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58 lines
2.6 KiB
Plaintext
58 lines
2.6 KiB
Plaintext
udev - userspace device management
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For more information see the files in the docs/ directory.
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Important Note:
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Integrating udev in the system has complex dependencies and differs from distro
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to distro. All major distros depend on udev these days and the system may not
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work without a properly installed version. The upstream udev project does not
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recommend to replace a distro's udev installation with the upstream version.
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Requirements:
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- Version 2.6.22 of the Linux kernel for reliable operation of this release of
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udev. The kernel must not use the CONFIG_SYSFS_DEPRECATED* option.
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- The kernel must have sysfs, unix domain sockets and networking enabled.
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Unix domain sockets (CONFIG_UNIX) as a loadable kernel module is not
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supported.
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- The proc filesystem must be mounted on /proc/, the sysfs filesystem must
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be mounted at /sys/. No other locations are supported by udev.
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- The system must have the following group names resolvable at udev startup:
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disk, cdrom, floppy, tape, audio, video, lp, tty, dialout, kmem.
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Especially in LDAP setups, it is required, that getgrnam() is able to resolve
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these group names with only the rootfs mounted, and while no network is
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available.
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Operation:
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Udev creates and removes device nodes in /dev/, based on events the kernel
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sends out on device discovery or removal.
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- Very early in the boot process, the /dev/ directory should get a 'tmpfs'
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filesystem mounted, which is populated from scratch by udev. Created nodes
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or changed permissions will not survive a reboot, which is intentional.
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- The content of /lib/udev/devices/ directory which contains the nodes,
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symlinks and directories, which are always expected to be in /dev, should
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be copied over to the tmpfs mounted /dev, to provide the required nodes
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to initialize udev and continue booting.
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- The old hotplug helper /sbin/hotplug should be disabled on bootup, before
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actions like loading kernel modules are taken, which may cause a lot of
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events.
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- The udevd daemon must be started on bootup to receive netlink uevents
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from the kernel driver core.
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- All kernel events are matched against a set of specified rules in
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/lib/udev/rules.d/ which make it possible to hook into the event
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processing to load required kernel modules and setup devices. For all
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devices the kernel exports a major/minor number, udev will create a
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device node with the default kernel name, or the one specified by a
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matching udev rule.
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Please direct any comment/question/concern to the linux-hotplug mailing list at:
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linux-hotplug@vger.kernel.org
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