1KEXEC_LOAD(2)              Linux Programmer's Manual             KEXEC_LOAD(2)
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NAME

6       kexec_load, kexec_file_load - load a new kernel for later execution
7

SYNOPSIS

9       #include <linux/kexec.h>      /* Definition of KEXEC_* constants */
10       #include <sys/syscall.h>      /* Definition of SYS_* constants */
11       #include <unistd.h>
12
13       long syscall(SYS_kexec_load, unsigned long entry,
14                    unsigned long nr_segments, struct kexec_segment *segments,
15                    unsigned long flags);
16       long syscall(SYS_kexec_file_load, int kernel_fd, int initrd_fd,
17                    unsigned long cmdline_len, const char *cmdline,
18                    unsigned long flags);
19
20       Note:  glibc provides no wrappers for these system calls, necessitating
21       the use of syscall(2).
22

DESCRIPTION

24       The kexec_load() system call loads a new kernel that  can  be  executed
25       later by reboot(2).
26
27       The  flags  argument  is  a bit mask that controls the operation of the
28       call.  The following values can be specified in flags:
29
30       KEXEC_ON_CRASH (since Linux 2.6.13)
31              Execute the new kernel automatically on a  system  crash.   This
32              "crash kernel" is loaded into an area of reserved memory that is
33              determined at boot time using the  crashkernel  kernel  command-
34              line  parameter.   The  location  of this reserved memory is ex‐
35              ported to user space via the /proc/iomem file, in an  entry  la‐
36              beled  "Crash  kernel".  A user-space application can parse this
37              file and prepare a list of segments  (see  below)  that  specify
38              this reserved memory as destination.  If this flag is specified,
39              the kernel checks that the target segments specified in segments
40              fall within the reserved region.
41
42       KEXEC_PRESERVE_CONTEXT (since Linux 2.6.27)
43              Preserve  the system hardware and software states before execut‐
44              ing the new kernel.  This could  be  used  for  system  suspend.
45              This  flag  is  available only if the kernel was configured with
46              CONFIG_KEXEC_JUMP, and  is  effective  only  if  nr_segments  is
47              greater than 0.
48
49       The  high-order  bits  (corresponding  to the mask 0xffff0000) of flags
50       contain the architecture of the to-be-executed  kernel.   Specify  (OR)
51       the constant KEXEC_ARCH_DEFAULT to use the current architecture, or one
52       of the following architecture constants KEXEC_ARCH_386, KEXEC_ARCH_68K,
53       KEXEC_ARCH_X86_64,  KEXEC_ARCH_PPC, KEXEC_ARCH_PPC64, KEXEC_ARCH_IA_64,
54       KEXEC_ARCH_ARM, KEXEC_ARCH_S390,  KEXEC_ARCH_SH,  KEXEC_ARCH_MIPS,  and
55       KEXEC_ARCH_MIPS_LE.   The architecture must be executable on the CPU of
56       the system.
57
58       The entry argument is the physical entry address in the  kernel  image.
59       The  nr_segments  argument  is the number of segments pointed to by the
60       segments pointer; the kernel imposes an (arbitrary) limit of 16 on  the
61       number of segments.  The segments argument is an array of kexec_segment
62       structures which define the kernel layout:
63
64           struct kexec_segment {
65               void   *buf;        /* Buffer in user space */
66               size_t  bufsz;      /* Buffer length in user space */
67               void   *mem;        /* Physical address of kernel */
68               size_t  memsz;      /* Physical address length */
69           };
70
71       The kernel image defined by segments is copied from the calling process
72       into  the  kernel  either  in  regular memory or in reserved memory (if
73       KEXEC_ON_CRASH is set).   The  kernel  first  performs  various  sanity
74       checks  on  the  information passed in segments.  If these checks pass,
75       the kernel copies the segment data  to  kernel  memory.   Each  segment
76       specified in segments is copied as follows:
77
78       *  buf  and  bufsz identify a memory region in the caller's virtual ad‐
79          dress space that is the source of the copy.  The value in bufsz  may
80          not exceed the value in the memsz field.
81
82       *  mem and memsz specify a physical address range that is the target of
83          the copy.  The values specified in both fields must be multiples  of
84          the system page size.
85
86       *  bufsz  bytes  are copied from the source buffer to the target kernel
87          buffer.  If bufsz is less than memsz, then the excess bytes  in  the
88          kernel buffer are zeroed out.
89
90       In  case  of a normal kexec (i.e., the KEXEC_ON_CRASH flag is not set),
91       the segment data is loaded in any available memory and is moved to  the
92       final destination at kexec reboot time (e.g., when the kexec(8) command
93       is executed with the -e option).
94
95       In case of kexec on panic (i.e., the KEXEC_ON_CRASH flag is  set),  the
96       segment data is loaded to reserved memory at the time of the call, and,
97       after a crash, the kexec mechanism simply passes control to  that  ker‐
98       nel.
99
100       The  kexec_load()  system call is available only if the kernel was con‐
101       figured with CONFIG_KEXEC.
102
103   kexec_file_load()
104       The kexec_file_load() system call is similar to  kexec_load(),  but  it
105       takes  a  different set of arguments.  It reads the kernel to be loaded
106       from the file referred to by the file  descriptor  kernel_fd,  and  the
107       initrd  (initial  RAM  disk)  to be loaded from file referred to by the
108       file descriptor initrd_fd.  The cmdline argument is a pointer to a buf‐
109       fer  containing  the  command line for the new kernel.  The cmdline_len
110       argument specifies size of the buffer.  The last  byte  in  the  buffer
111       must be a null byte ('\0').
112
113       The  flags  argument  is  a bit mask which modifies the behavior of the
114       call.  The following values can be specified in flags:
115
116       KEXEC_FILE_UNLOAD
117              Unload the currently loaded kernel.
118
119       KEXEC_FILE_ON_CRASH
120              Load the new kernel in the memory region reserved for the  crash
121              kernel  (as  for  KEXEC_ON_CRASH).  This kernel is booted if the
122              currently running kernel crashes.
123
124       KEXEC_FILE_NO_INITRAMFS
125              Loading initrd/initramfs is optional.  Specify this flag  if  no
126              initramfs  is  being  loaded.   If  this  flag is set, the value
127              passed in initrd_fd is ignored.
128
129       The kexec_file_load() system call was added to provide support for sys‐
130       tems  where  "kexec"  loading should be restricted to only kernels that
131       are signed.  This system call is available only if the kernel was  con‐
132       figured with CONFIG_KEXEC_FILE.
133

