feat: add optional nohz_full GRUB check

.claude/CLAUDE.md

@@ -65,6 +65,7 @@ sudo ./health_check.sh -h                 # Help
 | NVMe Wear | `nvmeWear` | Monitors NVMe drive wear levels against threshold |
 | GRUB Cmdline | `grubCmdline` | Verifies required parameters (`audit=1`, `audit_backlog_limit=8192`, `transparent_hugepage=never`) exist in GRUB_CMDLINE_LINUX_DEFAULT |
 | Huge Pages | `hugepages` | Verifies `hugepagesz=`/`hugepages=` in GRUB match `systemChecks.memory.hugepageSize` (default `2M`) and `hugepageCount` (minimum, default `256`), and that the running kernel has allocated them; reports pages in use (and agave-validator's share) and warns if the pool is exhausted |
+| nohz_full | `nohzFull` | **Off by default** (missing key = off). Fails if `nohz_full=` is missing from GRUB_CMDLINE_LINUX_DEFAULT; warns if the running kernel doesn't match yet (reboot pending). Enable per host in `local_config.json` |
 
 **NIC Exclusion**: Network interfaces can be excluded from ring buffer checks via config:
 ```json

README.md

@@ -18,6 +18,7 @@ The script verifies the following aspects of your system:
 - **CPU Driver**: Ensures that the p-state CPU scaling driver is being used
 - **SMT (Hyperthreading)**: Verifies SMT matches the configured state (default: disabled)
 - **Memory Management**: Confirms swap is disabled
+- **Tickless CPUs (nohz_full)**: Optional (off by default) - verifies `nohz_full=` is set in GRUB on hosts that use tickless CPU cores
 - **Huge Pages**: Verifies `hugepagesz`/`hugepages` are set in GRUB and that the running kernel has allocated at least that many huge pages
 - **Security Services**: Checks that fail2ban is installed, enabled, and running
 - **System Updates**: Validates that there are no more than 5 package updates pending
@@ -68,6 +69,7 @@ The configuration file is structured as follows:
     "smtStatus": true,
     "swapStatus": true,
     "hugepages": true,
+    "nohzFull": false,
     "packageUpdates": true,
     "ntpSync": true,
     "fail2ban": true,
@@ -172,5 +174,6 @@ The script provides color-coded output for easy interpretation:
 - CPU boost check handles both Intel and AMD-specific boost mechanisms
 - SMT check reads `/sys/devices/system/cpu/smt/active`; `systemChecks.cpu.smt` accepts `disabled` (default), `enabled`, or `any` (report only). If the key is missing from the config, the check still runs and expects `disabled`
 - Huge pages check reads `hugepagesz=`/`hugepages=` from `GRUB_CMDLINE_LINUX_DEFAULT` and `/sys/kernel/mm/hugepages/hugepages-<size>kB/nr_hugepages`; `systemChecks.memory.hugepageSize` (default `2M`) must match exactly and `hugepageCount` (default `256`) is a minimum. Pages in use are reported for information only (a stopped validator uses none); a warning is shown if every page is in use
+- The nohz_full check is off unless `checksToRun.nohzFull` is explicitly `true` (a missing key counts as off, unlike other checks). It fails if `nohz_full=` is missing from `GRUB_CMDLINE_LINUX_DEFAULT` and warns if the running kernel (`/proc/cmdline`) does not match yet
 - NTP check supports multiple time synchronization methods (systemd-timesyncd, chronyd, ntpd, OpenNTPD)
 - Package update checker automatically detects apt, dnf, yum, pacman, or zypper package managers

config.json

@@ -22,7 +22,8 @@
     "nvmeWear": true,
     "requiredPackages": true,
     "grubCmdline": true,
-    "hugepages": true
+    "hugepages": true,
+    "nohzFull": false
   },
   "systemChecks": {
     "cpu": {

health_check.sh

@@ -168,8 +168,10 @@ get_config() {
 # Function to check if a specific check should be run
 should_run_check() {
   local check_name="$1"
+  # Optional second argument: value to use when the key is missing from the config (default: true)
+  local default="${2:-true}"
   local result
-  result=$(get_config ".checksToRun.$check_name" "true")
+  result=$(get_config ".checksToRun.$check_name" "$default")
 
   # Convert to lowercase for standardization
   result=$(echo "$result" | tr '[:upper:]' '[:lower:]')
@@ -2224,6 +2226,63 @@ else
   echo -e "${BLUE}Checking huge page configuration... ${YELLOW}[SKIPPED]${NC}"
 fi
 
+# Function to check nohz_full is set in GRUB (only enabled on hosts that use tickless CPUs)
+check_nohz_full() {
+  echo -e "\n${YELLOW}=== Tickless CPUs (nohz_full) ===${NC}"
+  echo -e "${BLUE}Checking nohz_full in GRUB command line...${NC}"
+
+  local grub_file="/etc/default/grub"
+
+  if [ ! -f "$grub_file" ]; then
+    echo -e "  ${RED}FAIL: GRUB configuration file not found at $grub_file${NC}"
+    return 1
+  fi
+
+  local cmdline_default
+  cmdline_default=$(grep "^GRUB_CMDLINE_LINUX_DEFAULT=" "$grub_file" 2>/dev/null | head -1 | cut -d= -f2- | tr -d '"'"'")
+
+  # Match whole tokens so other parameters containing "nohz_full" are not mistaken for it
+  local grub_value="" token
+  for token in $cmdline_default; do
+    case "$token" in
+      nohz_full=*) grub_value=${token#nohz_full=} ;;
+    esac
+  done
+
+  if [ -z "$grub_value" ]; then
+    echo -e "  ${RED}FAIL: 'nohz_full=' missing from GRUB_CMDLINE_LINUX_DEFAULT${NC}"
+    echo -e "  ${YELLOW}Add 'nohz_full=<cpu list>' to GRUB_CMDLINE_LINUX_DEFAULT in $grub_file${NC}"
+    echo -e "  ${YELLOW}Then run: sudo update-grub && sudo reboot${NC}"
+    return 1
+  fi
+
+  echo -e "  ${GREEN}PASS: 'nohz_full=$grub_value' found in GRUB_CMDLINE_LINUX_DEFAULT${NC}"
+
+  # nohz_full only takes effect at boot, so flag a GRUB change that has not been applied yet
+  local running_value=""
+  for token in $(cat /proc/cmdline 2>/dev/null); do
+    case "$token" in
+      nohz_full=*) running_value=${token#nohz_full=} ;;
+    esac
+  done
+
+  if [ "$running_value" != "$grub_value" ]; then
+    echo -e "  ${YELLOW}WARNING: Running kernel has nohz_full='${running_value:-<not set>}' - run 'sudo update-grub' and reboot to apply${NC}"
+  fi
+  return 0
+}
+
+# Check nohz_full if enabled in config (off unless a config explicitly enables it)
+if should_run_check "nohzFull" "false"; then
+  if ! check_nohz_full; then
+    ((failures++))
+    failed_checks+=("Tickless CPUs: nohz_full")
+  fi
+else
+  echo -e "\n${YELLOW}=== Tickless CPUs (nohz_full) ===${NC}"
+  echo -e "${BLUE}Checking nohz_full in GRUB command line... ${YELLOW}[SKIPPED]${NC}"
+fi
+
 # Summary - Always show this part even in quiet mode
 if [ "$QUIET_MODE" = true ]; then
   # Restore stdout for the summary