man2/kexec_load.2

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  27 .TH KEXEC_LOAD 2 2017-05-03 "Linux" "Linux Programmer's Manual"
  28 .SH NAME
  29 kexec_load, kexec_file_load \- load a new kernel for later execution
  30 .SH SYNOPSIS
  31 .nf
  32 .B #include <linux/kexec.h>
  33 .PP
  34 .BI "long kexec_load(unsigned long " entry ", unsigned long " nr_segments ","
  35 .BI "                struct kexec_segment *" segments \
  36 ", unsigned long " flags ");"
  37 .PP
  38 .BI "long kexec_file_load(int " kernel_fd ", int " initrd_fd ","
  39 .BI "                    unsigned long " cmdline_len  \
  40 ", const char *" cmdline ","
  41 .BI "                    unsigned long " flags ");"
  42 .fi
  43 .PP
  44 .IR Note :
  45 There are no glibc wrappers for these system calls; see NOTES.
  46 .SH DESCRIPTION
  47 The
  48 .BR kexec_load ()
  49 system call loads a new kernel that can be executed later by
  50 .BR reboot (2).
  51 .PP
  52 The
  53 .I flags
  54 argument is a bit mask that controls the operation of the call.
  55 The following values can be specified in
  56 .IR flags :
  57 .TP
  58 .BR KEXEC_ON_CRASH " (since Linux 2.6.13)"
  59 Execute the new kernel automatically on a system crash.
  60 This "crash kernel" is loaded into an area of reserved memory that
  61 is determined at boot time using the
  62 .I crashkernel
  63 kernel command-line parameter.
  64 The location of this reserved memory is exported to user space via the
  65 .I /proc/iomem
  66 file, in an entry labeled "Crash kernel".
  67 A user-space application can parse this file and prepare a list of
  68 segments (see below) that specify this reserved memory as destination.
  69 If this flag is specified, the kernel checks that the
  70 target segments specified in
  71 .I segments
  72 fall within the reserved region.
  73 .TP
  74 .BR KEXEC_PRESERVE_CONTEXT " (since Linux 2.6.27)"
  75 Preserve the system hardware and
  76 software states before executing the new kernel.
  77 This could be used for system suspend.
  78 This flag is available only if the kernel was configured with
  79 .BR CONFIG_KEXEC_JUMP ,
  80 and is effective only if
  81 .I nr_segments
  82 is greater than 0.
  83 .PP
  84 The high-order bits (corresponding to the mask 0xffff0000) of
  85 .I flags
  86 contain the architecture of the to-be-executed kernel.
  87 Specify (OR) the constant
  88 .B KEXEC_ARCH_DEFAULT
  89 to use the current architecture,
  90 or one of the following architecture constants
  91 .BR KEXEC_ARCH_386 ,
  92 .BR KEXEC_ARCH_68K ,
  93 .BR KEXEC_ARCH_X86_64 ,
  94 .BR KEXEC_ARCH_PPC ,
  95 .BR KEXEC_ARCH_PPC64 ,
  96 .BR KEXEC_ARCH_IA_64 ,
  97 .BR KEXEC_ARCH_ARM ,
  98 .BR KEXEC_ARCH_S390 ,
  99 .BR KEXEC_ARCH_SH ,
 100 .BR KEXEC_ARCH_MIPS ,
 101 and
 102 .BR KEXEC_ARCH_MIPS_LE .
 103 The architecture must be executable on the CPU of the system.
 104 .PP
 105 The
 106 .I entry
 107 argument is the physical entry address in the kernel image.
 108 The
 109 .I nr_segments
 110 argument is the number of segments pointed to by the
 111 .I segments
 112 pointer;
 113 the kernel imposes an (arbitrary) limit of 16 on the number of segments.
 114 The
 115 .I segments
 116 argument is an array of
 117 .I kexec_segment
 118 structures which define the kernel layout:
 119 .PP
 120 .in +4n
 121 .EX
 122 struct kexec_segment {
 123     void   *buf;        /* Buffer in user space */
 124     size_t  bufsz;      /* Buffer length in user space */
 125     void   *mem;        /* Physical address of kernel */
 126     size_t  memsz;      /* Physical address length */
 127 };
 128 .EE
 129 .in
 130 .PP
 131 The kernel image defined by
 132 .I segments
 133 is copied from the calling process into
 134 the kernel either in regular
 135 memory or in reserved memory (if
 136 .BR KEXEC_ON_CRASH
 137 is set).
 138 The kernel first performs various sanity checks on the
 139 information passed in
 140 .IR segments .
 141 If these checks pass, the kernel copies the segment data to kernel memory.
 142 Each segment specified in
 143 .I segments
 144 is copied as follows:
 145 .IP * 3
 146 .I buf
 147 and
 148 .I bufsz
 149 identify a memory region in the caller's virtual address space
 150 that is the source of the copy.
 151 The value in
 152 .I bufsz
 153 may not exceed the value in the
 154 .I memsz
 155 field.
 156 .IP *
 157 .I mem
 158 and
 159 .I memsz
 160 specify a physical address range that is the target of the copy.
 161 The values specified in both fields must be multiples of
 162 the system page size.
 163 .IP *
 164 .I bufsz
 165 bytes are copied from the source buffer to the target kernel buffer.
 166 If
 167 .I bufsz
 168 is less than
 169 .IR memsz ,
 170 then the excess bytes in the kernel buffer are zeroed out.
 171 .PP
 172 In case of a normal kexec (i.e., the
 173 .BR KEXEC_ON_CRASH
 174 flag is not set), the segment data is loaded in any available memory
 175 and is moved to the final destination at kexec reboot time (e.g., when the
 176 .BR kexec (8)
 177 command is executed with the
 178 .I \-e
 179 option).
