calculate the age of a system

age-of-install.sh

#!/bin/bash

echo "System installed at $(stat -c %w /)"

INSTALL_DATE=$(stat -c %w /)
NOW_TIMESTAMP=$(date +%s)
INSTALL_TIMESTAMP=$(date -d "$INSTALL_DATE" +%s)

TIME_DIFF_SECONDS=$((NOW_TIMESTAMP - INSTALL_TIMESTAMP))

DAYS=$((TIME_DIFF_SECONDS / 86400))
REMAINDER_SECONDS=$((TIME_DIFF_SECONDS % 86400))
HOURS=$((REMAINDER_SECONDS / 3600))
REMAINDER_SECONDS=$((REMAINDER_SECONDS % 3600))
MINUTES=$((REMAINDER_SECONDS / 60))
SECONDS=$((REMAINDER_SECONDS % 60))

echo "Time difference: $DAYS days, $HOURS hours, $MINUTES minutes, $SECONDS seconds"

Outputs something like this

System installed at 2025-04-28 10:37:15.733432813 -0400
Time difference: 167 days, 7 hours, 14 minutes, 17 seconds