1.. _readme: 2 3Linux kernel release 4.x <http://kernel.org/> 4============================================= 5 6These are the release notes for Linux version 4. Read them carefully, 7as they tell you what this is all about, explain how to install the 8kernel, and what to do if something goes wrong. 9 10What is Linux? 11-------------- 12 13 Linux is a clone of the operating system Unix, written from scratch by 14 Linus Torvalds with assistance from a loosely-knit team of hackers across 15 the Net. It aims towards POSIX and Single UNIX Specification compliance. 16 17 It has all the features you would expect in a modern fully-fledged Unix, 18 including true multitasking, virtual memory, shared libraries, demand 19 loading, shared copy-on-write executables, proper memory management, 20 and multistack networking including IPv4 and IPv6. 21 22 It is distributed under the GNU General Public License v2 - see the 23 accompanying COPYING file for more details. 24 25On what hardware does it run? 26----------------------------- 27 28 Although originally developed first for 32-bit x86-based PCs (386 or higher), 29 today Linux also runs on (at least) the Compaq Alpha AXP, Sun SPARC and 30 UltraSPARC, Motorola 68000, PowerPC, PowerPC64, ARM, Hitachi SuperH, Cell, 31 IBM S/390, MIPS, HP PA-RISC, Intel IA-64, DEC VAX, AMD x86-64 Xtensa, and 32 ARC architectures. 33 34 Linux is easily portable to most general-purpose 32- or 64-bit architectures 35 as long as they have a paged memory management unit (PMMU) and a port of the 36 GNU C compiler (gcc) (part of The GNU Compiler Collection, GCC). Linux has 37 also been ported to a number of architectures without a PMMU, although 38 functionality is then obviously somewhat limited. 39 Linux has also been ported to itself. You can now run the kernel as a 40 userspace application - this is called UserMode Linux (UML). 41 42Documentation 43------------- 44 45 - There is a lot of documentation available both in electronic form on 46 the Internet and in books, both Linux-specific and pertaining to 47 general UNIX questions. I'd recommend looking into the documentation 48 subdirectories on any Linux FTP site for the LDP (Linux Documentation 49 Project) books. This README is not meant to be documentation on the 50 system: there are much better sources available. 51 52 - There are various README files in the Documentation/ subdirectory: 53 these typically contain kernel-specific installation notes for some 54 drivers for example. See Documentation/00-INDEX for a list of what 55 is contained in each file. Please read the 56 :ref:`Documentation/process/changes.rst <changes>` file, as it 57 contains information about the problems, which may result by upgrading 58 your kernel. 59 60Installing the kernel source 61---------------------------- 62 63 - If you install the full sources, put the kernel tarball in a 64 directory where you have permissions (e.g. your home directory) and 65 unpack it:: 66 67 xz -cd linux-4.X.tar.xz | tar xvf - 68 69 Replace "X" with the version number of the latest kernel. 70 71 Do NOT use the /usr/src/linux area! This area has a (usually 72 incomplete) set of kernel headers that are used by the library header 73 files. They should match the library, and not get messed up by 74 whatever the kernel-du-jour happens to be. 75 76 - You can also upgrade between 4.x releases by patching. Patches are 77 distributed in the xz format. To install by patching, get all the 78 newer patch files, enter the top level directory of the kernel source 79 (linux-4.X) and execute:: 80 81 xz -cd ../patch-4.x.xz | patch -p1 82 83 Replace "x" for all versions bigger than the version "X" of your current 84 source tree, **in_order**, and you should be ok. You may want to remove 85 the backup files (some-file-name~ or some-file-name.orig), and make sure 86 that there are no failed patches (some-file-name# or some-file-name.rej). 87 If there are, either you or I have made a mistake. 88 89 Unlike patches for the 4.x kernels, patches for the 4.x.y kernels 90 (also known as the -stable kernels) are not incremental but instead apply 91 directly to the base 4.x kernel. For example, if your base kernel is 4.0 92 and you want to apply the 4.0.3 patch, you must not first apply the 4.0.1 93 and 4.0.2 patches. Similarly, if you are running kernel version 4.0.2 and 94 want to jump to 4.0.3, you must first reverse the 4.0.2 patch (that is, 95 patch -R) **before** applying the 4.0.3 patch. You can read more on this in 96 :ref:`Documentation/process/applying-patches.rst <applying_patches>`. 