NAME
jigdo-file - Prepare files for Jigsaw Download (distribution of huge
files, e.g. CD images).
SYNOPSIS
jigdo-file COMMAND
[ --image=cdrom.iso ] [ --jigdo=cdrom.jigdo ] [
--template=cdrom.template ] [ --force ] [ MORE OPTIONS ] [ FILES ... |
--files-from=f ]
Common COMMANDs: make-template, make-image, verify
DESCRIPTION
Jigsaw Download, or short jigdo, is a scheme developed primarily to
make it easy to distribute huge filesystem images (e.g. CD (ISO9660) or
DVD (UDF) images) over the internet, but it could also be used for
other data which is awkward to handle due to its size, like audio/video
files or large software packages.
jigdo tries to ensure that the large file (always called image from now
on) is downloaded in small parts which can be stored on different
servers. People who want to download the image do so by telling the
jigdo(1) (NOT IMPLEMENTED YET) download tool to process one ‘.jigdo’
file; using it, jigdo downloads the parts and reassembles the image.
jigdo-file is used to prepare the files for download.
What makes jigdo special is that the parts that are used to reconstruct
the image can have any size and content - they only need to be
contained in a contiguous region anywhere in the image.
For example, if you wish to distribute an ISO9660 image which contains
a snapshot of an FTP server, you can instruct jigdo-file to prepare the
download data in such a way that when people use jigdo to download the
image, jigdo actually fetches the individual files from the FTP server
and assembles them into an exact copy of your image - during the
download! (If the image is not a filesystem dump, you can use split(1)
to create the small parts that the image will be reassembled from.)
You are completely free to choose where the individual parts of the
image are stored: They may be in entirely different directories on
different servers (e.g. because of storage/bandwidth constraints), but
this is invisible to the people downloading your image. The information
about available servers only needs to be added to the ‘.jigdo’ file by
you before distributing it.
The ‘DETAILS’ section below contains technical details on how jigdo
works. The ‘EXAMPLES’ section lists a number of common scenarios and
may help you to get an idea of what jigdo is useful for.
OPTIONS
Many options are specific to a particular COMMAND; the ones below are
general or used by several commands. Further options are listed below
with the individual commands. All options are silently ignored if they
are not applicable to the current command. For any BYTES parameters to
options, you can append one of the letters ‘k’, ‘M’ or ‘G’ to the
amount you specify, to indicate kilobytes, megabytes or gigabytes.
-h --help
Output short summary of commands and options.
-H --help-all
Output complete summary of commands and options.
-v --version
Output program version.
-i --image=cdrom.iso
Specify location of the file containing the image. The image is
the large file that you want to distribute.
-j --jigdo=cdrom.jigdo
Specify location of the Jigsaw Download description file. The
jigdo file is a human-readable file generated by jigdo-file, to
which you add information about all the servers you are going to
upload the files to. jigdo will download this file as the first
step of retrieving the image.
-t --template=cdrom.template
Specify location of the image ‘template’ file. The template file
is a binary file generated by jigdo-file, it contains
information on how to reassemble the image and also (in
compressed form) all the data from the image which was not found
in any of the parts.
Depending on the command, each of these three files is used
sometimes for input, sometimes for output. If the file is to be
used for output for a particular command and the output file
already exists, jigdo-file exits with an error, unless --force
is present.
In most cases, you will only need to specify one out of -i -j
-t, because any missing filenames will be deduced from the one
you specify. This is done by first stripping any extension from
the supplied name and then appending nothing (if deducing
--image), ‘.jigdo’ or ‘.template’.
-r --report=default|noprogress|quiet|grep
Control how verbose the program is, and what format the output
has: noprogress is the same as default except that no ‘x% done’
progress messages are printed. quiet restricts the output to
what is absolutely necessary, mostly error messages. grep is
only different from default for the make-template command: It
enables output in a simple ‘<offset> <file>’ format which is
useful when searching for binary files in other binary files.
-f --force
Overwrite existent output files without complaining.
--no-force
This is the default. Refuse to overwrite existent output files.
-c --cache=jigdo-cache.db
jigdo-file usually needs to read the entire contents of all the
FILES you specify. If you use it repeatedly (e.g. because you
make a new CD image available daily), caching the file
information will increase the program’s speed significantly. The
cache file is automatically created if it is not yet present.
Data is usually both read from and written to it.
--no-cache
This is the default. Do not use a cache.
