A machine is titled by its own hostname, and follows a rename

The name a machine was added under stays its identity — the URL, its accent, what the hub's
API calls it — and is what the Machines page shows as 'Added as'. The hostname is read live
rather than at start-up, so renaming a machine reaches the console without a restart.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

internal/api/alerts.go

@@ -210,7 +210,7 @@ func (e *alertEngine) evaluate() {
 		}
 	}
 	qb, _ := json.Marshal(query)
-	machines := append([]string{e.s.host}, e.s.nodes.Names()...)
+	machines := append([]string{e.s.hostName()}, e.s.nodes.Names()...)
 	results := map[string]map[string]any{} // machine → ruleID → value | {id: value}
 	reach := map[string]bool{}
 	var wg sync.WaitGroup
@@ -221,7 +221,7 @@ func (e *alertEngine) evaluate() {
 			defer wg.Done()
 			var res map[string]any
 			ok := false
-			if m == e.s.host {
+			if m == e.s.hostName() {
 				if out, err := sensors.Shape(e.s.sensors.All(), qb, false); err == nil {
 					res, ok = out.(map[string]any)
 				}
@@ -515,6 +515,6 @@ func (s *Server) alertsTest(w http.ResponseWriter, _ *http.Request) {
 		jsonErr(w, 400, "no channels to test")
 		return
 	}
-	e.notify(channels, AlertEvent{T: time.Now().UnixMilli(), Kind: "firing", Rule: "Test alert", Machine: s.host, Sensor: "hamlab.test", Value: "this is only a test", Severity: "info"})
+	e.notify(channels, AlertEvent{T: time.Now().UnixMilli(), Kind: "firing", Rule: "Test alert", Machine: s.hostName(), Sensor: "hamlab.test", Value: "this is only a test", Severity: "info"})
 	w.WriteHeader(204)
 }

internal/api/server.go

@@ -73,15 +73,17 @@ type Server struct {
 	version     string
 	started     time.Time
 	user        string
-	host        string
+	host        string // the machine's hostname as last read; use hostName(), it can change under us
+	hostMu      sync.Mutex
+	hostAt      time.Time
 	ui          fs.FS
 	mux         *http.ServeMux
 }
 
 func New(cfg *config.Config, sessions *auth.Sessions, mgr *term.Manager, col *metrics.Collector, st *store.Store, svc *services.Manager, cr *cron.Manager, tm *tasks.Manager, up *updates.Manager, sto *storage.Manager, fsLocal, fsSudo files.FS, nm *nodes.Manager, fingerprint string, ui fs.FS, version string) *Server {
-	host, _ := os.Hostname()
 	s := &Server{cfg: cfg, sessions: sessions, mgr: mgr, metrics: col, sensors: sensors.NewRegistry(col), store: st, svc: svc, cron: cr, tasks: tm, updates: up, storage: sto, fsLocal: fsLocal, fsSudo: fsSudo, nodes: nm, fingerprint: fingerprint, ui: ui, version: version,
-		started: time.Now(), host: host, user: os.Getenv("USER")}
+		started: time.Now(), user: os.Getenv("USER")}
+	s.hostName() // read it once now so the first request doesn't have to
 	if u, err := user.Current(); err == nil && u.Username != "" {
 		s.user = u.Username
 	}
@@ -572,7 +574,7 @@ func (s *Server) revokeToken(w http.ResponseWriter, r *http.Request) {
 // ---- nodes: the machines this hub manages ----
 
 func (s *Server) listNodes(w http.ResponseWriter, _ *http.Request) {
-	jsonOK(w, 200, map[string]any{"nodes": s.nodes.List(), "host": s.host, "fingerprint": s.fingerprint})
+	jsonOK(w, 200, map[string]any{"nodes": s.nodes.List(), "host": s.hostName(), "fingerprint": s.fingerprint})
 }
 
 func (s *Server) addNode(w http.ResponseWriter, r *http.Request) {
@@ -797,6 +799,25 @@ func clientIP(r *http.Request) string {
 
 // ---- me ----
 
+// hostName is this machine's hostname now, not when the daemon started: rename a machine
+// (hostnamectl, or a DHCP lease) and the console says so within a few seconds — in its header,
+// in the machine menu, in alerts and in the fleet's sensor queries — without a restart. Read
+// through a short cache because it is asked for on most requests and on every alert pass.
+func (s *Server) hostName() string {
+	s.hostMu.Lock()
+	defer s.hostMu.Unlock()
+	if time.Since(s.hostAt) > 5*time.Second {
+		if h, err := os.Hostname(); err == nil && h != "" {
+			if s.host != "" && h != s.host {
+				log.Printf("hostname: %s is now %s", s.host, h)
+			}
+			s.host = h
+		}
+		s.hostAt = time.Now()
+	}
+	return s.host
+}
+
 func (s *Server) me(w http.ResponseWriter, _ *http.Request) {
 	load := ""
 	if b, err := os.ReadFile("/proc/loadavg"); err == nil {
@@ -820,7 +841,7 @@ func (s *Server) me(w http.ResponseWriter, _ *http.Request) {
 		}
 	})
 	jsonOK(w, 200, map[string]any{
-		"host": s.host, "user": s.user, "version": s.version,
+		"host": s.hostName(), "user": s.user, "version": s.version,
 		"load": load, "uptime": uptime, "service_started": s.started,
 		"reboot_needed": rebootErr == nil, "fingerprint": s.fingerprint, "arch": runtime.GOARCH, "demo_url": demoURL, "addr": addr,
 	})
@@ -1086,7 +1107,7 @@ func (s *Server) fleetQuery(w http.ResponseWriter, r *http.Request) {
 		jsonErr(w, 400, err.Error())
 		return
 	}
-	names := append([]string{s.host}, s.nodes.Names()...)
+	names := append([]string{s.hostName()}, s.nodes.Names()...)
 	if len(want) > 0 {
 		names = names[:0]
 		for _, n := range want {
@@ -1107,7 +1128,7 @@ func (s *Server) fleetQuery(w http.ResponseWriter, r *http.Request) {
 	var mu sync.Mutex
 	var wg sync.WaitGroup
 	for _, name := range names {
-		if name == s.host {
+		if name == s.hostName() {
 			out[name] = local
 			continue
 		}
@@ -1478,7 +1499,7 @@ func (s *Server) power(w http.ResponseWriter, r *http.Request) {
 		Confirm string `json:"confirm"`
 	}
 	_ = json.NewDecoder(io.LimitReader(r.Body, 4096)).Decode(&body)
-	if body.Confirm != s.host {
+	if body.Confirm != s.hostName() {
 		jsonErr(w, 400, "confirmation must be the hostname")
 		return
 	}

internal/api/stacks.go

@@ -363,7 +363,7 @@ func (s *Server) hubStacks(ctx context.Context, node string) ([]stack, error) {
 			st.Note = note
 			continue
 		}
-		st.Remote, st.HeldBy = remote, s.host
+		st.Remote, st.HeldBy = remote, s.hostName()
 	}
 	var held []stack
 	for _, st := range res.Stacks {