runsc: Dup debug log file to stderr, so sentry panics don't get lost.

Docker and containerd do not expose runsc's stderr, so tracking down sentry
panics can be painful.

If we have a debug log file, we should send panics (and all stderr data) to the
log file.

PiperOrigin-RevId: 211992321
Change-Id: I5f0d2f45f35c110a38dab86bafc695aaba42f7a3

1 files changed, 8 insertions, 0 deletions

diff --git a/runsc/main.go b/runsc/main.go
index 0c9b9af78..c51b199aa 100644
--- a/runsc/main.go
+++ b/runsc/main.go
@@ -179,6 +179,10 @@ func main() {
 
 	if *debugLogFD > -1 {
 		f := os.NewFile(uintptr(*debugLogFD), "debug log file")
+		// Dup f to stderr so we capture stack traces on panic.
+		if err := syscall.Dup2(int(f.Fd()), int(os.Stderr.Fd())); err != nil {
+			cmd.Fatalf("error dup'ing fd %d to stderr: %v", f.Fd(), err)
+		}
 		e = log.MultiEmitter{e, log.GoogleEmitter{&log.Writer{Next: f}}}
 	} else if *debugLogDir != "" {
 		if err := os.MkdirAll(*debugLogDir, 0775); err != nil {
@@ -189,6 +193,10 @@ func main() {
 		if err != nil {
 			cmd.Fatalf("error opening debug log file in %q: %v", *debugLogDir, err)
 		}
+		// Dup f to stderr so we capture stack traces on panic.
+		if err := syscall.Dup2(int(f.Fd()), int(os.Stderr.Fd())); err != nil {
+			cmd.Fatalf("error dup'ing fd %d to stderr: %v", f.Fd(), err)
+		}
 		e = log.MultiEmitter{e, log.GoogleEmitter{&log.Writer{Next: f}}}
 	}