--cache-expiry=SECONDS
Set maximum age of cache entries. Any entries older than this
will be removed from the cache. The default is 30 days. You can
append one of the letters ‘h’, ‘d’, ‘w’, ‘m’, ‘y’ to denote
hours, days, weeks, months or years, respectively. A value of
‘0’ or ‘off’ disables expiry, so that all entries will stay in
the cache forever. See the section ‘CACHE FILES’ below for more
information.
--readbuffer=BYTES
Set size of internal buffers. The default is 128k - if you have
a fast disc, increasing this value may make jigdo-file faster,
but in general, changing it is not necessary.
--md5-block-size=BYTES
Uninteresting internal parameter. Set size of blocks into which
files are subdivided. The default is 128k. If you change it, any
cache file will have to be regenerated. Internally, jigdo-file
may choose to use a slightly larger or smaller value.
-T --files-from=file
Read file and directory names from the specified file. If file
is ‘-’, read names from standard input. Each line in the file is
taken as a name, so the names may contain spaces, but not
newline characters. An empty line causes jigdo-file to stop
reading from the file.
find(1) is a powerful tool for generating file lists, but make
sure to use ‘find -type f’ if possible - otherwise, if you
instruct find to output both a filename and a symlink to that
filename, jigdo-file will read the file contents twice.
--hex Output checksums in hexadecimal instead of Base64-like format.
This should not be used with the make-template command, because
the resulting ‘.jigdo’ file violates the ‘.jigdo’ file format.
Its intended use is to make jigdo-file more interoperable with
other Unix shell utilities like md5sum(1).
--no-hex
This is the default. Use jigdo’s own Base64-like encoding of
checksums.
--debug[=help|=all|=UNIT,~UNIT... ]
Switch on or off debugging output. Just ‘--debug’ is equivalent
to ‘--debug=all’. The argument is a comma-separated list of unit
names for which debugging output is to be enabled, or disabled
if the name is preceded by ‘~’. The special name ‘all’ means all
units. By default, debugging output is switched off except for
the units ‘assert’ and ‘general’. The exact list of available
units for which debugging can be switched on depends on whether
jigdo was compiled with debugging support - the list can be
printed with ‘--debug=help’.
FILES Names of files or directories to use as input. These are the
parts that are contained in the image. In case one of the names
is a directory, the program recursively scans the directory and
adds all files contained in it. While doing this, it follows
symbolic links, but avoids symlink loops.
If one of the filenames starts with the character ‘-’, you must
precede the list of files with ‘--’. A value of ‘-’ has no
special meaning in this list, it stands for a file whose name is
a single hyphen.
COMMANDS
The command name is the first non-option argument passed to jigdo-file.
Most commands have short abbreviations as well as long names. The short
command names should not be used in scripts - there may be incompatible
changes to them in the future!
MAKE-TEMPLATE, MT
Reads image and FILES, creates ‘.jigdo’ and ‘.template’. This is the
main functionality of jigdo-file.
It is possible to specify both --image=- and --files-from=-. In this
case, first the list of files is read from standard input until an
empty line is encountered. Everything following it is assumed to be the
image data. This can be useful if you use mkisofs(1) or similar
programs that can output the complete image on their standard output,
because there is no need to store the image on disc temporarily.
If a FILES argument contains the characters ‘//’ (Unix) or ‘\.\’
(Windows), this has special meaning. In the final jigdo file that users
will download, each of the parts is referenced in the ‘[Parts]’ section
with a URI of the form ‘Label:some/filename’. (See ‘FORMAT OF .JIGDO
FILES’ below for a detailed description.) The ‘[Servers]’ section gives
a mapping of labels to servers on the internet, with lines like
‘Label=http://myserver.org/jigdofiles/’. Using this information, jigdo
will create the final download URI for the part,
‘http://myserver.org/jigdofiles/some/filename’. Specifying ‘//’ (or
‘\.\’) in a file or directory name serves to ‘cut off’ the names at the
right directory level. For example, if the Unix path of one of your
FILES is ‘/path/some/filename’, you can tell jigdo-file to cut off
after the ‘/path’ by passing it the argument ‘/path//some/filename’, or
‘/path//’ if you want the whole directory scanned. The path names need
not be absolute; ‘somedirectory//’ is also possible.
--label Label=/path
Specify a name to use as the label name for a path on disc.
(Influences the output jigdo file.) If you used ‘//’ in the
FILES arguments as described above, jigdo-file will by default
pick label names automatically (‘A’, ‘B’ etc.). With this
option, you can give labels more meaningful names. Note that the
label name will only be used if one or more FILES begin with
‘/path//’.
