1par2(1) Parity archive utils par2(1)
2
6 par2 - PAR 2.0 compatible file verification and repair tool.
7
9 par2 c|v|r [options] <PAR2 file> [files]
10 par2 c(reate) [options] <PAR2 file> [files]
12 par2 v(erify) [options] <PAR2 file> [files]
13 par2 r(epair) [options] <PAR2 file> [files]
14 Also:
16 par2create [options] <PAR2 file> [files]
17 par2verify [options] <PAR2 file> [files]
18 par2repair [options] <PAR2 file> [files]
19
21 par2cmdline is a program for creating and using PAR2 files to detect
22 damage in data files and repair them if necessary. It can be used with
23 any kind of file.
24
26 -h Show this help
27 -V Show version
29 -VV Show version and copyright
31 -a <file>
33 Set the main PAR2 archive name; required on create, optional for
34 verify and repair
35 -b<n> Set the Block‐Count
37 -s<n> Set the Block‐Size (don't use both -b and -s)
39 -r<n> Level of redundancy (percentage)
42 -r<c><n>
44 Redundancy target size, <c>=g(iga),m(ega),k(ilo) bytes
45 -c<n> Recovery block count (don't use both -r and -c)
47 -f<n> First Recovery‐Block‐Number
49 -u Uniform recovery file sizes
51 -l Limit size of recovery files (don't use both -u and -l)
53 -n<n> Number of recovery files (don't use both -n and -l)
55 -m<n> Memory (in MB) to use
57 -t<n> Number of threads used for main processing (auto-detected)
59 -T<n> Number of files hashed in parallel (during file verification and
61 creation stages, 2 default)
62 -v [-v]
64 Be more verbose
65 -q [-q]
67 Be more quiet (-qq gives silence)
68 -p Purge backup files and par files on successful recovery or when
70 no recovery is needed
71 -R Recurse into subdirectories (only useful on create)
73 -N data skipping (find badly mispositioned data blocks)
75 -S<n> Skip leaway (distance +/- from expected block position)
77 -B<path>
79 Set the basepath to use as reference for the datafiles
80 -- Treat all following arguments as filenames
82
84 With PAR 2.0 you can create PAR2 recovery files for as few as 1 or as
85 many as 32768 files. If you wanted to create PAR1 recovery files for a
86 single file you are forced to split the file into muliple parts and RAR
87 is frequently used for this purpose. You do NOT need to split files
88 with PAR 2.0.
89 To create PAR 2 recovery files for a single data file (e.g. one called
91 test.mpg), you can use the following command:
92 par2 create test.mpg
94 If test.mpg is an 800 MB file, then this will create a total of 8 PAR2
96 files with the following filenames (taking roughly 6 minutes on a PC
97 with a 1500MHz CPU):
98 test.mpg.par2 - This is an index file for verification only
100 test.mpg.vol00+01.par2 - Recovery file with 1 recovery block
101 test.mpg.vol01+02.par2 - Recovery file with 2 recovery blocks
102 test.mpg.vol03+04.par2 - Recovery file with 4 recovery blocks
103 test.mpg.vol07+08.par2 - Recovery file with 8 recovery blocks
104 test.mpg.vol15+16.par2 - Recovery file with 16 recovery blocks
105 test.mpg.vol31+32.par2 - Recovery file with 32 recovery blocks
106 test.mpg.vol63+37.par2 - Recovery file with 37 recovery blocks
107 The test.mpg.par2 file is 39 KB in size and the other files vary in
109 size from 443 KB to 15 MB. These par2 files will enable the recovery of
110 up to 100 errors totalling 40 MB of lost or damaged data from the orig‐
111 inal test.mpg file when it and the par2 files are posted on UseNet.
112 When posting on UseNet it is recommended that you use the "-s" option
113 to set a blocksize that is equal to the Article size that you will use
114 to post the data file. If you wanted to post the test.mpg file using an
115 article size of 300 KB then the command you would type is:
116 par2 create -s307200 test.mpg
118 This will create 9 PAR2 files instead of 8, and they will be capable of
120 correcting up to 134 errors totalling 40 MB. It will take roughly 8
121 minutes to create the recovery files this time. In both of these two
122 examples, the total quantity of recovery data created was 40 MB (which
123 is 5% of 800 MB). If you wish to create a greater or lesser quantity of
124 recovery data, you can use the "-r" option. To create 10% recovery data
125 instead of the default of 5% and also to use a block size of 300 KB,
126 you would use the following command:
127 par2 create -s307200 -r10 test.mpg
129 This would also create 9 PAR2 files, but they would be able to correct
131 up to 269 errors totalling 80 MB. Since twice as much recovery data is
132 created, it will take about 16 minutes to do so with a 1500MHz CPU. The
133 "-u" and "-n" options can be used to control exactly how many recovery
134 files are created and how the recovery blocks are distributed amoungst
135 them. They do not affect the total quantity of recovery data created.
