1KEXEC_LOAD(2) Linux Programmer's Manual KEXEC_LOAD(2)
2
6 kexec_load, kexec_file_load - load a new kernel for later execution
7
9 #include <linux/kexec.h>
10 long kexec_load(unsigned long entry, unsigned long nr_segments,
12 struct kexec_segment *segments, unsigned long flags);
13 long kexec_file_load(int kernel_fd, int initrd_fd,
15 unsigned long cmdline_len, const char *cmdline,
16 unsigned long flags);
17 Note: There are no glibc wrappers for these system calls; see NOTES.
19
21 The kexec_load() system call loads a new kernel that can be executed
22 later by reboot(2).
23 The flags argument is a bit mask that controls the operation of the
25 call. The following values can be specified in flags:
26 KEXEC_ON_CRASH (since Linux 2.6.13)
28 Execute the new kernel automatically on a system crash. This
29 "crash kernel" is loaded into an area of reserved memory that is
30 determined at boot time using the crashkernel kernel command-
31 line parameter. The location of this reserved memory is
32 exported to user space via the /proc/iomem file, in an entry
33 labeled "Crash kernel". A user-space application can parse this
34 file and prepare a list of segments (see below) that specify
35 this reserved memory as destination. If this flag is specified,
36 the kernel checks that the target segments specified in segments
37 fall within the reserved region.
38 KEXEC_PRESERVE_CONTEXT (since Linux 2.6.27)
40 Preserve the system hardware and software states before execut‐
41 ing the new kernel. This could be used for system suspend.
42 This flag is available only if the kernel was configured with
43 CONFIG_KEXEC_JUMP, and is effective only if nr_segments is
44 greater than 0.
45 The high-order bits (corresponding to the mask 0xffff0000) of flags
47 contain the architecture of the to-be-executed kernel. Specify (OR)
48 the constant KEXEC_ARCH_DEFAULT to use the current architecture, or one
49 of the following architecture constants KEXEC_ARCH_386, KEXEC_ARCH_68K,
50 KEXEC_ARCH_X86_64, KEXEC_ARCH_PPC, KEXEC_ARCH_PPC64, KEXEC_ARCH_IA_64,
51 KEXEC_ARCH_ARM, KEXEC_ARCH_S390, KEXEC_ARCH_SH, KEXEC_ARCH_MIPS, and
52 KEXEC_ARCH_MIPS_LE. The architecture must be executable on the CPU of
53 the system.
54 The entry argument is the physical entry address in the kernel image.
56 The nr_segments argument is the number of segments pointed to by the
57 segments pointer; the kernel imposes an (arbitrary) limit of 16 on the
58 number of segments. The segments argument is an array of kexec_segment
59 structures which define the kernel layout:
60 struct kexec_segment {
62 void *buf; /* Buffer in user space */
63 size_t bufsz; /* Buffer length in user space */
64 void *mem; /* Physical address of kernel */
65 size_t memsz; /* Physical address length */
66 };
67 The kernel image defined by segments is copied from the calling process
69 into the kernel either in regular memory or in reserved memory (if
70 KEXEC_ON_CRASH is set). The kernel first performs various sanity
71 checks on the information passed in segments. If these checks pass,
72 the kernel copies the segment data to kernel memory. Each segment
73 specified in segments is copied as follows:
74 * buf and bufsz identify a memory region in the caller's virtual
76 address space that is the source of the copy. The value in bufsz
77 may not exceed the value in the memsz field.
78 * mem and memsz specify a physical address range that is the target of
80 the copy. The values specified in both fields must be multiples of
81 the system page size.
82 * bufsz bytes are copied from the source buffer to the target kernel
84 buffer. If bufsz is less than memsz, then the excess bytes in the
85 kernel buffer are zeroed out.
86 In case of a normal kexec (i.e., the KEXEC_ON_CRASH flag is not set),
88 the segment data is loaded in any available memory and is moved to the
89 final destination at kexec reboot time (e.g., when the kexec(8) command
90 is executed with the -e option).