RETURN VALUE

135       On success, these system calls returns 0.  On error, -1 is returned and
136       errno is set to indicate the error.
137

ERRORS

139       EADDRNOTAVAIL
140              The KEXEC_ON_CRASH flags was specified, but the region specified
141              by  the mem and memsz fields of one of the segments entries lies
142              outside the range of memory reserved for the crash kernel.
143
144       EADDRNOTAVAIL
145              The value in a mem or memsz field in one of the segments entries
146              is not a multiple of the system page size.
147
148       EBADF  kernel_fd or initrd_fd is not a valid file descriptor.
149
150       EBUSY  Another  crash  kernel is already being loaded or a crash kernel
151              is already in use.
152
153       EINVAL flags is invalid.
154
155       EINVAL The value of a bufsz field in one of the  segments  entries  ex‐
156              ceeds the value in the corresponding memsz field.
157
158       EINVAL nr_segments exceeds KEXEC_SEGMENT_MAX (16).
159
160       EINVAL Two or more of the kernel target buffers overlap.
161
162       EINVAL The value in cmdline[cmdline_len-1] is not '\0'.
163
164       EINVAL The  file referred to by kernel_fd or initrd_fd is empty (length
165              zero).
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167       ENOEXEC
168              kernel_fd does not refer to an open file, or  the  kernel  can't
169              load  this file.  Currently, the file must be a bzImage and con‐
170              tain an x86 kernel that is loadable above 4 GiB in  memory  (see
171              the kernel source file Documentation/x86/boot.txt).
172
173       ENOMEM Could not allocate memory.
174
175       EPERM  The caller does not have the CAP_SYS_BOOT capability.
176

VERSIONS

178       The  kexec_load()  system  call  first  appeared  in Linux 2.6.13.  The
179       kexec_file_load() system call first appeared in Linux 3.17.
180

CONFORMING TO

182       These system calls are Linux-specific.
183

SEE ALSO

185       reboot(2), syscall(2), kexec(8)
186
187       The kernel source files  Documentation/kdump/kdump.txt  and  Documenta‐
188       tion/admin-guide/kernel-parameters.txt
189

COLOPHON

191       This  page  is  part of release 5.13 of the Linux man-pages project.  A
192       description of the project, information about reporting bugs,  and  the
193       latest     version     of     this    page,    can    be    found    at
194       https://www.kernel.org/doc/man-pages/.
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198Linux                             2021-03-22                     KEXEC_LOAD(2)
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