136 The "-f" option is used when you create additional recovery data. e.g.
137 If you have already created 10% and want another 5% then you migh use
138 the following command:
139 par2 create -s307200 -r5 -f300 test.mpg
141 This specifies the same block size (which is a requirement for addi‐
143 tional recovery files), 5% recovery data, and a first block number of
144 300.
145 The "-m" option controls how much memory par2 uses. It defaults to 16
147 MB unless you override it.
148 CREATING PAR2 FILES FOR MULTIPLE DATA FILES
150 When creating PAR2 recovery files form multiple data files, you must
152 specify the base filename to use for the par2 files and the names of
153 all of the data files. If test.mpg had been split into multiple RAR
154 files, then you could use:
155 par2 create test.mpg.rar.par2 test.mpg.part*.rar
157 The files filename "test.mpg.rar.par2" says what you want the par2
159 files to be called and "test.mpg.part*.rar" should select all of the
160 RAR files.
161 VERIFYING AND REPAIRING
163 When using par2 recovery files to verify or repair the data files from
165 which they were created, you only need to specify the filename of one
166 of the par2 files to par2. For example:
167 par2 verify test.mpg.par2
169 This tells par2 to use the information in test.mpg.par2 to verify the
171 data files. Par2 will automatically search for the other par2 files
172 that were created and use the information they contain to determine the
173 filenames of the original data files and then to verify them. If all
174 of the data files are ok, then par2 will report that repair will not be
175 required. If any of the data files are missing or damaged, par2 will
176 report the details of what it has found. If the recovery files contain
177 enough recovery blocks to repair the damage, you will be told that
178 repair is possible. Otherwise you will be told exactly how many recov‐
179 ery blocks will be required in order to repair. To carry out a repair
180 use the following command:
181 par2 repair test.mpg.par2
183 This tells par2 to verify and if possible repair any damaged or missing
185 files. If a repair is carried out, then each file which is repaired
186 will be re-verified to confirm that the repair was successful.
187 MISSNAMED AND INCOMPLETE DATA FILES
189 If any of the recovery files or data files have the wrong filename,
191 then par2 will not automatically find and scan them. To have par2 scan
192 such files, you must include them on the command line when attempting
193 to verify or repair; e.g.:
194 par2 r test.mpg.par2 other.mpg
196 This tells par2 to scan the file called other.mpg to see if it contains
198 any data belonging to the original data files. If one of the extra
199 files specified in this way is an exact match for a data file, then the
200 repair process will rename the file so that it has the correct file‐
201 name. Because par2 is designed to be able to find good data within a
202 damaged file, it can do the same with incomplete files downloaded from
203 UseNet. If some of the articles for a file are missing, you should
204 still download the file and save it to disk for par2 to scan. If you do
205 this then you may find that you can carry out a repair in a situation
206 where you would not otherwise have sufficient recovery data. You can
207 have par2 scan all files that are in the current directory using a com‐
208 mand such as:
209 par2 r test.mpg.par2 *
211 WHAT TO DO WHEN YOU ARE TOLD YOU NEED MORE RECOVERY BLOCKS
213 If par2 determines that any of the data files are damaged or missing
215 and finds that there is insufficient recovery data to effect a repair,
216 you will be told that you need a certain number of recovery blocks. You
217 can obtain these by downloading additional recovery files. In order to
218 make things easy, par2 files have filenames that tell you exactly how
219 many recovery blocks each one contains. Assuming that the following
220 command was used to create recovery data:
221 par2 c -b1000 -r5 test.mpg
223 Then the recovery files that are created would be called:
225 test.mpg.par2
227 test.mpg.vol00+01.par2
228 test.mpg.vol01+02.par2
229 test.mpg.vol03+04.par2
230 test.mpg.vol07+08.par2
231 test.mpg.vol15+16.par2
232 test.mpg.vol31+19.par2
233 The first file in this list does not contain any recovery data, it only
235 contains information sufficient to verify the data files. Each of the
236 other files contains a different number of recovery blocks. The number
237 after the '+' sign is the number of recovery blocks and the number pre‐
238 ceding the '+' sign is the block number of the first recovery block in
239 that file. If par2 told you that you needed 10 recovery blocks, then
240 you would need "test.mpg.vol01+02.par2" and "test.mpg.vol07+08.par".
241 You might of course choose to fetch "test.mpg.vol15+16.par2" instead
242 (in which case you would have an extra 6 recovery blocks which would
243 not be used for the repair).
244 HASHING
246 Hashing portion (file verification and creation stages) of the code
248 can't be parallelized without processing multiple files simultaneously.
249 The 2 file/thread default is a good choice for HDDs, using more threads
250 can result in worse performance. Four or more threads can be used for
251 better performance with SSDs.
252
255 Peter Brian Clements <peterbclements@users.sourceforge.net>
256 Marcel Partap <mpartap@gmx.net>
257 Ike Devolder <ike.devolder@gmail.com>
258 Jussi Kansanen <jussi.kansanen@gmail.com>
2590.8.0 june 2017 par2(1)