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We now save the unique bus-name of a session-controller as CONTROLLER=%s in the session files. This allows us to restore the controller after a crash or restart. Note that we test whether the name is still valid (dbus guarantees that the name is unique as long as the machine is up and running). If it is, we know that the controller still exists and can safely restore it. Our dbus-name-tracking guarantees that we're notified once it exits. Also note that session-devices are *not* restored. We have no way to know which devices where used before the crash. We could store all these on disk, too, or mark them via udev. However, this seems to be rather cumbersome. Instead, we expect controllers to listen for NewSession signals for their own session. This is sent on session_load() and they can then re-request all devices. The only race I could find is if logind crashes, then the session controller tries calling ReleaseControl() (which will fail as logind is down) but keeps the bus-connection valid for other independent requests. If logind is restarted, it will restore the old controller and thus block the session. However, this seems unlikely for several reasons: - The ReleaseControl() call must occur exactly in the timespan where logind is dead. - A process which calls ReleaseControl() usually closes the bus-connection afterwards. Especially if ReleaseControl() fails, the process should notice that something is wrong and close the bus. - A process calling ReleaseControl() usually exits afterwards. There may be any cleanup pending, but other than that, usual compositors exit. - If a session-controller calls ReleaseControl(), a session is usually considered closing. There is no known use-case where we hand-over session-control in a single session. So we don't care whether the controller is locked afterwards. So this seems negligible.
systemd System and Service Manager
DETAILS:
http://0pointer.de/blog/projects/systemd.html
WEB SITE:
http://www.freedesktop.org/wiki/Software/systemd
GIT:
git://anongit.freedesktop.org/systemd/systemd
ssh://git.freedesktop.org/git/systemd/systemd
GITWEB:
http://cgit.freedesktop.org/systemd/systemd
MAILING LIST:
http://lists.freedesktop.org/mailman/listinfo/systemd-devel
http://lists.freedesktop.org/mailman/listinfo/systemd-commits
IRC:
#systemd on irc.freenode.org
BUG REPORTS:
https://bugs.freedesktop.org/enter_bug.cgi?product=systemd
AUTHOR:
Lennart Poettering
Kay Sievers
...and many others
LICENSE:
LGPLv2.1+ for all code
- except sd-daemon.[ch] and sd-readahead.[ch] which are MIT
- except src/shared/MurmurHash3.c which is Public Domain
- except src/journal/lookup3.c which is Public Domain
- except src/udev/* which is (currently still) GPLv2, GPLv2+
REQUIREMENTS:
Linux kernel >= 3.0
CONFIG_DEVTMPFS
CONFIG_CGROUPS (it's OK to disable all controllers)
CONFIG_INOTIFY_USER
CONFIG_SIGNALFD
CONFIG_TIMERFD
CONFIG_EPOLL
CONFIG_NET
CONFIG_SYSFS
Linux kernel >= 3.8 for Smack support
Udev will fail to work with the legacy layout:
CONFIG_SYSFS_DEPRECATED=n
Legacy hotplug slows down the system and confuses udev:
CONFIG_UEVENT_HELPER_PATH=""
Userspace firmware loading is deprecated, will go away, and
sometimes causes problems:
CONFIG_FW_LOADER_USER_HELPER=n
Some udev rules and virtualization detection relies on it:
CONFIG_DMIID
Mount and bind mount handling might require it:
CONFIG_FHANDLE
Support for some SCSI devices serial number retrieval, to
create additional symlinks in /dev/disk/ and /dev/tape:
CONFIG_BLK_DEV_BSG
Optional but strongly recommended:
CONFIG_IPV6
CONFIG_AUTOFS4_FS
CONFIG_TMPFS_POSIX_ACL
CONFIG_TMPFS_XATTR
CONFIG_SECCOMP
For systemd-bootchart, a kernel with procfs support and
several proc output options enabled is required:
CONFIG_PROC_FS
CONFIG_SCHEDSTATS
CONFIG_SCHED_DEBUG
For UEFI systems:
CONFIG_EFI_VARS
CONFIG_EFI_PARTITION
Note that kernel auditing is broken when used with systemd's
