time-sync-wait: add service (#8494)
This one-shot service waits until the kernel time has been set to synchronized.
This commit is contained in:
Peter A. Bigot
Lennart Poettering
parent
d9a43665eb
commit
5c3376efcd
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@ -639,6 +639,7 @@ manpages = [
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''],
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['systemd-sysusers', '8', ['systemd-sysusers.service'], ''],
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['systemd-sysv-generator', '8', [], 'HAVE_SYSV_COMPAT'],
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['systemd-time-wait-sync.service', '8', ['systemd-time-wait-sync'], 'ENABLE_TIMESYNCD'],
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['systemd-timedated.service', '8', ['systemd-timedated'], 'ENABLE_TIMEDATED'],
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['systemd-timesyncd.service', '8', ['systemd-timesyncd'], 'ENABLE_TIMESYNCD'],
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['systemd-tmpfiles',
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@ -0,0 +1,91 @@
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<?xml version='1.0'?> <!--*-nxml-*-->
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!--
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SPDX-License-Identifier: LGPL-2.1+
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This file is part of systemd.
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Copyright 2018 Peter A. Bigot
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systemd is free software; you can redistribute it and/or modify it
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under the terms of the GNU Lesser General Public License as published by
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the Free Software Foundation; either version 2.1 of the License, or
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(at your option) any later version.
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systemd is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with systemd; If not, see <http://www.gnu.org/licenses/>.
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-->
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<refentry id="systemd-time-wait-sync.service" conditional='ENABLE_TIMESYNCD'>
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<refentryinfo>
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<title>systemd-time-wait-sync.service</title>
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<productname>systemd</productname>
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<authorgroup>
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<author>
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<contrib>Developer</contrib>
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<firstname>Peter</firstname>
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<surname>Bigot</surname>
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<email>pab@pabigot.com</email>
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</author>
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</authorgroup>
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</refentryinfo>
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<refmeta>
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<refentrytitle>systemd-time-wait-sync.service</refentrytitle>
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<manvolnum>8</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>systemd-time-wait-sync.service</refname>
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<refname>systemd-time-wait-sync</refname>
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<refpurpose>Wait Until Kernel Time Synchronized</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<para><filename>systemd-time-wait-sync.service</filename></para>
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<para><filename>/usr/lib/systemd/systemd-time-wait-sync</filename></para>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para><filename>systemd-time-wait-sync</filename> is a system service that delays the start of units that depend on
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<filename>time-sync.target</filename> until <filename>systemd-timesyncd.service</filename> or something else has
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set the system time and marked it as synchronized. Reaching this state generally requires synchronization with an
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external source, such as an NTP server.</para>
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<para>When this unit is not enabled the <filename>time-sync.target</filename> synchronization point may be reached
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as soon as the system time is advanced by <filename>systemd-timesyncd.service</filename> to the time stored at the
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last shutdown. That time may not meet the expectations of dependent services that require an accurate
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clock.</para>
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</refsect1>
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<refsect1>
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<title>Notes</title>
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<para>This service works correctly with a time synchronization service like
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<filename>systemd-timesyncd.service</filename> that uses the same protocol as NTP to set the time from a
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synchronized source. When used with time synchronization services that follow a different protocol the event of
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setting synchronized time may not be detected in which case this service will not complete.</para>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<para>
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd-timesyncd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
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</para>
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</refsect1>
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</refentry>
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@ -1303,6 +1303,7 @@ includes = include_directories('src/basic',
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'src/journal',
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'src/resolve',
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'src/timesync',
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'src/time-wait-sync',
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'src/login',
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'src/udev',
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'src/libudev',
