kexec/kexec.8 - pub/scm/utils/kernel/kexec/kexec-tools - Git at Google

 .\" Process this file with
 .\" groff -man -Tascii kexec.8
 .\"
 .TH kexec 8 "April 2006" Linux "User Manuals"
 .SH NAME
 kexec \- directly boot into a new kernel
 .SH SYNOPSIS
 .B /sbin/kexec
 .B [-v (\-\-version)] [-f (\-\-force)] [-x (\-\-no-ifdown)] [-y (\-\-no-sync)] [-l (\-\-load)] [-p (\-\-load-panic)] [-u (\-\-unload)] [-e (\-\-exec)] [-t (\-\-type)]
 .BI [\-\-mem\-min= addr ]
 .BI [\-\-mem\-max= addr ]

 .SH DESCRIPTION
 .B kexec
 is a system call that enables you to load and boot into another
 kernel from the currently running kernel.
 .B kexec
 performs the function of the boot loader from within the kernel. The
 primary difference between a standard system boot and a
 .B kexec
 boot is that the hardware initialization normally performed by the BIOS
 or firmware (depending on architecture) is not performed during a
 .B kexec
 boot. This has the effect of reducing the time required for a reboot.
 .PP
 Make sure you have selected
 .B CONFIG_KEXEC=y
 when configuring the kernel. The
 .B CONFIG_KEXEC
 option enables the
 .B kexec
 system call.
 .SH USAGE
 Using
 .B kexec
 consists of

 .RS
 (1) loading the kernel to be rebooted to into memory, and
 .RE
 .RS
 (2) actually rebooting to the pre-loaded kernel.
 .RE
 .PP
 To load a kernel, the syntax is as follows:

 .RS
 .B kexec
 .RI \-l\  kernel-image
 .RI "\-\-append=" command\-line\-options
 .RI "\-\-initrd=" initrd\-image
 .RE

 where
 .I kernel\-image
 is the kernel file that you intend to reboot to.
 .PP
 Insert the command-line parameters that must be passed to the new
 kernel into
 .IR command\-line\-options .
 Passing the exact contents of /proc/cmdline into
 .I command\-line\-options
 is the safest way to ensure that correct values are passed to the
 rebooting kernel.
 .PP
 The optional
 .I initrd-image
 is the initrd image to be used during boot.
 .PP
 It's also possible to invoke
 .B kexec
 without an option parameter. In that case, kexec loads the specified
 kernel and then invokes
 .BR shutdown (8).
 If the shutdown scripts of your Linux distribution support
 kexec-based rebooting, they then call
 .B kexec
 .I -e
 just before actually rebooting the machine. That way, the machine does
 a clean shutdown including all shutdown scripts.

 .SH EXAMPLE
 .PP
 For example, if the kernel image you want to reboot to is
 .BR /boot/vmlinux ,
 the contents of /proc/cmdline is
 .BR "root\=/dev/hda1" ,
 and the path to the initrd is
 .BR /boot/initrd ,
 then you would use the following command to load the kernel:

 .RS
 .B kexec
 .RB \-l\  /boot/vmlinux
 .RB "\-\-append=" "root=/dev/hda1" "\ \-\-initrd=" /boot/initrd
 .RE
 .PP
 After this kernel is loaded, it can be booted to at any time using the
 command:

