Kernel messages (dmesg) source read from /dev/kmsg

New source in Settings > Sources, off by default: reads the kernel ring
buffer of the host through /dev/kmsg, dates records from the boot time and
resumes after the last sequence number of the same boot (no duplicates on
restart). Missing device or denied access is shown in the UI, retried every
10 s. docker-compose.yml and .env.example document the device and the
kernel.dmesg_restrict / CAP_SYSLOG options.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

main.go

@@ -38,6 +38,8 @@ type config struct {
 	backfill   time.Duration
 	hostRoot   string
 	hostFill   time.Duration
+	kmsgDevice string
+	kmsgFill   time.Duration
 	batchSize  int
 	queueSize  int
 	flushEvery time.Duration
@@ -115,6 +117,8 @@ func main() {
 		backfill:   getenvDuration("DOCKER_BACKFILL", time.Hour),
 		hostRoot:   getenv("HOST_LOGS_ROOT", "/host"),
 		hostFill:   getenvDuration("HOST_LOGS_BACKFILL", time.Hour),
+		kmsgDevice: getenv("DMESG_DEVICE", "/dev/kmsg"),
+		kmsgFill:   getenvDuration("DMESG_BACKFILL", time.Hour),
 		batchSize:  getenvInt("BATCH_SIZE", 1000),
 		queueSize:  getenvInt("QUEUE_SIZE", 100000),
 		flushEvery: time.Duration(getenvInt("FLUSH_MS", 1000)) * time.Millisecond,
@@ -186,6 +190,9 @@ func main() {
 	// System logs of the host (journal or /var/log), off until enabled in Settings > Sources.
 	api.host = NewHostLogs(cfg.hostRoot, cfg.dataDir, cfg.hostFill, sink)
 	go api.host.Run(ctx)
+	// Kernel messages of the host (/dev/kmsg), off until enabled in Settings > Sources.
+	api.dmesg = NewDmesg(cfg.kmsgDevice, cfg.dataDir, cfg.kmsgFill, sink)
+	go api.dmesg.Run(ctx)
 	api.Routes(mux)
 	mux.Handle("GET /", http.FileServer(http.FS(static)))