chiark / gitweb /
timesyncd: only run when the system has a carrier on a network interface
[elogind.git] / src / timesync / timesyncd.c
index a66d1e46c030fe1abea8185f5f149904d83c176e..eb55bc068c17b4556028a58ba567468a7284478a 100644 (file)
@@ -3,7 +3,7 @@
 /***
   This file is part of systemd.
 
-  Copyright 2014 Kay Sievers
+  Copyright 2014 Kay Sievers, Lennart Poettering
 
   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
 #include <sys/timerfd.h>
 #include <sys/timex.h>
 #include <sys/socket.h>
+#include <resolv.h>
 
 #include "missing.h"
 #include "util.h"
 #include "sparse-endian.h"
 #include "log.h"
 #include "socket-util.h"
+#include "list.h"
+#include "ratelimit.h"
+#include "strv.h"
+#include "conf-parser.h"
 #include "sd-event.h"
 #include "sd-resolve.h"
 #include "sd-daemon.h"
+#include "sd-network.h"
+#include "event-util.h"
+#include "network-util.h"
+#include "timesyncd.h"
 
 #define TIME_T_MAX (time_t)((1UL << ((sizeof(time_t) << 3) - 1)) - 1)
 
  */
 #define OFFSET_1900_1970        2208988800UL
 
+#define RETRY_USEC (30*USEC_PER_SEC)
+#define RATELIMIT_INTERVAL_USEC (10*USEC_PER_SEC)
+#define RATELIMIT_BURST 10
+
+#define TIMEOUT_USEC (10*USEC_PER_SEC)
+
 struct ntp_ts {
         be32_t sec;
         be32_t frac;
@@ -106,57 +121,14 @@ struct ntp_msg {
         struct ntp_ts trans_time;
 } _packed_;
 
-typedef struct Manager Manager;
-struct Manager {
-        sd_event *event;
-        sd_resolve *resolve;
-
-        /* peer */
-        sd_resolve_query *resolve_query;
-        sd_event_source *event_receive;
-        char *server;
-        union sockaddr_union server_addr;
-        socklen_t server_addr_length;
-        int server_socket;
-        uint64_t packet_count;
-
-        /* last sent packet */
-        struct timespec trans_time_mon;
-        struct timespec trans_time;
-        usec_t retry_interval;
-        bool pending;
-
-        /* poll timer */
-        sd_event_source *event_timer;
-        usec_t poll_interval_usec;
-        bool poll_resync;
-
-        /* history data */
-        struct {
-                double offset;
-                double delay;
-        } samples[8];
-        unsigned int samples_idx;
-        double samples_jitter;
-
-        /* last change */
-        bool jumped;
-        int drift_ppm;
-
-        /* watch for time changes */
-        sd_event_source *event_clock_watch;
-        int clock_watch_fd;
-
-        /* Handle SIGINT/SIGTERM */
-        sd_event_source *sigterm, *sigint;
-};
-
 static void manager_free(Manager *m);
 DEFINE_TRIVIAL_CLEANUP_FUNC(Manager*, manager_free);
 #define _cleanup_manager_free_ _cleanup_(manager_freep)
 
 static int manager_arm_timer(Manager *m, usec_t next);
 static int manager_clock_watch_setup(Manager *m);
+static int manager_connect(Manager *m);
+static void manager_disconnect(Manager *m);
 
 static double ntp_ts_to_d(const struct ntp_ts *ts) {
         return be32toh(ts->sec) + ((double)be32toh(ts->frac) / UINT_MAX);
@@ -174,7 +146,22 @@ static double square(double d) {
         return d * d;
 }
 
+static int manager_timeout(sd_event_source *source, usec_t usec, void *userdata) {
+        _cleanup_free_ char *pretty = NULL;
+        Manager *m = userdata;
+
+        assert(m);
+        assert(m->current_server_name);
+        assert(m->current_server_address);
+
+        sockaddr_pretty(&m->current_server_address->sockaddr.sa, m->current_server_address->socklen, true, &pretty);
+        log_info("Timed out waiting for reply from %s (%s).", strna(pretty), m->current_server_name->string);
+
+        return manager_connect(m);
+}
+
 static int manager_send_request(Manager *m) {
+        _cleanup_free_ char *pretty = NULL;
         struct ntp_msg ntpmsg = {
                 /*
                  * "The client initializes the NTP message header, sends the request
@@ -186,6 +173,13 @@ static int manager_send_request(Manager *m) {
                 .field = NTP_FIELD(0, 4, NTP_MODE_CLIENT),
         };
         ssize_t len;
+        int r;
+
+        assert(m);
+        assert(m->current_server_name);
+        assert(m->current_server_address);
+
+        m->event_timeout = sd_event_source_unref(m->event_timeout);
 
