com.apple.Boot.plist(5) BSD File Formats Manual com.apple.Boot.plist(5)NAMEcom.apple.Boot.plist — Configuration plist for Mac OS X booter
DESCRIPTION
The Mac OS X booter ( boot.efi on EFI-based Macintosh systems) is respon‐
sible for loading the initial parts of the operating system into memory
and executing them. Its default behavior is to start up Mac OS X in
graphical mode. However, certain behavior can be configured using the
com.apple.Boot.plist file, as well as NVRAM variables, EFI boot options,
and keyboard "snag keys".
The com.apple.Boot.plist is a standard plist(5) format Core Foundation
property list stored in XML format. Keys are generally strings like
Kernel Flags, with either string or integer values. The following key-
values are currently supported:
Kernel Flags
[string] This option specifies arguments to be passed directly to
the kernel to change its behavior (although some kernel options
are parsed by the booter as well for correctness). Common options
include "debug=0x144" to enable kernel debugging, "-v" to enable
verbose boot, "-s" to boot to single user mode, "cpus=1" to simu‐
late a single core system, and "maxmem=1024" to cap available mem‐
ory to 1024 MB RAM. All desired options should be space-separated
within the <string> tag. The default value is the empty string.
MKext Cache
[string] This option specifies the mkext file to be loaded, which
contains kernel extensions. The path uses backslash ("\ ") path
delimeters. The default value is System\ Library\ Caches\
com.apple.kext.caches\ Startup\ Extensions.mkext.
Kernel
[string] This option specifies the kernel file to be loaded. The
path uses backslash ("\ ") path delimeters. The default value is
mach_kernel.
Kernel Cache
[string] This option specifies the prelinked kernel file to be
loaded, which contains both the kernel and kernel extensions,
linked at their final load addresses. The path uses backslash ("\
") path delimeters. The default value is calculated programmati‐
cally using System\ Library\ Caches\ com.apple.kext.caches\
Startup\ kernelcache_${ARCH}.${CHECKSUM} as the template, where
${ARCH} is the architecture of the kernel ("i386" or "x86_64") and
${CHECKSUM} is a 32-bit hash of characteristics of the boot volume
and machine hardware.
Kernel Architecture
[string] This option specifies which kernel architecture to use
when the kernel file is a universal binary and the hardware sup‐
ports more than one kernel architecture. It can be either "i386"
or "x86_64" to choose the respective slice of the universal
binary. If the kernel is not a universal binary, this option has
no effect. If the hardware only supports the 32-bit kernel, this
option has no effect. The default value is determined programmati‐
cally based on the hardware, and whether Mac OS X Server is being
used.
Root UUID
[string] This option is rarely used and specifies to the kernel
what block device should be probed as the root filesystem ("/"),
and is most commonly overriden by the OS installation software
when installing onto AppleRAID volumes. It can be either a
filesystem volume UUID, as represented by diskutil info, or a GPT
partition UUID. The default is generated programmatically based on
which filesystem the booter itself was loaded from.
Since the com.apple.Boot.plist file exists on the root filesystem, it is
tied to that OS volume, and is no longer honored if Startup Disk or
bless(8) is used to change the boot preference to another volume.
The Kernel Flags options can also be specified via --optiontobless(8),
which encodes the string in the EFI boot options along with the OS boot
volume preference. The space-separated strings are merged with kernel
flags specified in the com.apple.Boot.plist and NVRAM.
At boot time, the booter checks to see if certain keys are being pressed,
and alters behavior accordingly. This is in addition to similar function‐
ality that the firmware itself may implement before starting the booter.
Since pressing keys requires physical interaction, they take precendence
over preferences set through other means, including the
com.apple.Boot.plist file and NVRAM. The following key combinations are
currently supported:
Shift Boot in Safe Mode. Effectively the same as passing "-x" in Kernel
Flags, and causes most caches to be ignored by the booter.
Command-S
Boot in Single User Mode. Effectively the same as passing "-s" in
Kernel Flags, and causes the system to boot to an interactive
shell with no system services started.
Command-V
Boot in Verbose Mode. Effectively the same as passing "-v" in
Kernel Flags, and causes the system to boot to verbose text log‐
ging before starting the graphical user interface.
Command-R
Boot in Recovery Mode. This causes the system to boot into spe‐
cial Recovery System image, which can be used used to restore the
system from Time Machine Backup, re-install Mac OS X, or use Disk
Utility to repair or erase disks.
3 2 Boot with the 32-bit kernel. Effectively the same as passing
"arch=i386" in Kernel Flags, and causes the system to prefer the
32-bit kernel on systems that would otherwise boot the 64-bit ker‐
nel.
6 4 Boot with the 64-bit kernel (if supported on this system). Effec‐
tively the same as passing "arch=x86_64" in Kernel Flags, and
causes the system to prefer the 64-bit kernel on systems that
would otherwise boot the 32-bit kernel. If the 64-bit kernel is
not supported, the option is ignored.
ENVIRONMENT
The Mac OS X booter can also be controlled by NVRAM variables, which are
analogous to environment variables. NVRAM variables are key-value pairs.
The "boot-args" NVRAM variable can be used to provide additional argu‐
ments to the kernel, and will be merged with Kernel Flags in the
com.apple.Boot.plist file and EFI boot options set with bless(8).
Since NVRAM variables are system-wide, they are consulted regardless of
what OS volume is set as the boot preference. NVRAM variables are persis‐
tent even when the boot preference is changed by Startup Disk or
bless(8).
FILES
/Library/Preferences/SystemConfiguration/com.apple.Boot.plist
Location of the com.apple.Boot.plist file.
SEE ALSOnvram(8), bless(8), kextcache(8)Darwin March 17, 2011 Darwin
