1Linux kernel release 4.x <http://kernel.org/> 2============================================= 3 4These are the release notes for Linux version 4. Read them carefully, 5as they tell you what this is all about, explain how to install the 6kernel, and what to do if something goes wrong. 7 8What is Linux? 9-------------- 10 11 Linux is a clone of the operating system Unix, written from scratch by 12 Linus Torvalds with assistance from a loosely-knit team of hackers across 13 the Net. It aims towards POSIX and Single UNIX Specification compliance. 14 15 It has all the features you would expect in a modern fully-fledged Unix, 16 including true multitasking, virtual memory, shared libraries, demand 17 loading, shared copy-on-write executables, proper memory management, 18 and multistack networking including IPv4 and IPv6. 19 20 It is distributed under the GNU General Public License - see the 21 accompanying COPYING file for more details. 22 23On what hardware does it run? 24----------------------------- 25 26 Although originally developed first for 32-bit x86-based PCs (386 or higher), 27 today Linux also runs on (at least) the Compaq Alpha AXP, Sun SPARC and 28 UltraSPARC, Motorola 68000, PowerPC, PowerPC64, ARM, Hitachi SuperH, Cell, 29 IBM S/390, MIPS, HP PA-RISC, Intel IA-64, DEC VAX, AMD x86-64, AXIS CRIS, 30 Xtensa, Tilera TILE, AVR32, ARC and Renesas M32R architectures. 31 32 Linux is easily portable to most general-purpose 32- or 64-bit architectures 33 as long as they have a paged memory management unit (PMMU) and a port of the 34 GNU C compiler (gcc) (part of The GNU Compiler Collection, GCC). Linux has 35 also been ported to a number of architectures without a PMMU, although 36 functionality is then obviously somewhat limited. 37 Linux has also been ported to itself. You can now run the kernel as a 38 userspace application - this is called UserMode Linux (UML). 39 40Documentation 41------------- 42 43 - There is a lot of documentation available both in electronic form on 44 the Internet and in books, both Linux-specific and pertaining to 45 general UNIX questions. I'd recommend looking into the documentation 46 subdirectories on any Linux FTP site for the LDP (Linux Documentation 47 Project) books. This README is not meant to be documentation on the 48 system: there are much better sources available. 49 50 - There are various README files in the Documentation/ subdirectory: 51 these typically contain kernel-specific installation notes for some 52 drivers for example. See Documentation/00-INDEX for a list of what 53 is contained in each file. Please read the Changes file, as it 54 contains information about the problems, which may result by upgrading 55 your kernel. 56 57 - The Documentation/DocBook/ subdirectory contains several guides for 58 kernel developers and users. These guides can be rendered in a 59 number of formats: PostScript (.ps), PDF, HTML, & man-pages, among others. 60 After installation, ``make psdocs``, ``make pdfdocs``, ``make htmldocs``, 61 or ``make mandocs`` will render the documentation in the requested format. 62 63Installing the kernel source 64---------------------------- 65 66 - If you install the full sources, put the kernel tarball in a 67 directory where you have permissions (e.g. your home directory) and 68 unpack it:: 69 70 xz -cd linux-4.X.tar.xz | tar xvf - 71 72 Replace "X" with the version number of the latest kernel. 73 74 Do NOT use the /usr/src/linux area! This area has a (usually 75 incomplete) set of kernel headers that are used by the library header 76 files. They should match the library, and not get messed up by 77 whatever the kernel-du-jour happens to be. 78 79 - You can also upgrade between 4.x releases by patching. Patches are 80 distributed in the xz format. To install by patching, get all the 81 newer patch files, enter the top level directory of the kernel source 82 (linux-4.X) and execute:: 83 84 xz -cd ../patch-4.x.xz | patch -p1 85 86 Replace "x" for all versions bigger than the version "X" of your current 87 source tree, **in_order**, and you should be ok. You may want to remove 88 the backup files (some-file-name~ or some-file-name.orig), and make sure 89 that there are no failed patches (some-file-name# or some-file-name.rej). 90 If there are, either you or I have made a mistake. 91 92 Unlike patches for the 4.x kernels, patches for the 4.x.y kernels 93 (also known as the -stable kernels) are not incremental but instead apply 94 directly to the base 4.x kernel. For example, if your base kernel is 4.0 95 and you want to apply the 4.0.3 patch, you must not first apply the 4.0.1 96 and 4.0.2 patches. Similarly, if you are running kernel version 4.0.2 and 97 want to jump to 4.0.3, you must first reverse the 4.0.2 patch (that is, 98 patch -R) **before** applying the 4.0.3 patch. You can read more on this in 99 :ref:`Documentation/applying-patches.txt <applying_patches>`. 