From 953bf4604f5ce02d1bd8abb09e82ea80e101c8a3 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Zbigniew=20J=C4=99drzejewski-Szmek?= Date: Tue, 29 Nov 2016 01:29:02 -0500 Subject: [PATCH] units: add system-update-cleanup.service to guard against offline-update loops Note: the name is "system-update-cleanup.service" rather than "system-update-done.service", because it should not run normally, and also because there's already "systemd-update-done.service", and having them named so similarly would be confusing. In https://bugzilla.redhat.com/show_bug.cgi?id=1395686 the system repeatedly entered system-update.target on boot. Because of a packaging issue, the tool that created the /system-update symlink could be installed without the service unit that was supposed to perform the upgrade (and remove the symlink). In fact, if there are no units in system-update.target, and /system-update symlink is created, systemd always "hangs" in system-update.target. This is confusing for users, because there's no feedback what is happening, and fixing this requires starting an emergency shell somehow, and also knowing that the symlink must be removed. We should be more resilient in this case, and remove the symlink automatically ourselves, if there are no upgrade service to handle it. This adds a service which is started after system-update.target is reached and the symlink still exists. It nukes the symlink and reboots the machine. It should subsequently boot into the default default.target. This is a more general fix for https://bugzilla.redhat.com/show_bug.cgi?id=1395686 (the packaging issue was already fixed). --- Makefile.am | 2 ++ man/systemd.offline-updates.xml | 4 +++- man/systemd.special.xml | 9 ++++++++ units/.gitignore | 1 + units/system-update-cleanup.service.in | 32 ++++++++++++++++++++++++++ units/system-update.target | 1 + 6 files changed, 48 insertions(+), 1 deletion(-) create mode 100644 units/system-update-cleanup.service.in diff --git a/Makefile.am b/Makefile.am index 5cec19fbb8..6c350b0ec4 100644 --- a/Makefile.am +++ b/Makefile.am @@ -529,6 +529,7 @@ nodist_systemunit_DATA = \ units/serial-getty@.service \ units/console-getty.service \ units/container-getty@.service \ + units/system-update-cleanup.service \ units/systemd-initctl.service \ units/systemd-remount-fs.service \ units/systemd-ask-password-wall.service \ @@ -592,6 +593,7 @@ EXTRA_DIST += \ units/console-getty.service.m4.in \ units/container-getty@.service.m4.in \ units/rescue.service.in \ + units/system-update-cleanup.service.in \ units/systemd-initctl.service.in \ units/systemd-remount-fs.service.in \ units/systemd-update-utmp.service.in \ diff --git a/man/systemd.offline-updates.xml b/man/systemd.offline-updates.xml index 22aa0354a8..d673cf5db8 100644 --- a/man/systemd.offline-updates.xml +++ b/man/systemd.offline-updates.xml @@ -115,7 +115,9 @@ The upgrade scripts should exit only after the update is finished. It is expected that the service which performs the upgrade will cause the machine to reboot after it - is done. + is done. If the system-update.target is successfully reached, i.e. + all update services have run, and the /system-update symlink still + exists, it will be removed and the machine rebooted as a safety measure. diff --git a/man/systemd.special.xml b/man/systemd.special.xml index de6a5ac6cd..b513a13b5a 100644 --- a/man/systemd.special.xml +++ b/man/systemd.special.xml @@ -102,6 +102,7 @@ sysinit.target, syslog.socket, system-update.target, + system-update-cleanup.service, time-sync.target, timers.target, umount.target, @@ -608,6 +609,7 @@ system-update.target + system-update-cleanup.service A special target unit that is used for offline system updates. systemd-system-update-generator8 @@ -615,6 +617,13 @@ exists. For more information see systemd.offline-updates7. + + Updates should happen before the system-update.target is + reached, and the services which implement them should cause the machine to reboot. As + a safety measure, if this does not happen, and /system-update + still exists after system-update.target is reached, + system-update-cleanup.service will remove this symlink and + reboot the machine. diff --git a/units/.gitignore b/units/.gitignore index 8f4949258e..8fdb6e9ab5 100644 --- a/units/.gitignore +++ b/units/.gitignore @@ -16,6 +16,7 @@ /rc-local.service /rescue.service /serial-getty@.service +/system-update-cleanup.service /systemd-ask-password-console.service /systemd-ask-password-wall.service /systemd-backlight@.service diff --git a/units/system-update-cleanup.service.in b/units/system-update-cleanup.service.in new file mode 100644 index 0000000000..116be8bc2d --- /dev/null +++ b/units/system-update-cleanup.service.in @@ -0,0 +1,32 @@ +# This file is part of systemd. +# +# systemd is free software; you can redistribute it and/or modify it +# under the terms of the GNU Lesser General Public License as published by +# the Free Software Foundation; either version 2.1 of the License, or +# (at your option) any later version. + +[Unit] +Description=Remove the Offline System Updates symlink +Documentation=man:systemd.special(5) man:systemd.offline-updates(7) +After=system-update.target +DefaultDependencies=no +Conflicts=shutdown.target + +# system-update-generator uses laccess("/system-update"), while a plain +# ConditionPathExists=/system-update uses access("/system-update"), so +# we need an alternate condition to cover the case of a dangling symlink. +# +# This service is only invoked if /system-update exists, i.e. if the +# condition tested by system-update-generator remains true and the system +# would be diverted into system-update.target again after reboot. This way +# we guard against being diverted into system-update.target again, which +# works as a safety measure, but we will not step on the toes of the +# update script if it successfully removed the symlink and scheduled a +# reboot or some other action on its own. +ConditionPathExists=|/system-update +ConditionPathIsSymbolicLink=|/system-update + +[Service] +Type=oneshot +ExecStart=/bin/rm -fv /system-update +ExecStart=@SYSTEMCTL@ reboot diff --git a/units/system-update.target b/units/system-update.target index 4054112c84..3542879706 100644 --- a/units/system-update.target +++ b/units/system-update.target @@ -14,3 +14,4 @@ Conflicts=shutdown.target After=sysinit.target Before=shutdown.target AllowIsolate=yes +Wants=system-update-cleanup.service