kexec - directly boot into a new kernel
/sbin/kexec [-v (--version)] [-f (--force)] [-x
(--no-ifdown)] [-y (--no-sync)] [-l (--load)] [-p (--load-panic)] [-u
(--unload)] [-e (--exec)] [-t (--type)]
[--mem-min=addr]
[--mem-max=addr]
kexec is a system call that enables you to load and boot
into another kernel from the currently running kernel. kexec performs
the function of the boot loader from within the kernel. The primary
difference between a standard system boot and a kexec boot is that
the hardware initialization normally performed by the BIOS or firmware
(depending on architecture) is not performed during a kexec boot.
This has the effect of reducing the time required for a reboot.
Make sure you have selected CONFIG_KEXEC=y when configuring
the kernel. The CONFIG_KEXEC option enables the kexec system
call.
Using kexec consists of
(1) loading the kernel to be rebooted to into memory,
and
(2) actually rebooting to the pre-loaded kernel.
To load a kernel, the syntax is as follows:
kexec -l kernel-image
--append=command-line-options --initrd=initrd-image
where kernel-image is the kernel file that you intend to
reboot to.
Insert the command-line parameters that must be passed to the new
kernel into command-line-options. Passing the exact contents of
/proc/cmdline into command-line-options is the safest way to ensure
that correct values are passed to the rebooting kernel.
The optional initrd-image is the initrd image to be used
during boot.
It's also possible to invoke kexec without an option
parameter. In that case, kexec loads the specified kernel and then invokes
shutdown(8). If the shutdown scripts of your Linux distribution
support kexec-based rebooting, they then call kexec -e just
before actually rebooting the machine. That way, the machine does a clean
shutdown including all shutdown scripts.
For example, if the kernel image you want to reboot to is
/boot/vmlinux, the contents of /proc/cmdline is
root=/dev/hda1, and the path to the initrd is /boot/initrd,
then you would use the following command to load the kernel:
kexec -l /boot/vmlinux
--append=root=/dev/hda1 --initrd=/boot/initrd
After this kernel is loaded, it can be booted to at any time using
the command:
kexec -e
- -d (--debug)
- Enable debugging messages.
- -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
not load or unload the kernel.
- -e (--exec)
- Run the currently loaded kernel. Note that it will reboot into the loaded
kernel without calling shutdown(8).
- -f (--force)
- Force an immediate kexec call, do not call shutdown(8)
(contrary to the default action without any option parameter). This option
performs the same actions like executing -l and -e in one
call.
- -h (--help)
- Open a help file for kexec.
- -i (--no-checks)
- Fast reboot, no memory integrity checks.
- -l (--load) kernel
- Load the specified kernel into the current kernel.
- -p (--load-panic)
- Load the new kernel for use on panic.
- -t (--type=type)
- Specify that the new kernel is of this type.
- -s (--kexec-file-syscall)
- Specify that the new KEXEC_FILE_LOAD syscall should be used
exclusively.
- -c (--kexec-syscall)
- Specify that the old KEXEC_LOAD syscall should be used exclusively (the
default).
- -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.
- -u (--unload)
- Unload the current kexec target kernel. If a capture kernel is
being unloaded then specify -p with -u.
- -v (--version)
- Return the version number of the installed utility.
- -x (--no-ifdown)
- Shut down the running kernel, but restore the interface on reload.
- -y (--no-sync)
- Shut down the running kernel, but skip syncing the filesystems.
- --mem-min=addr
- Specify the lowest memory address addr to load code into.
- --mem-max=addr
- Specify the highest memory address addr to load code into.
- --entry=addr
- Specify the jump back address. (0 means it's not jump back or preserve
context)
- --load-preserve-context
- Load the new kernel and preserve context of current kernel during
kexec.
- --load-jump-back-helper
- Load a helper image to jump back to original kernel.
- --reuseinitrd
- Reuse initrd from first boot.
- --print-ckr-size
- Print crash kernel region size, if available.
Beoboot-x86
elf-x86
- --append=string
- Append string to the kernel command line.
- --command-line=string
- Set the kernel command line to string.
- --reuse-cmdline
- Use the command line from the running system. When a panic kernel is
loaded, it strips the crashkernel parameter automatically. The
BOOT_IMAGE parameter is also stripped.
- --initrd=file
- Use file as the kernel's initial ramdisk.
- --ramdisk=file
- Use file as the kernel's initial ramdisk.
bzImage-x86
- --append=string
- Append string to the kernel command line.
- --command-line=string
- Set the kernel command line to string.
- --reuse-cmdline
- Use the command line from the running system. When a panic kernel is
loaded, it strips the crashkernel parameter automatically. The
BOOT_IMAGE parameter is also stripped.
- --initrd=file
- Use file as the kernel's initial ramdisk.
- --ramdisk=file
- Use file as the kernel's initial ramdisk.
- --real-mode
- Use real-mode entry point.
multiboot-x86
- --command-line=string
- Set the kernel command line to string.
- --reuse-cmdline
- Use the command line from the running system. When a panic kernel is
loaded, it strips the crashkernel parameter automatically. The
BOOT_IMAGE parameter is also stripped.
- --module=mod
arg1 arg2 ...
- Load module mod with command-line arguments arg1 arg2 ...
This parameter can be specified multiple times.