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)] [-l
10 (--load)] [-p (--load-panic)] [-u (--unload)] [-e (--exec)] [-t
11 (--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(1).
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 -e (--exec)
71 Run the currently loaded kernel.
72 -f (--force)
74 Force an immediate kexec call, do not call shutdown(1) (contrary
75 to the default action without any option parameter). This option
76 performs the same actions like executing -l and -e in one call.
77 -h (--help)
79 Open a help file for kexec.
80 -l (--load) kernel
82 Load the specified kernel into the current kernel.
83 -p (--load-panic)
85 Load the new kernel for use on panic.
86 -t (--type=type)
88 Specify that the new kernel is of this type.
89 -u (--unload)
91 Unload the current kexec target kernel. If a capture kernel is
92 being unloaded then specify -p with -u.
93 -v (--version)
95 Return the version number of the installed utility.
96 -x (--no-ifdown)
98 Shut down the running kernel, but restore the interface on
99 reload. (If this option is used, it must be specified last.)
100 --mem-min=addr
102 Specify the lowest memory address addr to load code into.
103 --mem-max=addr
105 Specify the highest memory address addr to load code into.
106
109 Beoboot-x86
110 --args-elf
112 Pass ELF boot notes.
113 --args-linux
115 Pass Linux kernel style options.
116 -d (--debug)
118 Enable debugging messages.
119 --real-mode
121 Use the kernel's real mode entry point.
122 elf-x86
124 --append=string
126 Append string to the kernel command line.
127 --command-line=string
129 Set the kernel command line to string.
130 --reuse-cmdline
132 Use the command line from the running system. When a
133 panic kernel is loaded, it strips the crashkernel parame‐
134 ter automatically. The BOOT_IMAGE parameter is also
135 stripped.
136 --initrd=file
138 Use file as the kernel's initial ramdisk.
139 --ramdisk=file
141 Use file as the kernel's initial ramdisk.
142 bzImage-x86
144 --append=string
146 Append string to the kernel command line.
147 --command-line=string
149 Set the kernel command line to string.
150 --reuse-cmdline
152 Use the command line from the running system. When a
153 panic kernel is loaded, it strips the crashkernel parame‐
154 ter automatically. The BOOT_IMAGE parameter is also
155 stripped.
156 --initrd=file
158 Use file as the kernel's initial ramdisk.
159 --ramdisk=file
161 Use file as the kernel's initial ramdisk.
162 --real-mode
164 Use real-mode entry point.
165 multiboot-x86
167 --command-line=string
169 Set the kernel command line to string.
170 --reuse-cmdline
172 Use the command line from the running system. When a
173 panic kernel is loaded, it strips the crashkernel parame‐
174 ter automatically. The BOOT_IMAGE parameter is also
175 stripped.
176 --module=mod arg1 arg2 ...
178 Load module mod with command-line arguments arg1 arg2 ...
179 This parameter can be specified multiple times.
180
183 --console-serial
184 Enable the serial console.
185 --console-vga
187 Enable the VGA console.
188 --elf32-core-headers
190 Prepare core headers in ELF32 format.
191 --elf64-core-headers
193 Prepare core headers in ELF64 format.
194 --reset-vga
196 Attempt to reset a standard VGA device.
197 --serial=port
199 Specify the serial port for debug output.
200 --serial-baud=baud_rate
202 Specify the baud rate of the serial port.
203Linux April 2006 kexec(8)