Master Linux I/O Monitoring: iostat, iotop, and lsof Explained

Introduce three commonly used Linux I/O commands that are useful for solving excessive I/O pressure.

iostat

Outputs CPU and disk I/O related statistics.

Average‑CPU section %user: percentage of CPU used by user programs %nice: percentage of CPU used by nice‑adjusted processes %sys: percentage of CPU used by the system %iowait: percentage of CPU waiting for I/O %idle: percentage of idle CPU time

Device section tps: I/O requests per second Blk_read/s: blocks read per second Blk_wrtn/s: blocks written per second Blk_read: total blocks read Blk_wrtn: total blocks written

Common parameters -c: display only CPU statistics (mutually exclusive with -d) -d: display only disk statistics (mutually exclusive with -c) -k: show values in kilobytes per second (default unit is blocks) -p device|ALL : show statistics for a specific device or all devices -x: display extended information sec: interval in seconds between displays

iotop

A top‑like tool for monitoring disk I/O usage, showing PID, user, I/O, and command information.

iotop is not included by default; install it (e.g., yum install iotop on CentOS).

Main options -o: display only processes doing I/O -b: batch mode, suitable for logging to a file -n NUM : display NUM iterations (non‑interactive mode) -d SEC : refresh interval in seconds -p PID : monitor a specific process ID -u USER : monitor processes owned by a specific user

lsof

lsof

(list open files) lists files opened by processes; it requires root privileges to access full information.

lsof is not installed by default; install it (e.g., yum install lsof on CentOS).

Output fields COMMAND: process name PID: process identifier USER: process owner FD: file descriptor TYPE: file type (e.g., DIR, REG) DEVICE: device name SIZE: file size NODE: inode number NAME: exact name of the opened file

Common usage examples lsof abc.txt: show processes that have abc.txt open lsof -c abc: show files opened by processes whose command name contains abc lsof -p 1234: list files opened by process ID 1234 lsof -g gid: show processes belonging to group ID gid lsof +d /DIR/: list files opened under directory /DIR/