mirror of https://github.com/mkerrisk/man-pages
350 lines
9.1 KiB
Groff
350 lines
9.1 KiB
Groff
.\" Copyright (C) 2010 Intel Corporation, Author: Andi Kleen
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.\" and Copyright 2014, Vivek Goyal <vgoyal@redhat.com>
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.\" and Copyright (c) 2015, Michael Kerrisk <mtk.manpages@gmail.com>
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.\"
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.\" %%%LICENSE_START(VERBATIM)
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\" %%%LICENSE_END
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.\"
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.TH KEXEC_LOAD 2 2017-09-15 "Linux" "Linux Programmer's Manual"
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.SH NAME
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kexec_load, kexec_file_load \- load a new kernel for later execution
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.SH SYNOPSIS
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.nf
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.B #include <linux/kexec.h>
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.PP
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.BI "long kexec_load(unsigned long " entry ", unsigned long " nr_segments ","
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.BI " struct kexec_segment *" segments \
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", unsigned long " flags ");"
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.PP
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.BI "long kexec_file_load(int " kernel_fd ", int " initrd_fd ","
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.BI " unsigned long " cmdline_len \
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", const char *" cmdline ","
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.BI " unsigned long " flags ");"
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.fi
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.PP
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.IR Note :
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There are no glibc wrappers for these system calls; see NOTES.
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.SH DESCRIPTION
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The
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.BR kexec_load ()
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system call loads a new kernel that can be executed later by
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.BR reboot (2).
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.PP
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The
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.I flags
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argument is a bit mask that controls the operation of the call.
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The following values can be specified in
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.IR flags :
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.TP
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.BR KEXEC_ON_CRASH " (since Linux 2.6.13)"
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Execute the new kernel automatically on a system crash.
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This "crash kernel" is loaded into an area of reserved memory that
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is determined at boot time using the
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.I crashkernel
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kernel command-line parameter.
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The location of this reserved memory is exported to user space via the
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.I /proc/iomem
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file, in an entry labeled "Crash kernel".
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A user-space application can parse this file and prepare a list of
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segments (see below) that specify this reserved memory as destination.
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If this flag is specified, the kernel checks that the
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target segments specified in
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.I segments
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fall within the reserved region.
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.TP
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.BR KEXEC_PRESERVE_CONTEXT " (since Linux 2.6.27)"
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Preserve the system hardware and
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software states before executing the new kernel.
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This could be used for system suspend.
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This flag is available only if the kernel was configured with
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.BR CONFIG_KEXEC_JUMP ,
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and is effective only if
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.I nr_segments
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is greater than 0.
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.PP
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The high-order bits (corresponding to the mask 0xffff0000) of
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.I flags
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contain the architecture of the to-be-executed kernel.
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Specify (OR) the constant
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.B KEXEC_ARCH_DEFAULT
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to use the current architecture,
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or one of the following architecture constants
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.BR KEXEC_ARCH_386 ,
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.BR KEXEC_ARCH_68K ,
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.BR KEXEC_ARCH_X86_64 ,
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.BR KEXEC_ARCH_PPC ,
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.BR KEXEC_ARCH_PPC64 ,
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.BR KEXEC_ARCH_IA_64 ,
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.BR KEXEC_ARCH_ARM ,
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.BR KEXEC_ARCH_S390 ,
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.BR KEXEC_ARCH_SH ,
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.BR KEXEC_ARCH_MIPS ,
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and
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.BR KEXEC_ARCH_MIPS_LE .
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The architecture must be executable on the CPU of the system.
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.PP
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The
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.I entry
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argument is the physical entry address in the kernel image.
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The
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.I nr_segments
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argument is the number of segments pointed to by the
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.I segments
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pointer;
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the kernel imposes an (arbitrary) limit of 16 on the number of segments.
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The
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.I segments
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argument is an array of
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.I kexec_segment
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structures which define the kernel layout:
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.PP
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.in +4n
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.EX
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struct kexec_segment {
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void *buf; /* Buffer in user space */
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size_t bufsz; /* Buffer length in user space */
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void *mem; /* Physical address of kernel */
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size_t memsz; /* Physical address length */
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};
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.EE
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.in
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.PP
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The kernel image defined by
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.I segments
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is copied from the calling process into
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the kernel either in regular
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memory or in reserved memory (if
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.BR KEXEC_ON_CRASH
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is set).
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The kernel first performs various sanity checks on the
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information passed in
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.IR segments .
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If these checks pass, the kernel copies the segment data to kernel memory.
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Each segment specified in
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.I segments
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is copied as follows:
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.IP * 3
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.I buf
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and
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.I bufsz
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identify a memory region in the caller's virtual address space
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that is the source of the copy.
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The value in
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.I bufsz
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may not exceed the value in the
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.I memsz
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field.
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.IP *
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.I mem
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and
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.I memsz
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specify a physical address range that is the target of the copy.
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The values specified in both fields must be multiples of
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the system page size.
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.IP *
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.I bufsz
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bytes are copied from the source buffer to the target kernel buffer.
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If
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.I bufsz
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is less than
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.IR memsz ,
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then the excess bytes in the kernel buffer are zeroed out.
