uptime – show how long the system has been running

uptime shows how long the system has been running, along with users logged in and system load.

Synopsis

uptime [OPTIONS]

Examples

Basic output

$ uptime
 14:30:00 up 7 days,  3:45,  2 users,  load average: 0.15, 0.20, 0.18

Pretty format

$ uptime -p
up 7 days, 3 hours, 45 minutes

Since when (boot time)

$ uptime -s
2025-01-22 10:45:00

Understanding Load Average

load average: 0.15, 0.20, 0.18
              │     │     │
              │     │     └─ 15-minute average
              │     └─ 5-minute average
              └─ 1-minute average

• Load < # of CPUs: System has spare capacity
• Load = # of CPUs: System is fully utilized
• Load > # of CPUs: Processes are waiting

Check CPU count

$ nproc
4

# Load of 4.0 on a 4-core system = 100% utilized
# Load of 8.0 on a 4-core system = overloaded

Common Patterns

Check in scripts

#!/bin/bash
LOAD=$(uptime | awk -F'load average:' '{print $2}' | cut -d, -f1)
if (( $(echo "$LOAD > 4" | bc -l) )); then
    echo "High load: $LOAD"
fi

Monitor uptime

$ watch uptime

Tips

• High load isn’t always bad: Check with top to see why
• I/O can cause high load: Processes waiting for disk
• Check history: Use sar for historical load data
• After reboot: Uptime resets to zero

See Also

Related Commands

• w — Uptime + who’s logged in + what they’re doing
• top — Real-time process and load info
• last — Reboot history

Tutorials

• Basic Unix Commands