         /*
          * Set transmit timestamp, remember it; the server will send that back
@@ -200,12 +194,16 @@ static int manager_send_request(Manager *m) {
         ntpmsg.trans_time.sec = htobe32(m->trans_time.tv_sec + OFFSET_1900_1970);
         ntpmsg.trans_time.frac = htobe32(m->trans_time.tv_nsec);
 
-        len = sendto(m->server_socket, &ntpmsg, sizeof(ntpmsg), MSG_DONTWAIT, &m->server_addr.sa, m->server_addr_length);
+        sockaddr_pretty(&m->current_server_address->sockaddr.sa, m->current_server_address->socklen, true, &pretty);
+
+        len = sendto(m->server_socket, &ntpmsg, sizeof(ntpmsg), MSG_DONTWAIT, &m->current_server_address->sockaddr.sa, m->current_server_address->socklen);
         if (len == sizeof(ntpmsg)) {
                 m->pending = true;
-                log_debug("Sent NTP request to: %s", m->server);
-        } else
-                log_debug("Sending NTP request to %s failed: %m", m->server);
+                log_debug("Sent NTP request to %s (%s).", strna(pretty), m->current_server_name->string);
+        } else {
+                log_debug("Sending NTP request to %s (%s) failed: %m", strna(pretty), m->current_server_name->string);
+                return manager_connect(m);
+        }
 
         /* re-arm timer with incresing timeout, in case the packets never arrive back */
         if (m->retry_interval > 0) {
@@ -214,7 +212,24 @@ static int manager_send_request(Manager *m) {
         } else
                 m->retry_interval = NTP_POLL_INTERVAL_MIN_SEC * USEC_PER_SEC;
 
-        return manager_arm_timer(m, m->retry_interval);
+        r = manager_arm_timer(m, m->retry_interval);
+        if (r < 0) {
+                log_error("Failed to rearm timer: %s", strerror(-r));
+                return r;
+        }
+
+        r = sd_event_add_time(
+                        m->event,
+                        &m->event_timeout,
+                        CLOCK_MONOTONIC,
+                        now(CLOCK_MONOTONIC) + TIMEOUT_USEC, 0,
+                        manager_timeout, m);
+        if (r < 0) {
+                log_error("Failed to arm timeout timer: %s", strerror(-r));
+                return r;
+        }
+
+        return 0;
 }
 
 static int manager_timer(sd_event_source *source, usec_t usec, void *userdata) {
@@ -284,7 +299,7 @@ static int manager_clock_watch_setup(Manager *m) {
         assert(m);
 
         m->event_clock_watch = sd_event_source_unref(m->event_clock_watch);
-        m->clock_watch_fd = safe_close(m->clock_watch_fd);
+        safe_close(m->clock_watch_fd);
 
         m->clock_watch_fd = timerfd_create(CLOCK_REALTIME, TFD_NONBLOCK|TFD_CLOEXEC);
         if (m->clock_watch_fd < 0) {
@@ -501,9 +516,12 @@ static int manager_receive_response(sd_event_source *source, int fd, uint32_t re
         int leap_sec;
         int r;
 
+        assert(source);
+        assert(m);
+
         if (revents & (EPOLLHUP|EPOLLERR)) {
-                log_debug("Server connection returned error.");
-                return -ENOTCONN;
+                log_warning("Server connection returned error.");
+                return manager_connect(m);
         }
 
         len = recvmsg(fd, &msghdr, MSG_DONTWAIT);
@@ -511,18 +529,20 @@ static int manager_receive_response(sd_event_source *source, int fd, uint32_t re
                 if (errno == EAGAIN)
                         return 0;
 
