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Support /etc/system-update for OSTree systems

Browse source 
This is required when / is immutable and cannot be written at runtime.

Co-authored-by: Richard Hughes <richard@hughsie.com>
This commit is contained in:
Eric Curtin 2023-04-17 22:09:24 +01:00 committed by Lennart Poettering
parent d30d5a0374
commit b9dac41837
5 changed files with 51 additions and 35 deletions
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2
man/systemd-system-update-generator.xml
View file

@ -30,7 +30,7 @@
<para><filename>systemd-system-update-generator</filename> is a
generator that automatically redirects the boot process to
<filename>system-update.target</filename>, if
<filename>/system-update</filename> exists. This is required to
<filename>/system-update</filename> or <filename>/etc/system-update</filename> exists. This is required to
implement the logic explained in the
<citerefentry><refentrytitle>systemd.offline-updates</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
</para>

46
man/systemd.offline-updates.xml
View file

@ -40,18 +40,20 @@
</listitem>
<listitem>
<para>When the user OK'ed the update, the symlink <filename>/system-update</filename> is
created that points to <filename index="false">/var/lib/system-update</filename> (or
wherever the directory with the upgrade files is located) and the system is rebooted. This
symlink is in the root directory, since we need to check for it very early at boot, at a
time where <filename>/var/</filename> is not available yet.</para>
<para>When the user OK'ed the update, the symlink <filename>/system-update</filename> or
<filename>/etc/system-update</filename> is created that points to
<filename index="false">/var/lib/system-update</filename> (or wherever the directory with
the upgrade files is located) and the system is rebooted. This symlink is in the root
directory, since we need to check for it very early at boot, at a time where
<filename>/var/</filename> is not available yet.</para>
</listitem>
<listitem>
<para>Very early in the new boot
<citerefentry><refentrytitle>systemd-system-update-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>
checks whether <filename>/system-update</filename> exists. If so, it (temporarily and for
this boot only) redirects (i.e. symlinks) <filename>default.target</filename> to
checks whether <filename>/system-update</filename> or
<filename>/etc/system-update</filename> exists. If so, it (temporarily and for this boot
only) redirects (i.e. symlinks) <filename>default.target</filename> to
<filename>system-update.target</filename>, a special target that pulls in the base system
(i.e. <filename>sysinit.target</filename>, so that all file systems are mounted but little
else) and the system update units.</para>
@ -68,12 +70,13 @@
<listitem>
<para>As the first step, an update service should check if the
<filename>/system-update</filename> symlink points to the location used by that update
service. In case it does not exist or points to a different location, the service must exit
without error. It is possible for multiple update services to be installed, and for multiple
update services to be launched in parallel, and only the one that corresponds to the tool
that <emphasis>created</emphasis> the symlink before reboot should perform any actions. It
is unsafe to run multiple updates in parallel.</para>
<filename>/system-update</filename> or <filename>/etc/system-update</filename> symlink
points to the location used by that update service. In case it does not exist or points to a
different location, the service must exit without error. It is possible for multiple update
services to be installed, and for multiple update services to be launched in parallel, and
only the one that corresponds to the tool that <emphasis>created</emphasis> the symlink
before reboot should perform any actions. It is unsafe to run multiple updates in
parallel.</para>
</listitem>
<listitem>
@ -88,14 +91,16 @@
<para>The update scripts should exit only after the update is finished. It is expected
that the service which performs the update will cause the machine to reboot after it
is done. If the <filename>system-update.target</filename> is successfully reached, i.e.
all update services have run, and the <filename>/system-update</filename> symlink still
exists, it will be removed and the machine rebooted as a safety measure.</para>
all update services have run, and the <filename>/system-update</filename> or
<filename>/etc/system-update</filename> symlink still exists, it will be removed and
the machine rebooted as a safety measure.</para>
</listitem>
<listitem>
<para>After a reboot, now that the <filename>/system-update</filename> symlink is gone,
the generator won't redirect <filename>default.target</filename> anymore and the system
now boots into the default target again.</para>
<para>After a reboot, now that the <filename>/system-update</filename> and
<filename>/etc/system-update</filename> symlink is gone, the generator won't redirect
<filename>default.target</filename> anymore and the system now boots into the default
target again.</para>
</listitem>
</orderedlist>
</refsect1>
@ -115,8 +120,9 @@
</listitem>
<listitem>
<para>Make sure to remove the <filename>/system-update</filename> symlink as early as
possible in the update script to avoid reboot loops in case the update fails.</para>
<para>Make sure to remove the <filename>/system-update</filename> and
<filename>/etc/system-update</filename> symlinks as early as possible in the update
script to avoid reboot loops in case the update fails.</para>
</listitem>
<listitem>