 .RS
 .BR kexec \ \-e
 .RE

 .SH OPTIONS
 .TP
 .B \-d\ (\-\-debug)
 Enable debugging messages.
 .TP
 .B \-S\ (\-\-status)
 Return 0 if the type (by default crash) is loaded. Can be used in conjuction
 with -l or -p to toggle the type. Note this option supersedes other options
 and it will
 .BR not\ load\ or\ unload\ the\ kernel.
 .TP
 .B \-e\ (\-\-exec)
 Run the currently loaded kernel. Note that it will reboot into the loaded kernel without calling shutdown(8).
 .TP
 .B \-f\ (\-\-force)
 Force an immediate
 .B kexec
 call, do not call
 .BR shutdown (8)
 (contrary to the default action without any option parameter). This option
 performs the same actions like executing
 .IR -l
 and
 .IR -e
 in one call.
 .TP
 .B \-h\ (\-\-help)
 Open a help file for
 .BR kexec .
 .TP
 .B \-i\ (\-\-no-checks)
 Fast reboot, no memory integrity checks.
 .TP
 .BI \-l\ (\-\-load) \ kernel
 Load the specified
 .I kernel
 into the current kernel.
 .TP
 .B \-p\ (\-\-load\-panic)
 Load the new kernel for use on panic.
 .TP
 .BI \-t\ (\-\-type= type )
 Specify that the new kernel is of this
 .I type.
 .TP
 .BI \-s\ (\-\-kexec-file-syscall)
 Specify that the new KEXEC_FILE_LOAD syscall should be used exclusively.
 .TP
 .BI \-c\ (\-\-kexec-syscall)
 Specify that the old KEXEC_LOAD syscall should be used exclusively (the default).
 .TP
 .BI \-a\ (\-\-kexec-syscall-auto)
 Try the new KEXEC_FILE_LOAD syscall first and when it is not supported or the
 kernel does not understand the supplied image fall back to the old KEXEC_LOAD
 interface.

 There is no one single interface that always works.

 KEXEC_FILE_LOAD is required on systems that use locked-down secure boot to
 verify the kernel signature.  KEXEC_LOAD may be also disabled in the kernel
 configuration.

 KEXEC_LOAD is required for some kernel image formats and on architectures that
 do not implement KEXEC_FILE_LOAD.
 .TP
 .B \-u\ (\-\-unload)
 Unload the current
 .B kexec
 target kernel. If a capture kernel is being unloaded then specify -p with -u.
 .TP
 .B \-v\ (\-\-version)
 Return the version number of the installed utility.
 .TP
 .B \-x\ (\-\-no\-ifdown)
 Shut down the running kernel, but restore the interface on reload.
 .TP
 .B \-y\ (\-\-no\-sync)
 Shut down the running kernel, but skip syncing the filesystems.
 .TP
 .BI \-\-mem\-min= addr
 Specify the lowest memory address
 .I addr
 to load code into.
 .TP
 .BI \-\-mem\-max= addr
 Specify the highest memory address
 .I addr
 to load code into.
 .TP
 .BI \-\-entry= addr
 Specify the jump back address. (0 means it's not jump back or preserve context)
 .TP
 .BI \-\-load\-preserve\-context
 Load the new kernel and preserve context of current kernel during kexec.
 .TP
 .BI \-\-load\-jump\-back\-helper
 Load a helper image to jump back to original kernel.
 .TP
 .BI \-\-reuseinitrd
 Reuse initrd from first boot.
 .TP
 .BI \-\-print-ckr-size
 Print crash kernel region size, if available.


 .SH SUPPORTED KERNEL FILE TYPES AND OPTIONS
 .B Beoboot-x86
 .RS
 .TP
 .B \-\-args\-elf
 Pass ELF boot notes.
 .TP
 .B \-\-args\-linux
 Pass Linux kernel style options.
 .TP
 .B \-\-real\-mode
 Use the kernel's real mode entry point.
 .RE
 .PP
 .B elf-x86
 .RS
 .TP
 .BI \-\-append= string
 Append
 .I string
 to the kernel command line.
 .TP
 .BI \-\-command\-line= string
 Set the kernel command line to
 .IR string .
 .TP
 .BI \-\-reuse-cmdline
 Use the command line from the running system. When a panic kernel is loaded, it
 strips the
 .I
 crashkernel
 parameter automatically. The
 .I BOOT_IMAGE
 parameter is also stripped.
 .TP
 .BI \-\-initrd= file
 Use
 .I file
 as the kernel's initial ramdisk.
 .TP
 .BI \-\-ramdisk= file
 Use
 .I file
 as the kernel's initial ramdisk.
 .RE
 .PP
 .B bzImage-x86
 .RS
 .TP
 .BI \-\-append= string
 Append
 .I string
 to the kernel command line.
 .TP
 .BI \-\-command\-line= string
 Set the kernel command line to
 .IR string .
 .TP
 .BI \-\-reuse-cmdline
 Use the command line from the running system. When a panic kernel is loaded, it
 strips the
 .I
 crashkernel
 parameter automatically. The
 .I BOOT_IMAGE
 parameter is also stripped.
 .TP
 .BI \-\-initrd= file
 Use
 .I file
 as the kernel's initial ramdisk.
 .TP
 .BI \-\-ramdisk= file
 Use
 .I file
 as the kernel's initial ramdisk.
 .TP
 .BI \-\-real-mode
 Use real-mode entry point.
 .RE
 .PP
 .B multiboot-x86
 .RS
 .TP
 .BI \-\-command\-line= string
 Set the kernel command line to
 .IR string .
 .TP
 .BI \-\-reuse-cmdline
 Use the command line from the running system. When a panic kernel is loaded, it
 strips the
 .I
 crashkernel
 parameter automatically. The
 .I BOOT_IMAGE
 parameter is also stripped.
 .TP
 .BI \-\-module= "mod arg1 arg2 ..."
 Load module
 .I mod
 with command-line arguments
 .I "arg1 arg2 ..."
 This parameter can be specified multiple times.
 .RE
 .PP
 .B multiboot2-x86
 .RS
 .TP
 .BI \-\-command\-line= string
 Set the kernel command line to
 .IR string .
 .TP
 .BI \-\-reuse-cmdline
 Use the command line from the running system. When a panic kernel is loaded, it
 strips the
 .I
 crashkernel
 parameter automatically. The
 .I BOOT_IMAGE
 parameter is also stripped.
 .TP
 .BI \-\-module= "mod arg1 arg2 ..."
 Load module
 .I mod
 with command-line arguments
 .I "arg1 arg2 ..."
 This parameter can be specified multiple times.
 .RE