Try to use label names that start with uppercase characters, to
disambiguate them clearly from protocol names like ‘http’,
‘ftp’.
--uri Label=http://some.server.org/
By default, using --label as described above will cause lines of
the form ‘Label=file:/path/’ to be written to the ‘[Servers]’
section of the output jigdo file. If you want to override the
‘file:’ URI so that the line reads
‘Label=http://some.server.org/’, you can do so by specifying
--uri along with --label. Giving just --uri Label=... without
the corresponding --label Label=... has no effect, and even if
you specify both, an entry is only added to the ‘[Servers]’
section if the label is referenced by at least one ‘[Parts]’
entry.
The supplied value is not quoted by the program; if it contains
characters such as space or any of the characters #"’\ then you
must quote it. (Under Unix, you may need to quote the value
twice to also protect it from the shell, e.g. \\\\ or ’\\’ to
get a single backslash in the URI.)
The mapping specified with an --uri option is ignored if it is
already present in the output jigdo file.
Users of the Windows version may notice that the ‘\’ directory
separators are converted into ‘/’ in the ‘file:’ URIs that are
generated by default. This is done to increase cross-platform
compatibility of ‘file:’ - the print-missing command of the
Windows version will automatically re-convert the characters
when it prints the URIs. In case you supply your own ‘file:’
URIs under Windows using --uri, you must also exchange ‘/’ and
‘\’.
-0 to -9
Set amount of compression in the output template file, from -0
(no compression) to -9 (maximum compression). The default is -9,
which can make the template generation quite slow. By default,
the compression algorithm used is the same as for gzip(1).
--gzip and --bzip2
Choose between the gzip and bzip2 compression algorithms. The
default is gzip. Bzip2 usually gives a better compression ratio,
but compression is significantly slower than with gzip.
--min-length=BYTES
Set minimum length of a part for jigdo-file to look for it in
the image. The default is 1k. Parts smaller than this will
never be found in the image, so their data will be included in
the template file. The search algorithm used requires such a
minimum length, otherwise template generation could become
extremely slow. If you know for sure that all your FILES are
larger than a certain amount, you can increase jigdo-file’s
speed slightly by specifying the amount with this option. There
is a hard-wired absolute minimum of 256 bytes - anything lower
will silently be set to 256.
--merge=FILE
Include the contents of FILE in the output ‘.jigdo’ file. The
file can contain data which you want added to the output (for
example, a ‘[Servers]’ section with a list of your servers as
entries), or it can be the jigdo file output by an earlier run
of jigdo-file.
It is possible to specify the same file for input with --merge
and for output with --jigdo. However, you will also need to use
--force to make the program overwrite the old version of the
jigdo file with the new one. FILE can be ‘-’ for standard
input.
When adding new information to the supplied file, jigdo-file
will not insert new lines into the ‘[Parts]’ section if an entry
for the same MD5 checksum (but not necessarily with the same
URI!) already exists, and it will not insert new lines into the
‘[Servers]’ section if a completely identical entry already
exists.
When reading in the existing FILE, the behaviour is slightly
different: The program preserves entries in the ‘[Parts]’
section with identical checksum, but different URIs. For
completely identical entries (same checksum and URI), only one
entry is preserved and the duplicates are removed. The
‘[Servers]’ section is left untouched.
--image-section
This is the default. Causes jigdo-file to add an ‘[Image]’
section to the ‘.jigdo’ file.
As an exception, a new ‘[Image]’ section is not added if you use
--merge and the file to merge contains an ‘[Image]’ section with
a line which reads ‘Template-MD5Sum=’ (end of line after the
‘=’). In this case, the generated template data’s MD5 checksum
value is just added after the ‘=’ of the first line of this form
in the file - no whole new ‘[Image]’ section is appended. This
behaviour is useful because it allows you to pass via --merge an
‘[Image]’ section with arbitrary content and then have the MD5
checksum automatically added by jigdo-file. The section ‘FORMAT
OF .JIGDO FILES’ below explains the ‘[Image]’ section contents
in greater detail.
--no-image-section
Do not include an ‘[Image]’ section in the ‘.jigdo’ file. You
need to add one yourself if you use this option. However, doing
that is not easy (you also need to add a ‘Template-MD5Sum’ line
with the correct checksum, or jigdo will complain), so use of
this option is discouraged.
