1 2 XZ 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. Translating the xz tool 13 5. Other implementations of the .xz format 14 6. Contact information 15 16 17 0. 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 doesn't support multithreaded compression or decompression 59 yet. It has been planned though and taken into account when designing 60 the .xz file format. 61 62 63 1. Documentation 64 ---------------- 65 66 1.1. Overall documentation 67 68 README This file 69 70 INSTALL.generic Generic install instructions for those not familiar 71 with packages using GNU Autotools 72 INSTALL Installation instructions specific to XZ Utils 73 PACKAGERS Information to packagers of XZ Utils 74 75 COPYING XZ Utils copyright and license information 76 COPYING.GPLv2 GNU General Public License version 2 77 COPYING.GPLv3 GNU General Public License version 3 78 COPYING.LGPLv2.1 GNU Lesser General Public License version 2.1 79 80 AUTHORS The main authors of XZ Utils 81 THANKS Incomplete list of people who have helped making 82 this software 83 NEWS User-visible changes between XZ Utils releases 84 ChangeLog Detailed list of changes (commit log) 85 TODO Known bugs and some sort of to-do list 86 87 Note that only some of the above files are included in binary 88 packages. 89 90 91 1.2. Documentation for command-line tools 92 93 The command-line tools are documented as man pages. In source code 94 releases (and possibly also in some binary packages), the man pages 95 are also provided in plain text (ASCII only) and PDF formats in the 96 directory "doc/man" to make the man pages more accessible to those 97 whose operating system doesn't provide an easy way to view man pages. 98 99 100 1.3. Documentation for liblzma 101 102 The liblzma API headers include short docs about each function 103 and data type as Doxygen tags. These docs should be quite OK as 104 a quick reference. 105 106 I have planned to write a bunch of very well documented example 107 programs, which (due to comments) should work as a tutorial to 108 various features of liblzma. No such example programs have been 109 written yet. 110 111 For now, if you have never used liblzma, libbzip2, or zlib, I 112 recommend learning the *basics* of the zlib API. Once you know that, 113 it should be easier to learn liblzma. 114 115 http://zlib.net/manual.html 116 http://zlib.net/zlib_how.html 117 118 119 2. Version numbering 120 -------------------- 121 122 The version number format of XZ Utils is X.Y.ZS: 123 124 - X is the major version. When this is incremented, the library 125 API and ABI break. 126 127 - Y is the minor version. It is incremented when new features 128 are added without breaking the existing API or ABI. An even Y 129 indicates a stable release and an odd Y indicates unstable 130 (alpha or beta version). 131 132 - Z is the revision. This has a different meaning for stable and 133 unstable releases: 134 135 * Stable: Z is incremented when bugs get fixed without adding 136 any new features. This is intended to be convenient for 137 downstream distributors that want bug fixes but don't want 138 any new features to minimize the risk of introducing new bugs. 139 140 * Unstable: Z is just a counter. API or ABI of features added 141 in earlier unstable releases having the same X.Y may break. 142 143 - S indicates stability of the release. It is missing from the 144 stable releases, where Y is an even number. When Y is odd, S 145 is either "alpha" or "beta" to make it very clear that such 146 versions are not stable releases. The same X.Y.Z combination is 147 not used for more than one stability level, i.e. after X.Y.Zalpha, 148 the next version can be X.Y.(Z+1)beta but not X.Y.Zbeta. 149 150 151 3. Reporting bugs 152 ----------------- 153 154 Naturally it is easiest for me if you already know what causes the 155 unexpected behavior. Even better if you have a patch to propose. 156 However, quite often the reason for unexpected behavior is unknown, 157 so here are a few things to do before sending a bug report: 158 159 1. Try to create a small example how to reproduce the issue. 160 161 2. Compile XZ Utils with debugging code using configure switches 162 --enable-debug and, if possible, --disable-shared. If you are 163 using GCC, use CFLAGS='-O0 -ggdb3'. Don't strip the resulting 164 binaries. 165 166 3. Turn on core dumps. The exact command depends on your shell; 167 for example in GNU bash it is done with "ulimit -c unlimited", 168 and in tcsh with "limit coredumpsize unlimited". 169 170 4. Try to reproduce the suspected bug. If you get "assertion failed" 171 message, be sure to include the complete message in your bug 172 report. If the application leaves a coredump, get a backtrace 173 using gdb: 174 $ gdb /path/to/app-binary # Load the app to the debugger. 175 (gdb) core core # Open the coredump. 176 (gdb) bt # Print the backtrace. Copy & paste to bug report. 177 (gdb) quit # Quit gdb. 178 179 Report your bug via email or IRC (see Contact information below). 180 Don't send core dump files or any executables. If you have a small 181 example file(s) (total size less than 256 KiB), please include 182 it/them as an attachment. If you have bigger test files, put them 183 online somewhere and include a URL to the file(s) in the bug report. 184 185 Always include the exact version number of XZ Utils in the bug report. 