---
name: "biosnoop.bt"
section: "8"
platform: "linux"
package: "bpftrace"
version: "0.27.0-2"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/biosnoop.bt"
---

# biosnoop.bt(8)

Block I/O tracing tool, showing per I/O latency. Uses bpftrace/eBPF.

## NAME

biosnoop.bt - Block I/O tracing tool, showing per I/O latency. Uses bpftrace/eBPF.

## SYNOPSIS

**biosnoop.bt**

## DESCRIPTION

This is a basic block I/O (disk I/O) tracing tool, showing each I/O event along with the issuing process ID, and the I/O latency. This can be used to investigate disk I/O performance issues.

This tool currently works by dynamic tracing of the blk\_account\*() kernel functions, which will need updating to match any changes to these functions in future kernels versions.

Since this uses BPF, only the root user can use this tool.

## REQUIREMENTS

CONFIG\_BPF and bpftrace.

## EXAMPLES

- Trace block I/O events, printing per-line summaries:

  \# **biosnoop.bt**

## FIELDS

- TIME

  Time of the I/O completion, in milliseconds since program start.

- DISK ID

  Major and minor device numbers of the disk device.

- COMM

  Issuing process name. This often identifies the issuing application process, but I/O may be initiated from kernel threads only.

- PID

  Issuing process ID. This often identifies the issuing application process, but I/O may be initiated from kernel threads only.

- LAT(ms)

  Per I/O latency.

## OVERHEAD

Since block device I/O usually has a relatively low frequency (\< 10,000/s), the overhead for this tool is expected to be negligible. For high IOPS storage systems, test and quantify before use.

## SOURCE

This is from bpftrace.

-

  https://github.com/bpftrace/bpftrace

Also look in the bpftrace distribution for a companion \_examples.txt file containing example usage, output, and commentary for this tool.

This is a bpftrace version of the bcc tool of the same name. The bcc tool provides more fields.

-

  https://github.com/iovisor/bcc

## OS

Linux

## STABILITY

Unstable - in development.

## AUTHOR

Brendan Gregg

## SEE ALSO

[opensnoop.bt(8)](/opensnoop.bt/8.md)