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71 lines
2.9 KiB
Plaintext
71 lines
2.9 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 2.6.25 of the Linux kernel with sysfs, procfs, signalfd, inotify,
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unix domain sockets, networking and hotplug enabled:
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CONFIG_HOTPLUG=y
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CONFIG_UEVENT_HELPER_PATH=""
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CONFIG_NET=y
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CONFIG_UNIX=y
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CONFIG_SYSFS=y
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CONFIG_SYSFS_DEPRECATED*=n
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CONFIG_PROC_FS=y
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CONFIG_TMPFS=y
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CONFIG_TMPFS_POSIX_ACL=y
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CONFIG_INOTIFY=y
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CONFIG_SIGNALFD=y
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- For reliable operation, the kernel must not use the CONFIG_SYSFS_DEPRECATED*
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option.
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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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- To build all udev extras, libacl, libglib2, libusb, usbutils, pciutils are
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needed. These dependencies can be disabled with the --disable-extras option.
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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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- Early in the boot process, the /dev/ directory should get a 'tmpfs'
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filesystem mounted, which is maintained by udev. Created nodes or changed
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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 in the kernel
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configuration, it is not needed, and may render the system unusable
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because of a fork-bombing behavior.
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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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