186 If you are using a snapshot from the git repository, use "git describe" 187 to get the exact snapshot version. If you are using XZ Utils shipped 188 in an operating system distribution, mention the distribution name, 189 distribution version, and exact xz package version; if you cannot 190 repeat the bug with the code compiled from unpatched source code, 191 you probably need to report a bug to your distribution's bug tracking 192 system. 193 194 195 4. Translating the xz tool 196 -------------------------- 197 198 The messages from the xz tool have been translated into a few 199 languages. Before starting to translate into a new language, ask 200 the author whether someone else hasn't already started working on it. 201 202 Test your translation. Testing includes comparing the translated 203 output to the original English version by running the same commands 204 in both your target locale and with LC_ALL=C. Ask someone to 205 proof-read and test the translation. 206 207 Testing can be done e.g. by installing xz into a temporary directory: 208 209 ./configure --disable-shared --prefix=/tmp/xz-test 210 # <Edit the .po file in the po directory.> 211 make -C po update-po 212 make install 213 bash debug/translation.bash | less 214 bash debug/translation.bash | less -S # For --list outputs 215 216 Repeat the above as needed (no need to re-run configure though). 217 218 Note especially the following: 219 220 - The output of --help and --long-help must look nice on 221 an 80-column terminal. It's OK to add extra lines if needed. 222 223 - In contrast, don't add extra lines to error messages and such. 224 They are often preceded with e.g. a filename on the same line, 225 so you have no way to predict where to put a \n. Let the terminal 226 do the wrapping even if it looks ugly. Adding new lines will be 227 even uglier in the generic case even if it looks nice in a few 228 limited examples. 229 230 - Be careful with column alignment in tables and table-like output 231 (--list, --list --verbose --verbose, --info-memory, --help, and 232 --long-help): 233 234 * All descriptions of options in --help should start in the 235 same column (but it doesn't need to be the same column as 236 in the English messages; just be consistent if you change it). 237 Check that both --help and --long-help look OK, since they 238 share several strings. 239 240 * --list --verbose and --info-memory print lines that have 241 the format "Description: %s". If you need a longer 242 description, you can put extra space between the colon 243 and %s. Then you may need to add extra space to other 244 strings too so that the result as a whole looks good (all 245 values start at the same column). 246 247 * The columns of the actual tables in --list --verbose --verbose 248 should be aligned properly. Abbreviate if necessary. It might 249 be good to keep at least 2 or 3 spaces between column headings 250 and avoid spaces in the headings so that the columns stand out 251 better, but this is a matter of opinion. Do what you think 252 looks best. 253 254 - Be careful to put a period at the end of a sentence when the 255 original version has it, and don't put it when the original 256 doesn't have it. Similarly, be careful with \n characters 257 at the beginning and end of the strings. 258 259 - Read the TRANSLATORS comments that have been extracted from the 260 source code and included in xz.pot. If they suggest testing the 261 translation with some type of command, do it. If testing needs 262 input files, use e.g. tests/files/good-*.xz. 263 264 - When updating the translation, read the fuzzy (modified) strings 265 carefully, and don't mark them as updated before you actually 266 have updated them. Reading through the unchanged messages can be 267 good too; sometimes you may find a better wording for them. 268 269 - If you find language problems in the original English strings, 270 feel free to suggest improvements. Ask if something is unclear. 271 272 - The translated messages should be understandable (sometimes this 273 may be a problem with the original English messages too). Don't 274 make a direct word-by-word translation from English especially if 275 the result doesn't sound good in your language. 276 277 In short, take your time and pay attention to the details. Making 278 a good translation is not a quick and trivial thing to do. The 279 translated xz should look as polished as the English version. 280 281 282 5. Other implementations of the .xz format 283 ------------------------------------------ 284 285 7-Zip and the p7zip port of 7-Zip support the .xz format starting 286 from the version 9.00alpha. 287 288 http://7-zip.org/ 289 http://p7zip.sourceforge.net/ 290 291 XZ Embedded is a limited implementation written for use in the Linux 292 kernel, but it is also suitable for other embedded use. 293 294 https://tukaani.org/xz/embedded.html 295 296 297 6. Contact information 298 ---------------------- 299 300 If you have questions, bug reports, patches etc. related to XZ Utils, 301 contact Lasse Collin <lasse.collin (a] tukaani.org> (in Finnish or English). 302 I'm sometimes slow at replying. If you haven't got a reply within two 303 weeks, assume that your email has got lost and resend it or use IRC. 304 305 You can find me also from #tukaani on Freenode; my nick is Larhzu. 306 The channel tends to be pretty quiet, so just ask your question and 307 someone may wake up. 308 309
Indexes created Mon Apr 06 00:22:49 UTC 2026