATE is not needed for non-writable CDROM media: $ /lib/udev/cdrom_id -d /dev/sr1 main: probing: '/dev/sr1' cd_inquiry: INQUIRY: [SanDisk ][U3 Cruzer Micro ][8.02] cd_profiles: GET CONFIGURATION: number of profiles 72 cd_profiles: current profile 0x08 cd_media_toc: READ TOC: len: 20 cd_media_toc: track=1 info=0x4(data) start_block=0 cd_media_toc: last track 1 starts at block 0 cd_media_info: disk type 00 ID_CDROM=1 ID_CDROM_MRW=1 ID_CDROM_MRW_W=1 ID_CDROM_MEDIA=1 ID_CDROM_MEDIA_CD=1 ID_CDROM_MEDIA_STATE=complete ID_CDROM_MEDIA_SESSION_COUNT=1 ID_CDROM_MEDIA_TRACK_COUNT=1 ID_CDROM_MEDIA_TRACK_COUNT_DATA=1
udev - userspace device management
For more information see the files in the docs/ directory.
Important Note:
Integrating udev in the system has complex dependencies and differs from distro
to distro. All major distros depend on udev these days and the system may not
work without a properly installed version. The upstream udev project does not
recommend to replace a distro's udev installation with the upstream version.
Requirements:
- Version 2.6.22 of the Linux kernel for reliable operation of this release of
udev. The kernel must not use the CONFIG_SYSFS_DEPRECATED* option.
- The kernel must have sysfs, unix domain sockets and networking enabled.
Unix domain sockets (CONFIG_UNIX) as a loadable kernel module is not
supported.
- The proc filesystem must be mounted on /proc/, the sysfs filesystem must
be mounted at /sys/. No other locations are supported by udev.
- The system must have the following group names resolvable at udev startup:
disk, cdrom, floppy, tape, audio, video, lp, tty, dialout, kmem.
Especially in LDAP setups, it is required, that getgrnam() is able to resolve
these group names with only the rootfs mounted, and while no network is
available.
Operation:
Udev creates and removes device nodes in /dev/, based on events the kernel
sends out on device discovery or removal.
- Very early in the boot process, the /dev/ directory should get a 'tmpfs'
filesystem mounted, which is populated from scratch by udev. Created nodes
or changed permissions will not survive a reboot, which is intentional.
- The content of /lib/udev/devices/ directory which contains the nodes,
symlinks and directories, which are always expected to be in /dev, should
be copied over to the tmpfs mounted /dev, to provide the required nodes
to initialize udev and continue booting.
- The old hotplug helper /sbin/hotplug should be disabled on bootup, before
actions like loading kernel modules are taken, which may cause a lot of
events.
- The udevd daemon must be started on bootup to receive netlink uevents
from the kernel driver core.
- All kernel events are matched against a set of specified rules in
/lib/udev/rules.d/ which make it possible to hook into the event
processing to load required kernel modules and setup devices. For all
devices the kernel exports a major/minor number, udev will create a
device node with the default kernel name, or the one specified by a
matching udev rule.
Please direct any comment/question/concern to the linux-hotplug mailing list at:
linux-hotplug@vger.kernel.org