kexec_load(2) — Linux manual page


kexec_load(2)              System Calls Manual             kexec_load(2)

NAME         top

       kexec_load, kexec_file_load - load a new kernel for later

LIBRARY         top

       Standard C library (libc, -lc)

SYNOPSIS         top

       #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).

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
       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.

       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:

              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

       ENOMEM Could not allocate memory.

       EPERM  The caller does not have the CAP_SYS_BOOT capability.

STANDARDS         top


HISTORY         top

              Linux 2.6.13.

              Linux 3.17.

SEE ALSO         top

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

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

COLOPHON         top

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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)