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Linux tracing records activity at selected points in kernel or user-space execution so you can investigate how a system behaves. It is a family of techniques—not one tool—and the right choice depends on what you need to observe, what evidence you need, and which features your kernel provides.
How tracing differs from debugging and profiling
These approaches can overlap in practice, but they answer questions in different ways. The Linux Foundation’s 2021 introductory tutorial describes debugging as an interactive, controlled process; profiling as statistical sampling; and tracing as collecting information at selected points for later analysis. Linux Foundation tutorial
- Debugging commonly lets you stop execution and inspect program state at a chosen point.
- Profiling samples execution or performance signals to show where time or resources are being spent.
- Tracing records selected events or execution points, which can help reconstruct sequences and examine behavior over time.
The categories are useful distinctions, not rigid boundaries: a tracing workflow can help debug a problem or analyze performance.
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The Linux kernel tracing guide treats tracing as a set of related mechanisms, rather than interchangeable alternatives. Linux kernel tracing documentation
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- Function tracing observes kernel function execution.
- Event tracing records predefined events and their associated data.
- Tracepoints and probes provide instrumentation sites or attachable observation mechanisms.
- Hardware and performance tracing uses hardware or performance-related signals.
- User-space tracing includes user events and uprobes for observing activity outside the kernel.
- Remote tracing can handle compatible ring-buffer data written outside the kernel.
These categories can complement one another. They differ in what they observe, where instrumentation is placed, and what kind of evidence they produce.
Ftrace and tracefs: a practical starting point
Ftrace is a kernel tracing framework, not merely a function tracer. Kernel documentation describes uses that include debugging, latency and performance analysis, and event tracing. Its control and output files are exposed through tracefs. When available, the documented mount location is /sys/kernel/tracing; a backward-compatible location exists under debugfs. Which tracers are available depends on the kernel’s configuration. Ftrace documentation
Check what the target kernel exposes
Before following an example, confirm that tracefs is mounted and inspect the files available on the target machine. For example, you can list the documented tracefs location with:
ls /sys/kernel/tracingIf that path is missing, tracefs may not be mounted, the system may expose a different arrangement, or the kernel may lack the relevant support. Permissions can also limit access. Do not assume that every distribution or kernel will present the same tracers and events.
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Understand the output controls
tracepresents trace output in a human-readable form.trace_pipeis intended for streaming; reading it consumes the data as it is read.tracing_oncontrols whether data is written to the tracing ring buffer.
Turning off writes with tracing_on does not necessarily mean all tracing-related overhead has stopped. The exact behavior depends on the instrumentation and configuration in use.
Tracepoints and probes: observe defined events
A kernel tracepoint is a statically placed instrumentation hook with defined parameters. A probe registered with a tracepoint runs when that tracepoint is enabled and executed. Tracepoints can support tracing, performance accounting, debugging, and analysis of kernel behavior. Linux kernel tracepoint documentation Tracepoint API guide
For example, the kernel documentation discusses IRQ handler entry and exit tracepoints. Pairing those events can help analyze how long an interrupt handler takes. More generally, useful event analysis involves selecting an event that represents a meaningful action, identifying the fields it provides, and relating matching events over time.
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Account for instrumentation cost
The kernel documentation says a disabled tracepoint still incurs a tiny branch-check time cost and a small space cost. When enabled, its connected probe runs in the caller’s execution context. These are documented characteristics, not a universal overhead benchmark: costs vary with the tracing mechanism, enabled instrumentation, workload, and system.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Choose a tracing approach by the question you need to answer
| Question or target | Mechanism to investigate | What to check |
|---|---|---|
| Which kernel functions are executing? | Function tracing through ftrace | Whether the target kernel includes the relevant tracer and how its output is collected. |
| What happened at a defined kernel event? | Event tracing or a tracepoint | Whether the event exists and which fields it records. |
| How do selected kernel events relate over time? | Tracepoints and probes, with event output | Whether events can be matched meaningfully and the collection method preserves the needed sequence. |
| What is happening in user-space code? | User events or uprobes | Whether the relevant instrumentation is supported and available on the system. |
| What do hardware or performance signals show? | Hardware and performance tracing | Which signals and features the hardware and kernel expose. |
| How can externally written trace data be observed? | Remote tracing for compatible ring buffers | Whether the data format and ring buffer are compatible with the tracing workflow. |
The kernel’s tracing guide gives an overview of these families, while its ftrace documentation explains the framework’s purposes and configuration-dependent availability. Tracing guide Ftrace documentation
A beginner’s workflow for finding useful events
- State the question narrowly. Decide whether you need a function sequence, a predefined event, user-space activity, latency evidence, or a performance signal.
- Check the target system. Confirm tracefs availability and inspect the tracers and events the kernel actually exposes; do not infer availability from another machine or kernel version.
- Choose the observation point. Prefer a defined tracepoint when it represents the event you need; consider function tracing, probes, or user-space mechanisms when the question calls for them.
- Identify the fields and relationships that matter. Determine what each event reports and how events can be associated across time or execution.
- Select an output workflow. Use the human-readable
tracefile for a snapshot-style view ortrace_pipewhen you need streaming output and understand that reads consume data. - Interpret results in context. Consider instrumentation overhead, system configuration, permissions, and whether the captured events are sufficient to support the conclusion you want to draw.
Why a tracing example may not work on your machine
- The tracer or event is absent: available options depend on what was compiled into the running kernel.
- The tracefs path is unavailable: verify whether tracefs is mounted and whether the system uses the documented location or a compatibility arrangement.
- Access is denied: permissions may prevent reading or changing tracing controls.
- Output appears to disappear: reads from
trace_pipeconsume streamed data; it does not behave like a static file snapshot. - Disabling writes does not eliminate all cost: the kernel documentation cautions that turning off ring-buffer writes does not necessarily stop tracing overhead.
The authoritative kernel pages are labeled “latest” and can change. Treat the documentation as a guide to concepts and interface behavior, then verify exact availability on the kernel you are investigating.
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