1kexec(8) User Manuals kexec(8)
2
6 kexec - directly boot into a new kernel
7
9 /sbin/kexec [-v (--version)] [-f (--force)] [-x (--no-ifdown)] [-y
10 (--no-sync)] [-l (--load)] [-p (--load-panic)] [-u (--unload)] [-e
11 (--exec)] [-t (--type)] [--mem-min=addr] [--mem-max=addr]
12
15 kexec is a system call that enables you to load and boot into another
16 kernel from the currently running kernel. kexec performs the function
17 of the boot loader from within the kernel. The primary difference
18 between a standard system boot and a kexec boot is that the hardware
19 initialization normally performed by the BIOS or firmware (depending on
20 architecture) is not performed during a kexec boot. This has the effect
21 of reducing the time required for a reboot.
22 Make sure you have selected CONFIG_KEXEC=y when configuring the kernel.
24 The CONFIG_KEXEC option enables the kexec system call.
25
27 Using kexec consists of
28 (1) loading the kernel to be rebooted to into memory, and
30 (2) actually rebooting to the pre-loaded kernel.
31 To load a kernel, the syntax is as follows:
33 kexec -l kernel-image --append=command-line-options --ini‐
35 trd=initrd-image
36 where kernel-image is the kernel file that you intend to reboot to.
38 Insert the command-line parameters that must be passed to the new ker‐
40 nel into command-line-options. Passing the exact contents of
41 /proc/cmdline into command-line-options is the safest way to ensure
42 that correct values are passed to the rebooting kernel.
43 The optional initrd-image is the initrd image to be used during boot.
45 It's also possible to invoke kexec without an option parameter. In that
47 case, kexec loads the specified kernel and then invokes shutdown(8).
48 If the shutdown scripts of your Linux distribution support kexec-based
49 rebooting, they then call kexec -e just before actually rebooting the
50 machine. That way, the machine does a clean shutdown including all
51 shutdown scripts.
52
55 For example, if the kernel image you want to reboot to is
56 /boot/vmlinux, the contents of /proc/cmdline is root=/dev/hda1, and the
57 path to the initrd is /boot/initrd, then you would use the following
58 command to load the kernel:
59 kexec -l /boot/vmlinux --append=root=/dev/hda1 --ini‐
61 trd=/boot/initrd
62 After this kernel is loaded, it can be booted to at any time using the
64 command:
65 kexec -e
67
70 -d (--debug)
71 Enable debugging messages.
72 -S (--status)
74 Return 0 if the type (by default crash) is loaded. Can be used
75 in conjuction with -l or -p to toggle the type. Note this option
76 supersedes other options and it will not load or unload the ker‐
77 nel.
78 -e (--exec)
80 Run the currently loaded kernel. Note that it will reboot into
81 the loaded kernel without calling shutdown(8).
82 -f (--force)
84 Force an immediate kexec call, do not call shutdown(8) (contrary
85 to the default action without any option parameter). This option
86 performs the same actions like executing -l and -e in one call.
87 -h (--help)
89 Open a help file for kexec.
90 -i (--no-checks)
92 Fast reboot, no memory integrity checks.
93 -l (--load) kernel
95 Load the specified kernel into the current kernel.
96 -p (--load-panic)
98 Load the new kernel for use on panic.
99 -t (--type=type)
101 Specify that the new kernel is of this type.
102 -s (--kexec-file-syscall)
104 Specify that the new KEXEC_FILE_LOAD syscall should be used
105 exclusively.
106 -c (--kexec-syscall)
108 Specify that the old KEXEC_LOAD syscall should be used exclu‐
109 sively (the default).
110 -a (--kexec-syscall-auto)
112 Try the new KEXEC_FILE_LOAD syscall first and when it is not
113 supported or the kernel does not understand the supplied image
114 fall back to the old KEXEC_LOAD interface.