 180 .PP
 181 In case of kexec on panic (i.e., the
 182 .BR KEXEC_ON_CRASH
 183 flag is set), the segment data is
 184 loaded to reserved memory at the time of the call, and, after a crash,
 185 the kexec mechanism simply passes control to that kernel.
 186 .PP
 187 The
 188 .BR kexec_load ()
 189 system call is available only if the kernel was configured with
 190 .BR CONFIG_KEXEC .
 191 .SS kexec_file_load()
 192 The
 193 .BR kexec_file_load ()
 194 system call is similar to
 195 .BR kexec_load (),
 196 but it takes a different set of arguments.
 197 It reads the kernel to be loaded from the file referred to by
 198 the file descriptor
 199 .IR kernel_fd ,
 200 and the initrd (initial RAM disk)
 201 to be loaded from file referred to by the file descriptor
 202 .IR initrd_fd .
 203 The
 204 .IR cmdline
 205 argument is a pointer to a buffer containing the command line
 206 for the new kernel.
 207 The
 208 .IR cmdline_len
 209 argument specifies size of the buffer.
 210 The last byte in the buffer must be a null byte (\(aq\\0\(aq).
 211 .PP
 212 The
 213 .IR flags
 214 argument is a bit mask which modifies the behavior of the call.
 215 The following values can be specified in
 216 .IR flags :
 217 .TP
 218 .BR KEXEC_FILE_UNLOAD
 219 Unload the currently loaded kernel.
 220 .TP
 221 .BR KEXEC_FILE_ON_CRASH
 222 Load the new kernel in the memory region reserved for the crash kernel
 223 (as for
 224 .BR KEXEC_ON_CRASH).
 225 This kernel is booted if the currently running kernel crashes.
 226 .TP
 227 .BR KEXEC_FILE_NO_INITRAMFS
 228 Loading initrd/initramfs is optional.
 229 Specify this flag if no initramfs is being loaded.
 230 If this flag is set, the value passed in
 231 .IR initrd_fd
 232 is ignored.
 233 .PP
 234 The
 235 .BR kexec_file_load ()
 236 .\" See also http://lwn.net/Articles/603116/
 237 system call was added to provide support for systems
 238 where "kexec" loading should be restricted to
 239 only kernels that are signed.
 240 This system call is available only if the kernel was configured with
 241 .BR CONFIG_KEXEC_FILE .
 242 .SH RETURN VALUE
 243 On success, these system calls returns 0.
 244 On error, \-1 is returned and
 245 .I errno
 246 is set to indicate the error.
 247 .SH ERRORS
 248 .TP
 249 .B EADDRNOTAVAIL
 250 .\" See kernel/kexec.::sanity_check_segment_list in the 3.19 kernel source
 251 The
 252 .B KEXEC_ON_CRASH
 253 flags was specified, but the region specified by the
 254 .I mem
 255 and
 256 .I memsz
 257 fields of one of the
 258 .I segments
 259 entries lies outside the range of memory reserved for the crash kernel.
 260 .TP
 261 .B EADDRNOTAVAIL
 262 The value in a
 263 .I mem
 264 or
 265 .I memsz
 266 field in one of the
 267 .I segments
 268 entries is not a multiple of the system page size.
 269 .TP
 270 .B EBADF
 271 .I kernel_fd
 272 or
 273 .I initrd_fd
 274 is not a valid file descriptor.
 275 .TP
 276 .B EBUSY
 277 Another crash kernel is already being loaded
 278 or a crash kernel is already in use.
 279 .TP
 280 .B EINVAL
 281 .I flags
 282 is invalid.
 283 .TP
 284 .B EINVAL
 285 The value of a
 286 .I bufsz
 287 field in one of the
 288 .I segments
 289 entries exceeds the value in the corresponding
 290 .I memsz
 291 field.
 292 .TP
 293 .B EINVAL
 294 .IR nr_segments
 295 exceeds
 296 .BR KEXEC_SEGMENT_MAX
 297 (16).
 298 .TP
 299 .B EINVAL
 300 Two or more of the kernel target buffers overlap.
 301 .TP
 302 .B EINVAL
 303 The value in
 304 .I cmdline[cmdline_len-1]
 305 is not \(aq\\0\(aq.
 306 .TP
 307 .B EINVAL
 308 The file referred to by
 309 .I kernel_fd
 310 or
 311 .I initrd_fd
 312 is empty (length zero).
 313 .TP
 314 .B ENOEXEC
 315 .I kernel_fd
 316 does not refer to an open file, or the kernel can't load this file.
 317 Currently, the file must be a bzImage and contain an x86 kernel that
 318 is loadable above 4\ GiB in memory (see the kernel source file
 319 .IR Documentation/x86/boot.txt ).
 320 .TP
 321 .B ENOMEM
 322 Could not allocate memory.
 323 .TP
 324 .B EPERM
 325 The caller does not have the
 326 .BR CAP_SYS_BOOT
 327 capability.
 328 .SH VERSIONS
 329 The
 330 .BR kexec_load ()
 331 system call first appeared in Linux 2.6.13.
 332 The
 333 .BR kexec_file_load ()
 334 system call first appeared in Linux 3.17.
 335 .SH CONFORMING TO
 336 These system calls are Linux-specific.
 337 .SH NOTES
 338 Currently, there is no glibc support for these system calls.
 339 Call them using
 340 .BR syscall (2).
 341 .SH SEE ALSO
 342 .BR reboot (2),
 343 .BR syscall (2),
 344 .BR kexec (8)
 345 .PP
 346 The kernel source files
 347 .IR Documentation/kdump/kdump.txt
 348 and
 349 .IR Documentation/admin-guide/kernel-parameters.txt