1kexec_load(2) System Calls Manual kexec_load(2)
2
6 kexec_load, kexec_file_load - load a new kernel for later execution
7
9 Standard C library (libc, -lc)
10
12 #include <linux/kexec.h> /* Definition of KEXEC_* constants */
13 #include <sys/syscall.h> /* Definition of SYS_* constants */
14 #include <unistd.h>
15 long syscall(SYS_kexec_load, unsigned long entry,
17 unsigned long nr_segments, struct kexec_segment *segments,
18 unsigned long flags);
19 long syscall(SYS_kexec_file_load, int kernel_fd, int initrd_fd,
20 unsigned long cmdline_len, const char *cmdline,
21 unsigned long flags);
22 Note: glibc provides no wrappers for these system calls, necessitating
24 the use of syscall(2).
25
27 The kexec_load() system call loads a new kernel that can be executed
28 later by reboot(2).
29 The flags argument is a bit mask that controls the operation of the
31 call. The following values can be specified in flags:
32 KEXEC_ON_CRASH (since Linux 2.6.13)
34 Execute the new kernel automatically on a system crash. This
35 "crash kernel" is loaded into an area of reserved memory that is
36 determined at boot time using the crashkernel kernel command-
37 line parameter. The location of this reserved memory is ex‐
38 ported to user space via the /proc/iomem file, in an entry la‐
39 beled "Crash kernel". A user-space application can parse this
40 file and prepare a list of segments (see below) that specify
41 this reserved memory as destination. If this flag is specified,
42 the kernel checks that the target segments specified in segments
43 fall within the reserved region.
44 KEXEC_PRESERVE_CONTEXT (since Linux 2.6.27)
46 Preserve the system hardware and software states before execut‐
47 ing the new kernel. This could be used for system suspend.
48 This flag is available only if the kernel was configured with
49 CONFIG_KEXEC_JUMP, and is effective only if nr_segments is
50 greater than 0.
51 The high-order bits (corresponding to the mask 0xffff0000) of flags
53 contain the architecture of the to-be-executed kernel. Specify (OR)
54 the constant KEXEC_ARCH_DEFAULT to use the current architecture, or one
55 of the following architecture constants KEXEC_ARCH_386, KEXEC_ARCH_68K,
56 KEXEC_ARCH_X86_64, KEXEC_ARCH_PPC, KEXEC_ARCH_PPC64, KEXEC_ARCH_IA_64,
57 KEXEC_ARCH_ARM, KEXEC_ARCH_S390, KEXEC_ARCH_SH, KEXEC_ARCH_MIPS, and
58 KEXEC_ARCH_MIPS_LE. The architecture must be executable on the CPU of
59 the system.
60 The entry argument is the physical entry address in the kernel image.
62 The nr_segments argument is the number of segments pointed to by the
63 segments pointer; the kernel imposes an (arbitrary) limit of 16 on the
64 number of segments. The segments argument is an array of kexec_segment
65 structures which define the kernel layout:
66 struct kexec_segment {
68 void *buf; /* Buffer in user space */
69 size_t bufsz; /* Buffer length in user space */
70 void *mem; /* Physical address of kernel */
71 size_t memsz; /* Physical address length */
72 };
73 The kernel image defined by segments is copied from the calling process
75 into the kernel either in regular memory or in reserved memory (if
76 KEXEC_ON_CRASH is set). The kernel first performs various sanity
77 checks on the information passed in segments. If these checks pass,
78 the kernel copies the segment data to kernel memory. Each segment
79 specified in segments is copied as follows:
80 • buf and bufsz identify a memory region in the caller's virtual ad‐
82 dress space that is the source of the copy. The value in bufsz may
83 not exceed the value in the memsz field.
84 • mem and memsz specify a physical address range that is the target of
86 the copy. The values specified in both fields must be multiples of
87 the system page size.
88 • bufsz bytes are copied from the source buffer to the target kernel
90 buffer. If bufsz is less than memsz, then the excess bytes in the
91 kernel buffer are zeroed out.
