Zbigniew Jędrzejewski-Szmek
cbd671772c
In the following scenario: server creates system.journal server creates user-1000.journal both journals share the same seqnum_id. Then server writes to user-1000.journal first, and server writes to system.journal a bit later, and everything is fine. The server then terminates (crash, reboot, rsyslog testing, whatever), and user-1000.journal has entries which end with a lower seqnum than system.journal. Now server is restarted server opens user-1000.journal and writes entries to it... BAM! duplicate seqnums for the same seqnum_id. Now, we usually don't see that happen, because system.journal is closed last, and opened first. Since usually at least one message is written during boot and lands in the system.journal, the seqnum is initialized from it, and is set to a number higher than than anything found in user journals. Nevertheless, if system.journal is corrupted and is rotated, it can happen that an entry is written to the user journal with a seqnum that is a duplicate with an entry found in the corrupted system.journal~. When browsing the journal, journalctl can fall into a loop where it tries to follow the seqnums, and tries to go the next location by seqnum, and is transported back in time to to the older duplicate seqnum. There is not way to find out the maximum seqnum used in a multiple files, without actually looking at all of them. But we don't want to do that because it would be slow, and actually it isn't really possible, because a file might e.g. be temporarily unaccessible. Fix the problem by using different seqnum series for user journals. Using the same seqnum series for rotated journals is still fine, because we know that nothing will write to the rotated journal anymore. Likely related: https://bugs.freedesktop.org/show_bug.cgi?id=64566 https://bugs.freedesktop.org/show_bug.cgi?id=59856 https://bugs.freedesktop.org/show_bug.cgi?id=64296 https://bugs.archlinux.org/task/35581 https://bugzilla.novell.com/show_bug.cgi?id=817778 Possibly related: https://bugs.freedesktop.org/show_bug.cgi?id=64293
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/udev/ which is (currently still) GPLv2+
REQUIREMENTS:
Linux kernel >= 2.6.39
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
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
dbus >= 1.4.0
libcap
libblkid >= 2.20 (from util-linux) (optional)
libkmod >= 5 (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)
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.