diff --git a/common/Logger.cpp b/common/Logger.cpp
index df469dfc4..de61bedff 100644
--- a/common/Logger.cpp
+++ b/common/Logger.cpp
@@ -9,7 +9,20 @@
 #include "Logger.h"
 #include "GitInfo.h"
 
+namespace {
+    spdlog::sink_ptr routed_sink;   // set once, at start-up, before any thread logs
+}
+
+void Logger::RouteAll(spdlog::sink_ptr sink) {
+    routed_sink = std::move(sink);
+}
+
 Logger::Logger(const std::string &service_name, const std::string &file_name) {
+    if (routed_sink) {
+        spdlog_logger = std::make_shared<spdlog::logger>(service_name, routed_sink);
+        spdlog_logger->set_level(spdlog::level::debug);
+        return;
+    }
     std::string variant = "";
 #ifdef JFJOCH_USE_CUDA
     variant += "C";
@@ -36,10 +49,15 @@ Logger::Logger(const std::string &service_name, const std::string &file_name) {
 
 class LogBufferSink : public spdlog::sinks::base_sink<std::mutex> {
 public:
-    std::vector<std::pair<spdlog::level::level_enum, std::string>> lines;
+    struct Line {
+        spdlog::log_clock::time_point time;
+        spdlog::level::level_enum level;
+        std::string text;
+    };
+    std::vector<Line> lines;
 protected:
     void sink_it_(const spdlog::details::log_msg &msg) override {
-        lines.emplace_back(msg.level, std::string(msg.payload.data(), msg.payload.size()));
+        lines.push_back({msg.time, msg.level, std::string(msg.payload.data(), msg.payload.size())});
     }
     void flush_() override {}
 };
@@ -53,10 +71,12 @@ Logger Logger::Buffered() {
     return Logger(std::make_shared<LogBufferSink>());
 }
 
-// Called once the work that logged is finished, so nothing is still writing to the buffer.
+// Called once the work that logged is finished, so nothing is still writing to the buffer. Each line
+// keeps the time it was logged at, not the time of the replay, so a timestamped log still shows when
+// the work happened.
 void Logger::ReplayInto(Logger &to) const {
-    for (const auto &[level, line] : buffer->lines)
-        to.spdlog_logger->log(level, line);
+    for (const auto &l : buffer->lines)
+        to.spdlog_logger->log(l.time, spdlog::source_loc{}, l.level, l.text);
 }
 
 void Logger::ErrorException(const std::exception &e) {
diff --git a/common/Logger.h b/common/Logger.h
index b2f8b39bc..1a6a01b72 100644
--- a/common/Logger.h
+++ b/common/Logger.h
@@ -56,6 +56,12 @@ public:
 
     Logger& Verbose(bool input);
 
+    // Every Logger made after this call writes to `sink` alone instead of the console, keeps every
+    // level down to debug (the sink decides what it shows), and skips the version line each Logger
+    // otherwise opens with. For a program that owns its terminal: rugnux sends the whole log to a file
+    // next to its outputs and shows only warnings and errors among its own step lines.
+    static void RouteAll(spdlog::sink_ptr sink);
+
     // A logger that keeps its lines instead of printing them, for work run beside other work that
     // logs: ReplayInto hands them to `to` afterwards, in order and as one block, so the two do not
     // interleave.
diff --git a/writer/HDF5DataFile.cpp b/writer/HDF5DataFile.cpp
index 1c47c12c8..88bc90ed9 100644
--- a/writer/HDF5DataFile.cpp
+++ b/writer/HDF5DataFile.cpp
@@ -18,6 +18,7 @@
 #include "../include/spdlog/fmt/fmt.h"
 #include "HDF5NXmx.h"
 #include "../common/time_utc.h"
+#include "../common/Logger.h"
 
 HDF5DataFile::HDF5DataFile(const StartMessage &msg, uint64_t file_number, const std::string &filename) :
 filename(filename),
@@ -123,9 +124,9 @@ HDF5DataFile::~HDF5DataFile() {
                 std::filesystem::remove(tmp_filename, ec);
             }
         } catch (const std::exception &e) {
-            std::cerr << "HDF5DataFile::~HDF5DataFile: " << e.what() << std::endl;
+            Logger("HDF5DataFile").Error("Closing the data file failed: {}", e.what());
         } catch (...) {
-            std::cerr << "HDF5DataFile::~HDF5DataFile: Unknown error " << std::endl;
+            Logger("HDF5DataFile").Error("Closing the data file failed with an unknown error");
         }
     }
 }