KEXEC_LOAD(2)		   Linux Programmer's Manual		 KEXEC_LOAD(2)



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  execut-
	      ing  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 ker-
       nel.

       The kexec_load() system call is available only if the kernel  was  con-
       figured 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 buf-
       fer 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 sys-
       tems where "kexec" loading should be restricted to  only	 kernels  that
       are  signed.  This system call is available only if the kernel was con-
       figured 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  con-
	      tain  an	x86  kernel that is loadable above 4GiB 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  Documenta-
       tion/kernel-parameters.txt.

COLOPHON
       This  page  is  part of release 4.10 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
       https://www.kernel.org/doc/man-pages/.



Linux				  2016-10-08			 KEXEC_LOAD(2)