1 # SPDX-License-Identifier: GPL-2.0
3 # Configuration for initramfs
6 config INITRAMFS_SOURCE
7 string "Initramfs source file(s)"
10 This can be either a single cpio archive with a .cpio suffix or a
11 space-separated list of directories and files for building the
12 initramfs image. A cpio archive should contain a filesystem archive
13 to be used as an initramfs image. Directories should contain a
14 filesystem layout to be included in the initramfs image. Files
15 should contain entries according to the format described by the
16 "usr/gen_init_cpio" program in the kernel tree.
18 When multiple directories and files are specified then the
19 initramfs image will be the aggregate of all of them.
21 See <file:Documentation/driver-api/early-userspace/early_userspace_support.rst> for more details.
23 If you are not sure, leave it blank.
25 config INITRAMFS_FORCE
26 bool "Ignore the initramfs passed by the bootloader"
27 depends on CMDLINE_EXTEND || CMDLINE_FORCE
29 This option causes the kernel to ignore the initramfs image
30 (or initrd image) passed to it by the bootloader. This is
31 analogous to CMDLINE_FORCE, which is found on some architectures,
32 and is useful if you cannot or don't want to change the image
33 your bootloader passes to the kernel.
35 config INITRAMFS_ROOT_UID
36 int "User ID to map to 0 (user root)"
37 depends on INITRAMFS_SOURCE!=""
40 If INITRAMFS_SOURCE points to a directory, files owned by this UID
41 (-1 = current user) will be owned by root in the resulting image.
43 If you are not sure, leave it set to "0".
45 config INITRAMFS_ROOT_GID
46 int "Group ID to map to 0 (group root)"
47 depends on INITRAMFS_SOURCE!=""
50 If INITRAMFS_SOURCE points to a directory, files owned by this GID
51 (-1 = current group) will be owned by root in the resulting image.
53 If you are not sure, leave it set to "0".
56 bool "Support initial ramdisk/ramfs compressed using gzip"
58 select DECOMPRESS_GZIP
60 Support loading of a gzip encoded initial ramdisk or cpio buffer.
64 bool "Support initial ramdisk/ramfs compressed using bzip2"
66 select DECOMPRESS_BZIP2
68 Support loading of a bzip2 encoded initial ramdisk or cpio buffer
72 bool "Support initial ramdisk/ramfs compressed using LZMA"
74 select DECOMPRESS_LZMA
76 Support loading of a LZMA encoded initial ramdisk or cpio buffer
80 bool "Support initial ramdisk/ramfs compressed using XZ"
84 Support loading of a XZ encoded initial ramdisk or cpio buffer.
88 bool "Support initial ramdisk/ramfs compressed using LZO"
92 Support loading of a LZO encoded initial ramdisk or cpio buffer
96 bool "Support initial ramdisk/ramfs compressed using LZ4"
100 Support loading of a LZ4 encoded initial ramdisk or cpio buffer
104 prompt "Built-in initramfs compression mode"
106 This option allows you to decide by which algorithm the builtin
107 initramfs will be compressed. Several compression algorithms are
108 available, which differ in efficiency, compression and
109 decompression speed. Compression speed is only relevant
110 when building a kernel. Decompression speed is relevant at
111 each boot. Also the memory usage during decompression may become
112 relevant on memory constrained systems. This is usually based on the
113 dictionary size of the algorithm with algorithms like XZ and LZMA
114 featuring large dictionary sizes.
116 High compression options are mostly useful for users who are
117 low on RAM, since it reduces the memory consumption during
120 Keep in mind that your build system needs to provide the appropriate
121 compression tool to compress the generated initram cpio file for
124 If in doubt, select 'None'
126 config INITRAMFS_COMPRESSION_NONE
129 Do not compress the built-in initramfs at all. This may sound wasteful
130 in space, but, you should be aware that the built-in initramfs will be
131 compressed at a later stage anyways along with the rest of the kernel,
132 on those architectures that support this. However, not compressing the
133 initramfs may lead to slightly higher memory consumption during a
134 short time at boot, while both the cpio image and the unpacked
135 filesystem image will be present in memory simultaneously
137 config INITRAMFS_COMPRESSION_GZIP
141 Use the old and well tested gzip compression algorithm. Gzip provides
142 a good balance between compression ratio and decompression speed and
143 has a reasonable compression speed. It is also more likely to be
144 supported by your build system as the gzip tool is present by default
147 config INITRAMFS_COMPRESSION_BZIP2
151 It's compression ratio and speed is intermediate. Decompression speed
152 is slowest among the choices. The initramfs size is about 10% smaller
153 with bzip2, in comparison to gzip. Bzip2 uses a large amount of
154 memory. For modern kernels you will need at least 8MB RAM or more for
157 If you choose this, keep in mind that you need to have the bzip2 tool
158 available to be able to compress the initram.
160 config INITRAMFS_COMPRESSION_LZMA
164 This algorithm's compression ratio is best but has a large dictionary
165 size which might cause issues in memory constrained systems.
166 Decompression speed is between the other choices. Compression is
167 slowest. The initramfs size is about 33% smaller with LZMA in
170 If you choose this, keep in mind that you may need to install the xz
171 or lzma tools to be able to compress the initram.
173 config INITRAMFS_COMPRESSION_XZ
177 XZ uses the LZMA2 algorithm and has a large dictionary which may cause
178 problems on memory constrained systems. The initramfs size is about
179 30% smaller with XZ in comparison to gzip. Decompression speed is
180 better than that of bzip2 but worse than gzip and LZO. Compression is
183 If you choose this, keep in mind that you may need to install the xz
184 tool to be able to compress the initram.
186 config INITRAMFS_COMPRESSION_LZO
190 It's compression ratio is the second poorest amongst the choices. The
191 kernel size is about 10% bigger than gzip. Despite that, it's
192 decompression speed is the second fastest and it's compression speed
195 If you choose this, keep in mind that you may need to install the lzop
196 tool to be able to compress the initram.
198 config INITRAMFS_COMPRESSION_LZ4
202 It's compression ratio is the poorest amongst the choices. The kernel
203 size is about 15% bigger than gzip; however its decompression speed
206 If you choose this, keep in mind that most distros don't provide lz4
207 by default which could cause a build failure.