Calculate system uptime duration and availability percentage from boot timestamp.
`/proc/uptime` reports two numbers: total seconds since boot, and total seconds the system has spent idle. Availability tracking uses the same ratio concept but at a service level — dividing total uptime by the sum of uptime and downtime over an observation window gives the availability percentage that SLA tiers ('three nines', 'four nines', etc.) are built around. This calculator projects that ratio forward to an expected annual downtime budget for easy comparison against SLA commitments.
Availability percentage
availability% = uptime / (uptime + downtime) × 100
`cat /proc/uptime` prints two space-separated values in seconds: total time since boot, and total time the system has been idle (which can exceed real time on multi-core systems since idle time is summed across cores in some kernel versions — always sanity-check against `uptime -p`).
Cloud providers commonly commit to 99.9%–99.99% for compute SLAs (roughly 8.7 hours to 52 minutes of allowed annual downtime). A single self-hosted Linux box with manual patching and no redundancy typically lands lower, often 99–99.5%, once planned maintenance and occasional unplanned reboots are counted.
Not fully — a host can be 'up' (kernel running) while the service it hosts is unresponsive (hung process, exhausted connections, network partition). True service availability should be measured via application-level health checks, not just kernel uptime.