 .SH ARCHITECTURE OPTIONS
 .TP
 .B \-\-console\-serial
 Enable the serial console.
 .TP
 .B \-\-console\-vga
 Enable the VGA console.
 .TP
 .B \-\-elf32\-core\-headers
 Prepare core headers in ELF32 format.
 .TP
 .B \-\-elf64\-core\-headers
 Prepare core headers in ELF64 format.
 .TP
 .B \-\-reset\-vga
 Attempt to reset a standard VGA device.
 .TP
 .BI \-\-serial= port
 Specify the serial
 .I port
 for debug output.
 .TP
 .BI \-\-serial\-baud= baud_rate
 Specify the
 .I baud rate
 of the serial port.
	.\" Process this file with
	.\" groff -man -Tascii kexec.8
	.\"
	.TH kexec 8 "April 2006" Linux "User Manuals"
	.SH NAME
	kexec \- directly boot into a new kernel
	.SH SYNOPSIS
	.B /sbin/kexec
	.B [-v (\-\-version)] [-f (\-\-force)] [-x (\-\-no-ifdown)] [-y (\-\-no-sync)] [-l (\-\-load)] [-p (\-\-load-panic)] [-u (\-\-unload)] [-e (\-\-exec)] [-t (\-\-type)]
	.BI [\-\-mem\-min= addr ]
	.BI [\-\-mem\-max= addr ]

	.SH DESCRIPTION
	.B kexec
	is a system call that enables you to load and boot into another
	kernel from the currently running kernel.
	.B kexec
	performs the function of the boot loader from within the kernel. The
	primary difference between a standard system boot and a
	.B kexec
	boot is that the hardware initialization normally performed by the BIOS
	or firmware (depending on architecture) is not performed during a
	.B kexec
	boot. This has the effect of reducing the time required for a reboot.
	.PP
	Make sure you have selected
	.B CONFIG_KEXEC=y
	when configuring the kernel. The
	.B CONFIG_KEXEC
	option enables the
	.B kexec
	system call.
	.SH USAGE
	Using
	.B kexec
	consists of

	.RS
	(1) loading the kernel to be rebooted to into memory, and
	.RE
	.RS
	(2) actually rebooting to the pre-loaded kernel.
	.RE
	.PP
	To load a kernel, the syntax is as follows:

	.RS
	.B kexec
	.RI \-l\ kernel-image
	.RI "\-\-append=" command\-line\-options
	.RI "\-\-initrd=" initrd\-image
	.RE

	where
	.I kernel\-image
	is the kernel file that you intend to reboot to.
	.PP
	Insert the command-line parameters that must be passed to the new
	kernel into
	.IR command\-line\-options .
	Passing the exact contents of /proc/cmdline into
	.I command\-line\-options
	is the safest way to ensure that correct values are passed to the
	rebooting kernel.
	.PP
	The optional
	.I initrd-image
	is the initrd image to be used during boot.
	.PP
	It's also possible to invoke
	.B kexec
	without an option parameter. In that case, kexec loads the specified
	kernel and then invokes
	.BR shutdown (8).
	If the shutdown scripts of your Linux distribution support
	kexec-based rebooting, they then call
	.B kexec
	.I -e
	just before actually rebooting the machine. That way, the machine does
	a clean shutdown including all shutdown scripts.

