iostat Command
Intermediate Performance & Debugging man(1)Report CPU and I/O statistics
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📅 Updated: Mar 15, 2026
SYNTAX
iostat [OPTION]... [DEVICE] [INTERVAL]
What Does iostat Do?
iostat reports CPU and I/O statistics for devices and partitions. It is the primary tool for monitoring disk I/O performance, identifying bottlenecks, and measuring throughput.
iostat shows read/write speeds, I/O operations per second (IOPS), average queue sizes, and service times. This data is essential for diagnosing slow disk performance.
iostat is part of the sysstat package and is commonly used alongside vmstat and sar for comprehensive system monitoring.
iostat shows read/write speeds, I/O operations per second (IOPS), average queue sizes, and service times. This data is essential for diagnosing slow disk performance.
iostat is part of the sysstat package and is commonly used alongside vmstat and sar for comprehensive system monitoring.
Options & Flags
| Option | Description | Example |
|---|---|---|
| -x | Extended statistics | iostat -x 1 |
| -d | Device statistics only | iostat -d 1 |
| -c | CPU statistics only | iostat -c 1 |
| -h | Human-readable | iostat -h 1 |
| -p | Include partitions | iostat -p sda 1 |
| N | Update interval in seconds | iostat 2 |
Practical Examples
#1 Extended I/O stats
Shows detailed I/O statistics for all devices, updating every second.
$ iostat -x 1
Output:
Device r/s w/s rkB/s wkB/s await %util
sda 10.5 25.3 420.0 1012.0 2.5 15.3
#2 Device stats only
Shows only disk I/O statistics every 2 seconds.
$ iostat -d 2#3 Human-readable
Shows I/O stats in human-readable format.
$ iostat -dh 1#4 Specific device
Shows extended stats for sda only.
$ iostat -x sda 1#5 Single snapshot
Shows a single snapshot of I/O statistics.
$ iostat -xTips & Best Practices
Key metrics to watch: %util >70% means device is busy. await >10ms on SSD = problem. r/s and w/s show IOPS.
Part of sysstat: Install with: apt install sysstat or yum install sysstat.
First report is averages: Like vmstat, the first report shows averages since boot. Subsequent reports show current values.
Frequently Asked Questions
How do I check disk I/O performance?
iostat -x 1 shows extended statistics per second. Watch %util, await, and r/s+w/s columns.
What does %util mean?
Percentage of time the device was busy. >70% indicates the disk is becoming a bottleneck.
How do I install iostat?
iostat is part of sysstat: sudo apt install sysstat (Debian/Ubuntu) or sudo yum install sysstat (RHEL).
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