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 COPYING.CC-BY-SA-4.0 Creative Commons Attribution-ShareAlike 4.0 83 International Public License 84 85 AUTHORS The main authors of XZ Utils 86 THANKS Incomplete list of people who have helped making 87 this software 88 NEWS User-visible changes between XZ Utils releases 89 ChangeLog Detailed list of changes (commit log) 90 TODO Known bugs and some sort of to-do list 91 92 Note that only some of the above files are included in binary 93 packages. 94 95 961.2. Documentation for command-line tools 97 98 The command-line tools are documented as man pages. In source code 99 releases (and possibly also in some binary packages), the man pages 100 are also provided in plain text (ASCII only) and PDF formats in the 101 directory "doc/man" to make the man pages more accessible to those 102 whose operating system doesn't provide an easy way to view man pages. 103 104 1051.3. Documentation for liblzma 106 107 The liblzma API headers include short docs about each function 108 and data type as Doxygen tags. These docs should be quite OK as 109 a quick reference. 110 111 There are a few example/tutorial programs that should help in 112 getting started with liblzma. In the source package the examples 113 are in "doc/examples" and in binary packages they may be under 114 "examples" in the same directory as this README. 115 116 Since the liblzma API has similarities to the zlib API, some people 117 may find it useful to read the zlib docs and tutorial too: 118 119 https://zlib.net/manual.html 120 https://zlib.net/zlib_how.html 121 122 1232. Version numbering 124-------------------- 125 126 The version number format of XZ Utils is X.Y.ZS: 127 128 - X is the major version. When this is incremented, the library 129 API and ABI break. 130 131 - Y is the minor version. It is incremented when new features 132 are added without breaking the existing API or ABI. An even Y 133 indicates a stable release and an odd Y indicates unstable 134 (alpha or beta version). 135 136 - Z is the revision. This has a different meaning for stable and 137 unstable releases: 138 139 * Stable: Z is incremented when bugs get fixed without adding 140 any new features. This is intended to be convenient for 141 downstream distributors that want bug fixes but don't want 142 any new features to minimize the risk of introducing new bugs. 143 144 * Unstable: Z is just a counter. API or ABI of features added 145 in earlier unstable releases having the same X.Y may break. 146 147 - S indicates stability of the release. It is missing from the 148 stable releases, where Y is an even number. When Y is odd, S 149 is either "alpha" or "beta" to make it very clear that such 150 versions are not stable releases. The same X.Y.Z combination is 151 not used for more than one stability level, i.e. after X.Y.Zalpha, 152 the next version can be X.Y.(Z+1)beta but not X.Y.Zbeta. 153 154 1553. Reporting bugs 156----------------- 157 158 Naturally it is easiest for me if you already know what causes the 159 unexpected behavior. Even better if you have a patch to propose. 160 However, quite often the reason for unexpected behavior is unknown, 161 so here are a few things to do before sending a bug report: 162 163 1. Try to create a small example how to reproduce the issue. 164 165 2. Compile XZ Utils with debugging code using configure switches 166 --enable-debug and, if possible, --disable-shared. If you are 167 using GCC, use CFLAGS='-O0 -ggdb3'. Don't strip the resulting 168 binaries. 169 170 3. Turn on core dumps. The exact command depends on your shell; 171 for example in GNU bash it is done with "ulimit -c unlimited", 172 and in tcsh with "limit coredumpsize unlimited". 173 174 4. Try to reproduce the suspected bug. If you get "assertion failed" 175 message, be sure to include the complete message in your bug 176 report. If the application leaves a coredump, get a backtrace 177 using gdb: 178 $ gdb /path/to/app-binary # Load the app to the debugger. 179 (gdb) core core # Open the coredump. 180 (gdb) bt # Print the backtrace. Copy & paste to bug report. 181 (gdb) quit # Quit gdb. 182 183 Report your bug via email or IRC (see Contact information below). 184 Don't send core dump files or any executables. If you have a small 185 example file(s) (total size less than 256 KiB), please include 186 it/them as an attachment. If you have bigger test files, put them 187 online somewhere and include a URL to the file(s) in the bug report. 188 189 Always include the exact version number of XZ Utils in the bug report. 