-                log_debug("Error receiving message. Disconnecting.");
-                return -errno;
+                log_warning("Error receiving message. Disconnecting.");
+                return manager_connect(m);
         }
 
         if (iov.iov_len < sizeof(struct ntp_msg)) {
-                log_debug("Invalid response from server. Disconnecting.");
-                return -EINVAL;
+                log_warning("Invalid response from server. Disconnecting.");
+                return manager_connect(m);
         }
 
-        if (!sockaddr_equal(&server_addr, &m->server_addr)) {
-                log_debug("Response from unknown server. Disconnecting.");
-                return -EINVAL;
+        if (!m->current_server_name ||
+            !m->current_server_address ||
+            !sockaddr_equal(&server_addr, &m->current_server_address->sockaddr)) {
+                log_debug("Response from unknown server.");
+                return 0;
         }
 
         recv_time = NULL;
@@ -537,7 +557,7 @@ static int manager_receive_response(sd_event_source *source, int fd, uint32_t re
                 }
         }
         if (!recv_time) {
-                log_debug("Invalid packet timestamp. Disconnecting.");
+                log_error("Invalid packet timestamp.");
                 return -EINVAL;
         }
 
@@ -553,19 +573,27 @@ static int manager_receive_response(sd_event_source *source, int fd, uint32_t re
                 return 0;
         }
 
+        m->event_timeout = sd_event_source_unref(m->event_timeout);
+
+        if (be32toh(ntpmsg.recv_time.sec) < TIME_EPOCH + OFFSET_1900_1970 ||
+            be32toh(ntpmsg.trans_time.sec) < TIME_EPOCH + OFFSET_1900_1970) {
+                log_debug("Invalid reply, returned times before epoch. Ignoring.");
+                return manager_connect(m);
+        }
+
         if (NTP_FIELD_LEAP(ntpmsg.field) == NTP_LEAP_NOTINSYNC) {
                 log_debug("Server is not synchronized. Disconnecting.");
-                return -EINVAL;
+                return manager_connect(m);
         }
 
-        if (NTP_FIELD_VERSION(ntpmsg.field) != 4) {
+        if (!IN_SET(NTP_FIELD_VERSION(ntpmsg.field), 3, 4)) {
                 log_debug("Response NTPv%d. Disconnecting.", NTP_FIELD_VERSION(ntpmsg.field));
-                return -EINVAL;
+                return manager_connect(m);
         }
 
         if (NTP_FIELD_MODE(ntpmsg.field) != NTP_MODE_SERVER) {
                 log_debug("Unsupported mode %d. Disconnecting.", NTP_FIELD_MODE(ntpmsg.field));
-                return -EINVAL;
+                return manager_connect(m);
         }
 
         /* valid packet */
@@ -641,11 +669,17 @@ static int manager_receive_response(sd_event_source *source, int fd, uint32_t re
                         log_error("Failed to call clock_adjtime(): %m");
         }
 
-        log_info("%s: interval/delta/delay/jitter/drift %llus/%+.3fs/%.3fs/%.3fs/%+ippm%s",
-                 m->server, m->poll_interval_usec / USEC_PER_SEC, offset, delay, m->samples_jitter, m->drift_ppm,
+        log_info("interval/delta/delay/jitter/drift %llus/%+.3fs/%.3fs/%.3fs/%+ippm%s",
+                 m->poll_interval_usec / USEC_PER_SEC, offset, delay, m->samples_jitter, m->drift_ppm,
                  spike ? " (ignored)" : "");
 
-        return manager_arm_timer(m, m->poll_interval_usec);
+        r = manager_arm_timer(m, m->poll_interval_usec);
+        if (r < 0) {
+                log_error("Failed to rearm timer: %s", strerror(-r));
+                return r;
+        }
+
+        return 0;
 }
 
 static int manager_listen_setup(Manager *m) {
@@ -658,14 +692,15 @@ static int manager_listen_setup(Manager *m) {
 
         assert(m->server_socket < 0);
         assert(!m->event_receive);
+        assert(m->current_server_address);
 
-        addr.sa.sa_family = m->server_addr.sa.sa_family;
+        addr.sa.sa_family = m->current_server_address->sockaddr.sa.sa_family;
 
         m->server_socket = socket(addr.sa.sa_family, SOCK_DGRAM | SOCK_CLOEXEC, 0);
         if (m->server_socket < 0)
                 return -errno;
 
