Linux Admin Tool: Iostat

The iostat command at its most basic provides an overview of CPU and disk I/O statistics:

#iostat

iostat
Linux 2.4.21-32.ELsmp (dw1.corp.co.com) 03/30/2007
avg-cpu: %user %nice %sys %iowait %idle
4.10 0.01 1.26 4.69 89.94

Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn
cciss/c0d0 19.43 24.51 27.90 726081316 826335200
cciss/c0d0p1 16.75 17.37 110.99 514613362 3287372808
cciss/c0d0p2 2.57 6.44 60.75 190884490 1799215720
cciss/c0d0p3 0.10 0.69 1.17 20583160 34713968

Below the first line (which contains the system's kernel version and hostname, along with the current date), iostat displays an overview of the system's average CPU utilization since the last reboot. The CPU utilization report includes the following percentages:

· Percentage of time spent in user mode (running applications, etc.)
· Percentage of time spent in user mode (for processes that have altered their scheduling priority using nice(2))
· Percentage of time spent in kernel mode
· Percentage of time spent idle

Below the CPU utilization report is the device utilization report. This report contains one line for each active disk device on the system and includes the following information:

· The device specification, displayed as dev-sequence-number, where is the device's major number[1], and is a sequence number starting at zero.
· The number of transfers (or I/O operations) per second.
· The number of 512-byte blocks read per second.
· The number of 512-byte blocks written per second.
· The total number of 512-byte blocks read.
· The total number of 512-byte block written.

This is just a sample of the information that can be obtained using iostat. For more information, refer to the iostat(1) man page.