man2/kexec_load.2

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  26 .TH KEXEC_LOAD 2 2014-08-19 "Linux" "Linux Programmer's Manual"
  27 .SH NAME
  28 kexec_load, kexec_file_load \- load a new kernel for later execution
  29 .SH SYNOPSIS
  30 .nf
  31 .B #include <linux/kexec.h>
  32
  33 .BI "long kexec_load(unsigned long " entry ", unsigned long " nr_segments ","
  34 .BI "                struct kexec_segment *" segments \
  35 ", unsigned long " flags ");"
  36
  37 .BI "long kexec_file_load(int " kernel_fd ", int " initrd_fd ","
  38 .br
  39 .BI "                    unsigned long " cmdline_len  \
  40 ", const char *" cmdline ","
  41 .BI "                    unsigned long " flags ");"
  42
  43 .fi
  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 .\" FIXME Explain in more detail how KEXEC_ON_CRASH is actually used
  61 .TP
  62 .BR KEXEC_PRESERVE_CONTEXT " (since Linux 2.6.27)"
  63 Preserve the system hardware and
  64 software states before executing the new kernel.
  65 This could be used for system suspend.
  66 This flag is available only if the kernel was configured with
  67 .BR CONFIG_KEXEC_JUMP ,
  68 and is effective only if
  69 .I nr_segments
  70 is greater than 0.
  71 .PP
  72 The high-order bits (corresponding to the mask 0xffff0000) of
  73 .I flags
  74 contain the architecture of the to-be-executed kernel.
  75 Specify (OR) the constant
  76 .B KEXEC_ARCH_DEFAULT
  77 to use the current architecture,
  78 or one of the following architecture constants
  79 .BR KEXEC_ARCH_386 ,
  80 .BR KEXEC_ARCH_68K ,
  81 .BR KEXEC_ARCH_X86_64 ,
  82 .BR KEXEC_ARCH_PPC ,
  83 .BR KEXEC_ARCH_PPC64 ,
  84 .BR KEXEC_ARCH_IA_64 ,
  85 .BR KEXEC_ARCH_ARM ,
  86 .BR KEXEC_ARCH_S390 ,
  87 .BR KEXEC_ARCH_SH ,
  88 .BR KEXEC_ARCH_MIPS ,
  89 and
  90 .BR KEXEC_ARCH_MIPS_LE .
  91 The architecture must be executable on the CPU of the system.
  92
  93 The
  94 .I entry
  95 argument is the physical entry address in the kernel image.
  96 The
  97 .I nr_segments
  98 argument is the number of segments pointed to by the
  99 .I segments
 100 pointer;
 101 the kernel imposes an (arbitrary) limit of 16 on the number of segments.
 102 The
 103 .I segments
 104 argument is an array of
 105 .I kexec_segment
 106 structures which define the kernel layout:
 107 .in +4n
 108 .nf
 109
 110 struct kexec_segment {
 111     void   *buf;        /* Buffer in user space */
 112     size_t  bufsz;      /* Buffer length in user space */
 113     void   *mem;        /* Physical address of kernel */
 114     size_t  memsz;      /* Physical address length */
 115 };
 116 .fi
 117 .in
 118 .PP
 119 .\" FIXME Explain the details of how the kernel image defined by segments
 120 .\" is copied from the calling process into previously reserved memory.
 121 The kernel image defined by
 122 .I segments
 123 is copied from the calling process into previously reserved memory.
 124
 125 The
 126 .BR kexec_load ()
 127 system call is available only if the kernel was configured with
 128 .BR CONFIG_KEXEC .
 129 .SS kexec_file_load()
 130 The
 131 .BR kexec_file_load ()
 132 system call is similar to
 133 .BR kexec_load (),
 134 but it takes a different set of arguments.
 135 It reads the kernel to be loaded from the file referred to by the descriptor
 136 .IR kernel_fd ,
 137 and the initrd (initial RAM disk)
 138 to be loaded from file referred to by the descriptor
 139 .IR initrd_fd .
 140 The
 141 .IR cmdline
 142 argument is a pointer to a string containing the command line
 143 for the new kernel; the
 144 .IR cmdline_len
 145 argument specifies the length of the string in
 146 .IR cmdline .
 147
 148 The
 149 .IR flags
 150 argument is a bit mask which modifies the behavior of the call.
 151 The following values can be specified in
 152 .IR flags :
 153 .TP
 154 .BR KEXEC_FILE_UNLOAD
 155 Unload the currently loaded kernel.
 156 .TP
 157 .BR KEXEC_FILE_ON_CRASH
 158 Load the new kernel in the memory region reserved for the crash kernel.
 159 This kernel is booted if the currently running kernel crashes.
 160 .TP
 161 .BR KEXEC_FILE_NO_INITRAMFS
 162 Loading initrd/initramfs is optional.
 163 Specify this flag if no initramfs is being loaded.
 164 If this flag is set, the value passed in
 165 .IR initrd_fd
 166 is ignored.
 167 .PP
 168 The
 169 .BR kexec_file_load ()
 170 .\" See also http://lwn.net/Articles/603116/
 171 system call was added to provide support for systems
 172 where "kexec" loading should be restricted to
 173 only kernels that are signed.
 174 This system call is available only if the kernel was configured with
 175 .BR CONFIG_KEXEC_FILE .
 176 .SH RETURN VALUE
 177 On success, these system calls returns 0.
 178 On error, \-1 is returned and
 179 .I errno
 180 is set to indicate the error.
 181 .SH ERRORS
 182 .TP
 183 .B EBUSY
 184 Another crash kernel is already being loaded
 185 or a crash kernel is already in use.
 186 .TP
 187 .B EINVAL
 188 .I flags
 189 is invalid; or
 190 .IR nr_segments
 191 is too large
 192 .\" KEXEC_SEGMENT_MAX == 16
 193 .TP
 194 .B ENOEXEC
 195 .I kernel_fd
 196 does not refer to an open file, or the kernel can't load this file.
 197 .TP
 198 .B EPERM
 199 The caller does not have the
 200 .BR CAP_SYS_BOOT
 201 capability.
 202 .SH VERSIONS
 203 The
 204 .BR kexec_load ()
 205 system call first appeared in Linux 2.6.13.
 206 The
 207 .BR kexec_file_load ()
 208 system call first appeared in Linux 3.17.
 209 .SH CONFORMING TO
 210 These system calls are Linux-specific.
 211 .SH NOTES
 212 Currently, there is no glibc support for these system calls.
 213 Call them using
 214 .BR syscall (2).
 215 .PP
 216 The required constants are in the Linux kernel source file
 217 .IR linux/kexec.h ,
 218 which is not currently exported to glibc.
 219 Therefore, these constants must be defined manually.
 220 .SH SEE ALSO
 221 .BR reboot (2),
 222 .BR syscall (2),
 223 .BR kexec (8)
 224
 225 The kernel source files
 226 .IR Documentation/kdump/kdump.txt
 227 and
 228 .IR Documentation/kernel-parameters.txt .