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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | STANDARDS | HISTORY | SEE ALSO | COLOPHON |
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kexec_load(2) System Calls Manual kexec_load(2)
kexec_load, kexec_file_load - load a new kernel for later
execution
Standard C library (libc, -lc)
#include <linux/kexec.h> /* Definition of KEXEC_* constants */
#include <sys/syscall.h> /* Definition of SYS_* constants */
#include <unistd.h>
long syscall(SYS_kexec_load, unsigned long entry,
unsigned long nr_segments, struct kexec_segment *segments,
unsigned long flags);
long syscall(SYS_kexec_file_load, int kernel_fd, int initrd_fd,
unsigned long cmdline_len, const char *cmdline,
unsigned long flags);
Note: glibc provides no wrappers for these system calls,
necessitating the use of syscall(2).
The kexec_load() system call loads a new kernel that can be
executed later by reboot(2).
The flags argument is a bit mask that controls the operation of
the call. The following values can be specified in flags:
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
crashkernel kernel command-line parameter. The location
of this reserved memory is exported to user space via the
/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
segments fall within the reserved region.
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 CONFIG_KEXEC_JUMP, and is effective only
if nr_segments is greater than 0.
The high-order bits (corresponding to the mask 0xffff0000) of
flags contain the architecture of the to-be-executed kernel.
Specify (OR) the constant KEXEC_ARCH_DEFAULT to use the current
architecture, or one of the following architecture constants
KEXEC_ARCH_386, KEXEC_ARCH_68K, KEXEC_ARCH_X86_64,
KEXEC_ARCH_PPC, KEXEC_ARCH_PPC64, KEXEC_ARCH_IA_64,
KEXEC_ARCH_ARM, KEXEC_ARCH_S390, KEXEC_ARCH_SH, KEXEC_ARCH_MIPS,
and KEXEC_ARCH_MIPS_LE. The architecture must be executable on
the CPU of the system.
The entry argument is the physical entry address in the kernel
image. The nr_segments argument is the number of segments
pointed to by the segments pointer; the kernel imposes an
(arbitrary) limit of 16 on the number of segments. The segments
argument is an array of kexec_segment structures which define the
kernel layout:
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 */
};
The kernel image defined by segments is copied from the calling
process into the kernel either in regular memory or in reserved
memory (if KEXEC_ON_CRASH is set). The kernel first performs
various sanity checks on the information passed in segments. If
these checks pass, the kernel copies the segment data to kernel
memory. Each segment specified in segments is copied as follows:
• buf and bufsz identify a memory region in the caller's virtual
address space that is the source of the copy. The value in
bufsz may not exceed the value in the memsz field.
• mem and 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.
• bufsz bytes are copied from the source buffer to the target
kernel buffer. If bufsz is less than memsz, then the excess
bytes in the kernel buffer are zeroed out.
In case of a normal kexec (i.e., the 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 kexec(8) command is executed with the -e option).
In case of kexec on panic (i.e., the 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.
The kexec_load() system call is available only if the kernel was
configured with CONFIG_KEXEC.
kexec_file_load()
The kexec_file_load() system call is similar to 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
kernel_fd, and the initrd (initial RAM disk) to be loaded from
file referred to by the file descriptor initrd_fd. The cmdline
argument is a pointer to a buffer containing the command line for
the new kernel. The cmdline_len argument specifies size of the
buffer. The last byte in the buffer must be a null byte ('\0').
The flags argument is a bit mask which modifies the behavior of
the call. The following values can be specified in flags:
KEXEC_FILE_UNLOAD
Unload the currently loaded kernel.
KEXEC_FILE_ON_CRASH
Load the new kernel in the memory region reserved for the
crash kernel (as for KEXEC_ON_CRASH). This kernel is
booted if the currently running kernel crashes.
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 initrd_fd is ignored.
The kexec_file_load() 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 CONFIG_KEXEC_FILE.
On success, these system calls returns 0. On error, -1 is
returned and errno is set to indicate the error.
EADDRNOTAVAIL
The KEXEC_ON_CRASH flags was specified, but the region
specified by the mem and memsz fields of one of the
segments entries lies outside the range of memory reserved
for the crash kernel.
EADDRNOTAVAIL
The value in a mem or memsz field in one of the segments
entries is not a multiple of the system page size.
EBADF kernel_fd or initrd_fd is not a valid file descriptor.
EBUSY Another crash kernel is already being loaded or a crash
kernel is already in use.
EINVAL flags is invalid.
EINVAL The value of a bufsz field in one of the segments entries
exceeds the value in the corresponding memsz field.
EINVAL nr_segments exceeds KEXEC_SEGMENT_MAX (16).
EINVAL Two or more of the kernel target buffers overlap.
EINVAL The value in cmdline[cmdline_len-1] is not '\0'.
EINVAL The file referred to by kernel_fd or initrd_fd is empty
(length zero).
ENOEXEC
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
Documentation/x86/boot.txt).
ENOMEM Could not allocate memory.
EPERM The caller does not have the CAP_SYS_BOOT capability.
Linux.
kexec_load()
Linux 2.6.13.
kexec_file_load()
Linux 3.17.
reboot(2), syscall(2), kexec(8)
The kernel source files Documentation/kdump/kdump.txt and
Documentation/admin-guide/kernel-parameters.txt
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
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for this manual page, see
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2024-06-26. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
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Linux man-pages 6.9.1 2024-06-15 kexec_load(2)
Pages that refer to this page: reboot(2), syscalls(2), capabilities(7)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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