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The block is reordered and split to have:
1. description + documentation
2. (optionally) conditions
3. all the dependencies
I think it's easier to read the units this way.
Also, the Conflicts+Before is seperated out to separate lines.
The ordering dependency is "fake", because it could just as well be
After=, we are adding it to force ordering wrt. shutdown.target, and
it plays a different role than the other Before=, which are about a
real ordering on boot.
This reverts commit f1e24a259c. Oops.
# systemctl emergency
Failed to start emergency.target: Transaction order is cyclic. See syste...
See system logs and 'systemctl status emergency.target' for details.
# systemctl status emergency.target
● emergency.target - Emergency Mode
Loaded: loaded (/usr/lib/systemd/system/emergency.target; static; vendor preset: disabled)
Active: inactive (dead) since Mon 2017-09-25 10:43:02 BST; 2h 42min ago
Docs: man:systemd.special(7)
systemd[1]: sysinit.target: Found dependency on sysinit.target/stop
sysinit.target: Unable to break cycle starting with sysinit.target/stop
network.target: Found ordering cycle on wpa_supplicant.service/stop
network.target: Found dependency on sysinit.target/stop
network.target: Found dependency on emergency.target/start
network.target: Found dependency on emergency.service/start
network.target: Found dependency on serial-getty@ttyS0.service/stop
network.target: Found dependency on systemd-user-sessions.service/stop
network.target: Found dependency on network.target/stop
network.target: Unable to break cycle starting with network.target/stop
IMO #6509 is ugly enough that we should aim to answer it. But it could
take some time to investigate, so let's re-open the issue as a first step.
Why
---
The advantage of this is that starting sysinit.target from the emergency
shell will no longer kill the emergency shell and lock you out of the
system. Our docs already claimed that emergency.target was useful for
"starting individual units in order to continue the boot process in steps".
This resolves#6509 for my purposes.
Remaining limitation
--------------------
Starting getty.target will still kill the shell, and if you don't have a
root password you will then be locked out at that point. This is relevant
to distributions which patch the sulogin system to permit logins when the
root password is locked. Both Debian and RedHat used to follow this
behaviour! Debian have been discussing what they could replace it with at
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=806852
So this doesn't quite achieve perfection, but I think it's a worthwhile
change. It should be easier to understand the logic now it doesn't have
such a big hole in it. Repairing the sysinit stage of the boot is the main
reason we have emergency.target. And as discussed in the issue,
sysinit.target gets pulled in implicitly as soon as any DefaultDependencies
service is activated.
How
---
sysinit.target only needs to conflict with emergency.target. It didn't
need to conflict with emergency.service as well. In theory the conflicts
are pointless, we could just change the dependency of sysinit.target on
local-fs.target from Wants to Requires. However, doing so would mean that
when local-fs fails, the screen is flooded with yellow [DEPEND] failures.
That would hinder the poor unfortunate admin, so let's not do that.
There is no additional ordering requirement against emergency. If the
failure happens, the job for sysinit will be cancelled instantly. We don't
need to worry about when sysinit.target and its dependents would be
stopped, because sysinit waits for local-fs before it starts.
emergency.target is still necessarily stopped once we reach sysinit
(you can't express a one-way conflict in pure unit directives).
This is largely cosmetic... though perhaps it symbolizes that you're no
longer in Emergency Mode if System Initialization is successful ;-).
As a secondary advantage, the getty's which conflict on rescue.service now
need to conflict on emergency.service as well. This makes the system more
uniform and simpler to understand.
The only other effect this should have is that
`systemctl start emergency.target` is now practically the same as
`systemctl start rescue.target`. The only units this command will stop are
the conflicting getty units. Neither of those commands should ever be
used. E.g. they will not stop the gdm.service unit on Fedora 26.
In a normal running system, non-passive targets and units used during
early bootup are always started. So refusing "manual start" for them
doesn't make any difference, because a "start" command doesn't cause
any action.
In early boot however, the administrator might want to start on
of those targets or services by hand. We shouldn't interfere with that.
Note: in case of systemd-tmpfiles-setup.service, really running the
unit after system is up would break the system. So e.g. restarting
should not be allowed. The unit has "RefuseManualStop=yes", which
prevents restart too.
This should help making the boot process a bit easier to explore and
understand for the administrator. The simple idea is that "systemctl
status" now shows a link to documentation alongside the other status and
decriptionary information of a service.
This patch adds the necessary fields to all our shipped units if we have
proper documentation for them.
We finally got the OK from all contributors with non-trivial commits to
relicense systemd from GPL2+ to LGPL2.1+.
Some udev bits continue to be GPL2+ for now, but we are looking into
relicensing them too, to allow free copy/paste of all code within
systemd.
The bits that used to be MIT continue to be MIT.
The big benefit of the relicensing is that closed source code may now
link against libsystemd-login.so and friends.