100 101 Alternatively, the script patch-kernel can be used to automate this 102 process. It determines the current kernel version and applies any 103 patches found:: 104 105 linux/scripts/patch-kernel linux 106 107 The first argument in the command above is the location of the 108 kernel source. Patches are applied from the current directory, but 109 an alternative directory can be specified as the second argument. 110 111 - Make sure you have no stale .o files and dependencies lying around:: 112 113 cd linux 114 make mrproper 115 116 You should now have the sources correctly installed. 117 118Software requirements 119--------------------- 120 121 Compiling and running the 4.x kernels requires up-to-date 122 versions of various software packages. Consult 123 :ref:`Documentation/Changes <changes>` for the minimum version numbers 124 required and how to get updates for these packages. Beware that using 125 excessively old versions of these packages can cause indirect 126 errors that are very difficult to track down, so don't assume that 127 you can just update packages when obvious problems arise during 128 build or operation. 129 130Build directory for the kernel 131------------------------------ 132 133 When compiling the kernel, all output files will per default be 134 stored together with the kernel source code. 135 Using the option ``make O=output/dir`` allows you to specify an alternate 136 place for the output files (including .config). 137 Example:: 138 139 kernel source code: /usr/src/linux-4.X 140 build directory: /home/name/build/kernel 141 142 To configure and build the kernel, use:: 143 144 cd /usr/src/linux-4.X 145 make O=/home/name/build/kernel menuconfig 146 make O=/home/name/build/kernel 147 sudo make O=/home/name/build/kernel modules_install install 148 149 Please note: If the ``O=output/dir`` option is used, then it must be 150 used for all invocations of make. 151 152Configuring the kernel 153---------------------- 154 155 Do not skip this step even if you are only upgrading one minor 156 version. New configuration options are added in each release, and 157 odd problems will turn up if the configuration files are not set up 158 as expected. If you want to carry your existing configuration to a 159 new version with minimal work, use ``make oldconfig``, which will 160 only ask you for the answers to new questions. 161 162 - Alternative configuration commands are:: 163 164 "make config" Plain text interface. 165 166 "make menuconfig" Text based color menus, radiolists & dialogs. 167 168 "make nconfig" Enhanced text based color menus. 169 170 "make xconfig" Qt based configuration tool. 171 172 "make gconfig" GTK+ based configuration tool. 173 174 "make oldconfig" Default all questions based on the contents of 175 your existing ./.config file and asking about 176 new config symbols. 177 178 "make silentoldconfig" 179 Like above, but avoids cluttering the screen 180 with questions already answered. 181 Additionally updates the dependencies. 182 183 "make olddefconfig" 184 Like above, but sets new symbols to their default 185 values without prompting. 186 187 "make defconfig" Create a ./.config file by using the default 188 symbol values from either arch/$ARCH/defconfig 189 or arch/$ARCH/configs/${PLATFORM}_defconfig, 190 depending on the architecture. 191 192 "make ${PLATFORM}_defconfig" 193 Create a ./.config file by using the default 194 symbol values from 195 arch/$ARCH/configs/${PLATFORM}_defconfig. 196 Use "make help" to get a list of all available 197 platforms of your architecture. 198 199 "make allyesconfig" 200 Create a ./.config file by setting symbol 201 values to 'y' as much as possible. 202 203 "make allmodconfig" 204 Create a ./.config file by setting symbol 205 values to 'm' as much as possible. 206 207 "make allnoconfig" Create a ./.config file by setting symbol 208 values to 'n' as much as possible. 209 210 "make randconfig" Create a ./.config file by setting symbol 211 values to random values. 212 213 "make localmodconfig" Create a config based on current config and 214 loaded modules (lsmod). Disables any module 215 option that is not needed for the loaded modules. 216 217 To create a localmodconfig for another machine, 218 store the lsmod of that machine into a file 219 and pass it in as a LSMOD parameter. 