1 2XZ Utils 3======== 4 5 0. Overview 6 1. Documentation 7 1.1. Overall documentation 8 1.2. Documentation for command-line tools 9 1.3. Documentation for liblzma 10 2. Version numbering 11 3. Reporting bugs 12 4. Translations 13 5. Other implementations of the .xz format 14 6. Contact information 15 16 170. Overview 18----------- 19 20 XZ Utils provide a general-purpose data-compression library plus 21 command-line tools. The native file format is the .xz format, but 22 also the legacy .lzma format is supported. The .xz format supports 23 multiple compression algorithms, which are called "filters" in the 24 context of XZ Utils. The primary filter is currently LZMA2. With 25 typical files, XZ Utils create about 30 % smaller files than gzip. 26 27 To ease adapting support for the .xz format into existing applications 28 and scripts, the API of liblzma is somewhat similar to the API of the 29 popular zlib library. For the same reason, the command-line tool xz 30 has a command-line syntax similar to that of gzip. 31 32 When aiming for the highest compression ratio, the LZMA2 encoder uses 33 a lot of CPU time and may use, depending on the settings, even 34 hundreds of megabytes of RAM. However, in fast modes, the LZMA2 encoder 35 competes with bzip2 in compression speed, RAM usage, and compression 36 ratio. 37 38 LZMA2 is reasonably fast to decompress. It is a little slower than 39 gzip, but a lot faster than bzip2. Being fast to decompress means 40 that the .xz format is especially nice when the same file will be 41 decompressed very many times (usually on different computers), which 42 is the case e.g. when distributing software packages. In such 43 situations, it's not too bad if the compression takes some time, 44 since that needs to be done only once to benefit many people. 45 46 With some file types, combining (or "chaining") LZMA2 with an 47 additional filter can improve the compression ratio. A filter chain may 48 contain up to four filters, although usually only one or two are used. 49 For example, putting a BCJ (Branch/Call/Jump) filter before LZMA2 50 in the filter chain can improve compression ratio of executable files. 51 52 Since the .xz format allows adding new filter IDs, it is possible that 53 some day there will be a filter that is, for example, much faster to 54 compress than LZMA2 (but probably with worse compression ratio). 55 Similarly, it is possible that some day there is a filter that will 56 compress better than LZMA2. 57 58 XZ Utils supports multithreaded compression. XZ Utils doesn't support 59 multithreaded decompression yet. It has been planned though and taken 60 into account when designing the .xz file format. In the future, files 61 that were created in threaded mode can be decompressed in threaded 62 mode too. 63 64 651. Documentation 66---------------- 67 681.1. Overall documentation 69 70 README This file 71 72 INSTALL.generic Generic install instructions for those not 73 familiar with packages using GNU Autotools 74 INSTALL Installation instructions specific to XZ Utils 75 PACKAGERS Information to packagers of XZ Utils 76 77 COPYING XZ Utils copyright and license information 78 COPYING.0BSD BSD Zero Clause License 79 COPYING.GPLv2 GNU General Public License version 2 80 COPYING.GPLv3 GNU General Public License version 3 81 COPYING.LGPLv2.1 GNU Lesser General Public License version 2.1 82 83 AUTHORS The main authors of XZ Utils 84 THANKS Incomplete list of people who have helped making 85 this software 86 NEWS User-visible changes between XZ Utils releases 87 ChangeLog Detailed list of changes (commit log) 88 TODO Known bugs and some sort of to-do list 89 90 Note that only some of the above files are included in binary 91 packages. 92 93 941.2. Documentation for command-line tools 95 96 The command-line tools are documented as man pages. In source code 97 releases (and possibly also in some binary packages), the man pages 98 are also provided in plain text (ASCII only) format in the directory 99 "doc/man" to make the man pages more accessible to those whose 100 operating system doesn't provide an easy way to view man pages. 101 102 1031.3. Documentation for liblzma 104 105 The liblzma API headers include short docs about each function 106 and data type as Doxygen tags. These docs should be quite OK as 107 a quick reference. 108 109 There are a few example/tutorial programs that should help in 110 getting started with liblzma. In the source package the examples 111 are in "doc/examples" and in binary packages they may be under 112 "examples" in the same directory as this README. 113 114 Since the liblzma API has similarities to the zlib API, some people 115 may find it useful to read the zlib docs and tutorial too: 116 117 https://zlib.net/manual.html 118 https://zlib.net/zlib_how.html 119 120 1212. Version numbering 122-------------------- 123 124 The version number format of XZ Utils is X.Y.ZS: 125 126 - X is the major version. When this is incremented, the library 127 API and ABI break. 128 129 - Y is the minor version. It is incremented when new features 130 are added without breaking the existing API or ABI. An even Y 131 indicates a stable release and an odd Y indicates unstable 132 (alpha or beta version). 133 134 - Z is the revision. This has a different meaning for stable and 135 unstable releases: 136 137 * Stable: Z is incremented when bugs get fixed without adding 138 any new features. This is intended to be convenient for 139 downstream distributors that want bug fixes but don't want 140 any new features to minimize the risk of introducing new bugs. 141 142 * Unstable: Z is just a counter. API or ABI of features added 143 in earlier unstable releases having the same X.Y may break. 144 145 - S indicates stability of the release. It is missing from the 146 stable releases, where Y is an even number. When Y is odd, S 147 is either "alpha" or "beta" to make it very clear that such 148 versions are not stable releases. The same X.Y.Z combination is 149 not used for more than one stability level, i.e. after X.Y.Zalpha, 150 the next version can be X.Y.(Z+1)beta but not X.Y.Zbeta. 151 152 1533. Reporting bugs 154----------------- 155 156 Naturally it is easiest for me if you already know what causes the 157 unexpected behavior. Even better if you have a patch to propose. 