fix(cli): ignore a half-populated socket activation environment (#11394)

A container engine started from a socket-activated system unit leaks a bare
LISTEN_PID into every container it spawns, with no matching LISTEN_FDS. LocalAI
read that as a malformed activation attempt and refused to start:

    ERROR Error running the application error=loading systemd socket
    activation listeners: invalid LISTEN_FDS ""

systemd's own sd_listen_fds() treats either variable being absent as "not
activated" rather than as an error, so do the same and fall back to ordinary
--address binding. A value that is present but malformed is still rejected, so
a real activation attempt cannot silently bind the wrong socket.

Fixes #11390


Assisted-by: Claude:claude-opus-5 [golangci-lint]

Signed-off-by: Ettore Di Giacinto <mudler@localai.io>
Co-authored-by: Ettore Di Giacinto <mudler@localai.io>

core/cli/run_socket_activation_linux.go

@@ -24,6 +24,14 @@ func systemdActivatedListeners() ([]net.Listener, error) {
 		}
 	}()
 
+	// A half-populated environment is not an activation attempt. Container runtimes
+	// started from a socket-activated system unit leak a bare LISTEN_PID into every
+	// container they spawn, and systemd's own sd_listen_fds() treats either variable
+	// being absent as "not activated" rather than as an error.
+	if listenPID == "" || listenFDs == "" {
+		return nil, nil
+	}
+
 	pid, err := strconv.Atoi(listenPID)
 	if err != nil {
 		return nil, fmt.Errorf("invalid LISTEN_PID %q: %w", listenPID, err)

core/cli/run_socket_activation_test.go

@@ -85,6 +85,34 @@ var _ = Describe("systemdActivatedListeners", func() {
 		Expect(os.Getenv("LISTEN_FDNAMES")).To(BeEmpty())
 	})
 
+	It("binds normally when the environment leaks LISTEN_PID without LISTEN_FDS", func() {
+		Expect(os.Setenv("LISTEN_PID", strconv.Itoa(os.Getpid()))).To(Succeed())
+		Expect(os.Unsetenv("LISTEN_FDS")).To(Succeed())
+		DeferCleanup(func() {
+			_ = os.Unsetenv("LISTEN_PID")
+		})
+
+		listeners, err := systemdActivatedListeners()
+
+		Expect(err).NotTo(HaveOccurred())
+		Expect(listeners).To(BeEmpty())
+		Expect(os.Getenv("LISTEN_PID")).To(BeEmpty())
+	})
+
+	It("binds normally when the environment leaks LISTEN_FDS without LISTEN_PID", func() {
+		Expect(os.Unsetenv("LISTEN_PID")).To(Succeed())
+		Expect(os.Setenv("LISTEN_FDS", "1")).To(Succeed())
+		DeferCleanup(func() {
+			_ = os.Unsetenv("LISTEN_FDS")
+		})
+
+		listeners, err := systemdActivatedListeners()
+
+		Expect(err).NotTo(HaveOccurred())
+		Expect(listeners).To(BeEmpty())
+		Expect(os.Getenv("LISTEN_FDS")).To(BeEmpty())
+	})
+
 	It("reports malformed activation metadata instead of silently binding another socket", func() {
 		Expect(os.Setenv("LISTEN_PID", strconv.Itoa(os.Getpid()))).To(Succeed())
 		Expect(os.Setenv("LISTEN_FDS", "not-a-number")).To(Succeed())

docs/content/getting-started/linux.md

@@ -111,6 +111,11 @@ For a Podman-managed container, configure Podman to preserve and pass the
 systemd socket file descriptor into the container. The LocalAI process inside
 the container consumes the same activation protocol.
 
+Activation needs both `LISTEN_PID` and `LISTEN_FDS`. If only one of them is set,
+LocalAI ignores them and binds `--address` as usual. A container engine started
+from a socket-activated system unit can leak a bare `LISTEN_PID` into every
+container it spawns, and that is not an activation attempt.
+
 ## Next Steps
 
 - [Try it out with examples](/basics/try/)