+ - Version 2.6.34 of the Linux kernel with sysfs, procfs, signalfd, inotify,
+ unix domain sockets, networking and hotplug enabled
+
+ - Some architectures might need a later kernel, that supports accept4(),
+ or need to backport the accept4() syscall wiring in the kernel.
+
+ - These options are needed:
+ CONFIG_HOTPLUG=y
+ CONFIG_UEVENT_HELPER_PATH=""
+ CONFIG_NET=y
+ CONFIG_UNIX=y
+ CONFIG_SYSFS=y
+ CONFIG_SYSFS_DEPRECATED*=n
+ CONFIG_PROC_FS=y
+ CONFIG_INOTIFY_USER=y
+ CONFIG_SIGNALFD=y
+
+ - These options might be needed:
+ CONFIG_TMPFS=y
+ CONFIG_TMPFS_POSIX_ACL=y (user ACLs for device nodes)
+ CONFIG_BLK_DEV_BSG=y (SCSI devices)
+
+ - Udev does not work with the CONFIG_SYSFS_DEPRECATED* option.
+
+ - Unix domain sockets (CONFIG_UNIX) as a loadable kernel module may work,
+ but it is not supported.
+
+ - The deprecated hotplug helper /sbin/hotplug should be disabled in the
+ kernel configuration, it is not needed today, and may render the system
+ unusable because the kernel may create too many processes in parallel
+ so that the system runs out-of-memory.
+
+ - The proc filesystem must be mounted on /proc, and the sysfs filesystem must
+ be mounted at /sys. No other locations are supported by a standard
+ udev installation.
+
+ - The default rule sset requires the following group names resolvable at udev startup:
+ disk, cdrom, floppy, tape, audio, video, lp, tty, dialout, and kmem.
+ Especially in LDAP setups, it is required that getgrnam() be able to resolve
+ these group names with only the rootfs mounted and while no network is
+ available.
+
+ - Some udev extras have external dependencies like:
+ libacl, libglib2, usbutils, pciutils, and gperf.
+ All these extras can be disabled with configure options.
+
+Setup:
+ - At bootup, the /dev directory should get the 'devtmpfs' filesystem
+ mounted. Udev manages the permissions and ownership of the kernel-created
+ device nodes, and udev possibly creates additional symlinks. If needed, udev also
+ works on an empty 'tmpfs' filesystem, but some device nodes like
+ /dev/null, /dev/console, /dev/kmsg should be created before udevd is started.
+
+ - The udev daemon should be started to handle device events sent by the kernel.
+ During bootup, the events for already existing devices can be replayed, so
+ that they are configured by udev. This is usually done by:
+ /sbin/udevadm trigger --action=add --type=subsystems
+ /sbin/udevadm trigger --action=add --type=devices
+
+ - Restarting the daemon never applies any rules to existing devices.
+
+ - New/changed rule files are picked up automatically; there is no daemon
+ restart or signal needed.