92 In case of a normal kexec (i.e., the KEXEC_ON_CRASH flag is not set),
94 the segment data is loaded in any available memory and is moved to the
95 final destination at kexec reboot time (e.g., when the kexec(8) command
96 is executed with the -e option).
97 In case of kexec on panic (i.e., the KEXEC_ON_CRASH flag is set), the
99 segment data is loaded to reserved memory at the time of the call, and,
100 after a crash, the kexec mechanism simply passes control to that ker‐
101 nel.
102 The kexec_load() system call is available only if the kernel was con‐
104 figured with CONFIG_KEXEC.
105 kexec_file_load()
107 The kexec_file_load() system call is similar to kexec_load(), but it
108 takes a different set of arguments. It reads the kernel to be loaded
109 from the file referred to by the file descriptor kernel_fd, and the
110 initrd (initial RAM disk) to be loaded from file referred to by the
111 file descriptor initrd_fd. The cmdline argument is a pointer to a buf‐
112 fer containing the command line for the new kernel. The cmdline_len
113 argument specifies size of the buffer. The last byte in the buffer
114 must be a null byte ('\0').
115 The flags argument is a bit mask which modifies the behavior of the
117 call. The following values can be specified in flags:
118 KEXEC_FILE_UNLOAD
120 Unload the currently loaded kernel.
121 KEXEC_FILE_ON_CRASH
123 Load the new kernel in the memory region reserved for the crash
124 kernel (as for KEXEC_ON_CRASH). This kernel is booted if the
125 currently running kernel crashes.
126 KEXEC_FILE_NO_INITRAMFS
128 Loading initrd/initramfs is optional. Specify this flag if no
129 initramfs is being loaded. If this flag is set, the value
130 passed in initrd_fd is ignored.
131 The kexec_file_load() system call was added to provide support for sys‐
133 tems where "kexec" loading should be restricted to only kernels that
134 are signed. This system call is available only if the kernel was con‐
135 figured with CONFIG_KEXEC_FILE.
136
138 On success, these system calls returns 0. On error, -1 is returned and
139 errno is set to indicate the error.
140
142 EADDRNOTAVAIL
143 The KEXEC_ON_CRASH flags was specified, but the region specified
144 by the mem and memsz fields of one of the segments entries lies
145 outside the range of memory reserved for the crash kernel.
146 EADDRNOTAVAIL
148 The value in a mem or memsz field in one of the segments entries
149 is not a multiple of the system page size.
150 EBADF kernel_fd or initrd_fd is not a valid file descriptor.
152 EBUSY Another crash kernel is already being loaded or a crash kernel
154 is already in use.
155 EINVAL flags is invalid.
157 EINVAL The value of a bufsz field in one of the segments entries ex‐
159 ceeds the value in the corresponding memsz field.
160 EINVAL nr_segments exceeds KEXEC_SEGMENT_MAX (16).
162 EINVAL Two or more of the kernel target buffers overlap.
164 EINVAL The value in cmdline[cmdline_len-1] is not '\0'.
166 EINVAL The file referred to by kernel_fd or initrd_fd is empty (length
168 zero).
169 ENOEXEC
171 kernel_fd does not refer to an open file, or the kernel can't
172 load this file. Currently, the file must be a bzImage and con‐
173 tain an x86 kernel that is loadable above 4 GiB in memory (see
174 the kernel source file Documentation/x86/boot.txt).
175 ENOMEM Could not allocate memory.
177 EPERM The caller does not have the CAP_SYS_BOOT capability.
179
181 Linux.
182
184 kexec_load()
185 Linux 2.6.13.
186 kexec_file_load()
188 Linux 3.17.
189
191 reboot(2), syscall(2), kexec(8)
192 The kernel source files Documentation/kdump/kdump.txt and Documenta‐
194 tion/admin-guide/kernel-parameters.txt
195Linux man-pages 6.04 2023-03-30 kexec_load(2)