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86 lines
3.9 KiB
Markdown
86 lines
3.9 KiB
Markdown
Tips & Tricks with the kernel cmdline
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=====================================
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This document summarizes the different boot parameters that can be
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passed on the Linux kernel command line. Not limited to Finit.
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The `bool` setting is one of `on, off, true false, 1, 0`.
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> **NOTE:** remember to use `--` to separate kernel parameters from
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> parameters to init. E.g., `init=/sbin/finit -- finit.debug rescue`
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* `debug`: Enable kernel debug. Debug messages are printed to the
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console until Finit starts up, unless `loglevel=7` (below) is used.
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* `finit.debug[=bool]`: Enable finit debug. This is operated
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independently of the kernel `debug` setting. New as of Finit v4.
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* `finit.fstab=</path/to/etc/fstab.alternative>`: Tell Finit to use an
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alternate `fstab` to mount the file system from. Remember, this file
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must be on the `root=...` file system provided to Finit from the
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kernel. By default the built-in fstab is used, which itself defaults
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to `/etc/fstab`, but can be changed at build time with:
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./configure --with-fstab=/path/to/fstab
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It is even possible to disable a built-in default using:
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./configure --without-fstab
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Making `finit.fstab=/path/to/fstab` a *mandatory* command line option.
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Note, if the command line fstab is missing, Finit falls back to the
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built-in fstab, and if both are missing, the system treats this as a
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bad `fsck` and thus calls `sulogin`. If, in turn, `sulogin` is not
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available on the system, Finit calls reboot, which is also what will
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happen when a user exits from `sulogin`.
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* `finit.status[=bool]`: Control finit boot progress, including banner.
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(Used to be `finit.show_status`, which works but is deprecated.)
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* `finit.status_style=<classic,modern>`: Set Finit boot progress style,
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when enabled.
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* `init=/bin/sh`: Bypass system default init and tell kernel to start a
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shell. Note, this shell is very limited and does not support
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signals and has no job control. Recommend using, and modifying,
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`rescue` mode instead.
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* `loglevel=<0-7>`, sets the kernel's log level, which is more granular
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than `debug`. Also, when `loglevel=7`, Finit will *not disable*
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kernel logs to the console. This is very useful when debugging the
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kernel at system bring-up. Since `loglevel=7` is the same as `debug`
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this means you have to use `quiet` for a quiet boot, until sysklogd
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takes over logging of kernel events.
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* `panic=SEC`: By default the kernel does not reboot after a kernel
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panic. This setting will cause a kernel reboot after SEC seconds.
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* `quiet`: Suppress kernel logging to console, except for warnings and
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errors. Also, see `loglevel` and `quiet` above.
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* `rescue`: Start rescue/maintenance mode. If your system comes with
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the bundled `sulogin` program (Finit, or from util-linux/Busybox),
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you will be given a root login to a maintenance shell. However, if
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`sulogin` is missing, the file `/lib/finit/rescue.conf` is read and
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the system booted in a limited fallback mode. See [config.md][]
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for more information.
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**Note:** in this mode `initctl` will not work. Correct the problem
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and use `reboot -f` to force reboot.
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* `single`, or `S`: Single user mode, runlevel 1, in Finit. Useful to
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debug problems with the regular runlevel. All services and TTYs in
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`[1]` will be started, so a `tty [1] @console nologin` configuration
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presents you with a root console without login.
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* `1-9`, except `6`: override the configured `runlevel`. Like the `S`
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and `rescue`, giving a single number on the kernel command line tells
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Finit to ignore any `runlevel` in `/etc/finit.conf` as well as the
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configure fallback `--with-runlevel=N` setting. Remember, `6` is the
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reboot runlevel and is not permitted. Any other values are ignored.
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For more on kernel boot parameters, see the man page [bootparam(7)][].
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[config.md]: config.md#rescue-mode
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[bootparam(7)]: https://www.man7.org/linux/man-pages/man7/bootparam.7.html
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