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.PP
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In case of a normal kexec (i.e., the
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.BR KEXEC_ON_CRASH
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flag is not set), the segment data is loaded in any available memory
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and is moved to the final destination at kexec reboot time (e.g., when the
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.BR kexec (8)
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command is executed with the
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.I \-e
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option).
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.PP
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In case of kexec on panic (i.e., the
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.BR KEXEC_ON_CRASH
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flag is set), the segment data is
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loaded to reserved memory at the time of the call, and, after a crash,
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the kexec mechanism simply passes control to that kernel.
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.PP
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The
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.BR kexec_load ()
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system call is available only if the kernel was configured with
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.BR CONFIG_KEXEC .
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.SS kexec_file_load()
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The
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.BR kexec_file_load ()
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system call is similar to
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.BR kexec_load (),
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but it takes a different set of arguments.
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It reads the kernel to be loaded from the file referred to by
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the file descriptor
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.IR kernel_fd ,
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and the initrd (initial RAM disk)
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to be loaded from file referred to by the file descriptor
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.IR initrd_fd .
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The
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.IR cmdline
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argument is a pointer to a buffer containing the command line
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for the new kernel.
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The
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.IR cmdline_len
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argument specifies size of the buffer.
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The last byte in the buffer must be a null byte (\(aq\\0\(aq).
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.PP
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The
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.IR flags
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argument is a bit mask which modifies the behavior of the call.
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The following values can be specified in
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.IR flags :
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.TP
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.BR KEXEC_FILE_UNLOAD
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Unload the currently loaded kernel.
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.TP
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.BR KEXEC_FILE_ON_CRASH
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Load the new kernel in the memory region reserved for the crash kernel
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(as for
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.BR KEXEC_ON_CRASH).
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This kernel is booted if the currently running kernel crashes.
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.TP
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.BR KEXEC_FILE_NO_INITRAMFS
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Loading initrd/initramfs is optional.
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Specify this flag if no initramfs is being loaded.
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If this flag is set, the value passed in
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.IR initrd_fd
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is ignored.
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.PP
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The
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.BR kexec_file_load ()
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.\" See also http://lwn.net/Articles/603116/
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system call was added to provide support for systems
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where "kexec" loading should be restricted to
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only kernels that are signed.
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This system call is available only if the kernel was configured with
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.BR CONFIG_KEXEC_FILE .
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.SH RETURN VALUE
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On success, these system calls returns 0.
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On error, \-1 is returned and
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.I errno
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is set to indicate the error.
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.SH ERRORS
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.TP
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.B EADDRNOTAVAIL
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.\" See kernel/kexec.::sanity_check_segment_list in the 3.19 kernel source
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The
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.B KEXEC_ON_CRASH
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flags was specified, but the region specified by the
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.I mem
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and
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.I memsz
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fields of one of the
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.I segments
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entries lies outside the range of memory reserved for the crash kernel.
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.TP
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.B EADDRNOTAVAIL
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The value in a
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.I mem
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or
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.I memsz
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field in one of the
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.I segments
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entries is not a multiple of the system page size.
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.TP
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.B EBADF
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.I kernel_fd
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or
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.I initrd_fd
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is not a valid file descriptor.
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.TP
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.B EBUSY
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Another crash kernel is already being loaded
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or a crash kernel is already in use.
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.TP
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.B EINVAL
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.I flags
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is invalid.
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.TP
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.B EINVAL
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The value of a
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.I bufsz
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field in one of the
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.I segments
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entries exceeds the value in the corresponding
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.I memsz
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field.
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.TP
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.B EINVAL
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.IR nr_segments
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exceeds
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.BR KEXEC_SEGMENT_MAX
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(16).
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.TP
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.B EINVAL
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Two or more of the kernel target buffers overlap.
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.TP
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.B EINVAL
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The value in
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.I cmdline[cmdline_len-1]
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is not \(aq\\0\(aq.
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.TP
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.B EINVAL
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The file referred to by
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.I kernel_fd
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or
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.I initrd_fd
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is empty (length zero).
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.TP
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.B ENOEXEC
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.I kernel_fd
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does not refer to an open file, or the kernel can't load this file.
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Currently, the file must be a bzImage and contain an x86 kernel that
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is loadable above 4\ GiB in memory (see the kernel source file
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.IR Documentation/x86/boot.txt ).
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.TP
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.B ENOMEM
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Could not allocate memory.
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.TP
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.B EPERM
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The caller does not have the
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.BR CAP_SYS_BOOT
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capability.
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.SH VERSIONS
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The
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.BR kexec_load ()
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system call first appeared in Linux 2.6.13.
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The
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.BR kexec_file_load ()
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system call first appeared in Linux 3.17.
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.SH CONFORMING TO
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These system calls are Linux-specific.
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.SH NOTES
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Currently, there is no glibc support for these system calls.
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Call them using
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.BR syscall (2).
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.SH SEE ALSO
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.BR reboot (2),
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.BR syscall (2),
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.BR kexec (8)
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.PP
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The kernel source files
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.IR Documentation/kdump/kdump.txt
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and
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.IR Documentation/admin-guide/kernel-parameters.txt
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