X-Git-Url: https://www.chiark.greenend.org.uk/ucgi/~ianmdlvl/git?p=elogind.git;a=blobdiff_plain;f=README;h=38459c6b226141408e3b7d2d33c32324dd42c822;hp=34d1267430ddd56c4f0ae5780e6a355c5680a030;hb=d8d2af0635507623971ce59e058847a700978cd8;hpb=d5d6a7f3040992f853eb23eb1bafac3b77891c2d

diff --git a/README b/README
index 34d126743..38459c6b2 100644
--- a/README
+++ b/README
@@ -7,34 +7,45 @@ does not recommend replacing a distro's udev installation with the upstream
 version.
 
 The upstream udev project's set of default rules may require a most recent
-kernel release to work properly. This is currently version 2.6.31.
+kernel release to work properly.
 
 Tools and rules shipped by udev are not public API and may change at any time.
-Never call any private tool in /lib/udev from any external application; it might
-just go away in the next release. Access to udev information is only offered
-by udevadm and libudev. Tools and rules in /lib/udev and the entire contents of
-the /dev/.udev directory are private to udev and do change whenever needed.
+Never call any private tool in /usr/lib/udev from any external application; it
+might just go away in the next release. Access to udev information is only offered
+by udevadm and libudev. Tools and rules in /usr/lib/udev and the entire contents
+of the /run/udev directory are private to udev and do change whenever needed.
 
 Requirements:
-  - Version 2.6.27 of the Linux kernel with sysfs, procfs, signalfd, inotify,
-    unix domain sockets, networking and hotplug enabled:
+  - 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 required:
+      CONFIG_DEVTMPFS=y
       CONFIG_HOTPLUG=y
-      CONFIG_UEVENT_HELPER_PATH=""
+      CONFIG_INOTIFY_USER=y
       CONFIG_NET=y
-      CONFIG_UNIX=y
-      CONFIG_SYSFS=y
-      CONFIG_SYSFS_DEPRECATED*=n
       CONFIG_PROC_FS=y
-      CONFIG_TMPFS=y
-      CONFIG_INOTIFY_USER=y
       CONFIG_SIGNALFD=y
-      CONFIG_TMPFS_POSIX_ACL=y (user ACLs for device nodes)
+      CONFIG_SYSFS=y
+      CONFIG_SYSFS_DEPRECATED*=n
+      CONFIG_UEVENT_HELPER_PATH=""
+
+  - These options might be needed:
       CONFIG_BLK_DEV_BSG=y (SCSI devices)
+      CONFIG_TMPFS_POSIX_ACL=y (user ACLs for device nodes)
+
+  - The /dev directory needs the 'devtmpfs' filesystem mounted.
+    Udev only manages the permissions and ownership of the
+    kernel-provided device nodes, and possibly creates additional symlinks.
 
-  - Udev does not work with the CONFIG_SYSFS_DEPRECATED* option.
+  - Udev requires /run to be writable, which is usually done by mounting a
+    'tmpfs' filesystem.
 
-  - Unix domain sockets (CONFIG_UNIX) as a loadable kernel module may work,
-    but it is not supported.
+  - This version of udev does not work properly with the CONFIG_SYSFS_DEPRECATED*
+    option enabled.
 
   - The deprecated hotplug helper /sbin/hotplug should be disabled in the
     kernel configuration, it is not needed today, and may render the system
@@ -45,43 +56,36 @@ Requirements:
     be mounted at /sys. No other locations are supported by a standard
     udev installation.
 
-  - The system must have the following group names resolvable at udev startup:
+  - 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, libusb, usbutils, pciutils, and gperf.
+      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 static device nodes like
-    /dev/null, /dev/console, /dev/kmsg are needed to be able to start udev itself.
-
   - The udev daemon should be started to handle device events sent by the kernel.
-    During bootup, the kernel can be asked to send events for all already existing
-    devices so that they too can be configured by udev. This is usually done by:
-      /sbin/udevadm trigger --type=subsystems
-      /sbin/udevadm trigger --type=devices
+    During bootup, the events for already existing devices can be replayed, so
+    that they are configured by udev. The systemd service files contain the
+    needed commands to start the udev daemon and the coldplug sequence.
 
   - 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.
+  - New/changed rule files are picked up automatically; there is usually no
+    daemon restart or signal needed.
 
 Operation:
   - Based on events the kernel sends out on device creation/removal, udev
-    creates/removes device nodes in the /dev directory.
+    creates/removes device nodes and symlinks in the /dev directory.
 
   - All kernel events are matched against a set of specified rules, which
     possibly hook into the event processing and load required kernel
     modules to set up devices. For all devices, the kernel exports a major/minor
     number; if needed, udev creates a device node with the default kernel
-    name. If specified, udev applies permissions/ownership to the device
+    device name. If specified, udev applies permissions/ownership to the device
     node, creates additional symlinks pointing to the node, and executes
     programs to handle the device.