os, syscall: skip tests when environment doesn't permit testing

Fixes #14693

Change-Id: Id0a6a80b4c37c0b0f1c2755667b7233ed8964e40
Reviewed-on: https://go-review.googlesource.com/20342Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/os/os_test.go

@@ -1275,15 +1275,19 @@ func TestOpenNoName(t *testing.T) {
 	}
 }
 
-func run(t *testing.T, cmd []string) string {
+func runBinHostname(t *testing.T) string {
 	// Run /bin/hostname and collect output.
 	r, w, err := Pipe()
 	if err != nil {
 		t.Fatal(err)
 	}
 	defer r.Close()
-	p, err := StartProcess("/bin/hostname", []string{"hostname"}, &ProcAttr{Files: []*File{nil, w, Stderr}})
+	const path = "/bin/hostname"
+	p, err := StartProcess(path, []string{"hostname"}, &ProcAttr{Files: []*File{nil, w, Stderr}})
 	if err != nil {
+		if _, err := Stat(path); IsNotExist(err) {
+			t.Skipf("skipping test; test requires %s but it does not exist", path)
+		}
 		t.Fatal(err)
 	}
 	w.Close()
@@ -1303,7 +1307,7 @@ func run(t *testing.T, cmd []string) string {
 		output = output[0 : n-1]
 	}
 	if output == "" {
-		t.Fatalf("%v produced no output", cmd)
+		t.Fatalf("/bin/hostname produced no output")
 	}
 
 	return output
@@ -1345,7 +1349,7 @@ func TestHostname(t *testing.T) {
 	if err != nil {
 		t.Fatalf("%v", err)
 	}
-	want := run(t, []string{"/bin/hostname"})
+	want := runBinHostname(t)
 	if hostname != want {
 		i := strings.Index(hostname, ".")
 		if i < 0 || hostname[0:i] != want {

src/syscall/exec_linux_test.go

@@ -31,6 +31,9 @@ func whoamiCmd(t *testing.T, uid, gid int, setgroups bool) *exec.Cmd {
 		if os.IsNotExist(err) {
 			t.Skip("kernel doesn't support user namespaces")
 		}
+		if os.IsPermission(err) {
+			t.Skip("unable to test user namespaces due to permissions")
+		}
 		t.Fatalf("Failed to stat /proc/self/ns/user: %v", err)
 	}
 	if isChrooted(t) {