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Boot Loader

Haiku's Boot Loader Options can help when you experience hardware related problems or want to choose which Haiku installation to start, if you have more than one (maybe on an installation CD or USB stick). It's also handy if you have installed a software component that acts up and prevents you from booting Haiku, see Troubleshooting below.

To enter the Boot Loader Options, you have to press and keep holding the SHIFT key before the beginning of Haiku's boot process. If there's a boot manager installed, you can start holding SHIFT before invoking the boot entry for Haiku. If Haiku is the only operating system on the machine, you can begin holding the key while still seeing boot messages from the BIOS.

With some hardware, you'll have to make sure USB keyboards are enabled in the BIOS.
On computers that use UEFI for booting instead of the classic BIOS, you need to use the SPACEBAR instead of SHIFT.

Boot Loader Options

Once it's there, you're offered four menus:

Select boot volume/state		Choose which Haiku installation/state to start (see Troubleshooting below).
Select safe mode options		There are several options to try in case of hardware related trouble or if the system becomes unstable or unbootable because of a misbehaving add-on. When moving the selection bar to an option, a short explanation appears at the bottom of the screen.
		Safe mode Puts the system into safe mode. This can be enabled independently from the other options. Disable user add-ons Prevents all user installed add-ons from being loaded. Only the add-ons in the system directory will be used. See Troubleshooting below. Disable IDE DMA Disables IDE DMA, increasing IDE compatibility at the expense of performance. Ignore memory beyond 4 GiB Ignores all memory beyond the 4 GiB address limit, overriding the setting in the kernel settings file. Use fail-safe graphics driver The system will use VESA mode and won't try to use any video graphics drivers. Disable IO-APIC Disables using the IO APIC for interrupt routing, forcing the use of the legacy PIC instead. Disable local APIC Disables using the local APIC, also disables SMP. Disable X2APIC Disables second generation APIC. Disable SMEP and SMAP Disables SMEP/SMAP security features of the CPU. Disable SMP Disables all but one CPU core. Don't call the BIOS Stops the system from calling BIOS functions. Disable APM Disables Advanced Power Management hardware support, overriding the APM setting in the kernel settings file. Disable ACPI Disables Advanced Configuration and Power Interface hardware support, overriding the ACPI setting in the kernel settings file. Disable system components Allows to select system files that shall be ignored. Useful e.g. to disable drivers temporarily. See Troubleshooting below.
Select debug options		Here you'll find several options that help with debugging or getting details for a bug report. Again, a short explanation for each option is displayed at the bottom.
		Enable serial debug output Turns on forwarding the syslog output to the serial interface (default: 115200, 8N1). Enable on screen debug output Display debug output on screen while the system is booting, instead of the normal boot logo. Disable on screen paging Disables paging when on screen debug output is enabled. Enable debug syslog Enables a special in-memory syslog buffer for this session that the boot loader will be able to access after rebooting. Display current boot loader log Displays the debug info the boot loader has logged (press Q to exit the log) Add advanced debug option Allows advanced debugging options to be entered directly.
		If Enable debug syslog is activated, a warm reboot after a crash shows these additional options:
		Save syslog from previous session during boot Saves the syslog from the previous Haiku session to /var/log/previous_syslog when booting. Display syslog from previous session Displays the syslog from the previous Haiku session. Save syslog from previous session Saves the syslog from the previous Haiku session to disk. Currently only FAT32 volumes are supported.
Select screen resolution		Lets you force a certain screen resolution and color depth.

Troubleshooting

If Haiku refuses to boot on your hardware from the get-go, try out setting different options under Select safe mode options. Consider filing a bug report in any case.

On the other hand, if Haiku only suddenly acts up after you have installed some software, especially hardware drivers, you have several options to get Haiku bootable again so you can uninstall the offending package:

Activating Safe mode will prevent most servers, daemons and the UserBootscript from being started.
Activating Disable user add-ons will prevent using any add-ons (drivers, translators, etc.) you have installed in the user hierarchy under your Home folder.
If activating Use fail-safe graphics driver solves your troubles by falling back to VESA graphics, you can make the setting permanent by removing the # of the line #fail_safe_video_mode true in the text file /boot/home/config/settings/kernel/drivers/kernel.
If the offending driver, add-on etc. is installed in the system hierarchy, things get a bit more complicated, because that area is read-only. Here, the Disable system components comes into play. With it, you can navigate through the whole system hierarchy and disable the component that's messing things up for you by checking an entry with the SPACE or ENTER key. ESC returns you up one level to the parent directory.

Online, there's the guide Disabling components of packages showing how to make that setting stick.
Under Select boot volume/state you can specify what former "version" of Haiku to boot. Every time you un/install a package, the old state is saved and you can boot into it by choosing it from the list presented in the boot loader options.
So, if you encounter boot problems after installing some package, boot a Haiku state from before that time and uninstall the offending package. You can permanently revert to a specific Haiku revision as described in the topic SoftwareUpdater.

Booting Haiku

After activating one or more options, you return to the main menu and continue booting, which presents you with this boot screen:

If everything works OK, one symbol after another quickly lights up.
The different symbols roughly correspond to these boot stages:

Atom		Initializing modules.
Disk + magnifier		Creating rootfs (/) and mounting devfs (/dev).
Plug-in card		Initializing device manager.
Boot disk		Mounting boot disk.
Chip		Loading CPU specific modules.
Folder		Final initialization of subsystems.
Rocket		Launch_daemon has started the system.