220 221 target$ lsmod > /tmp/mylsmod 222 target$ scp /tmp/mylsmod host:/tmp 223 224 host$ make LSMOD=/tmp/mylsmod localmodconfig 225 226 The above also works when cross compiling. 227 228 "make localyesconfig" Similar to localmodconfig, except it will convert 229 all module options to built in (=y) options. 230 231 You can find more information on using the Linux kernel config tools 232 in Documentation/kbuild/kconfig.txt. 233 234 - NOTES on ``make config``: 235 236 - Having unnecessary drivers will make the kernel bigger, and can 237 under some circumstances lead to problems: probing for a 238 nonexistent controller card may confuse your other controllers 239 240 - A kernel with math-emulation compiled in will still use the 241 coprocessor if one is present: the math emulation will just 242 never get used in that case. The kernel will be slightly larger, 243 but will work on different machines regardless of whether they 244 have a math coprocessor or not. 245 246 - The "kernel hacking" configuration details usually result in a 247 bigger or slower kernel (or both), and can even make the kernel 248 less stable by configuring some routines to actively try to 249 break bad code to find kernel problems (kmalloc()). Thus you 250 should probably answer 'n' to the questions for "development", 251 "experimental", or "debugging" features. 252 253Compiling the kernel 254-------------------- 255 256 - Make sure you have at least gcc 3.2 available. 257 For more information, refer to :ref:`Documentation/Changes <changes>`. 258 259 Please note that you can still run a.out user programs with this kernel. 260 261 - Do a ``make`` to create a compressed kernel image. It is also 262 possible to do ``make install`` if you have lilo installed to suit the 263 kernel makefiles, but you may want to check your particular lilo setup first. 264 265 To do the actual install, you have to be root, but none of the normal 266 build should require that. Don't take the name of root in vain. 267 268 - If you configured any of the parts of the kernel as ``modules``, you 269 will also have to do ``make modules_install``. 270 271 - Verbose kernel compile/build output: 272 273 Normally, the kernel build system runs in a fairly quiet mode (but not 274 totally silent). However, sometimes you or other kernel developers need 275 to see compile, link, or other commands exactly as they are executed. 276 For this, use "verbose" build mode. This is done by passing 277 ``V=1`` to the ``make`` command, e.g.:: 278 279 make V=1 all 280 281 To have the build system also tell the reason for the rebuild of each 282 target, use ``V=2``. The default is ``V=0``. 283 284 - Keep a backup kernel handy in case something goes wrong. This is 285 especially true for the development releases, since each new release 286 contains new code which has not been debugged. Make sure you keep a 287 backup of the modules corresponding to that kernel, as well. If you 288 are installing a new kernel with the same version number as your 289 working kernel, make a backup of your modules directory before you 290 do a ``make modules_install``. 291 292 Alternatively, before compiling, use the kernel config option 293 "LOCALVERSION" to append a unique suffix to the regular kernel version. 294 LOCALVERSION can be set in the "General Setup" menu. 295 296 - In order to boot your new kernel, you'll need to copy the kernel 297 image (e.g. .../linux/arch/x86/boot/bzImage after compilation) 298 to the place where your regular bootable kernel is found. 299 300 - Booting a kernel directly from a floppy without the assistance of a 301 bootloader such as LILO, is no longer supported. 302 303 If you boot Linux from the hard drive, chances are you use LILO, which 304 uses the kernel image as specified in the file /etc/lilo.conf. The 305 kernel image file is usually /vmlinuz, /boot/vmlinuz, /bzImage or 306 /boot/bzImage. To use the new kernel, save a copy of the old image 307 and copy the new image over the old one. Then, you MUST RERUN LILO 308 to update the loading map! If you don't, you won't be able to boot 309 the new kernel image. 310 311 Reinstalling LILO is usually a matter of running /sbin/lilo. 312 You may wish to edit /etc/lilo.conf to specify an entry for your 313 old kernel image (say, /vmlinux.old) in case the new one does not 314 work. See the LILO docs for more information. 315 316 After reinstalling LILO, you should be all set. Shutdown the system, 317 reboot, and enjoy! 318 319 If you ever need to change the default root device, video mode, 320 ramdisk size, etc. in the kernel image, use the ``rdev`` program (or 321 alternatively the LILO boot options when appropriate). No need to 322 recompile the kernel to change these parameters. 