Run sudo iotop to see which Linux processes or threads are generating I/O, then press o to hide idle rows. Use -P for one row per process, filters to focus on a user or PID, and batch mode when you need a timestamped log.
What iotop shows
iotop is a top-like monitor that reads I/O usage information exposed by the Linux kernel and displays current usage by processes or threads. The Linux man-pages project documents it for Linux kernel 2.6.20 and later, with kernel accounting support required: CONFIG_TASK_DELAY_ACCT, CONFIG_TASK_IO_ACCOUNTING, CONFIG_TASKSTATS, and CONFIG_VM_EVENT_COUNTERS. See the iotop(8) manual.
The display includes read and write activity, swap-in percentage, I/O-wait percentage, priority, user, process or thread identity, and command. Its read/write totals describe traffic between processes or kernel threads and the kernel block-device subsystem; they are not guaranteed to match device-level counters at every instant. For that reason, use iotop to investigate process attribution, not as a substitute for a device-level I/O monitor.
Monitor disk activity interactively
- Start the monitor with
sudo iotop. Running as root is the simplest way to obtain process I/O data. - Press
oto show only processes or threads currently doing I/O. This removes idle rows from the view. - Use the left and right arrow keys to select a sort column, then press
ror Space to reverse the sort order. - Press
pto switch to process-level rows, or start with-Pto show processes rather than individual threads. - Press
cto show full command lines. Pressfto edit UID or PID filters. - Press
qto quit.
Focus on a process or user
Use these options to narrow the display without manually scanning unrelated rows:
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sudo iotop -o -Pshows active I/O only, with one row per process.sudo iotop -p 1234filters by PID or TID; replace1234with the identifier you want to inspect.sudo iotop -u www-datafilters by user; replacewww-datawith the relevant account.
The -o option means active I/O only, -P selects process rather than thread granularity, -p filters by PID or TID, and -u filters by user. Option details are in the iotop(8) manual and Debian iotop manual.
Capture a short I/O log
For a finite text capture, run:
sudo iotop -b -o -n 5 -d 2 -t -k > iotop.log
This command samples every two seconds and stops after five iterations. It writes only active rows, adds timestamps, and uses kilobytes for consistent script-friendly units. Batch mode (-b) is non-interactive and is suitable for logging I/O over time. The output is redirected to iotop.log in the current directory.
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Choose interval or accumulated I/O
By default, iotop displays activity for the sampling interval. Use -a when you want totals accumulated since iotop started. Use --accum-bw when you want bandwidth averaged over the entire sampling period. These modes answer different questions: interval values reveal current bursts, while accumulated values give a view across the run. The exact option behavior is documented in the iotop(8) manual.
Why iotop may require sudo or show little data
Permission to read process I/O
Root access is the straightforward way to obtain process I/O data. The manual also documents a non-root route using the CAP_NET_ADMIN capability. Granting capabilities is an administrator decision: it allows other users to run the program with that capability, so do not apply it casually.
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Delay accounting disabled on newer kernels
On Linux 5.14.x and later, kernel.task_delayacct can be configured at runtime and is off by default in the scenario documented by the manuals. For a diagnostic window, enable it with:
sudo sysctl kernel.task_delayacct=1
When the diagnostic is finished, disable it if appropriate:
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sudo sysctl kernel.task_delayacct=0
The iotop manual cautions that enabling delay accounting has some effect on system performance. If the kernel accounting features required by iotop are unavailable or disabled, the program may not provide the expected data; consult the manual’s kernel requirements for the complete list.
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