-        r = bind(m->server_socket, &addr.sa, m->server_addr_length);
+        r = bind(m->server_socket, &addr.sa, m->current_server_address->socklen);
         if (r < 0)
                 return -errno;
 
@@ -678,78 +713,229 @@ static int manager_listen_setup(Manager *m) {
         return sd_event_add_io(m->event, &m->event_receive, m->server_socket, EPOLLIN, manager_receive_response, m);
 }
 
-static int manager_resolve_handler(sd_resolve_query *q, int ret, const struct addrinfo *ai, void *userdata) {
+static int manager_begin(Manager *m) {
         _cleanup_free_ char *pretty = NULL;
-        Manager *m = userdata;
         int r;
 
+        assert(m);
+        assert_return(m->current_server_name, -EHOSTUNREACH);
+        assert_return(m->current_server_address, -EHOSTUNREACH);
+
+        m->poll_interval_usec = NTP_POLL_INTERVAL_MIN_SEC * USEC_PER_SEC;
+
+        sockaddr_pretty(&m->current_server_address->sockaddr.sa, m->current_server_address->socklen, true, &pretty);
+        log_info("Using NTP server %s (%s).", strna(pretty), m->current_server_name->string);
+        sd_notifyf(false, "STATUS=Using Time Server %s (%s).", strna(pretty), m->current_server_name->string);
+
+        r = manager_listen_setup(m);
+        if (r < 0) {
+                log_warning("Failed to setup connection socket: %s", strerror(-r));
+                return r;
+        }
+
+        r = manager_clock_watch_setup(m);
+        if (r < 0)
+                return r;
+
+        return manager_send_request(m);
+}
+
+static void server_name_flush_addresses(ServerName *n) {
+        ServerAddress *a;
+
+        assert(n);
+
+        while ((a = n->addresses)) {
+                LIST_REMOVE(addresses, n->addresses, a);
+                free(a);
+        }
+}
+
+static void manager_flush_names(Manager *m) {
+        ServerName *n;
+
+        assert(m);
+
+        while ((n = m->servers)) {
+                LIST_REMOVE(names, m->servers, n);
+                free(n->string);
+                server_name_flush_addresses(n);
+                free(n);
+        }
+}
+
+static int manager_resolve_handler(sd_resolve_query *q, int ret, const struct addrinfo *ai, void *userdata) {
+        Manager *m = userdata;
+        ServerAddress *a, *last = NULL;
+
         assert(q);
         assert(m);
+        assert(m->current_server_name);
 
         m->resolve_query = sd_resolve_query_unref(m->resolve_query);
 
         if (ret != 0) {
-                log_error("Failed to resolve %s: %s", m->server, gai_strerror(ret));
-                return -EHOSTUNREACH;
+                log_info("Failed to resolve %s: %s", m->current_server_name->string, gai_strerror(ret));
+
+                /* Try next host */
+                return manager_connect(m);
         }
 
-        assert(ai);
-        assert(ai->ai_addr);
-        assert(ai->ai_addrlen >= offsetof(struct sockaddr, sa_data));
-        assert(ai->ai_addrlen <= sizeof(union sockaddr_union));
+        server_name_flush_addresses(m->current_server_name);
 
-        if (!IN_SET(ai->ai_addr->sa_family, AF_INET, AF_INET6)) {
-                log_warning("Failed to find IP address for %s", m->server);
-                return -EHOSTUNREACH;
-        }
+        for (; ai; ai = ai->ai_next) {
+                _cleanup_free_ char *pretty = NULL;
 
-        memcpy(&m->server_addr, ai->ai_addr, ai->ai_addrlen);
-        m->server_addr_length = ai->ai_addrlen;
+                assert(ai->ai_addr);
+                assert(ai->ai_addrlen >= offsetof(struct sockaddr, sa_data));
+                assert(ai->ai_addrlen <= sizeof(union sockaddr_union));
 
