-udev - Linux userspace device management
-
-Integrating udev in the system has complex dependencies and may differ from
-distribution to distribution. A system may not be able to boot up or work
-reliably without a properly installed udev version. The upstream udev project
-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 2.6.32.
-
-Tools and rules shipped by udev are not public API and may change at any time.
-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 2.6.34 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:
- udevadm trigger --action=add --type=subsystems
- 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.
-
-Operation:
- - Based on events the kernel sends out on device creation/removal, udev
- 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
- 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.
-
- - The events udev handles, and the information udev merges into its device
- database, can be accessed with libudev:
- http://www.kernel.org/pub/linux/utils/kernel/hotplug/libudev/
- http://www.kernel.org/pub/linux/utils/kernel/hotplug/gudev/
-
-For more details about udev and udev rules, see the udev man pages:
- http://www.kernel.org/pub/linux/utils/kernel/hotplug/udev/
-
-Please direct any comment/question to the linux-hotplug mailing list at:
- linux-hotplug@vger.kernel.org
+Elogind User, Seat and Session Manager
+
+Introduction
+------------
+
+Elogind is the systemd project's "logind", extracted out to be a
+standalone daemon. It integrates with PAM to know the set of users
+that are logged in to a system and whether they are logged in
+graphically, on the console, or remotely. Elogind exposes this
+information via the standard org.freedesktop.login1 D-Bus interface,
+as well as through the file system using systemd's standard
+/run/systemd layout. Elogind also provides "libelogind", which is a
+subset of the facilities offered by "libsystemd". There is a
+"libelogind.pc" pkg-config file as well.
+
+All of the credit for elogind should go to the systemd developers.
+For more on systemd, see
+http://www.freedesktop.org/wiki/Software/systemd. All of the blame
+should go to Andy Wingo, who extracted elogind from systemd.
+
+Contributing
+------------
+
+Elogind was branched from systemd version 219, and preserves the git
+history of the systemd project. The version of elogind is the
+upstream systemd version, followed by the patchlevel of elogind. For
+example version 219.12 is the twelfth elogind release, which aims to
+provide a subset of the interfaces of systemd 219.
+
+To contribute to elogind, fork the current source code from github:
+
+ https://github.com/wingo/elogind
+
+Send a pull request for the changes you like.
+
+To chat about elogind:
+
+ #guix on irc.freenode.org
+
+Finally, bug reports:
+
+ https://github.com/wingo/elogind/issues
+
+Why bother?
+-----------
+
+Elogind has been developed for use in GuixSD, the OS distribution of
+GNU Guix. See http://gnu.org/s/guix for more on Guix. GuixSD uses a
+specific init manager (DMD), for reasons that are not relevant here,
+but still aims to eventually be a full-featured distribution that can
+run GNOME and other desktop environments. However, to run GNOME these
+days means that you need to have support for the login1 D-Bus
+interface, which is currently only provided by systemd. That is the
+origin of this project: to take the excellent logind functionality
+from systemd and provide it as a standalone package.
+
+We like systemd. We realize that there are people out there that hate
+it. You're welcome to use elogind for whatever purpose you like --
+as-is, or as a jumping-off point for other things -- but please don't
+use it as part of some anti-systemd vendetta. Systemd hackers are
+smart folks that are trying to solve interesting problems on the free
+desktop, and their large adoption is largely because they solve
+problems that users and developers of user-focused applications care
+about. We are appreciative of their logind effort and think that
+everyone deserves to run it if they like, even if they use a different
+PID 1.
+
+Differences relative to systemd
+-------------------------------
+
+The pkg-config file is called libelogind, not libsystemd or
+libsystemd-logind.
+
+The headers are in <elogind/...>, so like <elogind/sd-login.h> instead
+of <systemd/sd-login.h>.
+
+Libelogind just implements login-related functionality. It also
+provides the sd-bus API.
+
+Unlike systemd, whose logind arranges to manage resources for user
+sessions via RPC calls to systemd, in elogind there is no systemd so
+there is no global cgroup-based resource management. This has a few
+implications:
+
+ * Elogind does not create "slices" for users. Elogind will not
+ record that users are associated with slices.
+
+ * The /run/systemd/slices directory will always be empty.
+
+ * Elogind does not have the concept of a "scope", internally, as
+ it's the same as a session. Any API that refers to scopes will
+ always return an error code.
+
+On the other hand, elogind does use a similar strategy to systemd in
+that it places processes in a private cgroup for organizational
+purposes, without installing any controllers (see
+http://0pointer.de/blog/projects/cgroups-vs-cgroups.html). This
+allows elogind to map arbitrary processes to sessions, even if the
+process does the usual double-fork to be reparented to PID 1.
+
+Elogind does not manage virtual terminals.
+
+Elogind does monitor power button and the lid switch, like systemd,
+but instead of doing RPC to systemd to suspend, poweroff, or restart
+the machine, elogind just does this directly. For suspend, hybernate,
+and hybrid-sleep, elogind uses the same code as systemd-sleep.
+Instead of using a separate sleep.conf file to configure the sleep
+behavior, this is included in the [Sleep] section of
+/etc/elogind/login.conf. See the example login.conf for more. For
+shutdown, reboot, and kexec, elogind shells out to "halt", "reboot",
+and "kexec" binaries.
+
+The loginctl command has the poweroff, reboot, sleep, hibernate, and
+hybrid-sleep commands from systemd, as well as the --ignore-inhibitors
+flag.
+
+The PAM module is called pam_elogind.so, not pam_systemd.so.
+
+License
+-------
+
+LGPLv2.1+ for all code
+
+ - except src/shared/MurmurHash2.c which is Public Domain
+ - except src/shared/siphash24.c which is CC0 Public Domain
+ - except src/journal/lookup3.c which is Public Domain
+
+Dependencies
+------------
+
+ glibc >= 2.14
+ libcap
+ libmount >= 2.20 (from util-linux)
+ libseccomp >= 1.0.0 (optional)
+ libblkid >= 2.24 (from util-linux) (optional)
+ PAM >= 1.1.2 (optional)
+ libacl (optional)
+ libselinux (optional)
+ make, gcc, and similar tools
+
+During runtime, you need the following additional dependencies:
+
+ dbus >= 1.4.0 (strictly speaking optional, but recommended)
+ PolicyKit (optional)
+
+When building from git, you need the following additional
+dependencies:
+
+ pkg-config
+ docbook-xsl
+ xsltproc
+ automake
+ autoconf
+ libtool
+ intltool
+ gperf
+ gtkdocize (optional)
~ianmdlvl / elogind.git / blobdiff