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@ -1885,6 +1886,14 @@ if conf.get('ENABLE_TIMESYNCD') == 1
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install_rpath : rootlibexecdir,
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install : true,
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install_dir : rootlibexecdir)
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executable('systemd-time-wait-sync',
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'src/time-wait-sync/time-wait-sync.c',
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include_directories : includes,
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link_with : [libshared],
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install_rpath : rootlibexecdir,
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install : true,
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install_dir : rootlibexecdir)
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endif
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if conf.get('ENABLE_MACHINED') == 1
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@ -0,0 +1,191 @@
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/*
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* systemd service to wait until kernel realtime clock is synchronized
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*
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* Copyright 2018 Peter A. Bigot
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License as
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* published by the Free Software Foundation; either version 2 of the
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* License, or (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
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* USA
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*/
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#include <errno.h>
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#include <signal.h>
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#include <stdbool.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <sys/timerfd.h>
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#include <sys/timex.h>
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#include <unistd.h>
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#include "sd-event.h"
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#include "fd-util.h"
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#include "missing.h"
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#include "signal-util.h"
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#include "time-util.h"
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typedef struct ClockState {
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int fd; /* non-negative is descriptor from timerfd_create */
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int adjtime_state; /* return value from last adjtimex(2) call */
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sd_event_source *event_source; /* non-null is the active io event source */
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} ClockState;
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static void clock_state_release(ClockState *sp) {
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sp->event_source = sd_event_source_unref(sp->event_source);
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sp->fd = safe_close(sp->fd);
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}
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static int clock_state_update(ClockState *sp,
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sd_event *event);
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static int io_handler(sd_event_source * s,
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int fd,
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uint32_t revents,
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void *userdata) {
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ClockState *sp = userdata;
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return clock_state_update(sp, sd_event_source_get_event(s));
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}
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static int clock_state_update(ClockState *sp,
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sd_event *event) {
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static const struct itimerspec its = {
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.it_value.tv_sec = TIME_T_MAX,
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};
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int r;
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struct timex tx = {};
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char buf[MAX((size_t)FORMAT_TIMESTAMP_MAX, STRLEN("unrepresentable"))];
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usec_t t;
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const char * ts;
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clock_state_release(sp);
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/* The kernel supports cancelling timers whenever its realtime clock is "set" (which can happen in a variety of
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* ways, generally adjustments of at least 500 ms). The way this module works is we set up a timer that will
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* wake when it the clock is set, and when that happens we read the clock synchronization state from the return
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* value of adjtimex(2), which supports the NTP time adjustment protocol.
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*
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* The kernel determines whether the clock is synchronized using driver-specific tests, based on time
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* information passed by an application, generally through adjtimex(2). If the application asserts the clock
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* is synchronized, but does not also do something that "sets the clock", the timer will not be cancelled and
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* synchronization will not be detected. Should this behavior be observed with a time synchronization provider
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* this code might be reworked to do a periodic check as well.
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*
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* Similarly, this service will never complete if the application sets the time without also providing
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* information that adjtimex(2) can use to determine that the clock is synchronized.