-        r = sockaddr_pretty(&m->server_addr.sa, m->server_addr_length, true, &pretty);
-        if (r < 0) {
-                log_warning("Failed to decode address of %s: %s", m->server, strerror(-r));
-                return r;
-        }
+                if (!IN_SET(ai->ai_addr->sa_family, AF_INET, AF_INET6)) {
+                        log_warning("Unsuitable address protocol for %s", m->current_server_name->string);
+                        continue;
+                }
 
-        log_debug("Connecting to NTP server %s.", pretty);
-        sd_notifyf(false, "STATUS=Using Time Server %s", pretty);
+                a = new0(ServerAddress, 1);
+                if (!a)
+                        return log_oom();
 
-        r = manager_listen_setup(m);
-        if (r < 0) {
-                log_warning("Failed to setup connection socket: %s", strerror(-r));
-                return r;
+                memcpy(&a->sockaddr, ai->ai_addr, ai->ai_addrlen);
+                a->socklen = ai->ai_addrlen;
+
+                LIST_INSERT_AFTER(addresses, m->current_server_name->addresses, last, a);
+                last = a;
+
+                sockaddr_pretty(&a->sockaddr.sa, a->socklen, true, &pretty);
+                log_debug("Resolved address %s for %s.", pretty, m->current_server_name->string);
         }
 
-        r = manager_clock_watch_setup(m);
-        if (r < 0) {
-                log_warning("Failed to setup clock watch: %s", strerror(-r));
-                return r;
+        if (!m->current_server_name->addresses) {
+                log_error("Failed to find suitable address for host %s.", m->current_server_name->string);
+
+                /* Try next host */
+                return manager_connect(m);
         }
 
-        return manager_send_request(m);
+        m->current_server_address = m->current_server_name->addresses;
+
+        return manager_begin(m);
+}
+
+static int manager_retry(sd_event_source *source, usec_t usec, void *userdata) {
+        Manager *m = userdata;
+
+        assert(m);
+
+        return manager_connect(m);
 }
 
-static int manager_connect(Manager *m, const char *server) {
+static int manager_connect(Manager *m) {
 
         struct addrinfo hints = {
                 .ai_flags = AI_NUMERICSERV|AI_ADDRCONFIG,
                 .ai_socktype = SOCK_DGRAM,
         };
+        int r;
+
+        assert(m);
+
+        manager_disconnect(m);
+
+        m->event_retry = sd_event_source_unref(m->event_retry);
+        if (!ratelimit_test(&m->ratelimit)) {
+                log_debug("Slowing down attempts to contact servers.");
+
+                r = sd_event_add_time(m->event, &m->event_retry, CLOCK_MONOTONIC, now(CLOCK_MONOTONIC) + RETRY_USEC, 0, manager_retry, m);
+                if (r < 0) {
+                        log_error("Failed to create retry timer: %s", strerror(-r));
+                        return r;
+                }
+
+                return 0;
+        }
+
+        /* If we already are operating on some address, switch to the
+         * next one. */
+        if (m->current_server_address && m->current_server_address->addresses_next)
+                m->current_server_address = m->current_server_address->addresses_next;
+        else {
+                /* Hmm, we are through all addresses, let's look for the next host instead */
+                m->current_server_address = NULL;
+
+                if (m->current_server_name && m->current_server_name->names_next)
+                        m->current_server_name = m->current_server_name->names_next;
+                else {
+                        if (!m->servers) {
+                                m->current_server_name = NULL;
+                                log_debug("No server found.");
+                                return 0;
+                        }
+
+                        m->current_server_name = m->servers;
+                }
+
+                /* Tell the resolver to reread /etc/resolv.conf, in
+                 * case it changed. */
+                res_init();
+
+                r = sd_resolve_getaddrinfo(m->resolve, &m->resolve_query, m->current_server_name->string, "123", &hints, manager_resolve_handler, m);
+                if (r < 0) {
+                        log_error("Failed to create resolver: %s", strerror(-r));
+                        return r;
+                }
+
+                return 1;
+        }
+
+        r = manager_begin(m);
+        if (r < 0)
+                return r;
+
+        return 1;
+}
+
+static int manager_add_server(Manager *m, const char *server) {
+        ServerName *n, *tail;
 
         assert(m);
         assert(server);
 
-        if (m->server)
-                return -EBUSY;
+        n = new0(ServerName, 1);
+        if (!n)
+                return -ENOMEM;
 
