Ubuntu Manpage: kexec_load, kexec_file_load - load a new kernel for later execution

NAME

       kexec_load, kexec_file_load - load a new kernel for later execution

SYNOPSIS

       #include <linux/kexec.h>

       long kexec_load(unsigned long entry, unsigned long nr_segments,
                       struct kexec_segment *segments, unsigned long flags);

       long kexec_file_load(int kernel_fd, int initrd_fd,
                           unsigned long cmdline_len, const char *cmdline,
                           unsigned long flags);

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

DESCRIPTION

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 craskkernel 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 descriptor kernel_fd, and the initrd
(initial RAM disk) to be loaded from file referred to by the 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.

RETURN VALUE

       On success, these system calls returns 0.  On error, -1 is returned and errno  is  set  to  indicate  the
       error.

ERRORS

       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).

       ENOMEM Could not allocate memory.

       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 4GiB in memory (see the kernel
              source file Documentation/x86/boot.txt).

       EPERM  The caller does not have the CAP_SYS_BOOT capability.

VERSIONS

       The kexec_load() system call first appeared in Linux 2.6.13.  The  kexec_file_load()  system  call  first
       appeared in Linux 3.17.

CONFORMING TO

       These system calls are Linux-specific.

NOTES

       Currently, there is no glibc support for these system calls.  Call them using syscall(2).

COLOPHON

       This  page  is  part  of  release  4.04  of  the  Linux man-pages project.  A description of the project,
       information  about  reporting  bugs,  and  the  latest  version  of  this   page,   can   be   found   at
       http://www.kernel.org/doc/man-pages/.