158 However, quite often the reason for unexpected behavior is unknown, 159 so here are a few things to do before sending a bug report: 160 161 1. Try to create a small example how to reproduce the issue. 162 163 2. Compile XZ Utils with debugging code using configure switches 164 --enable-debug and, if possible, --disable-shared. If you are 165 using GCC, use CFLAGS='-O0 -ggdb3'. Don't strip the resulting 166 binaries. 167 168 3. Turn on core dumps. The exact command depends on your shell; 169 for example in GNU bash it is done with "ulimit -c unlimited", 170 and in tcsh with "limit coredumpsize unlimited". 171 172 4. Try to reproduce the suspected bug. If you get "assertion failed" 173 message, be sure to include the complete message in your bug 174 report. If the application leaves a coredump, get a backtrace 175 using gdb: 176 $ gdb /path/to/app-binary # Load the app to the debugger. 177 (gdb) core core # Open the coredump. 178 (gdb) bt # Print the backtrace. Copy & paste to bug report. 179 (gdb) quit # Quit gdb. 180 181 Report your bug via email or IRC (see Contact information below). 182 Don't send core dump files or any executables. If you have a small 183 example file(s) (total size less than 256 KiB), please include 184 it/them as an attachment. If you have bigger test files, put them 185 online somewhere and include a URL to the file(s) in the bug report. 186 187 Always include the exact version number of XZ Utils in the bug report. 188 If you are using a snapshot from the git repository, use "git describe" 189 to get the exact snapshot version. If you are using XZ Utils shipped 190 in an operating system distribution, mention the distribution name, 191 distribution version, and exact xz package version; if you cannot 192 repeat the bug with the code compiled from unpatched source code, 193 you probably need to report a bug to your distribution's bug tracking 194 system. 195 196 1974. Translations 198--------------- 199 200 The xz command line tool and all man pages can be translated. 201 The translations are handled via the Translation Project. If you 202 wish to help translating xz, please join the Translation Project: 203 204 https://translationproject.org/html/translators.html 205 206 Below are notes and testing instructions specific to xz 207 translations. 208 209 Testing can be done by installing xz into a temporary directory: 210 211 ./configure --disable-shared --prefix=/tmp/xz-test 212 # <Edit the .po file in the po directory.> 213 make -C po update-po 214 make install 215 bash debug/translation.bash | less 216 bash debug/translation.bash | less -S # For --list outputs 217 218 Repeat the above as needed (no need to re-run configure though). 219 220 Note especially the following: 221 222 - The output of --help and --long-help must look nice on 223 an 80-column terminal. It's OK to add extra lines if needed. 224 225 - In contrast, don't add extra lines to error messages and such. 226 They are often preceded with e.g. a filename on the same line, 227 so you have no way to predict where to put a \n. Let the terminal 228 do the wrapping even if it looks ugly. Adding new lines will be 229 even uglier in the generic case even if it looks nice in a few 230 limited examples. 231 232 - Be careful with column alignment in tables and table-like output 233 (--list, --list --verbose --verbose, --info-memory, --help, and 234 --long-help): 235 236 * All descriptions of options in --help should start in the 237 same column (but it doesn't need to be the same column as 238 in the English messages; just be consistent if you change it). 239 Check that both --help and --long-help look OK, since they 240 share several strings. 241 242 * --list --verbose and --info-memory print lines that have 243 the format "Description: %s". If you need a longer 244 description, you can put extra space between the colon 245 and %s. Then you may need to add extra space to other 246 strings too so that the result as a whole looks good (all 247 values start at the same column). 248 249 * The columns of the actual tables in --list --verbose --verbose 250 should be aligned properly. Abbreviate if necessary. It might 251 be good to keep at least 2 or 3 spaces between column headings 252 and avoid spaces in the headings so that the columns stand out 253 better, but this is a matter of opinion. Do what you think 254 looks best. 255 256 - Be careful to put a period at the end of a sentence when the 257 original version has it, and don't put it when the original 258 doesn't have it. Similarly, be careful with \n characters 259 at the beginning and end of the strings. 260 261 - Read the TRANSLATORS comments that have been extracted from the 262 source code and included in xz.pot. Some comments suggest 263 testing with a specific command which needs an .xz file. You 264 may use e.g. any tests/files/good-*.xz. However, these test 265 commands are included in translations.bash output, so reading 266 translations.bash output carefully can be enough. 267 268 - If you find language problems in the original English strings, 269 feel free to suggest improvements. Ask if something is unclear. 270 271 - The translated messages should be understandable (sometimes this 272 may be a problem with the original English messages too). Don't 273 make a direct word-by-word translation from English especially if 274 the result doesn't sound good in your language. 275 276 Thanks for your help! 277 278 2795. Other implementations of the .xz format 280------------------------------------------ 281 282 7-Zip and the p7zip port of 7-Zip support the .xz format starting 283 from the version 9.00alpha. 284 285 https://7-zip.org/ 286 https://p7zip.sourceforge.net/ 287 288 XZ Embedded is a limited implementation written for use in the Linux 289 kernel, but it is also suitable for other embedded use. 290 291 https://tukaani.org/xz/embedded.html 292 293 XZ for Java is a complete implementation written in pure Java. 294 295 https://tukaani.org/xz/java.html 296 297 2986. Contact information 299---------------------- 300 301 XZ Utils in general: 302 - Home page: https://tukaani.org/xz/ 303 - Email to maintainer(s): xz@tukaani.org 304 - IRC: #tukaani on Libera Chat 305 - GitHub: https://github.com/tukaani-project/xz 306 307 Lead maintainer: 308 - Email: Lasse Collin <lasse.collin@tukaani.org> 309 - IRC: Larhzu on Libera Chat 310 311