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.TH KEXEC_LOAD 2 2017-09-15 "Linux" "Linux Programmer's Manual"

.SH NAME

kexec_load, kexec_file_load \- load a new kernel for later execution

.SH SYNOPSIS

.nf

.B #include <linux/kexec.h>

.PP

.BI "long kexec_load(unsigned long " entry ", unsigned long " nr_segments ","

.BI "                struct kexec_segment *" segments \

", unsigned long " flags ");"

.PP

.BI "long kexec_file_load(int " kernel_fd ", int " initrd_fd ","

.BI "                    unsigned long " cmdline_len  \

", const char *" cmdline ","

.BI "                    unsigned long " flags ");"

.fi

.PP

.IR Note :

There are no glibc wrappers for these system calls; see NOTES.

.SH DESCRIPTION

The

.BR kexec_load ()

system call loads a new kernel that can be executed later by

.BR reboot (2).

.PP

The

.I flags

argument is a bit mask that controls the operation of the call.

The following values can be specified in

.IR flags :

.TP

.BR KEXEC_ON_CRASH " (since Linux 2.6.13)"

Execute the new kernel automatically on a system crash.

This "crash kernel" is loaded into an area of reserved memory that

is determined at boot time using the

.I crashkernel

kernel command-line parameter.

The location of this reserved memory is exported to user space via the

.I /proc/iomem

file, in an entry labeled "Crash kernel".

A user-space application can parse this file and prepare a list of

segments (see below) that specify this reserved memory as destination.

If this flag is specified, the kernel checks that the

target segments specified in

.I segments

fall within the reserved region.

.TP

.BR KEXEC_PRESERVE_CONTEXT " (since Linux 2.6.27)"

Preserve the system hardware and

software states before executing the new kernel.

This could be used for system suspend.

This flag is available only if the kernel was configured with

.BR CONFIG_KEXEC_JUMP ,

and is effective only if

.I nr_segments

is greater than 0.

.PP

The high-order bits (corresponding to the mask 0xffff0000) of

.I flags

contain the architecture of the to-be-executed kernel.

Specify (OR) the constant

.B KEXEC_ARCH_DEFAULT

to use the current architecture,

or one of the following architecture constants

.BR KEXEC_ARCH_386 ,

.BR KEXEC_ARCH_68K ,

.BR KEXEC_ARCH_X86_64 ,

.BR KEXEC_ARCH_PPC ,

.BR KEXEC_ARCH_PPC64 ,

.BR KEXEC_ARCH_IA_64 ,

.BR KEXEC_ARCH_ARM ,

.BR KEXEC_ARCH_S390 ,

.BR KEXEC_ARCH_SH ,

.BR KEXEC_ARCH_MIPS ,

and

.BR KEXEC_ARCH_MIPS_LE .

The architecture must be executable on the CPU of the system.

.PP

The

.I entry

argument is the physical entry address in the kernel image.

The

.I nr_segments

argument is the number of segments pointed to by the

.I segments

pointer;

the kernel imposes an (arbitrary) limit of 16 on the number of segments.

The

.I segments

argument is an array of

.I kexec_segment

structures which define the kernel layout:

.PP

.in +4n

.EX

struct kexec_segment {

    void   *buf;        /* Buffer in user space */

    size_t  bufsz;      /* Buffer length in user space */

    void   *mem;        /* Physical address of kernel */

    size_t  memsz;      /* Physical address length */

};

.EE

.in

.PP

The kernel image defined by

.I segments

is copied from the calling process into

the kernel either in regular

memory or in reserved memory (if

.BR KEXEC_ON_CRASH

is set).

The kernel first performs various sanity checks on the

information passed in

.IR segments .

If these checks pass, the kernel copies the segment data to kernel memory.

Each segment specified in

.I segments

is copied as follows:

.IP * 3

.I buf

and

.I bufsz

identify a memory region in the caller's virtual address space

that is the source of the copy.

The value in

.I bufsz

may not exceed the value in the

.I memsz

field.

.IP *

.I mem

and

.I memsz

specify a physical address range that is the target of the copy.

The values specified in both fields must be multiples of

the system page size.

.IP *

.I bufsz

bytes are copied from the source buffer to the target kernel buffer.

If

.I bufsz

is less than

.IR memsz ,

then the excess bytes in the kernel buffer are zeroed out.

.PP

In case of a normal kexec (i.e., the

.BR KEXEC_ON_CRASH

flag is not set), the segment data is loaded in any available memory

and is moved to the final destination at kexec reboot time (e.g., when the

.BR kexec (8)

command is executed with the

.I \-e

option).

