diff --git a/README.md b/README.md
index 82e4914..b11a1d3 100644
--- a/README.md
+++ b/README.md
@@ -152,6 +152,8 @@ git push origin v0.2.0
 
 The Release workflow checks that the tag is on `main`, runs `make check`, builds the archives with `make release`, and creates the GitHub release with both archives and `checksums.txt`. A tag with a pre-release suffix, such as `v0.2.0-rc.1`, becomes a pre-release, so installed CLIs do not update to it.
 
+`install.sh` and `fly update` install only a release that has `checksums.txt`. Releases before v0.2.0 have none, so push the tag right after the merge into `main`: until the release is published, `install.sh` from `main` stops.
+
 ### Dev pre-releases
 
 To test a branch on real servers before it merges, publish a dev pre-release of its current commit:
diff --git a/cmd/version.go b/cmd/version.go
index 9a28f90..a32680a 100644
--- a/cmd/version.go
+++ b/cmd/version.go
@@ -6,6 +6,8 @@ import (
 	"fmt"
 	"io"
 	"os"
+	"os/signal"
+	"syscall"
 
 	"github.com/flywp/server-cli/internal/release"
 	"github.com/flywp/server-cli/internal/service"
@@ -37,7 +39,11 @@ command also restarts the agent, so that the agent runs the new binary.`,
 			return errors.New("the update command must be run as root, please run 'sudo fly update'")
 		}
 
-		update, err := release.CheckForUpdates(cmd.Context())
+		// Ctrl-C stops the download, and the partial download is removed.
+		ctx, stop := signal.NotifyContext(cmd.Context(), os.Interrupt, syscall.SIGTERM)
+		defer stop()
+
+		update, err := release.CheckForUpdates(ctx)
 		if err != nil {
 			return fmt.Errorf("checking for updates: %w", err)
 		}
@@ -48,7 +54,7 @@ command also restarts the agent, so that the agent runs the new binary.`,
 			fmt.Printf("This is not a release build (version %s). Latest release: %s\n", version.Version, latest)
 		case !update.Available:
 			fmt.Println("You are already running the latest version.")
-			return restartStaleAgent(cmd.Context())
+			return restartStaleAgent(ctx)
 		default:
 			fmt.Printf("New version available: %s\n", latest)
 		}
@@ -65,12 +71,12 @@ command also restarts the agent, so that the agent runs the new binary.`,
 		}
 
 		fmt.Println("Updating...")
-		if err := release.SelfUpdate(cmd.Context(), update.Release); err != nil {
+		if err := release.SelfUpdate(ctx, update.Release); err != nil {
 			return fmt.Errorf("updating: %w", err)
 		}
 		fmt.Printf("Updated to %s.\n", latest)
 
-		return restartAgent(cmd.Context())
+		return restartAgent(ctx)
 	},
 }
 
diff --git a/install.sh b/install.sh
index a587a84..9dccd3d 100644
--- a/install.sh
+++ b/install.sh
@@ -148,6 +148,25 @@ download_release() {
     info_msg "Download completed successfully."
 }
 
+# Examine the download with the checksum file of the release. The file has
+# one line for each archive: "<sha256>  <file name>".
+verify_download() {
+    info_msg "Verifying the download with checksums.txt..."
+
+    CHECKSUMS_URL="https://github.com/flywp/server-cli/releases/download/${TAG_NAME}/checksums.txt"
+    if ! curl -fsSL -o "$TEMP_DIR/checksums.txt" "$CHECKSUMS_URL"; then
+        rm -rf "$TEMP_DIR"
+        error_exit "Failed to download checksums.txt of ${TAG_NAME}. The download cannot be checked, so it is not installed."
+    fi
+
+    if ! (cd "$TEMP_DIR" && grep " fly-${OS}-${ARCH}.tar.gz\$" checksums.txt | sha256sum -c --status -); then
+        rm -rf "$TEMP_DIR"
+        error_exit "The checksum of fly-${OS}-${ARCH}.tar.gz does not agree with checksums.txt. The download is not installed."
+    fi
+
+    info_msg "Checksum verified."
+}
+
 # Extract and install
 install_binary() {
     info_msg "Extracting $DOWNLOAD_FILE..."
@@ -215,6 +234,9 @@ main() {
     
