Net-SNMP was crashing (signal 11) on every operation despite fork isolation.
The issue was that init_snmp() tries to load MIB files by default, which can
cause crashes if MIB files are missing, corrupted, or incompatible.
Since we only use numeric OIDs (e.g., "1.3.6.1.2.1.1.1.0"), we don't need
MIB name resolution at all. This change explicitly disables MIB loading in
the child process by:
1. Setting MIBS and MIBDIRS environment variables to empty
2. Calling netsnmp_set_mib_directory("") to disable MIB directory search
3. These must happen BEFORE calling init_snmp()
This should fix the persistent SIGSEGV crashes in SNMP operations.
Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>
Each SNMP GET/WALK now runs in a forked child process. If libnetsnmp
triggers a SIGSEGV or other fatal signal, only the child dies - the
parent agent logs the crash and continues operating for all other devices.
Key changes:
- C helper: snmp_get_isolated() and snmp_walk_isolated() using
fork+pipe pattern with 60s alarm watchdog and mutex-serialized forks
- Rust: IsolationMode enum (Fork/Direct) controlled by
TOWEROPS_SNMP_ISOLATION env var, defaults to Fork
- New CrashRecovered error variant with signal info and logging
- Device poller logs crash recovery events at error level
- Startup logs active isolation mode
Set TOWEROPS_SNMP_ISOLATION=direct to disable isolation for debugging.
