Simpler autoreboot calculation (#119)

pkg/kernel/kernel.go

@@ -1,10 +1,9 @@
 package kernel
 
 import (
-	"crypto/rand"
 	"fmt"
 	"log/slog"
-	"math/big"
+	"math/rand/v2"
 	"os"
 	"strings"
 	"time"
@@ -132,21 +131,16 @@ func Watchdog(log *slog.Logger) {
 // AutoReboot will start a timer and reboot after given duration a random variation spread is added
 func AutoReboot(log *slog.Logger, after, spread time.Duration, callback func()) {
 	log.Info("autoreboot set to", "after", after.String(), "spread", spread.String())
-	spreadMinutes, err := rand.Int(rand.Reader, big.NewInt(int64(spread.Minutes())))
-	if err != nil {
-		log.Warn("autoreboot", "unable to calculate spread, disable spread", err)
-		spread = time.Duration(0)
-	}
-	spread = time.Minute * time.Duration(spreadMinutes.Int64())
-	after = after + spread
+	spreadMinutes := rand.N(spread)
+	after = after + spreadMinutes
 
 	log.Info("autoreboot with spread", "after", after.String())
 	rebootTimer := time.NewTimer(after)
 	<-rebootTimer.C
 	log.Info("autoreboot", "timeout reached", "rebooting in 10sec")
 	callback()
 	time.Sleep(10 * time.Second)
-	err = Reboot()
+	err := Reboot()
 	if err != nil {
 		log.Error("autoreboot", "unable to reboot, error", err)
 	}