97 98 Alternatively, the script patch-kernel can be used to automate this 99 process. It determines the current kernel version and applies any 100 patches found:: 101 102 linux/scripts/patch-kernel linux 103 104 The first argument in the command above is the location of the 105 kernel source. Patches are applied from the current directory, but 106 an alternative directory can be specified as the second argument. 107 108 - Make sure you have no stale .o files and dependencies lying around:: 109 110 cd linux 111 make mrproper 112 113 You should now have the sources correctly installed. 114 115Software requirements 116--------------------- 117 118 Compiling and running the 4.x kernels requires up-to-date 119 versions of various software packages. Consult 120 :ref:`Documentation/process/changes.rst <changes>` for the minimum version numbers 121 required and how to get updates for these packages. Beware that using 122 excessively old versions of these packages can cause indirect 123 errors that are very difficult to track down, so don't assume that 124 you can just update packages when obvious problems arise during 125 build or operation. 126 127Build directory for the kernel 128------------------------------ 129 130 When compiling the kernel, all output files will per default be 131 stored together with the kernel source code. 132 Using the option ``make O=output/dir`` allows you to specify an alternate 133 place for the output files (including .config). 134 Example:: 135 136 kernel source code: /usr/src/linux-4.X 137 build directory: /home/name/build/kernel 138 139 To configure and build the kernel, use:: 140 141 cd /usr/src/linux-4.X 142 make O=/home/name/build/kernel menuconfig 143 make O=/home/name/build/kernel 144 sudo make O=/home/name/build/kernel modules_install install 145 146 Please note: If the ``O=output/dir`` option is used, then it must be 147 used for all invocations of make. 148 149Configuring the kernel 150---------------------- 151 152 Do not skip this step even if you are only upgrading one minor 153 version. New configuration options are added in each release, and 154 odd problems will turn up if the configuration files are not set up 155 as expected. If you want to carry your existing configuration to a 156 new version with minimal work, use ``make oldconfig``, which will 157 only ask you for the answers to new questions. 158 159 - Alternative configuration commands are:: 160 161 "make config" Plain text interface. 162 163 "make menuconfig" Text based color menus, radiolists & dialogs. 164 165 "make nconfig" Enhanced text based color menus. 166 167 "make xconfig" Qt based configuration tool. 168 169 "make gconfig" GTK+ based configuration tool. 170 171 "make oldconfig" Default all questions based on the contents of 172 your existing ./.config file and asking about 173 new config symbols. 174 175 "make olddefconfig" 176 Like above, but sets new symbols to their default 177 values without prompting. 178 179 "make defconfig" Create a ./.config file by using the default 180 symbol values from either arch/$ARCH/defconfig 181 or arch/$ARCH/configs/${PLATFORM}_defconfig, 182 depending on the architecture. 183 184 "make ${PLATFORM}_defconfig" 185 Create a ./.config file by using the default 186 symbol values from 187 arch/$ARCH/configs/${PLATFORM}_defconfig. 188 Use "make help" to get a list of all available 189 platforms of your architecture. 190 191 "make allyesconfig" 192 Create a ./.config file by setting symbol 193 values to 'y' as much as possible. 194 195 "make allmodconfig" 196 Create a ./.config file by setting symbol 197 values to 'm' as much as possible. 198 199 "make allnoconfig" Create a ./.config file by setting symbol 200 values to 'n' as much as possible. 201 202 "make randconfig" Create a ./.config file by setting symbol 203 values to random values. 204 205 "make localmodconfig" Create a config based on current config and 206 loaded modules (lsmod). Disables any module 207 option that is not needed for the loaded modules. 208 209 To create a localmodconfig for another machine, 210 store the lsmod of that machine into a file 211 and pass it in as a LSMOD parameter. 212 213 target$ lsmod > /tmp/mylsmod 214 target$ scp /tmp/mylsmod host:/tmp 215 216 host$ make LSMOD=/tmp/mylsmod localmodconfig 217 218 The above also works when cross compiling. 219 220 "make localyesconfig" Similar to localmodconfig, except it will convert 221 all module options to built in (=y) options. 222 223 "make kvmconfig" Enable additional options for kvm guest kernel support. 