container code. When using systemd in conjunction with
containers, please make sure to either turn off auditing at
runtime using the kernel command line option "audit=0", or
turn it off at kernel compile time using:
CONFIG_AUDIT=n
glibc >= 2.14
libcap
libblkid >= 2.20 (from util-linux) (optional)
libkmod >= 15 (optional)
PAM >= 1.1.2 (optional)
libcryptsetup (optional)
libaudit (optional)
libacl (optional)
libattr (optional)
libselinux (optional)
liblzma (optional)
tcpwrappers (optional)
libgcrypt (optional)
libqrencode (optional)
libmicrohttpd (optional)
libpython (optional)
make, gcc, and similar tools
During runtime, you need the following additional
dependencies:
util-linux >= v2.19 (requires fsck -l, agetty -s)
dbus >= 1.4.0 (strictly speaking optional, but recommended)
sulogin (from util-linux >= 2.22 or sysvinit-tools, optional but recommended)
dracut (optional)
PolicyKit (optional)
When building from git, you need the following additional
dependencies:
docbook-xsl
xsltproc
automake
autoconf
libtool
intltool
gperf
gtkdocize (optional)
python (optional)
sphinx (optional)
python-lxml (entirely optional)
When systemd-hostnamed is used, it is strongly recommended to
install nss-myhostname to ensure that, in a world of
dynamically changing hostnames, the hostname stays resolvable
under all circumstances. In fact, systemd-hostnamed will warn
if nss-myhostname is not installed.
Note that D-Bus can link against libsystemd-login.so, which
results in a cyclic build dependency. To accommodate for
this, please build D-Bus without systemd first, then build
systemd, then rebuild D-Bus with systemd support.
To build HTML documentation for python-systemd using sphinx,
please first install systemd (using 'make install'), and then
invoke sphinx-build with 'make sphinx-<target>', with <target>
being 'html' or 'latexpdf'. If using DESTDIR for installation,
pass the same DESTDIR to 'make sphinx-html' invocation.
USERS AND GROUPS:
Default udev rules use the following standard system group
names, which need to be resolvable by getgrnam() at any time,
even in the very early boot stages, where no other databases
and network are available:
tty, dialout, kmem, video, audio, lp, floppy, cdrom, tape, disk
During runtime, the journal daemon requires the
"systemd-journal" system group to exist. New journal files will
be readable by this group (but not writable), which may be used
to grant specific users read access.
It is also recommended to grant read access to all journal
files to the system groups "wheel" and "adm" with a command
like the following in the post installation script of the
package:
# setfacl -nm g:wheel:rx,d:g:wheel:rx,g:adm:rx,d:g:adm:rx /var/log/journal/
The journal gateway daemon requires the
"systemd-journal-gateway" system user and group to
exist. During execution this network facing service will drop
privileges and assume this uid/gid for security reasons.
WARNINGS:
systemd will warn you during boot if /etc/mtab is not a
symlink to /proc/mounts. Please ensure that /etc/mtab is a
proper symlink.
systemd will warn you during boot if /usr is on a different
file system than /. While in systemd itself very little will
break if /usr is on a separate partition, many of its
dependencies very likely will break sooner or later in one
form or another. For example, udev rules tend to refer to
binaries in /usr, binaries that link to libraries in /usr or
binaries that refer to data files in /usr. Since these
breakages are not always directly visible, systemd will warn
about this, since this kind of file system setup is not really
supported anymore by the basic set of Linux OS components.
For more information on this issue consult
http://freedesktop.org/wiki/Software/systemd/separate-usr-is-broken
To run systemd under valgrind, compile with VALGRIND defined
(e.g. ./configure CPPFLAGS='... -DVALGRIND=1'). Otherwise,
false positives will be triggered by code which violates
some rules but is actually safe.