-        m->server = strdup(server);
-        if (!m->server)
+        n->string = strdup(server);
+        if (!n->string) {
+                free(n);
                 return -ENOMEM;
+        }
 
-        m->poll_interval_usec = NTP_POLL_INTERVAL_MIN_SEC * USEC_PER_SEC;
+        LIST_FIND_TAIL(names, m->servers, tail);
+        LIST_INSERT_AFTER(names, m->servers, tail, n);
 
-        return sd_resolve_getaddrinfo(m->resolve, &m->resolve_query, m->server, "123", &hints, manager_resolve_handler, m);
+        return 0;
+}
+
+static int manager_add_server_string(Manager *m, const char *string) {
+        char *w, *state;
+        size_t l;
+        int r;
+
+        assert(m);
+        assert(string);
+
+        FOREACH_WORD_QUOTED(w, l, string, state) {
+                char t[l+1];
+
+                memcpy(t, w, l);
+                t[l] = 0;
+
+                r = manager_add_server(m, t);
+                if (r < 0)
+                        log_error("Failed to add server %s to configuration, ignoring: %s", t, strerror(-r));
+        }
+
+        return 0;
 }
 
 static void manager_disconnect(Manager *m) {
@@ -762,14 +948,12 @@ static void manager_disconnect(Manager *m) {
         m->event_receive = sd_event_source_unref(m->event_receive);
         m->server_socket = safe_close(m->server_socket);
 
-        zero(m->server_addr);
-        m->server_addr_length = 0;
-
-        free(m->server);
-        m->server = NULL;
-
         m->event_clock_watch = sd_event_source_unref(m->event_clock_watch);
         m->clock_watch_fd = safe_close(m->clock_watch_fd);
+
+        m->event_timeout = sd_event_source_unref(m->event_timeout);
+
+        sd_notifyf(false, "STATUS=Idle.");
 }
 
 static int manager_new(Manager **ret) {
@@ -782,6 +966,8 @@ static int manager_new(Manager **ret) {
 
         m->server_socket = m->clock_watch_fd = -1;
 
+        RATELIMIT_INIT(m->ratelimit, RATELIMIT_INTERVAL_USEC, RATELIMIT_BURST);
+
         r = sd_event_default(&m->event);
         if (r < 0)
                 return r;
@@ -812,24 +998,174 @@ static void manager_free(Manager *m) {
                 return;
 
         manager_disconnect(m);
+        manager_flush_names(m);
 
         sd_event_source_unref(m->sigint);
         sd_event_source_unref(m->sigterm);
 
+        sd_event_source_unref(m->event_retry);
+
+        sd_event_source_unref(m->network_event_source);
+        sd_network_monitor_unref(m->network_monitor);
+
         sd_resolve_unref(m->resolve);
         sd_event_unref(m->event);
 
