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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
              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.

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).

       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.

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).

SEE ALSO

       reboot(2), syscall(2), kexec(8)

       The   kernel   source   files   Documentation/kdump/kdump.txt   and   Documentation/admin-
       guide/kernel-parameters.txt

COLOPHON

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       project,  information  about  reporting  bugs, and the latest version of this page, can be
       found at https://www.kernel.org/doc/man-pages/.