91 In case of kexec on panic (i.e., the KEXEC_ON_CRASH flag is set), the
93 segment data is loaded to reserved memory at the time of the call, and,
94 after a crash, the kexec mechanism simply passes control to that ker‐
95 nel.
96 The kexec_load() system call is available only if the kernel was con‐
98 figured with CONFIG_KEXEC.
99 kexec_file_load()
101 The kexec_file_load() system call is similar to kexec_load(), but it
102 takes a different set of arguments. It reads the kernel to be loaded
103 from the file referred to by the file descriptor kernel_fd, and the
104 initrd (initial RAM disk) to be loaded from file referred to by the
105 file descriptor initrd_fd. The cmdline argument is a pointer to a buf‐
106 fer containing the command line for the new kernel. The cmdline_len
107 argument specifies size of the buffer. The last byte in the buffer
108 must be a null byte ('\0').
109 The flags argument is a bit mask which modifies the behavior of the
111 call. The following values can be specified in flags:
112 KEXEC_FILE_UNLOAD
114 Unload the currently loaded kernel.
115 KEXEC_FILE_ON_CRASH
117 Load the new kernel in the memory region reserved for the crash
118 kernel (as for KEXEC_ON_CRASH). This kernel is booted if the
119 currently running kernel crashes.
120 KEXEC_FILE_NO_INITRAMFS
122 Loading initrd/initramfs is optional. Specify this flag if no
123 initramfs is being loaded. If this flag is set, the value
124 passed in initrd_fd is ignored.
125 The kexec_file_load() system call was added to provide support for sys‐
127 tems where "kexec" loading should be restricted to only kernels that
128 are signed. This system call is available only if the kernel was con‐
129 figured with CONFIG_KEXEC_FILE.
130
132 On success, these system calls returns 0. On error, -1 is returned and
133 errno is set to indicate the error.
134
136 EADDRNOTAVAIL
137 The KEXEC_ON_CRASH flags was specified, but the region specified
138 by the mem and memsz fields of one of the segments entries lies
139 outside the range of memory reserved for the crash kernel.
140 EADDRNOTAVAIL
142 The value in a mem or memsz field in one of the segments entries
143 is not a multiple of the system page size.
144 EBADF kernel_fd or initrd_fd is not a valid file descriptor.
146 EBUSY Another crash kernel is already being loaded or a crash kernel
148 is already in use.
149 EINVAL flags is invalid.
151 EINVAL The value of a bufsz field in one of the segments entries
153 exceeds the value in the corresponding memsz field.
154 EINVAL nr_segments exceeds KEXEC_SEGMENT_MAX (16).
156 EINVAL Two or more of the kernel target buffers overlap.
158 EINVAL The value in cmdline[cmdline_len-1] is not '\0'.
160 EINVAL The file referred to by kernel_fd or initrd_fd is empty (length
162 zero).
163 ENOEXEC
165 kernel_fd does not refer to an open file, or the kernel can't
166 load this file. Currently, the file must be a bzImage and con‐
167 tain an x86 kernel that is loadable above 4 GiB in memory (see
168 the kernel source file Documentation/x86/boot.txt).
169 ENOMEM Could not allocate memory.
171 EPERM The caller does not have the CAP_SYS_BOOT capability.
173
175 The kexec_load() system call first appeared in Linux 2.6.13. The
176 kexec_file_load() system call first appeared in Linux 3.17.
177
179 These system calls are Linux-specific.
180
182 Currently, there is no glibc support for these system calls. Call them
183 using syscall(2).
184
186 reboot(2), syscall(2), kexec(8)
187 The kernel source files Documentation/kdump/kdump.txt and Documenta‐
189 tion/admin-guide/kernel-parameters.txt
190
192 This page is part of release 4.16 of the Linux man-pages project. A
193 description of the project, information about reporting bugs, and the
194 latest version of this page, can be found at
195 https://www.kernel.org/doc/man-pages/.
196Linux 2017-09-15 KEXEC_LOAD(2)