error-handler: keep the start explanation and the final IP lookup from failing the run

.github/workflows/verify-split-files.yml

@@ -39,6 +39,7 @@ on:
       - "tests/incus-target.sh"
       - "tests/incus-storage-space.sh"
       - "tests/release-stamp-pending.sh"
+      - "tests/pct-start-reason.sh"
       - ".github/workflows/verify-split-files.yml"
   push:
     branches: [main]
@@ -69,6 +70,7 @@ on:
       - "tests/incus-target.sh"
       - "tests/incus-storage-space.sh"
       - "tests/release-stamp-pending.sh"
+      - "tests/pct-start-reason.sh"
       - ".github/workflows/verify-split-files.yml"
   workflow_dispatch:
 
@@ -139,6 +141,8 @@ jobs:
         run: bash tests/incus-storage-space.sh
       - name: Release stamp pending marker tests
         run: bash tests/release-stamp-pending.sh
+      - name: pct start reason tests
+        run: bash tests/pct-start-reason.sh
 
       - name: Prefetch lists cover every engine file
         run: |

pve/backend.func

@@ -158,7 +158,7 @@ _pct_start_failed() {
   reason="$(journalctl -u "pve-container@${ctid}" -n 80 --no-pager -o cat 2>/dev/null |
     awk '/^Starting pve-container@/ { n = 0; next } { l[++n] = $0 } END { for (i = 1; i <= n; i++) print l[i] }' |
     grep -vE '^pve-container@[0-9]+\.service: |^Failed to start pve-container@|To get more details, run the container in foreground mode' |
-    tail -n 10)"
+    tail -n 10 || true)"
   {
     echo "--- pct start ${ctid} ---"
     [[ -n "$out" ]] && echo "$out"
@@ -3591,7 +3591,8 @@ create_lxc_container() {
 # - Posts final "done" status to API telemetry
 # ------------------------------------------------------------------------------
 description() {
-  IP=$(pct exec "$CTID" ip a s dev eth0 | awk '/inet / {print $2}' | cut -d/ -f1)
+  IP=$(pct exec "$CTID" -- ip -4 addr show dev eth0 2>/dev/null | awk '/inet / {print $2}' | cut -d/ -f1 | head -n1 || true)
+  [[ -n "$IP" ]] || IP=$(pct exec "$CTID" -- ip -6 addr show dev eth0 scope global 2>/dev/null | awk '/inet6 / {print $2}' | cut -d/ -f1 | head -n1 || true)
 
   # Links follow the repository the script actually came from, which
   # detect_repo_source() has already established. Hardcoding DevScripts sent

tests/pct-start-reason.sh

@@ -0,0 +1,59 @@
+#!/usr/bin/env bash
+# _pct_start_failed runs under the host's errexit and ERR trap. Its journal
+# filter ends in grep -v, which exits 1 when nothing survives, so the helper
+# that explains a failed start was itself reported as the failure.
+set -uo pipefail
+
+CORE_DIR="$(cd -- "$(dirname -- "${BASH_SOURCE[0]}")/.." && pwd)"
+eval "$(awk '/^_pct_start_failed[(][)] [{]/,/^}/' "$CORE_DIR/pve/backend.func")"
+
+TEST_DIR="$(mktemp -d)"
+trap 'rm -rf -- "$TEST_DIR"' EXIT
+export TAB="  " YW="" CL=""
+BUILD_LOG="$TEST_DIR/build.log"
+JOURNAL="$TEST_DIR/journal"
+: >"$JOURNAL"
+passed=0 failed=0
+
+journalctl() { cat "$JOURNAL"; }
+msg_custom() { :; }
+
+expect() {
+  if [[ "$2" == "$3" ]]; then
+    echo "PASS $1"
+    passed=$((passed + 1))
+  else
+    echo "FAIL $1: expected <$2>, got <$3>" >&2
+    failed=$((failed + 1))
+  fi
+}
+
+# The helper as the host runs it: errexit, errtrace, pipefail and an ERR trap.
+run_helper() {
+  (
+    set -Eeo pipefail
+    trap 'echo TRAPPED; exit 99' ERR
+    _pct_start_failed 100 "$1"
+    echo "rc=$?"
+  ) 2>&1
+}
+
+out="$(run_helper "startup for container '100' failed")"
+expect "an empty journal does not trip the ERR trap" 0 "$(grep -c TRAPPED <<<"$out")"
+expect "the helper returns 0" 1 "$(grep -c '^rc=0$' <<<"$out")"
+expect "the pct output is shown instead" 1 "$(grep -c "startup for container" <<<"$out")"
+expect "the build log gets the pct output" 1 "$(grep -c "startup for container" "$BUILD_LOG")"
+
+: >"$BUILD_LOG"
+printf '%s\n' 'Starting pve-container@100.service - PVE LXC Container: 100...' \
+  'lxc-start: 100: conf.c: mount_entry: No such file or directory' \
+  'pve-container@100.service: Control process exited, code=exited, status=1/FAILURE' \
+  'Failed to start pve-container@100.service - PVE LXC Container: 100.' >"$JOURNAL"
+out="$(run_helper "pct out")"
+expect "the journal reason survives the filter" 1 "$(grep -c 'conf.c: mount_entry' <<<"$out")"
+expect "systemd bookkeeping is dropped" 0 "$(grep -c 'Control process exited' <<<"$out")"
+expect "a journal with lines does not trip the trap either" 0 "$(grep -c TRAPPED <<<"$out")"
+expect "the reason lands in the build log" 1 "$(grep -c 'conf.c: mount_entry' "$BUILD_LOG")"
+
+echo "$passed passed, $failed failed"
+((failed == 0))