Do these 3 things before closing this tab:
1Clear out junk files and repair common Windows errors2Fix the driver behind crashes, sound loss and screen glitches3Repair Windows errors before they cause bigger problemsLinux bootconfig adds structured settings to the kernel command line or init process, while boot-time tracing uses ftrace to record activity during early startup. The two work together: bootconfig can express tracing setups that are too complex for ordinary command-line parameters. Exactly when tracing begins—and which setup route is available—depends on the target kernel, its configuration, bootloader, and initrd arrangement.
What Linux bootconfig does
Bootconfig is a structured, key-value configuration mechanism that extends rather than replaces kernel command-line parameters. Settings under a kernel subtree are passed to the kernel command line; settings under an init subtree are passed to the init process. Dot-connected keys organize the settings.
This gives administrators a way to keep additional boot settings together instead of expressing everything as a long command line. It is especially useful for boot-time tracing, whose filters, triggers, histograms, and related options can be too elaborate for ordinary kernel parameters.
Ways to supply bootconfig
| Route | How it works | When it may fit | Important condition |
|---|---|---|---|
| Attach to an initrd | The kernel’s tools/bootconfig utility appends the configuration to an initrd; it can also remove it later. |
The system already uses an initrd and it is practical to update that image. | The kernel must be configured to look for bootconfig unless a force configuration is enabled. The bootloader must pass the correct initrd size. |
| Embed in the kernel build | A bootconfig file is specified through kernel build configuration and included in the kernel. | Rebuilding or maintaining a custom kernel is practical. | Bootconfig must be activated unless a force configuration is enabled. Build-time and runtime parameter handling can differ. |
For the initrd route, the kernel decodes the attached data from the end of the image. This makes correct image handling and the bootloader’s initrd-size information part of the setup, not optional details. The exact options and workflow should be checked against the documentation and configuration of the kernel being booted: Linux kernel bootconfig documentation.
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How bootconfig and the command line interact
The general documented order is that bootconfig parameters are concatenated before user-supplied command-line parameters. Where a parameter handler uses last-one-wins behavior, a later command-line value can override an earlier bootconfig value. Do not assume this applies to every parameter: handlers can differ, and embedded bootconfig, early-parameter parsing, initrd-supplied bootconfig, and build-time rendering introduce path-specific behavior.
If a setting must be available to an early parameter handler, verify that the chosen bootconfig route exposes it at the required stage. Treat precedence as something to confirm for the particular option and kernel path, rather than as a universal override rule.
What boot-time tracing can capture
Boot-time tracing is an ftrace setup path for observing startup, including device initialization. The kernel tracing documentation describes support for event filters and actions, histograms, kprobe events, synthetic events, and trace instances. These facilities let a configuration select events, correlate data, and control tracing around functions; they are capabilities documented by the kernel, not a guarantee that every kernel enables every feature.
The documentation’s examples include filtering events, building a histogram from initcall start and finish data, and using a kprobe-triggered action to switch tracing on or off around a function. Bootconfig is useful here because these multi-part configurations cannot be expressed conveniently as ordinary kernel command-line parameters. See the Linux kernel boot-time tracing documentation for syntax and examples.
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When tracing starts—and what that means
The start point matters if the event of interest occurs very early. The documented ftrace-prefixed boot-time tracing settings are enabled at the end of core_initcall, which allows tracing from postcore_initcall. Some kernel-prefixed settings can take effect earlier, before initcall processing.
Consequently, an ftrace configuration should not be assumed to capture all startup activity from the first instruction. Match the setting type and capture window to the event you need, and verify that the target kernel supports the relevant options. Kernel configuration requirements are described in the kernel tracing Kconfig.
Check support and configuration limits
- Check build options: bootconfig and boot-time tracing depend on kernel configuration; tracing support and bootconfig are among the relevant requirements.
- Check the delivery path: confirm whether the kernel expects an initrd-attached configuration or uses an embedded one, and whether bootconfig activation or a force setting is enabled.
- Check the event window: identify whether the target operation happens before initcalls, at or after
postcore_initcall, or later in startup. - Check configuration size and complexity: the current kernel bootconfig documentation lists a maximum size of 32 KB and a maximum of 1,024 keyword nodes. The parser can reach the node limit even when the file is below the byte limit; these are documentation limits, not timeless guarantees for every kernel version.
About the mentorship session
The Linux Foundation event page lists Masami Hiramatsu, identified there as Tech Lead at Linaro, as the speaker for a session recorded July 13, 2021. The event described the session as an explanation of extra boot configuration, boot-time tracing, and writing settings in bootconfig. The underlying kernel documentation is the practical reference for current behavior and syntax: Linux Foundation webinars.
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