224 225 "make xenconfig" Enable additional options for xen dom0 guest kernel 226 support. 227 228 "make tinyconfig" Configure the tiniest possible kernel. 229 230 You can find more information on using the Linux kernel config tools 231 in Documentation/kbuild/kconfig.txt. 232 233 - NOTES on ``make config``: 234 235 - Having unnecessary drivers will make the kernel bigger, and can 236 under some circumstances lead to problems: probing for a 237 nonexistent controller card may confuse your other controllers. 238 239 - A kernel with math-emulation compiled in will still use the 240 coprocessor if one is present: the math emulation will just 241 never get used in that case. The kernel will be slightly larger, 242 but will work on different machines regardless of whether they 243 have a math coprocessor or not. 244 245 - The "kernel hacking" configuration details usually result in a 246 bigger or slower kernel (or both), and can even make the kernel 247 less stable by configuring some routines to actively try to 248 break bad code to find kernel problems (kmalloc()). Thus you 249 should probably answer 'n' to the questions for "development", 250 "experimental", or "debugging" features. 251 252Compiling the kernel 253-------------------- 254 255 - Make sure you have at least gcc 3.2 available. 256 For more information, refer to :ref:`Documentation/process/changes.rst <changes>`. 257 258 Please note that you can still run a.out user programs with this kernel. 259 260 - Do a ``make`` to create a compressed kernel image. It is also 261 possible to do ``make install`` if you have lilo installed to suit the 262 kernel makefiles, but you may want to check your particular lilo setup first. 263 264 To do the actual install, you have to be root, but none of the normal 265 build should require that. Don't take the name of root in vain. 266 267 - If you configured any of the parts of the kernel as ``modules``, you 268 will also have to do ``make modules_install``. 269 270 - Verbose kernel compile/build output: 271 272 Normally, the kernel build system runs in a fairly quiet mode (but not 273 totally silent). However, sometimes you or other kernel developers need 274 to see compile, link, or other commands exactly as they are executed. 275 For this, use "verbose" build mode. This is done by passing 276 ``V=1`` to the ``make`` command, e.g.:: 277 278 make V=1 all 279 280 To have the build system also tell the reason for the rebuild of each 281 target, use ``V=2``. The default is ``V=0``. 282 283 - Keep a backup kernel handy in case something goes wrong. This is 284 especially true for the development releases, since each new release 285 contains new code which has not been debugged. Make sure you keep a 286 backup of the modules corresponding to that kernel, as well. If you 287 are installing a new kernel with the same version number as your 288 working kernel, make a backup of your modules directory before you 289 do a ``make modules_install``. 290 291 Alternatively, before compiling, use the kernel config option 292 "LOCALVERSION" to append a unique suffix to the regular kernel version. 293 LOCALVERSION can be set in the "General Setup" menu. 294 295 - In order to boot your new kernel, you'll need to copy the kernel 296 image (e.g. .../linux/arch/x86/boot/bzImage after compilation) 297 to the place where your regular bootable kernel is found. 298 299 - Booting a kernel directly from a floppy without the assistance of a 300 bootloader such as LILO, is no longer supported. 301 302 If you boot Linux from the hard drive, chances are you use LILO, which 303 uses the kernel image as specified in the file /etc/lilo.conf. The 304 kernel image file is usually /vmlinuz, /boot/vmlinuz, /bzImage or 305 /boot/bzImage. To use the new kernel, save a copy of the old image 306 and copy the new image over the old one. Then, you MUST RERUN LILO 307 to update the loading map! If you don't, you won't be able to boot 308 the new kernel image. 309 310 Reinstalling LILO is usually a matter of running /sbin/lilo. 311 You may wish to edit /etc/lilo.conf to specify an entry for your 312 old kernel image (say, /vmlinux.old) in case the new one does not 313 work. See the LILO docs for more information. 314 315 After reinstalling LILO, you should be all set. Shutdown the system, 316 reboot, and enjoy! 317 318 If you ever need to change the default root device, video mode, 319 ramdisk size, etc. in the kernel image, use the ``rdev`` program (or 320 alternatively the LILO boot options when appropriate). No need to 321 recompile the kernel to change these parameters. 