	.SH EXAMPLE
	.PP
	For example, if the kernel image you want to reboot to is
	.BR /boot/vmlinux ,
	the contents of /proc/cmdline is
	.BR "root\=/dev/hda1" ,
	and the path to the initrd is
	.BR /boot/initrd ,
	then you would use the following command to load the kernel:

	.RS
	.B kexec
	.RB \-l\ /boot/vmlinux
	.RB "\-\-append=" "root=/dev/hda1" "\ \-\-initrd=" /boot/initrd
	.RE
	.PP
	After this kernel is loaded, it can be booted to at any time using the
	command:

	.RS
	.BR kexec \ \-e
	.RE

	.SH OPTIONS
	.TP
	.B \-d\ (\-\-debug)
	Enable debugging messages.
	.TP
	.B \-S\ (\-\-status)
	Return 0 if the type (by default crash) is loaded. Can be used in conjuction
	with -l or -p to toggle the type. Note this option supersedes other options
	and it will
	.BR not\ load\ or\ unload\ the\ kernel.
	.TP
	.B \-e\ (\-\-exec)
	Run the currently loaded kernel. Note that it will reboot into the loaded kernel without calling shutdown(8).
	.TP
	.B \-f\ (\-\-force)
	Force an immediate
	.B kexec
	call, do not call
	.BR shutdown (8)
	(contrary to the default action without any option parameter). This option
	performs the same actions like executing
	.IR -l
	and
	.IR -e
	in one call.
	.TP
	.B \-h\ (\-\-help)
	Open a help file for
	.BR kexec .
	.TP
	.B \-i\ (\-\-no-checks)
	Fast reboot, no memory integrity checks.
	.TP
	.BI \-l\ (\-\-load) \ kernel
	Load the specified
	.I kernel
	into the current kernel.
	.TP
	.B \-p\ (\-\-load\-panic)
	Load the new kernel for use on panic.
	.TP
	.BI \-t\ (\-\-type= type )
	Specify that the new kernel is of this
	.I type.
	.TP
	.BI \-s\ (\-\-kexec-file-syscall)
	Specify that the new KEXEC_FILE_LOAD syscall should be used exclusively.
	.TP
	.BI \-c\ (\-\-kexec-syscall)
	Specify that the old KEXEC_LOAD syscall should be used exclusively (the default).
	.TP
	.BI \-a\ (\-\-kexec-syscall-auto)
	Try the new KEXEC_FILE_LOAD syscall first and when it is not supported or the
	kernel does not understand the supplied image fall back to the old KEXEC_LOAD
	interface.

	There is no one single interface that always works.

	KEXEC_FILE_LOAD is required on systems that use locked-down secure boot to
	verify the kernel signature. KEXEC_LOAD may be also disabled in the kernel
	configuration.

	KEXEC_LOAD is required for some kernel image formats and on architectures that
	do not implement KEXEC_FILE_LOAD.
	.TP
	.B \-u\ (\-\-unload)
	Unload the current
	.B kexec
	target kernel. If a capture kernel is being unloaded then specify -p with -u.
	.TP
	.B \-v\ (\-\-version)
	Return the version number of the installed utility.
	.TP
	.B \-x\ (\-\-no\-ifdown)
	Shut down the running kernel, but restore the interface on reload.
	.TP
	.B \-y\ (\-\-no\-sync)
	Shut down the running kernel, but skip syncing the filesystems.
	.TP
	.BI \-\-mem\-min= addr
	Specify the lowest memory address
	.I addr
	to load code into.
	.TP
	.BI \-\-mem\-max= addr
	Specify the highest memory address
	.I addr
	to load code into.
	.TP
	.BI \-\-entry= addr
	Specify the jump back address. (0 means it's not jump back or preserve context)
	.TP
	.BI \-\-load\-preserve\-context
	Load the new kernel and preserve context of current kernel during kexec.
	.TP
	.BI \-\-load\-jump\-back\-helper
	Load a helper image to jump back to original kernel.
	.TP
	.BI \-\-reuseinitrd
	Reuse initrd from first boot.
	.TP
	.BI \-\-print-ckr-size
	Print crash kernel region size, if available.


