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. Translating the xz tool 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 and 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 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 similar command line syntax than that of gzip. 31 32 When aiming for the highest compression ratio, 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, 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 compression ratio. A filter chain may 48 contain up to four filters, although usually only one two is 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 62 631. Documentation 64---------------- 65 661.1. 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 90 911.2. 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 1001.3. 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 *basics* of zlib API. Once you know that, it 113 should be easier to learn liblzma. 114 115 http://zlib.net/manual.html 116 http://zlib.net/zlib_how.html 117 118 1192. 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 are 128 added without breaking existing API or ABI. Even Y indicates 129 stable release and odd Y indicates unstable (alpha or beta 130 version). 131 132 - Z is the revision. This has different meaning for stable and 133 unstable releases: 134 * Stable: Z is incremented when bugs get fixed without adding 135 any new features. 136 * Unstable: Z is just a counter. API or ABI of features added 137 in earlier unstable releases having the same X.Y may break. 138 139 - S indicates stability of the release. It is missing from the 140 stable releases where Y is an even number. When Y is odd, S 141 is either "alpha" or "beta" to make it very clear that such 142 versions are not stable releases. The same X.Y.Z combination is 143 not used for more than one stability level i.e. after X.Y.Zalpha, 144 the next version can be X.Y.(Z+1)beta but not X.Y.Zbeta. 145 146 1473. Reporting bugs 148----------------- 149 150 Naturally it is easiest for me if you already know what causes the 151 unexpected behavior. Even better if you have a patch to propose. 152 However, quite often the reason for unexpected behavior is unknown, 153 so here are a few things to do before sending a bug report: 154 155 1. Try to create a small example how to reproduce the issue. 156 157 2. Compile XZ Utils with debugging code using configure switches 158 --enable-debug and, if possible, --disable-shared. If you are 159 using GCC, use CFLAGS='-O0 -ggdb3'. Don't strip the resulting 160 binaries. 161 162 3. Turn on core dumps. The exact command depends on your shell; 163 for example in GNU bash it is done with "ulimit -c unlimited", 164 and in tcsh with "limit coredumpsize unlimited". 165 166 4. Try to reproduce the suspected bug. If you get "assertion failed" 167 message, be sure to include the complete message in your bug 168 report. If the application leaves a coredump, get a backtrace 169 using gdb: 170 $ gdb /path/to/app-binary # Load the app to the debugger. 171 (gdb) core core # Open the coredump. 172 (gdb) bt # Print the backtrace. Copy & paste to bug report. 173 (gdb) quit # Quit gdb. 174 175 Report your bug via email or IRC (see Contact information below). 176 Don't send core dump files or any executables. If you have a small 177 example file(s) (total size less than 256 KiB), please include 178 it/them as an attachment. If you have bigger test files, put them 179 online somewhere and include an URL to the file(s) in the bug report. 180 181 Always include the exact version number of XZ Utils in the bug report. 182 If you are using a snapshot from the git repository, use "git describe" 183 to get the exact snapshot version. If you are using XZ Utils shipped 184 in an operating system distribution, mention the distribution name, 185 distribution version, and exact xz package version; if you cannot 186 repeat the bug with the code compiled from unpatched source code, 187 you probably need to report a bug to your distribution's bug tracking 188 system. 189 190 1914. Translating the xz tool 192-------------------------- 193 194 The messages from the xz tool have been translated into a few 195 languages. Before starting to translate into a new language, ask 196 the author that someone else hasn't already started working on it. 197 198 Test your translation. Testing includes comparing the translated 199 output to the original English version by running the same commands 200 in both your target locale and with LC_ALL=C. Ask someone to 201 proof-read and test the translation. 202 203 Testing can be done e.g. by installing xz into a temporary directory: 204 205 ./configure --disable-shared --prefix=/tmp/xz-test 206 # <Edit the .po file in the po directory.> 207 make -C po update-po 208 make install 209 bash debug/translations.bash | less 210 bash debug/translations.bash | less -S # For --list outputs 211 212 Repeat the above as needed (no need to re-run configure though). 213 214 Note especially the following: 215 216 - The output of --help and --long-help must look nice on 217 a 80-column terminal. It's OK to add extra lines if needed. 218 219 - In contrast, don't add extra lines to error messages and such. 220 They are often preceded with e.g. a filename on the same line, 221 so you have no way to predict where to put a \n. Let the terminal 222 do the wrapping even if it looks ugly. Adding new lines will be 223 even uglier in the generic case even if it looks nice in a few 224 limited examples. 225 226 - Be careful with column alignment in tables and table-like output 227 (--list, --list --verbose --verbose, --info-memory, --help, and 228 --long-help): 229 230 * All descriptions of options in --help should start in the 231 same column (but it doesn't need to be the same column as 232 in the English messages; just be consistent if you change it). 233 Check that both --help and --long-help look OK, since they 234 share several strings. 235 236 * --list --verbose and --info-memory print lines that have 237 the format "Description: %s". If you need a longer 238 description, you can put extra space between the colon 239 and %s. Then you may need to add extra space to other 240 strings too so that the result as a whole looks good (all 241 values start at the same column). 242 243 * The columns of the actual tables in --list --verbose --verbose 244 should be aligned properly. Abbreviate if necessary. It might 245 be good to keep at least 2 or 3 spaces between column headings 246 and avoid spaces in the headings so that the columns stand out 247 better, but this is a matter of opinion. Do what you think 248 looks best. 249 250 - Be careful to put a period at the end of a sentence when the 251 original version has it, and don't put it when the original 252 doesn't have it. Similarly, be careful with \n characters 253 at the beginning and end of the strings. 254 255 - Read the TRANSLATORS comments that have been extracted from the 256 source code and included in xz.pot. If they suggest testing the 257 translation with some type of command, do it. If testing needs 258 input files, use e.g. tests/files/good-*.xz. 259 260 - When updating the translation, read the fuzzy (modified) strings 261 carefully, and don't mark them as updated before you actually 262 have updated them. Reading through the unchanged messages can be 263 good too; sometimes you may find a better wording for them. 264 265 - If you find language problems in the original English strings, 266 feel free to suggest improvements. Ask if something is unclear. 267 268 - The translated messages should be understandable (sometimes this 269 may be a problem with the original English messages too). Don't 270 make a direct word-by-word translation from English especially if 271 the result doesn't sound good in your language. 272 273 In short, take your time and pay attention to the details. Making 274 a good translation is not a quick and trivial thing to do. The 275 translated xz should look as polished as the English version. 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 http://7-zip.org/ 285 http://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 http://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 contact Lasse Collin <lasse.collin@tukaani.org> (in Finnish or English). 298 I'm sometimes slow at replying. If you haven't got a reply within two 299 weeks, assume that your email has got lost and resend it or use IRC. 300 301 You can find me also from #tukaani on Freenode; my nick is Larhzu. 302 The channel tends to be pretty quiet, so just ask your question and 303 someone may wake up. 304 305