See which processes are reading and writing the disk right now and hunt down bottlenecks. 16.11.2025 | reading time: 3 min If disks feel slow, he needs to know which process is chewing throughput; iotop shows per-process I/O activity live so he can act fast. Hands-on: reproduce and observe Generate load in one terminal and watch it with iotop in another; for example run the writer and the monitor like this: ```bash # terminal A: watch only active I/O, show processes, accumulate totals sudo iotop -oPa # terminal B: create heavy writes (use a safe path) sudo dd if=/dev/zero of=/tmp/testfile bs=1M count=200 oflag=direct ``` A typical iotop snapshot then might look like this: ```text Total DISK READ: 0.00 B/s | Total DISK WRITE: 18.4 M/s TID PRIO USER DISK READ DISK WRITE SWAPIN IO> COMMAND 12345 be/4 root 0.00 B/s 18.4 M/s 0.00 % 0.00 % dd ``` Options that change the view Use `-o` to show only processes doing I/O, `-P` to collapse threads into processes, and `-a` to display accumulated totals instead of instantaneous rates; add `-b -n <count>` to run in batch mode for logging, and `-p <pid>` to focus on a single PID; remember that iotop usually needs root and depends on kernel I/O accounting to report correctly. How to read the numbers DISK READ and DISK WRITE show bandwidth, SWAPIN flags processes blocked by swap activity, and IO% reflects time spent waiting on I/O; a high DISK WRITE from a short-lived process points to bursts, while steady high IO% across many processes hints at a device-level bottleneck. Related ways to measure I/O iotop is great for per-process visibility, but for device-level trends use `iostat`, for comprehensive system snapshots use `atop`, and for low-level tracing use `blktrace` or `perf` depending on how deep he needs to go. Next steps Use iotop to validate hypotheses: reproduce a slow job, run iotop, and correlate with process names and PIDs before changing configuration or killing tasks; log with batch mode when you need historical proof for a ticket. Final word Mastering a small toolbox for I/O analysis speeds troubleshooting and makes performance tuning repeatable; explore further and consider formal certification like CompTIA Linux+ or LPIC-1 with intensive exam preparation at bitsandbytes.academy to turn hands-on skill into credentials. Join Bits & Bytes Academy First class LINUX exam preparation. utilities processes storage troubleshooting