	.SH SUPPORTED KERNEL FILE TYPES AND OPTIONS
	.B Beoboot-x86
	.RS
	.TP
	.B \-\-args\-elf
	Pass ELF boot notes.
	.TP
	.B \-\-args\-linux
	Pass Linux kernel style options.
	.TP
	.B \-\-real\-mode
	Use the kernel's real mode entry point.
	.RE
	.PP
	.B elf-x86
	.RS
	.TP
	.BI \-\-append= string
	Append
	.I string
	to the kernel command line.
	.TP
	.BI \-\-command\-line= string
	Set the kernel command line to
	.IR string .
	.TP
	.BI \-\-reuse-cmdline
	Use the command line from the running system. When a panic kernel is loaded, it
	strips the
	.I
	crashkernel
	parameter automatically. The
	.I BOOT_IMAGE
	parameter is also stripped.
	.TP
	.BI \-\-initrd= file
	Use
	.I file
	as the kernel's initial ramdisk.
	.TP
	.BI \-\-ramdisk= file
	Use
	.I file
	as the kernel's initial ramdisk.
	.RE
	.PP
	.B bzImage-x86
	.RS
	.TP
	.BI \-\-append= string
	Append
	.I string
	to the kernel command line.
	.TP
	.BI \-\-command\-line= string
	Set the kernel command line to
	.IR string .
	.TP
	.BI \-\-reuse-cmdline
	Use the command line from the running system. When a panic kernel is loaded, it
	strips the
	.I
	crashkernel
	parameter automatically. The
	.I BOOT_IMAGE
	parameter is also stripped.
	.TP
	.BI \-\-initrd= file
	Use
	.I file
	as the kernel's initial ramdisk.
	.TP
	.BI \-\-ramdisk= file
	Use
	.I file
	as the kernel's initial ramdisk.
	.TP
	.BI \-\-real-mode
	Use real-mode entry point.
	.RE
	.PP
	.B multiboot-x86
	.RS
	.TP
	.BI \-\-command\-line= string
	Set the kernel command line to
	.IR string .
	.TP
	.BI \-\-reuse-cmdline
	Use the command line from the running system. When a panic kernel is loaded, it
	strips the
	.I
	crashkernel
	parameter automatically. The
	.I BOOT_IMAGE
	parameter is also stripped.
	.TP
	.BI \-\-module= "mod arg1 arg2 ..."
	Load module
	.I mod
	with command-line arguments
	.I "arg1 arg2 ..."
	This parameter can be specified multiple times.
	.RE
	.PP
	.B multiboot2-x86
	.RS
	.TP
	.BI \-\-command\-line= string
	Set the kernel command line to
	.IR string .
	.TP
	.BI \-\-reuse-cmdline
	Use the command line from the running system. When a panic kernel is loaded, it
	strips the
	.I
	crashkernel
	parameter automatically. The
	.I BOOT_IMAGE
	parameter is also stripped.
	.TP
	.BI \-\-module= "mod arg1 arg2 ..."
	Load module
	.I mod
	with command-line arguments
	.I "arg1 arg2 ..."
	This parameter can be specified multiple times.
	.RE

	.SH ARCHITECTURE OPTIONS
	.TP
	.B \-\-console\-serial
	Enable the serial console.
	.TP
	.B \-\-console\-vga
	Enable the VGA console.
	.TP
	.B \-\-elf32\-core\-headers
	Prepare core headers in ELF32 format.
	.TP
	.B \-\-elf64\-core\-headers
	Prepare core headers in ELF64 format.
	.TP
	.B \-\-reset\-vga
	Attempt to reset a standard VGA device.
	.TP
	.BI \-\-serial= port
	Specify the serial
	.I port
	for debug output.
	.TP
	.BI \-\-serial\-baud= baud_rate
	Specify the
	.I baud rate
	of the serial port.