9
man/systemd.special.xml
View file

@ -753,8 +753,8 @@
<listitem>
<para>A special target unit that is used for offline system updates.
<citerefentry><refentrytitle>systemd-system-update-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>
will redirect the boot process to this target if <filename>/system-update</filename>
exists. For more information see
will redirect the boot process to this target if <filename>/system-update</filename> or
<filename>/etc/system-update</filename> exists. For more information see
<citerefentry><refentrytitle>systemd.offline-updates</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
</para>
@ -764,9 +764,10 @@
<filename>system-update-pre.target</filename> but not pull it in. Services which want to
run during system updates only, but before the actual system update is executed should
order themselves before this unit and pull it in. As a safety measure, if this does not
happen, and <filename>/system-update</filename> still exists after
happen, and <filename>/system-update</filename> or
<filename>/etc/system-update</filename> still exists after
<filename>system-update.target</filename> is reached,
<filename>system-update-cleanup.service</filename> will remove this symlink and reboot
<filename>system-update-cleanup.service</filename> will remove the symlinks and reboot
the machine.</para>
</listitem>
</varlistentry>

25
src/system-update-generator/system-update-generator.c
View file

@ -6,6 +6,7 @@
#include "fs-util.h"
#include "generator.h"
#include "log.h"
#include "path-util.h"
#include "proc-cmdline.h"
#include "special.h"
#include "string-util.h"
@ -18,19 +19,25 @@
static const char *arg_dest = NULL;
static int generate_symlink(void) {
const char *p = NULL;
_cleanup_free_ char *j = NULL;
if (laccess("/system-update", F_OK) < 0) {
if (errno == ENOENT)
return 0;
FOREACH_STRING(p, "/system-update", "/etc/system-update") {
if (laccess(p, F_OK) >= 0)
goto link_found;
log_error_errno(errno, "Failed to check for system update: %m");
return -EINVAL;
if (errno != ENOENT)
log_warning_errno(errno, "Failed to check if %s symlink exists, ignoring: %m", p);
}
p = strjoina(arg_dest, "/" SPECIAL_DEFAULT_TARGET);
if (symlink(SYSTEM_DATA_UNIT_DIR "/system-update.target", p) < 0)
return log_error_errno(errno, "Failed to create symlink %s: %m", p);
return 0;
link_found:
j = path_join(arg_dest, SPECIAL_DEFAULT_TARGET);
if (!j)
return log_oom();
if (symlink(SYSTEM_DATA_UNIT_DIR "/system-update.target", j) < 0)
return log_error_errno(errno, "Failed to create symlink %s: %m", j);
return 1;
}

4
units/system-update-cleanup.service
View file

@ -29,7 +29,9 @@ SuccessAction=reboot
# reboot or some other action on its own.
ConditionPathExists=|/system-update
ConditionPathIsSymbolicLink=|/system-update
ConditionPathExists=|/etc/system-update
ConditionPathIsSymbolicLink=|/etc/system-update
[Service]
Type=oneshot
ExecStart=rm -fv /system-update
ExecStart=rm -fv /system-update /etc/system-update