smartmon.sh: NVMe devices report false smart_healthy=0 due to bash integer initialization bug

[moonD4rk]

Problem

smartmon.sh incorrectly reports smartmon_device_smart_healthy=0 (FAILED) for healthy NVMe devices. This causes false alerts in monitoring systems (e.g., Grafana alerting on smartmon_device_smart_healthy < 1).

Additionally, smartmon_device_smart_available and smartmon_device_smart_enabled are always 0 for NVMe devices, even though SMART is mandatory per the NVMe specification.

Root Cause

Two issues in the parse_smartctl_info() function:

1. local -i smart_healthy= initializes to 0, not empty string

https://github.com/prometheus-community/node-exporter-textfile-collector-scripts/blob/master/smartmon.sh#L112

local -i smart_available=0 smart_enabled=0 smart_healthy=

The -i (integer) flag causes smart_healthy= to initialize to 0 instead of an empty string. The guard at the end of the function is intended to skip output when the health status is unknown:

[[ "${smart_healthy}" != "" ]] && echo "device_smart_healthy{...} ${smart_healthy}"

But since "0" != "" is always true, the guard never works — the metric is always emitted, and if smartctl fails to return the health line for any transient reason, the metric reports 0 (unhealthy) instead of being omitted.

Verified in bash:

$ f() { local -i x=; echo "[$x]"; [[ "$x" != "" ]] && echo "not empty"; }; f
[0]
not empty

2. NVMe devices lack SMART support is: output lines

For SATA devices, smartctl -i -H outputs:

SMART support is: Available - device has SMART capability.
SMART support is: Enabled

For NVMe devices, these lines do not exist — NVMe has a different output format. As a result, smart_available and smart_enabled remain at their default value of 0.

However, SMART / Health Information (Log Identifier 02h) is mandatory for all NVMe I/O controllers per NVM Express Base Specification (revision 2.0a, Section 3.1.2.1.2, Figure 24):

Log Page Name	Support Requirements
SMART / Health Information (Controller scope)	M (Mandatory)

Environment

• Proxmox VE 8.2.4
• smartctl 7.3 (2022-02-28)
• Samsung SSD 980 1TB NVMe (smartctl -H reports PASSED, 0 errors, 100% spare)
• smartmon.sh from prometheus-node-exporter-collectors Debian package (same code as upstream master)