--- /dev/null
+<?xml version='1.0'?> <!--*-nxml-*-->
+<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
+ "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
+
+<!--
+ SPDX-License-Identifier: LGPL-2.1+
+
+ This file is part of systemd.
+
+ Copyright 2018 Peter A. Bigot
+
+ 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.
+
+ systemd is distributed in the hope that it will be useful, but
+ WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public License
+ along with systemd; If not, see <http://www.gnu.org/licenses/>.
+-->
+
+<refentry id="systemd-time-wait-sync.service" conditional='ENABLE_TIMESYNCD'>
+
+ <refentryinfo>
+ <title>systemd-time-wait-sync.service</title>
+ <productname>systemd</productname>
+
+ <authorgroup>
+ <author>
+ <contrib>Developer</contrib>
+ <firstname>Peter</firstname>
+ <surname>Bigot</surname>
+ <email>pab@pabigot.com</email>
+ </author>
+ </authorgroup>
+ </refentryinfo>
+
+ <refmeta>
+ <refentrytitle>systemd-time-wait-sync.service</refentrytitle>
+ <manvolnum>8</manvolnum>
+ </refmeta>
+
+ <refnamediv>
+ <refname>systemd-time-wait-sync.service</refname>
+ <refname>systemd-time-wait-sync</refname>
+ <refpurpose>Wait Until Kernel Time Synchronized</refpurpose>
+ </refnamediv>
+
+ <refsynopsisdiv>
+ <para><filename>systemd-time-wait-sync.service</filename></para>
+ <para><filename>/usr/lib/systemd/systemd-time-wait-sync</filename></para>
+ </refsynopsisdiv>
+
+ <refsect1>
+ <title>Description</title>
+
+ <para><filename>systemd-time-wait-sync</filename> is a system service that delays the start of units that depend on
+ <filename>time-sync.target</filename> until <filename>systemd-timesyncd.service</filename> or something else has
+ set the system time and marked it as synchronized. Reaching this state generally requires synchronization with an
+ external source, such as an NTP server.</para>
+
+ <para>When this unit is not enabled the <filename>time-sync.target</filename> synchronization point may be reached
+ as soon as the system time is advanced by <filename>systemd-timesyncd.service</filename> to the time stored at the
+ last shutdown. That time may not meet the expectations of dependent services that require an accurate
+ clock.</para>
+
+ </refsect1>
+
+ <refsect1>
+ <title>Notes</title>
+
+ <para>This service works correctly with a time synchronization service like
+ <filename>systemd-timesyncd.service</filename> that uses the same protocol as NTP to set the time from a
+ synchronized source. When used with time synchronization services that follow a different protocol the event of
+ setting synchronized time may not be detected in which case this service will not complete.</para>
+ </refsect1>
+
+ <refsect1>
+ <title>See Also</title>
+ <para>
+ <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>systemd-timesyncd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
+ </para>
+ </refsect1>
+
+</refentry>
--- /dev/null
+/*
+ * systemd service to wait until kernel realtime clock is synchronized
+ *
+ * Copyright 2018 Peter A. Bigot
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
+ * USA
+ */
+
+#include <errno.h>
+#include <signal.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/timerfd.h>
+#include <sys/timex.h>
+#include <unistd.h>
+
+#include "sd-event.h"
+
+#include "fd-util.h"
+#include "missing.h"
+#include "signal-util.h"
+#include "time-util.h"
+
+typedef struct ClockState {
+ int fd; /* non-negative is descriptor from timerfd_create */
+ int adjtime_state; /* return value from last adjtimex(2) call */
+ sd_event_source *event_source; /* non-null is the active io event source */
+} ClockState;
+
+static void clock_state_release(ClockState *sp) {
+ sp->event_source = sd_event_source_unref(sp->event_source);
+ sp->fd = safe_close(sp->fd);
+}
+
+static int clock_state_update(ClockState *sp,
+ sd_event *event);
+
+static int io_handler(sd_event_source * s,
+ int fd,
+ uint32_t revents,
+ void *userdata) {
+ ClockState *sp = userdata;
+
+ return clock_state_update(sp, sd_event_source_get_event(s));
+}
+
+static int clock_state_update(ClockState *sp,
+ sd_event *event) {
+ static const struct itimerspec its = {
+ .it_value.tv_sec = TIME_T_MAX,
+ };
+ int r;
+ struct timex tx = {};
+ char buf[MAX((size_t)FORMAT_TIMESTAMP_MAX, STRLEN("unrepresentable"))];
+ usec_t t;
+ const char * ts;
+
+ clock_state_release(sp);
+
+ /* The kernel supports cancelling timers whenever its realtime clock is "set" (which can happen in a variety of
+ * ways, generally adjustments of at least 500 ms). The way this module works is we set up a timer that will
+ * wake when it the clock is set, and when that happens we read the clock synchronization state from the return
+ * value of adjtimex(2), which supports the NTP time adjustment protocol.
