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1da6c797fd
<zzam> kay: ping I found out why udev-145 fails on some
systems with kernel 2.6.25 and 2.6.26
<zzam> kay: it is because glibc was compiled against linux-headers-2.6.27
or newer and issues signalfd4 syscall which was introduced in
kernel 2.6.27 and not older signalfd syscall
77 lines
3.4 KiB
Plaintext
77 lines
3.4 KiB
Plaintext
udev - userspace device management
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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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Tools and rules shipped by udev are not public API and may change at any time.
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Never call any private tool in /lib/udev from any external application, it might
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just go away in the next release. Access to udev information is only offered
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by udevadm and libudev. Tools and rules in /lib/udev, and the entire content of
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the /dev/.udev directory is private to udev and does change whenever needed.
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Requirements:
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- Version 2.6.27 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_INOTIFY_USER=y
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CONFIG_SIGNALFD=y
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CONFIG_TMPFS_POSIX_ACL=y (user ACLs for device nodes)
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CONFIG_BLK_DEV_BSG=y (SCSI devices)
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- For reliable operations, 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 may work,
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but it is not 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,
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gperf are needed. These dependencies can be disabled with the
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--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 deprecated hotplug helper /sbin/hotplug should be disabled in the
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kernel configuration, it is not needed today, and may render the system
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unusable because the kernel may create too many processes in parallel
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so that the system runs out-of-memory.
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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 to the linux-hotplug mailing list at:
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linux-hotplug@vger.kernel.org
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