version/distro: detect Ubuntu separately from Debian

(for an upcoming change where I wanted to easily distinguish these
two)

Change-Id: Icb6a0144275cc9bf8978a7cb96b601d516d8da46
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

net/tstun/tun_linux.go

@@ -59,8 +59,9 @@ func diagnoseLinuxTUNFailure(tunName string, logf logger.Logf, createErr error)
 	}
 	logf("is CONFIG_TUN enabled in your kernel? `modprobe tun` failed with: %s", modprobeOut)
 
-	switch distro.Get() {
-	case distro.Debian:
+	dist := distro.Get()
+	switch {
+	case dist.LikeDebian():
 		dpkgOut, err := exec.Command("dpkg", "-S", "kernel/drivers/net/tun.ko").CombinedOutput()
 		if len(bytes.TrimSpace(dpkgOut)) == 0 || err != nil {
 			logf("tun module not loaded nor found on disk")
@@ -69,7 +70,7 @@ func diagnoseLinuxTUNFailure(tunName string, logf logger.Logf, createErr error)
 		if !bytes.Contains(dpkgOut, []byte(kernel)) {
 			logf("kernel/drivers/net/tun.ko found on disk, but not for current kernel; are you in middle of a system update and haven't rebooted? found: %s", dpkgOut)
 		}
-	case distro.Arch:
+	case dist == distro.Arch:
 		findOut, err := exec.Command("find", "/lib/modules/", "-path", "*/net/tun.ko*").CombinedOutput()
 		if len(bytes.TrimSpace(findOut)) == 0 || err != nil {
 			logf("tun module not loaded nor found on disk")
@@ -78,7 +79,7 @@ func diagnoseLinuxTUNFailure(tunName string, logf logger.Logf, createErr error)
 		if !bytes.Contains(findOut, []byte(kernel)) {
 			logf("kernel/drivers/net/tun.ko found on disk, but not for current kernel; are you in middle of a system update and haven't rebooted? found: %s", findOut)
 		}
-	case distro.OpenWrt:
+	case dist == distro.OpenWrt:
 		out, err := exec.Command("opkg", "list-installed").CombinedOutput()
 		if err != nil {
 			logf("error querying OpenWrt installed packages: %s", out)

version/distro/distro.go

@@ -10,13 +10,16 @@
 	"runtime"
 	"strconv"
 
+	"go4.org/mem"
 	"tailscale.com/syncs"
+	"tailscale.com/util/lineread"
 )
 
 type Distro string
 
 const (
 	Debian    = Distro("debian")
+	Ubuntu    = Distro("ubuntu")
 	Arch      = Distro("arch")
 	Synology  = Distro("synology")
 	OpenWrt   = Distro("openwrt")
@@ -62,9 +65,20 @@ func linuxDistro() Distro {
 	case haveDir("/usr/syno"):
 		return Synology
 	case have("/usr/local/bin/freenas-debug"):
-		// TrueNAS Scale runs on debian
+		// TrueNAS Scale runs on debian so test for it before Debian.
 		return TrueNAS
 	case have("/etc/debian_version"):
+		// Ubuntu also has an /etc/debian_version file, so see if it's actually Ubuntu.
+		isUbuntu := false
+		lineread.File("/etc/os-release", func(line []byte) error {
+			if mem.HasPrefix(mem.B(line), mem.S("ID=ubuntu")) {
+				isUbuntu = true
+			}
+			return nil
+		})
+		if isUbuntu {
+			return Ubuntu
+		}
 		return Debian
 	case have("/etc/arch-release"):
 		return Arch
@@ -110,3 +124,8 @@ func DSMVersion() int {
 	v, _ := strconv.Atoi(os.Getenv("SYNOPKG_DSM_VERSION_MAJOR"))
 	return v
 }
+
+// LikeDebian reports whether d is Debian-derived.
+func (d Distro) LikeDebian() bool {
+	return d == Debian || d == Ubuntu
+}

version/distro/distro_test.go

@@ -14,3 +14,8 @@ func BenchmarkGet(b *testing.B) {
 	}
 	_ = d
 }
+
+func TestGet(t *testing.T) {
+	d := Get()
+	t.Logf("Get = %q", d)
+}