         free(m);
 }
 
+int config_parse_servers(
+                const char *unit,
+                const char *filename,
+                unsigned line,
+                const char *section,
+                unsigned section_line,
+                const char *lvalue,
+                int ltype,
+                const char *rvalue,
+                void *data,
+                void *userdata) {
+
+        Manager *m = userdata;
+
+        assert(filename);
+        assert(lvalue);
+        assert(rvalue);
+
+        manager_flush_names(m);
+        manager_add_server_string(m, rvalue);
+
+        return 0;
+}
+
+static int manager_parse_config_file(Manager *m) {
+        static const char fn[] = "/etc/systemd/timesyncd.conf";
+        _cleanup_fclose_ FILE *f = NULL;
+        int r;
+
+        assert(m);
+
+        f = fopen(fn, "re");
+        if (!f) {
+                if (errno == ENOENT)
+                        return 0;
+
+                log_warning("Failed to open configuration file %s: %m", fn);
+                return -errno;
+        }
+
+        r = config_parse(NULL, fn, f, "Time\0", config_item_perf_lookup,
+                         (void*) timesyncd_gperf_lookup, false, false, m);
+        if (r < 0)
+                log_warning("Failed to parse configuration file: %s", strerror(-r));
+
+        return r;
+}
+
+static bool network_is_online(void) {
+        _cleanup_free_ unsigned *indices = NULL;
+        int r, n, i;
+
+        n = sd_network_get_ifindices(&indices);
+        if (n <= 0)
+                return false;
+
+        for (i = 0; i < n; i++) {
+                _cleanup_free_ char *oper_state = NULL;
+
+                if (sd_network_link_is_loopback(indices[i]))
+                        /* ignore loopback devices */
+                        continue;
+
+                r = sd_network_get_link_operational_state(indices[i], &oper_state);
+                if (r >= 0 && streq(oper_state, "carrier"))
+                        return true;
+        }
+
+        return false;
+}
+
+static int manager_network_event_handler(sd_event_source *s, int fd, uint32_t revents,
+                                         void *userdata) {
+        Manager *m = userdata;
+        bool connected, online;
+        int r;
+
+        assert(m);
+
+        /* check if the machine is online */
+        online = network_is_online();
+
+        /* check if the client is currently connected */
+        connected = (m->server_socket != -1);
+
+        if (connected && !online) {
+                log_info("No network connectivity. Suspending.");
+                manager_disconnect(m);
+        } else if (!connected && online) {
+                log_info("Network connectivity detected. Resuming.");
+                if (m->current_server_address) {
+                        r = manager_begin(m);
+                        if (r < 0)
+                                return r;
+                } else {
+                        r = manager_connect(m);
+                        if (r < 0)
+                                return r;
+                }
+        }
+
+        sd_network_monitor_flush(m->network_monitor);
+
+        return 0;
+}
+
+static int manager_network_monitor_listen(Manager *m) {
+        _cleanup_event_source_unref_ sd_event_source *event_source = NULL;
+        _cleanup_network_monitor_unref_ sd_network_monitor *monitor = NULL;
+        int r, fd, events;
+
+        r = sd_network_monitor_new(NULL, &monitor);
+        if (r < 0)
+                return r;
+
+        fd = sd_network_monitor_get_fd(monitor);
+        if (fd < 0)
+                return fd;
+
+        events = sd_network_monitor_get_events(monitor);
+        if (events < 0)
+                return events;
+
+        r = sd_event_add_io(m->event, &event_source, fd, events,
+                            &manager_network_event_handler, m);
+        if (r < 0)
+                return r;
+
+        m->network_monitor = monitor;
+        m->network_event_source = event_source;
+        monitor = NULL;
+        event_source = NULL;
+
+        return 0;
+}
+
 int main(int argc, char *argv[]) {
         _cleanup_manager_free_ Manager *m = NULL;
         int r;
 
+        if (argc > 1) {
+                log_error("This program does not take arguments.");
+                return EXIT_FAILURE;
+        }
+
         log_set_target(LOG_TARGET_AUTO);
+        log_set_facility(LOG_CRON);
         log_parse_environment();
         log_open();
 
+        umask(0022);
+
         assert_se(sigprocmask_many(SIG_BLOCK, SIGTERM, SIGINT, -1) == 0);
 
         r = manager_new(&m);
@@ -838,14 +1174,24 @@ int main(int argc, char *argv[]) {
                 goto out;
         }
 
-        sd_notify(false, "READY=1");
+        manager_add_server_string(m, NTP_SERVERS);
+        manager_parse_config_file(m);
 
-        r = manager_connect(m, "time1.google.com");
+        r = manager_network_monitor_listen(m);
         if (r < 0) {
-                log_error("Failed to initiate connection: %s", strerror(-r));
+                log_error("Failed to listen to networkd events: %s", strerror(-r));
                 goto out;
         }
 
+        log_debug("systemd-timesyncd running as pid %lu", (unsigned long) getpid());
+        sd_notify(false, "READY=1");
+
+        if (network_is_online()) {
+                r = manager_connect(m);
+                if (r < 0)
+                        goto out;
+        }
+
         r = sd_event_loop(m->event);
         if (r < 0) {
                 log_error("Failed to run event loop: %s", strerror(-r));
@@ -855,5 +1201,7 @@ int main(int argc, char *argv[]) {
         sd_event_get_exit_code(m->event, &r);
 
 out:
+        sd_notify(false, "STATUS=Shutting down...");
+
         return r < 0 ? EXIT_FAILURE : EXIT_SUCCESS;
 }