Michal Schmidt
e0209d83e7
Two of our current job types are special: JOB_TRY_RESTART, JOB_RELOAD_OR_START. They differ from other job types by being sensitive to the unit active state. They perform some action when the unit is active and some other action otherwise. This raises a question: when exactly should the unit state be checked to make the decision? Currently the unit state is checked when the job becomes runnable. It's more sensible to check the state immediately when the job is added by the user. When the user types "systemctl try-restart foo.service", he really intends to restart the service if it's running right now. If it isn't running right now, the restart is pointless. Consider the example (from Bugzilla[1]): sleep.service takes some time to start. hello.service has After=sleep.service. Both services get started. Two jobs will appear: hello.service/start waiting sleep.service/start running Then someone runs "systemctl try-restart hello.service". Currently the try-restart operation will block and wait for sleep.service/start to complete. The correct result is to complete the try-restart operation immediately with success, because hello.service is not running. The two original jobs must not be disturbed by this. To fix this we introduce two new concepts: - a new job type: JOB_NOP A JOB_NOP job does not do anything to the unit. It does not pull in any dependencies. It is always immediately runnable. When installed to a unit, it sits in a special slot (u->nop_job) where it never conflicts with the installed job (u->job) of a different type. It never merges with jobs of other types, but it can merge into an already installed JOB_NOP job. - "collapsing" of job types When a job of one of the two special types is added, the state of the unit is checked immediately and the job type changes: JOB_TRY_RESTART -> JOB_RESTART or JOB_NOP JOB_RELOAD_OR_START -> JOB_RELOAD or JOB_START Should a job type JOB_RELOAD_OR_START appear later during job merging, it collapses immediately afterwards. Collapsing actually makes some things simpler, because there are now fewer job types that are allowed in the transaction. [1] Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=753586
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 GPLv2.0+
REQUIREMENTS:
Linux kernel >= 2.6.39
with devtmpfs
with cgroups (but it's OK to disable all controllers)
optional but strongly recommended: autofs4, ipv6
dbus >= 1.4.0
libcap
PAM >= 1.1.2 (optional)
libcryptsetup (optional)
libaudit (optional)
libselinux (optional)
tcpwrappers (optional)
When you build from git you need the following additional dependencies:
docbook-xsl
xsltproc
automake
autoconf
libtool
gperf
make, gcc, and similar tools
During runtime you need the following dependencies:
util-linux > v2.18 (requires fsck -l, agetty -s)
sulogin (from sysvinit-tools, optional but recommended)
plymouth (optional)
dracut (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 resolveable
under all circumstances. In fact, systemd-hostnamed will warn
if nss-myhostname is not installed. Packagers are encouraged to
add a dependency on nss-myhostname to the package that
includes systemd-hostnamed.
Note that D-Bus can link against libsystemd-login.so, which
results in a cyclic build dependency. To accomodate for this
please build D-Bus without systemd first, then build systemd,
then rebuild D-Bus with systemd support.
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
ENGINEERING AND CONSULTING SERVICES:
ProFUSION <http://profusion.mobi> offers professional
engineering and consulting services for systemd for embedded
and other use. Please contact Gustavo Barbieri
<barbieri@profusion.mobi> for more information.
Disclaimer: This notice is not a recommendation or official
endorsement. However, ProFUSION's upstream work has been very
beneficial for the systemd project.