     # Download the release
     download_release
+
+    # Examine the download
+    verify_download
     
     # Install the binary
     install_binary
diff --git a/internal/release/download_test.go b/internal/release/download_test.go
index eaac30d..4b05a2c 100644
--- a/internal/release/download_test.go
+++ b/internal/release/download_test.go
@@ -145,3 +145,83 @@ func TestRemoveTempKeepsYoungFiles(t *testing.T) {
 		t.Errorf("directory holds %v, want the young download and the binary only", names)
 	}
 }
+
+// testRelease serves a release with the archive and a checksum file, and
+// returns its description.
+func testRelease(t *testing.T, archive []byte, checksums string) *GithubRelease {
+	t.Helper()
+
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		switch r.URL.Path {
+		case "/fly-linux-amd64.tar.gz":
+			_, _ = w.Write(archive)
+		case "/checksums.txt":
+			_, _ = w.Write([]byte(checksums))
+		default:
+			http.NotFound(w, r)
+		}
+	}))
+	t.Cleanup(srv.Close)
+
+	rel := &GithubRelease{TagName: "v0.3.0"}
+	for _, name := range []string{"fly-linux-amd64.tar.gz", "checksums.txt"} {
+		if name == "checksums.txt" && checksums == "" {
+			continue
+		}
+		rel.Assets = append(rel.Assets, Asset{Name: name, BrowserDownloadURL: srv.URL + "/" + name})
+	}
+	return rel
+}
+
+func TestSelfUpdateChecksTheArchive(t *testing.T) {
+	data := archive(t, map[string]string{"fly-linux-amd64": "new"}).Bytes()
+	other := sum([]byte("other"))
+
+	tests := []struct {
+		name, checksums, want string
+	}{
+		{"checksum agrees", sum(data) + "  fly-linux-arm64.tar.gz\n" + sum(data) + "  fly-linux-amd64.tar.gz\n", ""},
+		{"binary mode mark", sum(data) + " *fly-linux-amd64.tar.gz\n", ""},
+		{"checksum does not agree", other + "  fly-linux-amd64.tar.gz\n", "the sha256 of"},
+		{"no line for the archive", other + "  fly-linux-arm64.tar.gz\n", "has no line for fly-linux-amd64.tar.gz"},
+		{"no checksum file", "", "has no checksums.txt"},
+		{"CRLF line ends", sum(data) + "  fly-linux-amd64.tar.gz\r\n", ""},
+		{"upper case hex", strings.ToUpper(sum(data)) + "  fly-linux-amd64.tar.gz\n", ""},
+		{"the same line two times", sum(data) + "  fly-linux-amd64.tar.gz\n" + sum(data) + "  fly-linux-amd64.tar.gz\n", ""},
+		{"two different sums", sum(data) + "  fly-linux-amd64.tar.gz\n" + other + "  fly-linux-amd64.tar.gz\n", "two different sums"},
+		{"a similar name", sum(data) + "  fly-linux-amd64.tar.gz.sig\n", "has no line for fly-linux-amd64.tar.gz"},
+		{"empty checksum file", "\n", "has no line for fly-linux-amd64.tar.gz"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			dir := t.TempDir()
+			exe := filepath.Join(dir, "fly")
+			if err := os.WriteFile(exe, []byte("old"), 0o755); err != nil {
+				t.Fatal(err)
+			}
+
+			err := selfUpdate(context.Background(), testRelease(t, data, tt.checksums), exe, "linux", "amd64")
+
+			got, _ := os.ReadFile(exe)
+			if tt.want == "" {
+				if err != nil || string(got) != "new" {
+					t.Fatalf("selfUpdate() = %v, binary %q; want the new binary", err, got)
+				}
+				if entries, _ := os.ReadDir(dir); len(entries) != 1 {
+					t.Errorf("the directory holds %d files after the update, want only the binary", len(entries))
+				}
+				return
+			}
+			if err == nil || !strings.Contains(err.Error(), tt.want) {
+				t.Fatalf("selfUpdate() error = %v, want %q", err, tt.want)
+			}
+			if string(got) != "old" {
+				t.Errorf("binary = %q, want the old binary unchanged", got)
+			}
+			if entries, _ := os.ReadDir(dir); len(entries) != 1 {
+				t.Errorf("the directory holds %d files, want only the binary", len(entries))
+			}
+		})
+	}
+}
diff --git a/internal/release/release.go b/internal/release/release.go
index e962ad9..62747ab 100644
--- a/internal/release/release.go
+++ b/internal/release/release.go
@@ -16,6 +16,7 @@ import (
 	"path/filepath"
 	"regexp"
 	"runtime"
+	"strings"
 	"syscall"
 	"time"
 