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*
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* Well-behaved implementations including systemd-timesyncd should not produce either situation. For timesyncd
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* the initial set of the timestamp uses settimeofday(2), which sets the clock but does not mark it
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* synchronized. When an NTP source is selected it sets the clock again with clock_adjtime(2) which does mark
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* it synchronized. */
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r = timerfd_create(CLOCK_REALTIME, TFD_NONBLOCK | TFD_CLOEXEC);
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if (r < 0) {
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log_error_errno(errno, "Failed to create timerfd: %m");
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goto finish;
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}
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sp->fd = r;
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r = timerfd_settime(sp->fd, TFD_TIMER_ABSTIME | TFD_TIMER_CANCEL_ON_SET, &its, NULL);
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if (r < 0) {
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log_error_errno(errno, "Failed to set timerfd conditions: %m");
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goto finish;
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}
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r = adjtimex(&tx);
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if (r < 0) {
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log_error_errno(errno, "Failed to read adjtimex state: %m");
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goto finish;
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}
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sp->adjtime_state = r;
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if (tx.status & STA_NANO)
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tx.time.tv_usec /= 1000;
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t = timeval_load(&tx.time);
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ts = format_timestamp_us_utc(buf, sizeof(buf), t);
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if (!ts)
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strcpy(buf, "unrepresentable");
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log_info("adjtime state %d status %x time %s", sp->adjtime_state, tx.status, ts);
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if (sp->adjtime_state == TIME_ERROR) {
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/* Not synchronized. Do a one-shot wait on the descriptor and inform the caller we need to keep
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* running. */
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r = sd_event_add_io(event, &sp->event_source, sp->fd,
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EPOLLIN, io_handler, sp);
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if (r < 0) {
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log_error_errno(r, "Failed to create time change monitor source: %m");
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goto finish;
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}
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r = 1;
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} else {
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/* Synchronized; we can exit. */
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(void) sd_event_exit(event, 0);
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r = 0;
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}
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finish:
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if (r < 0)
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(void) sd_event_exit(event, r);
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return r;
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}
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int main(int argc,
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char * argv[]) {
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int r;
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_cleanup_(sd_event_unrefp) sd_event *event;
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ClockState state = {
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.fd = -1,
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};
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assert_se(sigprocmask_many(SIG_BLOCK, NULL, SIGTERM, SIGINT, -1) >= 0);
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r = sd_event_default(&event);
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if (r < 0) {
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log_error_errno(r, "Failed to allocate event loop: %m");
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goto finish;
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}
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r = sd_event_add_signal(event, NULL, SIGTERM, NULL, NULL);
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if (r < 0) {
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log_error_errno(r, "Failed to create sigterm event source: %m");
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goto finish;
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}
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r = sd_event_add_signal(event, NULL, SIGINT, NULL, NULL);
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if (r < 0) {
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log_error_errno(r, "Failed to create sigint event source: %m");
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goto finish;
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}
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r = sd_event_set_watchdog(event, true);
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if (r < 0) {
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log_error_errno(r, "Failed to create watchdog event source: %m");
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goto finish;
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}
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r = clock_state_update(&state, event);
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if (r > 0) {
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r = sd_event_loop(event);
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if (0 > r)
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log_error_errno(r, "Failed in event loop: %m");
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else if (state.adjtime_state == TIME_ERROR) {
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log_error("Event loop terminated without synchronizing");
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r = -ECANCELED;
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}
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}
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finish:
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clock_state_release(&state);
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return r < 0 ? EXIT_FAILURE : EXIT_SUCCESS;
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}
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@ -210,6 +210,8 @@ in_units = [
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'dbus-org.freedesktop.timedate1.service'],
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['systemd-timesyncd.service', 'ENABLE_TIMESYNCD',
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join_paths(pkgsysconfdir, 'system/sysinit.target.wants/')],
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['systemd-time-wait-sync.service', '',
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join_paths(pkgsysconfdir, 'system/sysinit.target.wants/')],
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['systemd-tmpfiles-clean.service', 'ENABLE_TMPFILES'],
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['systemd-tmpfiles-setup-dev.service', 'ENABLE_TMPFILES',
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'sysinit.target.wants/'],
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@ -0,0 +1,25 @@
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# SPDX-License-Identifier: LGPL-2.1+
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#
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# This file is part of systemd.
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#
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# systemd is free software; you can redistribute it and/or modify it
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# under the terms of the GNU Lesser General Public License as published by
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# the Free Software Foundation; either version 2.1 of the License, or
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# (at your option) any later version.
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[Unit]
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Description=Wait Until Kernel Time Synchronized
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Documentation=man:systemd-time-wait-sync.service(8)
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DefaultDependencies=no
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Before=time-sync.target shutdown.target
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Wants=time-sync.target
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Conflicts=shutdown.target
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[Service]
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Type=oneshot
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ExecStart=@rootlibexecdir@/systemd-time-wait-sync
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TimeoutStartSec=infinity
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RemainAfterExit=yes
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[Install]
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WantedBy=sysinit.target
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