kexec_file_load(2) — Linux manual page


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

NAME         top

       kexec_load, kexec_file_load - load a new kernel for later execution

SYNOPSIS         top

       #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         top

       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_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 mem‐
       ory (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 seg‐
       ment specified in segments is copied as follows:

       *  buf and bufsz identify a memory region in the caller's virtual ad‐
          dress 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 multi‐
          ples 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

       The kexec_load() system call is available only if the kernel was con‐
       figured with CONFIG_KEXEC.

       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 cmd‐
       line_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:

              Unload the currently loaded kernel.

              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.

              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         top

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

ERRORS         top

              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.

              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).

              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         top

       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         top

       These system calls are Linux-specific.

NOTES         top

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

SEE ALSO         top

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

       The kernel source files Documentation/kdump/kdump.txt and

COLOPHON         top

       This page is part of release 5.09 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

Linux                            2019-03-06                    KEXEC_LOAD(2)

Pages that refer to this page: syscalls(2)