@@ -32,12 +33,16 @@ var httpClient = &http.Client{Timeout: 60 * time.Second}
 // maxBinarySize limits the size of the binary in a release archive.
 const maxBinarySize = 200 << 20
 
+// GithubRelease is a release in the GitHub API.
 type GithubRelease struct {
-	TagName string `json:"tag_name"`
-	Assets  []struct {
-		Name               string `json:"name"`
-		BrowserDownloadURL string `json:"browser_download_url"`
-	} `json:"assets"`
+	TagName string  `json:"tag_name"`
+	Assets  []Asset `json:"assets"`
+}
+
+// Asset is a file of a release.
+type Asset struct {
+	Name               string `json:"name"`
+	BrowserDownloadURL string `json:"browser_download_url"`
 }
 
 // Update compares the latest release with the running version.
@@ -124,13 +129,17 @@ func get(ctx context.Context, url string) (*http.Response, error) {
 	return resp, nil
 }
 
-// SelfUpdate replaces the running binary with the binary from release.
-func SelfUpdate(ctx context.Context, release *GithubRelease) error {
-	assetURL := assetURL(release, runtime.GOOS, runtime.GOARCH)
-	if assetURL == "" {
-		return fmt.Errorf("no suitable binary found for this system (OS: %s, ARCH: %s)", runtime.GOOS, runtime.GOARCH)
-	}
+// ChecksumsAsset is the checksum file of each release: one line for each
+// archive, "<sha256>  <file name>" (the output of sha256sum).
+const ChecksumsAsset = "checksums.txt"
 
+// selfUpdateTimeout limits the download of an update.
+const selfUpdateTimeout = 10 * time.Minute
+
+// SelfUpdate replaces the running binary with the binary from release. It
+// installs the archive only when its sha256 agrees with the checksum file of
+// the release.
+func SelfUpdate(ctx context.Context, release *GithubRelease) error {
 	exe, err := os.Executable()
 	if err != nil {
 		return fmt.Errorf("finding the current executable: %w", err)
@@ -140,13 +149,71 @@ func SelfUpdate(ctx context.Context, release *GithubRelease) error {
 		return fmt.Errorf("resolving symlinks: %w", err)
 	}
 