115 There is no one single interface that always works.
117 KEXEC_FILE_LOAD is required on systems that use locked-down
119 secure boot to verify the kernel signature. KEXEC_LOAD may be
120 also disabled in the kernel configuration.
121 KEXEC_LOAD is required for some kernel image formats and on
123 architectures that do not implement KEXEC_FILE_LOAD.
124 -u (--unload)
126 Unload the current kexec target kernel. If a capture kernel is
127 being unloaded then specify -p with -u.
128 -v (--version)
130 Return the version number of the installed utility.
131 -x (--no-ifdown)
133 Shut down the running kernel, but restore the interface on
134 reload.
135 -y (--no-sync)
137 Shut down the running kernel, but skip syncing the filesystems.
138 --mem-min=addr
140 Specify the lowest memory address addr to load code into.
141 --mem-max=addr
143 Specify the highest memory address addr to load code into.
144 --entry=addr
146 Specify the jump back address. (0 means it's not jump back or
147 preserve context)
148 --load-preserve-context
150 Load the new kernel and preserve context of current kernel dur‐
151 ing kexec.
152 --load-jump-back-helper
154 Load a helper image to jump back to original kernel.
155 --reuseinitrd
157 Reuse initrd from first boot.
158 --print-ckr-size
160 Print crash kernel region size, if available.
161
165 Beoboot-x86
166 --args-elf
168 Pass ELF boot notes.
169 --args-linux
171 Pass Linux kernel style options.
172 --real-mode
174 Use the kernel's real mode entry point.
175 elf-x86
177 --append=string
179 Append string to the kernel command line.
180 --command-line=string
182 Set the kernel command line to string.
183 --reuse-cmdline
185 Use the command line from the running system. When a
186 panic kernel is loaded, it strips the crashkernel parame‐
187 ter automatically. The BOOT_IMAGE parameter is also
188 stripped.
189 --initrd=file
191 Use file as the kernel's initial ramdisk.
192 --ramdisk=file
194 Use file as the kernel's initial ramdisk.
195 bzImage-x86
197 --append=string
199 Append string to the kernel command line.
200 --command-line=string
202 Set the kernel command line to string.
203 --reuse-cmdline
205 Use the command line from the running system. When a
206 panic kernel is loaded, it strips the crashkernel parame‐
207 ter automatically. The BOOT_IMAGE parameter is also
208 stripped.
209 --initrd=file
211 Use file as the kernel's initial ramdisk.
212 --ramdisk=file
214 Use file as the kernel's initial ramdisk.
215 --real-mode
217 Use real-mode entry point.
218 multiboot-x86
220 --command-line=string
222 Set the kernel command line to string.
223 --reuse-cmdline
225 Use the command line from the running system. When a
226 panic kernel is loaded, it strips the crashkernel parame‐
227 ter automatically. The BOOT_IMAGE parameter is also
228 stripped.
229 --module=mod arg1 arg2 ...
231 Load module mod with command-line arguments arg1 arg2 ...
232 This parameter can be specified multiple times.
233 multiboot2-x86
235 --command-line=string
237 Set the kernel command line to string.
238 --reuse-cmdline
240 Use the command line from the running system. When a
241 panic kernel is loaded, it strips the crashkernel parame‐
242 ter automatically. The BOOT_IMAGE parameter is also
243 stripped.
244 --module=mod arg1 arg2 ...
246 Load module mod with command-line arguments arg1 arg2 ...
247 This parameter can be specified multiple times.
248
251 --console-serial
252 Enable the serial console.
253 --console-vga
255 Enable the VGA console.
256 --elf32-core-headers
258 Prepare core headers in ELF32 format.
259 --elf64-core-headers
261 Prepare core headers in ELF64 format.
262 --reset-vga
264 Attempt to reset a standard VGA device.
265 --serial=port
267 Specify the serial port for debug output.
268 --serial-baud=baud_rate
270 Specify the baud rate of the serial port.
271Linux April 2006 kexec(8)