190 If you are using a snapshot from the git repository, use "git describe" 191 to get the exact snapshot version. If you are using XZ Utils shipped 192 in an operating system distribution, mention the distribution name, 193 distribution version, and exact xz package version; if you cannot 194 repeat the bug with the code compiled from unpatched source code, 195 you probably need to report a bug to your distribution's bug tracking 196 system. 197 198 1994. Translations 200--------------- 201 202 The xz command line tool and all man pages can be translated. 203 The translations are handled via the Translation Project. If you 204 wish to help translating xz, please join the Translation Project: 205 206 https://translationproject.org/html/translators.html 207 208 Below are notes and testing instructions specific to xz 209 translations. 210 211 Testing can be done by installing xz into a temporary directory: 212 213 ./configure --disable-shared --prefix=/tmp/xz-test 214 # <Edit the .po file in the po directory.> 215 make -C po update-po 216 make install 217 bash debug/translation.bash | less 218 bash debug/translation.bash | less -S # For --list outputs 219 220 Repeat the above as needed (no need to re-run configure though). 221 222 Note especially the following: 223 224 - The output of --help and --long-help must look nice on 225 an 80-column terminal. It's OK to add extra lines if needed. 226 227 - In contrast, don't add extra lines to error messages and such. 228 They are often preceded with e.g. a filename on the same line, 229 so you have no way to predict where to put a \n. Let the terminal 230 do the wrapping even if it looks ugly. Adding new lines will be 231 even uglier in the generic case even if it looks nice in a few 232 limited examples. 233 234 - Be careful with column alignment in tables and table-like output 235 (--list, --list --verbose --verbose, --info-memory, --help, and 236 --long-help): 237 238 * All descriptions of options in --help should start in the 239 same column (but it doesn't need to be the same column as 240 in the English messages; just be consistent if you change it). 241 Check that both --help and --long-help look OK, since they 242 share several strings. 243 244 * --list --verbose and --info-memory print lines that have 245 the format "Description: %s". If you need a longer 246 description, you can put extra space between the colon 247 and %s. Then you may need to add extra space to other 248 strings too so that the result as a whole looks good (all 249 values start at the same column). 250 251 * The columns of the actual tables in --list --verbose --verbose 252 should be aligned properly. Abbreviate if necessary. It might 253 be good to keep at least 2 or 3 spaces between column headings 254 and avoid spaces in the headings so that the columns stand out 255 better, but this is a matter of opinion. Do what you think 256 looks best. 257 258 - Be careful to put a period at the end of a sentence when the 259 original version has it, and don't put it when the original 260 doesn't have it. Similarly, be careful with \n characters 261 at the beginning and end of the strings. 262 263 - Read the TRANSLATORS comments that have been extracted from the 264 source code and included in xz.pot. Some comments suggest 265 testing with a specific command which needs an .xz file. You 266 may use e.g. any tests/files/good-*.xz. However, these test 267 commands are included in translations.bash output, so reading 268 translations.bash output carefully can be enough. 269 270 - If you find language problems in the original English strings, 271 feel free to suggest improvements. Ask if something is unclear. 272 273 - The translated messages should be understandable (sometimes this 274 may be a problem with the original English messages too). Don't 275 make a direct word-by-word translation from English especially if 276 the result doesn't sound good in your language. 277 278 Thanks for your help! 279 280 2815. Other implementations of the .xz format 282------------------------------------------ 283 284 7-Zip and the p7zip port of 7-Zip support the .xz format starting 285 from the version 9.00alpha. 286 287 https://7-zip.org/ 288 https://p7zip.sourceforge.net/ 289 290 XZ Embedded is a limited implementation written for use in the Linux 291 kernel, but it is also suitable for other embedded use. 292 293 https://xz.tukaani.org/xz-embedded/ 294 295 XZ for Java is a complete implementation written in pure Java. 296 297 https://xz.tukaani.org/xz-for-java/ 298 299 3006. Contact information 301---------------------- 302 303 If you have questions, bug reports, patches etc. related to XZ Utils, 304 the project maintainers Lasse Collin and Jia Tan can be reached via 305 <xz@tukaani.org>. 306 307 You might find Lasse also from #tukaani on Libera Chat (IRC). 308 The nick is Larhzu. The channel tends to be pretty quiet, 309 so just ask your question and someone might wake up. 310 311