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 familiar 73 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.GPLv2 GNU General Public License version 2 79 COPYING.GPLv3 GNU General Public License version 3 80 COPYING.LGPLv2.1 GNU Lesser General Public License version 2.1 81 82 AUTHORS The main authors of XZ Utils 83 THANKS Incomplete list of people who have helped making 84 this software 85 NEWS User-visible changes between XZ Utils releases 86 ChangeLog Detailed list of changes (commit log) 87 TODO Known bugs and some sort of to-do list 88 89 Note that only some of the above files are included in binary 90 packages. 91 92 931.2. Documentation for command-line tools 94 95 The command-line tools are documented as man pages. In source code 96 releases (and possibly also in some binary packages), the man pages 97 are also provided in plain text (ASCII only) and PDF formats in the 98 directory "doc/man" to make the man pages more accessible to those 99 whose operating system doesn't provide an easy way to view man pages. 100 101 1021.3. Documentation for liblzma 103 104 The liblzma API headers include short docs about each function 105 and data type as Doxygen tags. These docs should be quite OK as 106 a quick reference. 107 108 There are a few example/tutorial programs that should help in 109 getting started with liblzma. In the source package the examples 110 are in "doc/examples" and in binary packages they may be under 111 "examples" in the same directory as this README. 112 113 Since the liblzma API has similarities to the zlib API, some people 114 may find it useful to read the zlib docs and tutorial too: 115 116 https://zlib.net/manual.html 117 https://zlib.net/zlib_how.html 118 119 1202. Version numbering 121-------------------- 122 123 The version number format of XZ Utils is X.Y.ZS: 124 125 - X is the major version. When this is incremented, the library 126 API and ABI break. 127 128 - Y is the minor version. It is incremented when new features 129 are added without breaking the existing API or ABI. An even Y 130 indicates a stable release and an odd Y indicates unstable 131 (alpha or beta version). 132 133 - Z is the revision. This has a different meaning for stable and 134 unstable releases: 135 136 * Stable: Z is incremented when bugs get fixed without adding 137 any new features. This is intended to be convenient for 138 downstream distributors that want bug fixes but don't want 139 any new features to minimize the risk of introducing new bugs. 140 141 * Unstable: Z is just a counter. API or ABI of features added 142 in earlier unstable releases having the same X.Y may break. 143 144 - S indicates stability of the release. It is missing from the 145 stable releases, where Y is an even number. When Y is odd, S 146 is either "alpha" or "beta" to make it very clear that such 147 versions are not stable releases. The same X.Y.Z combination is 148 not used for more than one stability level, i.e. after X.Y.Zalpha, 149 the next version can be X.Y.(Z+1)beta but not X.Y.Zbeta. 150 151 1523. Reporting bugs 153----------------- 154 155 Naturally it is easiest for me if you already know what causes the 156 unexpected behavior. Even better if you have a patch to propose. 157 However, quite often the reason for unexpected behavior is unknown, 158 so here are a few things to do before sending a bug report: 159 160 1. Try to create a small example how to reproduce the issue. 161 162 2. Compile XZ Utils with debugging code using configure switches 163 --enable-debug and, if possible, --disable-shared. If you are 164 using GCC, use CFLAGS='-O0 -ggdb3'. Don't strip the resulting 165 binaries. 166 167 3. Turn on core dumps. The exact command depends on your shell; 168 for example in GNU bash it is done with "ulimit -c unlimited", 169 and in tcsh with "limit coredumpsize unlimited". 170 171 4. Try to reproduce the suspected bug. If you get "assertion failed" 172 message, be sure to include the complete message in your bug 173 report. If the application leaves a coredump, get a backtrace 174 using gdb: 175 $ gdb /path/to/app-binary # Load the app to the debugger. 176 (gdb) core core # Open the coredump. 177 (gdb) bt # Print the backtrace. Copy & paste to bug report. 178 (gdb) quit # Quit gdb. 179 180 Report your bug via email or IRC (see Contact information below). 181 Don't send core dump files or any executables. If you have a small 182 example file(s) (total size less than 256 KiB), please include 183 it/them as an attachment. If you have bigger test files, put them 184 online somewhere and include a URL to the file(s) in the bug report. 185 186 Always include the exact version number of XZ Utils in the bug report. 