+ *
+ * The kernel determines whether the clock is synchronized using driver-specific tests, based on time
+ * information passed by an application, generally through adjtimex(2). If the application asserts the clock
+ * is synchronized, but does not also do something that "sets the clock", the timer will not be cancelled and
+ * synchronization will not be detected. Should this behavior be observed with a time synchronization provider
+ * this code might be reworked to do a periodic check as well.
+ *
+ * Similarly, this service will never complete if the application sets the time without also providing
+ * information that adjtimex(2) can use to determine that the clock is synchronized.
+ *
+ * Well-behaved implementations including systemd-timesyncd should not produce either situation. For timesyncd
+ * the initial set of the timestamp uses settimeofday(2), which sets the clock but does not mark it
+ * synchronized. When an NTP source is selected it sets the clock again with clock_adjtime(2) which does mark
+ * it synchronized. */
+ r = timerfd_create(CLOCK_REALTIME, TFD_NONBLOCK | TFD_CLOEXEC);
+ if (r < 0) {
+ log_error_errno(errno, "Failed to create timerfd: %m");
+ goto finish;
+ }
+ sp->fd = r;
+
+ r = timerfd_settime(sp->fd, TFD_TIMER_ABSTIME | TFD_TIMER_CANCEL_ON_SET, &its, NULL);
+ if (r < 0) {
+ log_error_errno(errno, "Failed to set timerfd conditions: %m");
+ goto finish;
+ }
+
+ r = adjtimex(&tx);
+ if (r < 0) {
+ log_error_errno(errno, "Failed to read adjtimex state: %m");
+ goto finish;
+ }
+ sp->adjtime_state = r;
+
+ if (tx.status & STA_NANO)
+ tx.time.tv_usec /= 1000;
+ t = timeval_load(&tx.time);
+ ts = format_timestamp_us_utc(buf, sizeof(buf), t);
+ if (!ts)
+ strcpy(buf, "unrepresentable");
+ log_info("adjtime state %d status %x time %s", sp->adjtime_state, tx.status, ts);
+
+ if (sp->adjtime_state == TIME_ERROR) {
+ /* Not synchronized. Do a one-shot wait on the descriptor and inform the caller we need to keep
+ * running. */
+ r = sd_event_add_io(event, &sp->event_source, sp->fd,
+ EPOLLIN, io_handler, sp);
+ if (r < 0) {
+ log_error_errno(r, "Failed to create time change monitor source: %m");
+ goto finish;
+ }
+ r = 1;
+ } else {
+ /* Synchronized; we can exit. */
+ (void) sd_event_exit(event, 0);
+ r = 0;
+ }
+
+ finish:
+ if (r < 0)
+ (void) sd_event_exit(event, r);
+ return r;
+}
+
+int main(int argc,
+ char * argv[]) {
+ int r;
+ _cleanup_(sd_event_unrefp) sd_event *event;
+ ClockState state = {
+ .fd = -1,
+ };
+
+ assert_se(sigprocmask_many(SIG_BLOCK, NULL, SIGTERM, SIGINT, -1) >= 0);
+
+ r = sd_event_default(&event);
+ if (r < 0) {
+ log_error_errno(r, "Failed to allocate event loop: %m");
+ goto finish;
+ }
+
+ r = sd_event_add_signal(event, NULL, SIGTERM, NULL, NULL);
+ if (r < 0) {
+ log_error_errno(r, "Failed to create sigterm event source: %m");
+ goto finish;
+ }
+
+ r = sd_event_add_signal(event, NULL, SIGINT, NULL, NULL);
+ if (r < 0) {
+ log_error_errno(r, "Failed to create sigint event source: %m");
+ goto finish;
+ }
+
+ r = sd_event_set_watchdog(event, true);
+ if (r < 0) {
+ log_error_errno(r, "Failed to create watchdog event source: %m");
+ goto finish;
+ }
+
+ r = clock_state_update(&state, event);
+ if (r > 0) {
+ r = sd_event_loop(event);
+ if (0 > r)
+ log_error_errno(r, "Failed in event loop: %m");
+ else if (state.adjtime_state == TIME_ERROR) {
+ log_error("Event loop terminated without synchronizing");
+ r = -ECANCELED;
+ }
+ }
+
+ finish:
+ clock_state_release(&state);
+ return r < 0 ? EXIT_FAILURE : EXIT_SUCCESS;
+}
projects / thirdparty / systemd.git / commitdiff
