[PATCH 6/7] client: job: add battery-check example pre-run hook

[Thomas Lamprecht <t.lamprecht@proxmox.com>]

Skip the run below 30% charge on battery, or below 10% on AC, where the
load of a backup would slow down charging a nearly empty battery. The
average over all batteries counts, as laptops with two batteries drain
one first, and every unclear case proceeds, since a hook that silently
skips forever is worse than one extra backup.

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
---
 debian/proxmox-backup-client-static.examples |  1 +
 debian/proxmox-backup-client.examples        |  1 +
 examples/pbs-check-battery.sh                | 47 ++++++++++++++++++++
 3 files changed, 49 insertions(+)
 create mode 100644 debian/proxmox-backup-client-static.examples
 create mode 100644 debian/proxmox-backup-client.examples
 create mode 100755 examples/pbs-check-battery.sh

diff --git a/debian/proxmox-backup-client-static.examples b/debian/proxmox-backup-client-static.examples
new file mode 100644
index 000000000..b28044ebd
--- /dev/null
+++ b/debian/proxmox-backup-client-static.examples
@@ -0,0 +1 @@
+examples/pbs-check-battery.sh
diff --git a/debian/proxmox-backup-client.examples b/debian/proxmox-backup-client.examples
new file mode 100644
index 000000000..b28044ebd
--- /dev/null
+++ b/debian/proxmox-backup-client.examples
@@ -0,0 +1 @@
+examples/pbs-check-battery.sh
diff --git a/examples/pbs-check-battery.sh b/examples/pbs-check-battery.sh
new file mode 100755
index 000000000..d7779cb04
--- /dev/null
+++ b/examples/pbs-check-battery.sh
@@ -0,0 +1,47 @@
+#!/bin/bash
+# Pre-run hook for proxmox-backup-client scheduled backups. Skips the backup below 30% battery
+# while discharging, or below 10% on AC, where the load of a backup would slow down charging.
+#
+# Exit 0 proceeds with the backup, exit 1 skips this run, and anything else fails the job, so
+# proceed when in doubt, for example on a system without a battery.
+
+set -euo pipefail
+
+SUPPLY_PATH="/sys/class/power_supply"
+
+capacity_sum=0
+batteries=0
+status="Unknown"
+
+# batteries are found by their type, as their names depend on the driver
+for bat in "$SUPPLY_PATH"/*; do
+    [ "$(cat "$bat/type" 2>/dev/null)" = "Battery" ] || continue
+    # an empty bay is listed as well
+    [ "$(cat "$bat/present" 2>/dev/null || echo 1)" = 1 ] || continue
+    capacity=$(cat "$bat/capacity" 2>/dev/null) || continue
+    case "$capacity" in
+        ''|*[!0-9]*) continue ;;
+    esac
+
+    capacity_sum=$((capacity_sum + capacity))
+    batteries=$((batteries + 1))
+    if [ "$(cat "$bat/status" 2>/dev/null)" = "Discharging" ]; then
+        status="Discharging"
+    fi
+done
+
+# no battery, so a desktop or a server
+[ "$batteries" -gt 0 ] || exit 0
+
+# the average of all batteries, as laptops with two of them often drain one first
+charge=$((capacity_sum / batteries))
+if [ "$status" = "Discharging" ]; then
+    threshold=30
+else
+    threshold=10
+fi
+
+if [ "$charge" -lt "$threshold" ]; then
+    echo "battery at ${charge}%, below the ${threshold}% threshold, skipping backup" >&2
+    exit 1
+fi
-- 
2.47.3