-	resp, err := get(ctx, assetURL)
+	return selfUpdate(ctx, release, exe, runtime.GOOS, runtime.GOARCH)
+}
+
+func selfUpdate(ctx context.Context, release *GithubRelease, exe, goos, goarch string) error {
+	ctx, cancel := context.WithTimeout(ctx, selfUpdateTimeout)
+	defer cancel()
+
+	archiveURL := assetURL(release, goos, goarch)
+	if archiveURL == "" {
+		return fmt.Errorf("no suitable binary found for this system (OS: %s, ARCH: %s)", goos, goarch)
+	}
+
+	name := BinaryName(goos, goarch)
+	sum, err := checksum(ctx, release, name+".tar.gz")
+	if err != nil {
+		return err
+	}
+
+	archive, err := Download(ctx, archiveURL, sum, filepath.Dir(exe))
+	if err != nil {
+		return err
+	}
+	defer func() { _ = os.Remove(archive) }()
+
+	return Install(archive, exe, name)
+}
+
+// checksum returns the sha256 of the release file name from the checksum
+// file of the release.
+func checksum(ctx context.Context, release *GithubRelease, name string) (string, error) {
+	url := asset(release, ChecksumsAsset)
+	if url == "" {
+		return "", fmt.Errorf("release %s has no %s, so its download cannot be checked", release.TagName, ChecksumsAsset)
+	}
+
+	resp, err := get(ctx, url)
 	if err != nil {
-		return fmt.Errorf("downloading update: %w", err)
+		return "", fmt.Errorf("downloading %s: %w", ChecksumsAsset, err)
 	}
 	defer func() { _ = resp.Body.Close() }()
 
-	return replaceBinary(exe, resp.Body, BinaryName(runtime.GOOS, runtime.GOARCH))
+	data, err := io.ReadAll(io.LimitReader(resp.Body, 1<<20))
+	if err != nil {
+		return "", fmt.Errorf("downloading %s: %w", ChecksumsAsset, err)
+	}
+
+	// install.sh reads the file with the same rules. Two different sums for
+	// one file make the file not valid: it is not clear which one is correct.
+	var sum string
+	for line := range strings.Lines(string(data)) {
+		// sha256sum marks a file that it read in binary mode with "*".
+		fields := strings.Fields(line)
+		if len(fields) != 2 || strings.TrimPrefix(fields[1], "*") != name {
+			continue
+		}
+		if sum != "" && !strings.EqualFold(sum, fields[0]) {
+			return "", fmt.Errorf("%s of release %s has two different sums for %s", ChecksumsAsset, release.TagName, name)
+		}
+		sum = fields[0]
+	}
+	if sum == "" {
+		return "", fmt.Errorf("%s of release %s has no line for %s", ChecksumsAsset, release.TagName, name)
+	}
+
+	return sum, nil
 }
 
 // BinaryName is the name of the binary in a release archive. Releases must
@@ -162,10 +229,14 @@ func assetURL(release *GithubRelease, goos, goarch string) string {
 		return ""
 	}
 
-	expectedName := BinaryName(goos, goarch) + ".tar.gz"
-	for _, asset := range release.Assets {
-		if asset.Name == expectedName {
-			return asset.BrowserDownloadURL
+	return asset(release, BinaryName(goos, goarch)+".tar.gz")
+}
+
+// asset returns the download URL of the release file name, or "".
+func asset(release *GithubRelease, name string) string {
+	for _, a := range release.Assets {
+		if a.Name == name {
+			return a.BrowserDownloadURL
 		}
 	}
 
diff --git a/internal/release/release_test.go b/internal/release/release_test.go
index a967c2a..a4681bb 100644
--- a/internal/release/release_test.go
+++ b/internal/release/release_test.go
@@ -121,10 +121,7 @@ func TestLatestReleaseErrors(t *testing.T) {
 func TestAssetURL(t *testing.T) {
 	release := &GithubRelease{TagName: "v0.2.0"}
 	for _, name := range []string{"fly-linux-amd64.tar.gz", "fly-linux-arm64.tar.gz"} {
-		release.Assets = append(release.Assets, struct {
-			Name               string `json:"name"`
-			BrowserDownloadURL string `json:"browser_download_url"`
-		}{Name: name, BrowserDownloadURL: "https://example.com/" + name})
+		release.Assets = append(release.Assets, Asset{Name: name, BrowserDownloadURL: "https://example.com/" + name})
 	}
 
 	tests := []struct{ goos, goarch, want string }{