322 323 - Reboot with the new kernel and enjoy. 324 325If something goes wrong 326----------------------- 327 328 - If you have problems that seem to be due to kernel bugs, please check 329 the file MAINTAINERS to see if there is a particular person associated 330 with the part of the kernel that you are having trouble with. If there 331 isn't anyone listed there, then the second best thing is to mail 332 them to me (torvalds@linux-foundation.org), and possibly to any other 333 relevant mailing-list or to the newsgroup. 334 335 - In all bug-reports, *please* tell what kernel you are talking about, 336 how to duplicate the problem, and what your setup is (use your common 337 sense). If the problem is new, tell me so, and if the problem is 338 old, please try to tell me when you first noticed it. 339 340 - If the bug results in a message like:: 341 342 unable to handle kernel paging request at address C0000010 343 Oops: 0002 344 EIP: 0010:XXXXXXXX 345 eax: xxxxxxxx ebx: xxxxxxxx ecx: xxxxxxxx edx: xxxxxxxx 346 esi: xxxxxxxx edi: xxxxxxxx ebp: xxxxxxxx 347 ds: xxxx es: xxxx fs: xxxx gs: xxxx 348 Pid: xx, process nr: xx 349 xx xx xx xx xx xx xx xx xx xx 350 351 or similar kernel debugging information on your screen or in your 352 system log, please duplicate it *exactly*. The dump may look 353 incomprehensible to you, but it does contain information that may 354 help debugging the problem. The text above the dump is also 355 important: it tells something about why the kernel dumped code (in 356 the above example, it's due to a bad kernel pointer). More information 357 on making sense of the dump is in Documentation/admin-guide/bug-hunting.rst 358 359 - If you compiled the kernel with CONFIG_KALLSYMS you can send the dump 360 as is, otherwise you will have to use the ``ksymoops`` program to make 361 sense of the dump (but compiling with CONFIG_KALLSYMS is usually preferred). 362 This utility can be downloaded from 363 https://www.kernel.org/pub/linux/utils/kernel/ksymoops/ . 364 Alternatively, you can do the dump lookup by hand: 365 366 - In debugging dumps like the above, it helps enormously if you can 367 look up what the EIP value means. The hex value as such doesn't help 368 me or anybody else very much: it will depend on your particular 369 kernel setup. What you should do is take the hex value from the EIP 370 line (ignore the ``0010:``), and look it up in the kernel namelist to 371 see which kernel function contains the offending address. 372 373 To find out the kernel function name, you'll need to find the system 374 binary associated with the kernel that exhibited the symptom. This is 375 the file 'linux/vmlinux'. To extract the namelist and match it against 376 the EIP from the kernel crash, do:: 377 378 nm vmlinux | sort | less 379 380 This will give you a list of kernel addresses sorted in ascending 381 order, from which it is simple to find the function that contains the 382 offending address. Note that the address given by the kernel 383 debugging messages will not necessarily match exactly with the 384 function addresses (in fact, that is very unlikely), so you can't 385 just 'grep' the list: the list will, however, give you the starting 386 point of each kernel function, so by looking for the function that 387 has a starting address lower than the one you are searching for but 388 is followed by a function with a higher address you will find the one 389 you want. In fact, it may be a good idea to include a bit of 390 "context" in your problem report, giving a few lines around the 391 interesting one. 392 393 If you for some reason cannot do the above (you have a pre-compiled 394 kernel image or similar), telling me as much about your setup as 395 possible will help. Please read the :ref:`admin-guide/reporting-bugs.rst <reportingbugs>` 396 document for details. 397 398 - Alternatively, you can use gdb on a running kernel. (read-only; i.e. you 399 cannot change values or set break points.) To do this, first compile the 400 kernel with -g; edit arch/x86/Makefile appropriately, then do a ``make 401 clean``. You'll also need to enable CONFIG_PROC_FS (via ``make config``). 402 403 After you've rebooted with the new kernel, do ``gdb vmlinux /proc/kcore``. 404 You can now use all the usual gdb commands. The command to look up the 405 point where your system crashed is ``l *0xXXXXXXXX``. (Replace the XXXes 406 with the EIP value.) 407 408 gdb'ing a non-running kernel currently fails because ``gdb`` (wrongly) 409 disregards the starting offset for which the kernel is compiled. 410