runner: allow coredump collection (#931)

Fixes #784 

I didn't find a way to set ulimit globally, as our init system doesn't
call `/etc/initscript`

---------

Signed-off-by: Oleg Vasilev <[email protected]>

Author: Omrigan

neonvm/runner/main.go

@@ -676,11 +676,14 @@ func run(logger *zap.Logger) error {
 	}
 
 	// create iso9660 disk with runtime options (command, args, envs, mounts)
-	sysctl := []string{}
+	sysctl := []string{
+		"kernel.core_pattern=core",
+		"kernel.core_uses_pid=1",
+	}
 	var shmSize *resource.Quantity
 	var swapInfo *vmv1.SwapInfo
 	if vmSpec.Guest.Settings != nil {
-		sysctl = vmSpec.Guest.Settings.Sysctl
+		sysctl = append(sysctl, vmSpec.Guest.Settings.Sysctl...)
 		swapInfo, err = vmSpec.Guest.Settings.GetSwapInfo()
 		if err != nil {
 			return fmt.Errorf("failed to get SwapInfo from VirtualMachine object: %w", err)

neonvm/tools/vm-builder/main.go

@@ -236,6 +236,8 @@ func main() {
 		tmplArgs.ShutdownHook = strings.ReplaceAll(spec.ShutdownHook, "\n", "\n\t")
 
 		for _, c := range spec.Commands {
+			// Allow core dumps for all inittab targets
+			c.Shell = fmt.Sprintf("ulimit -c unlimited; %s", c.Shell)
 			tmplArgs.InittabCommands = append(tmplArgs.InittabCommands, inittabCommand{
 				SysvInitAction:      c.SysvInitAction,
 				CommandUser:         c.User,