323 324 - Reboot with the new kernel and enjoy. 325 326If something goes wrong 327----------------------- 328 329 - If you have problems that seem to be due to kernel bugs, please check 330 the file MAINTAINERS to see if there is a particular person associated 331 with the part of the kernel that you are having trouble with. If there 332 isn't anyone listed there, then the second best thing is to mail 333 them to me (torvalds@linux-foundation.org), and possibly to any other 334 relevant mailing-list or to the newsgroup. 335 336 - In all bug-reports, *please* tell what kernel you are talking about, 337 how to duplicate the problem, and what your setup is (use your common 338 sense). If the problem is new, tell me so, and if the problem is 339 old, please try to tell me when you first noticed it. 340 341 - If the bug results in a message like:: 342 343 unable to handle kernel paging request at address C0000010 344 Oops: 0002 345 EIP: 0010:XXXXXXXX 346 eax: xxxxxxxx ebx: xxxxxxxx ecx: xxxxxxxx edx: xxxxxxxx 347 esi: xxxxxxxx edi: xxxxxxxx ebp: xxxxxxxx 348 ds: xxxx es: xxxx fs: xxxx gs: xxxx 349 Pid: xx, process nr: xx 350 xx xx xx xx xx xx xx xx xx xx 351 352 or similar kernel debugging information on your screen or in your 353 system log, please duplicate it *exactly*. The dump may look 354 incomprehensible to you, but it does contain information that may 355 help debugging the problem. The text above the dump is also 356 important: it tells something about why the kernel dumped code (in 357 the above example, it's due to a bad kernel pointer). More information 358 on making sense of the dump is in Documentation/oops-tracing.txt 359 360 - If you compiled the kernel with CONFIG_KALLSYMS you can send the dump 361 as is, otherwise you will have to use the ``ksymoops`` program to make 362 sense of the dump (but compiling with CONFIG_KALLSYMS is usually preferred). 363 This utility can be downloaded from 364 ftp://ftp.<country>.kernel.org/pub/linux/utils/kernel/ksymoops/ . 365 Alternatively, you can do the dump lookup by hand: 366 367 - In debugging dumps like the above, it helps enormously if you can 368 look up what the EIP value means. The hex value as such doesn't help 369 me or anybody else very much: it will depend on your particular 370 kernel setup. What you should do is take the hex value from the EIP 371 line (ignore the ``0010:``), and look it up in the kernel namelist to 372 see which kernel function contains the offending address. 373 374 To find out the kernel function name, you'll need to find the system 375 binary associated with the kernel that exhibited the symptom. This is 376 the file 'linux/vmlinux'. To extract the namelist and match it against 377 the EIP from the kernel crash, do:: 378 379 nm vmlinux | sort | less 380 381 This will give you a list of kernel addresses sorted in ascending 382 order, from which it is simple to find the function that contains the 383 offending address. Note that the address given by the kernel 384 debugging messages will not necessarily match exactly with the 385 function addresses (in fact, that is very unlikely), so you can't 386 just 'grep' the list: the list will, however, give you the starting 387 point of each kernel function, so by looking for the function that 388 has a starting address lower than the one you are searching for but 389 is followed by a function with a higher address you will find the one 390 you want. In fact, it may be a good idea to include a bit of 391 "context" in your problem report, giving a few lines around the 392 interesting one. 393 394 If you for some reason cannot do the above (you have a pre-compiled 395 kernel image or similar), telling me as much about your setup as 396 possible will help. Please read the :ref:`REPORTING-BUGS <reportingbugs>` 397 document for details. 398 399 - Alternatively, you can use gdb on a running kernel. (read-only; i.e. you 400 cannot change values or set break points.) To do this, first compile the 401 kernel with -g; edit arch/x86/Makefile appropriately, then do a ``make 402 clean``. You'll also need to enable CONFIG_PROC_FS (via ``make config``). 403 404 After you've rebooted with the new kernel, do ``gdb vmlinux /proc/kcore``. 405 You can now use all the usual gdb commands. The command to look up the 406 point where your system crashed is ``l *0xXXXXXXXX``. (Replace the XXXes 407 with the EIP value.) 408 409 gdb'ing a non-running kernel currently fails because ``gdb`` (wrongly) 410 disregards the starting offset for which the kernel is compiled. 411 412