.PP

In case of kexec on panic (i.e., the

.BR KEXEC_ON_CRASH

flag is set), the segment data is

loaded to reserved memory at the time of the call, and, after a crash,

the kexec mechanism simply passes control to that kernel.

.PP

The

.BR kexec_load ()

system call is available only if the kernel was configured with

.BR CONFIG_KEXEC .

.SS kexec_file_load()

The

.BR kexec_file_load ()

system call is similar to

.BR kexec_load (),

but it takes a different set of arguments.

It reads the kernel to be loaded from the file referred to by

the file descriptor

.IR kernel_fd ,

and the initrd (initial RAM disk)

to be loaded from file referred to by the file descriptor

.IR initrd_fd .

The

.IR cmdline

argument is a pointer to a buffer containing the command line

for the new kernel.

The

.IR cmdline_len

argument specifies size of the buffer.

The last byte in the buffer must be a null byte (\(aq\\0\(aq).

.PP

The

.IR flags

argument is a bit mask which modifies the behavior of the call.

The following values can be specified in

.IR flags :

.TP

.BR KEXEC_FILE_UNLOAD

Unload the currently loaded kernel.

.TP

.BR KEXEC_FILE_ON_CRASH

Load the new kernel in the memory region reserved for the crash kernel

(as for

.BR KEXEC_ON_CRASH).

This kernel is booted if the currently running kernel crashes.

.TP

.BR KEXEC_FILE_NO_INITRAMFS

Loading initrd/initramfs is optional.

Specify this flag if no initramfs is being loaded.

If this flag is set, the value passed in

.IR initrd_fd

is ignored.

.PP

The

.BR kexec_file_load ()

.\" See also http://lwn.net/Articles/603116/

system call was added to provide support for systems

where "kexec" loading should be restricted to

only kernels that are signed.

This system call is available only if the kernel was configured with

.BR CONFIG_KEXEC_FILE .

.SH RETURN VALUE

On success, these system calls returns 0.

On error, \-1 is returned and

.I errno

is set to indicate the error.

.SH ERRORS

.TP

.B EADDRNOTAVAIL

.\" See kernel/kexec.::sanity_check_segment_list in the 3.19 kernel source

The

.B KEXEC_ON_CRASH

flags was specified, but the region specified by the

.I mem

and

.I memsz

fields of one of the

.I segments

entries lies outside the range of memory reserved for the crash kernel.

.TP

.B EADDRNOTAVAIL

The value in a

.I mem

or

.I memsz

field in one of the

.I segments

entries is not a multiple of the system page size.

.TP

.B EBADF

.I kernel_fd

or

.I initrd_fd

is not a valid file descriptor.

.TP

.B EBUSY

Another crash kernel is already being loaded

or a crash kernel is already in use.

.TP

.B EINVAL

.I flags

is invalid.

.TP

.B EINVAL

The value of a

.I bufsz

field in one of the

.I segments

entries exceeds the value in the corresponding

.I memsz

field.

.TP

.B EINVAL

.IR nr_segments

exceeds

.BR KEXEC_SEGMENT_MAX

(16).

.TP

.B EINVAL

Two or more of the kernel target buffers overlap.

.TP

.B EINVAL

The value in

.I cmdline[cmdline_len-1]

is not \(aq\\0\(aq.

.TP

.B EINVAL

The file referred to by

.I kernel_fd

or

.I initrd_fd

is empty (length zero).

.TP

.B ENOEXEC

.I kernel_fd

does not refer to an open file, or the kernel can't load this file.

Currently, the file must be a bzImage and contain an x86 kernel that

is loadable above 4\ GiB in memory (see the kernel source file

.IR Documentation/x86/boot.txt ).

.TP

.B ENOMEM

Could not allocate memory.

.TP

.B EPERM

The caller does not have the

.BR CAP_SYS_BOOT

capability.

.SH VERSIONS

The

.BR kexec_load ()

system call first appeared in Linux 2.6.13.

The

.BR kexec_file_load ()

system call first appeared in Linux 3.17.

.SH CONFORMING TO

These system calls are Linux-specific.

.SH NOTES

Currently, there is no glibc support for these system calls.

Call them using

.BR syscall (2).

.SH SEE ALSO

.BR reboot (2),

.BR syscall (2),

.BR kexec (8)

.PP

The kernel source files

.IR Documentation/kdump/kdump.txt

and

.IR Documentation/admin-guide/kernel-parameters.txt

.SH COLOPHON

This page is part of release 4.15 of the Linux

.I man-pages

project.

A description of the project,

information about reporting bugs,

and the latest version of this page,

can be found at

\%https://www.kernel.org/doc/man\-pages/.