187 If you are using a snapshot from the git repository, use "git describe" 188 to get the exact snapshot version. If you are using XZ Utils shipped 189 in an operating system distribution, mention the distribution name, 190 distribution version, and exact xz package version; if you cannot 191 repeat the bug with the code compiled from unpatched source code, 192 you probably need to report a bug to your distribution's bug tracking 193 system. 194 195 1964. Translations 197--------------- 198 199 The xz command line tool and all man pages can be translated. 200 The translations are handled via the Translation Project. If you 201 wish to help translating xz, please join the Translation Project: 202 203 https://translationproject.org/html/translators.html 204 205 Below are notes and testing instructions specific to xz 206 translations. 207 208 Testing can be done by installing xz into a temporary directory: 209 210 ./configure --disable-shared --prefix=/tmp/xz-test 211 # <Edit the .po file in the po directory.> 212 make -C po update-po 213 make install 214 bash debug/translation.bash | less 215 bash debug/translation.bash | less -S # For --list outputs 216 217 Repeat the above as needed (no need to re-run configure though). 218 219 Note especially the following: 220 221 - The output of --help and --long-help must look nice on 222 an 80-column terminal. It's OK to add extra lines if needed. 223 224 - In contrast, don't add extra lines to error messages and such. 225 They are often preceded with e.g. a filename on the same line, 226 so you have no way to predict where to put a \n. Let the terminal 227 do the wrapping even if it looks ugly. Adding new lines will be 228 even uglier in the generic case even if it looks nice in a few 229 limited examples. 230 231 - Be careful with column alignment in tables and table-like output 232 (--list, --list --verbose --verbose, --info-memory, --help, and 233 --long-help): 234 235 * All descriptions of options in --help should start in the 236 same column (but it doesn't need to be the same column as 237 in the English messages; just be consistent if you change it). 238 Check that both --help and --long-help look OK, since they 239 share several strings. 240 241 * --list --verbose and --info-memory print lines that have 242 the format "Description: %s". If you need a longer 243 description, you can put extra space between the colon 244 and %s. Then you may need to add extra space to other 245 strings too so that the result as a whole looks good (all 246 values start at the same column). 247 248 * The columns of the actual tables in --list --verbose --verbose 249 should be aligned properly. Abbreviate if necessary. It might 250 be good to keep at least 2 or 3 spaces between column headings 251 and avoid spaces in the headings so that the columns stand out 252 better, but this is a matter of opinion. Do what you think 253 looks best. 254 255 - Be careful to put a period at the end of a sentence when the 256 original version has it, and don't put it when the original 257 doesn't have it. Similarly, be careful with \n characters 258 at the beginning and end of the strings. 259 260 - Read the TRANSLATORS comments that have been extracted from the 261 source code and included in xz.pot. Some comments suggest 262 testing with a specific command which needs an .xz file. You 263 may use e.g. any tests/files/good-*.xz. However, these test 264 commands are included in translations.bash output, so reading 265 translations.bash output carefully can be enough. 266 267 - If you find language problems in the original English strings, 268 feel free to suggest improvements. Ask if something is unclear. 269 270 - The translated messages should be understandable (sometimes this 271 may be a problem with the original English messages too). Don't 272 make a direct word-by-word translation from English especially if 273 the result doesn't sound good in your language. 274 275 Thanks for your help! 276 277 2785. Other implementations of the .xz format 279------------------------------------------ 280 281 7-Zip and the p7zip port of 7-Zip support the .xz format starting 282 from the version 9.00alpha. 283 284 https://7-zip.org/ 285 https://p7zip.sourceforge.net/ 286 287 XZ Embedded is a limited implementation written for use in the Linux 288 kernel, but it is also suitable for other embedded use. 289 290 https://tukaani.org/xz/embedded.html 291 292 2936. Contact information 294---------------------- 295 296 If you have questions, bug reports, patches etc. related to XZ Utils, 297 the project maintainers Lasse Collin and Jia Tan can be reached via 298 <xz@tukaani.org>. 299 300 You might find Lasse also from #tukaani on Libera Chat (IRC). 301 The nick is Larhzu. The channel tends to be pretty quiet, 302 so just ask your question and someone might wake up. 303 304