--servers-section
This is the default. Causes jigdo-file to add a ‘[Servers]’
section to the ‘.jigdo’ file. This default section uses ‘file:’
URIs, which allows for immediate reassembly of the image from
the local filesystem, and is also useful if you want to edit the
file manually and replace the ‘file:’ URIs with other URIs.
--no-servers-section
Do not add a ‘[Servers]’ section at the end of the ‘.jigdo’
file. Useful e.g. if you are going to append the section with a
script.
--match-exec=SHELLCOMMAND
Whenever a file is found in the image, execute the supplied
command string by passing it to a shell. jigdo-file sets up a
number of environment variables with information about the file
match. For example, if the file ‘/path//a/b/file’ was found in
the image and ‘Label:a/b/file’ is going to be written to the
‘.jigdo’ file:
· LABEL="Label" - Name of the label for the file. The example
assumes that ‘--label Label=/path’ was specified by you. In
the absence of such an option, LABEL will be set but empty.
· LABELPATH="/path/" - The path corresponding to the label, or
in other words, the prefix of the matched file’s path that
will not appear in the output ‘.jigdo’ file. Is set even
without any ‘--label’ option present. Ends with a slash.
· MATCHPATH="a/b/" - The rest of the path, without the leafname
of the matched file. Is either empty or ends with a slash.
· LEAF="file" - The leafname of the matched file.
· MD5SUM="lNVdUSqbo2yqm33webrhnw" - The md5sum of the matched
file, in Base64-like format.
· FILE="/path//a/b/file" - For convenience, the complete path of
the file. The variable is always set to
$LABELPATH$MATCHPATH$LEAF.
Please be careful to correctly quote the string passed to this option,
otherwise your supplied command will not work with filenames that
contain spaces. As an example, to create a backup of hard links to the
matched files, use the following option: --match-exec=’mkdir -p
"${LABEL:-.}/$MATCHPATH" && ln -f "$FILE"
"${LABEL:-.}/$MATCHPATH$LEAF"’
By default, no command is executed. Use --match-exec="" to remove a
command string which was set with an earlier use of this option.
--greedy-matching
This is the default. Imagine that your image contains a .tar
file which in turn contains another file x, and that you provide
both the .tar and the files inside it on the command line. When
jigdo-file scans the image, it encounters the beginning of the
.tar file, and then the file x.
At this point, a decision must be made: Should the smaller file
x be recorded as matched, or should it be ignored in favour of
the larger (and thus better) match of the .tar file?
Unfortunately, at this point it is not clear whether there will
actually be a full match of the .tar, so by default, the program
prefers the small match.
--no-greedy-matching
In the case where a large partial match is present and a shorter
match has been confirmed, ignore the small match. (See the
option above.)
MAKE-IMAGE, MI
Reads ‘.template’ and FILES, creates image (or ‘imagename.tmp’).
Provides a rudimentary way of reassembling images - jigdo is usually
better suited for this task. However, in contrast to jigdo, no ‘.jigdo’
file is required.
If the image is to be written to a file (and not to standard output),
it is possible to create the image in several steps, with several
invocations of ‘jigdo-file make-image’, as follows: You first invoke
jigdo-file, specifying as many files as are available at this time. The
program scans the files, and those that are contained in the image are
copied to a temporary file, whose name is formed by appending ‘.tmp’ to
the image filename.
For all further files which could be parts of the image, you repeat
this process. As soon as all parts are present, the temporary file will
be truncated slightly (to delete some administrative data that jigdo-
file appends at the end) and renamed to the final image name. The
possibility of reassembling the image in several steps is especially
useful for gathering files from removable media, e.g. several older
CDs.
Scripts using make-image can detect whether image creation is complete
by checking the exit status: 0 signals successful creation, whereas 1
means that more files need to be supplied. Other errors result in an
exit status of 2 (‘recoverable’, e.g. file not found) or 3 (non-
recoverable, e.g. write error).
--check-files
This is the default. Whenever any part is copied to the image,
re-check its checksum against the checksum stored in the
template. It is recommended that you leave this switched on,
even if it slows down image creation a bit.
--no-check-files
Do not check files’ checksums when copying them to the image.
This can be safely used when no cache file is used (which means
that files will be written to the image immediately after being
scanned) or the whole image is checked later with the verify
command.
PRINT-MISSING, PM
Reads ‘.jigdo’, ‘.template’ and (if present) ‘imagename.tmp’, outputs a
list of URIs still needed to completely reassemble the image.
Together with the make-image command, this provides most of the
functionality of jigdo on the command line.
For each part that is not yet present in the temporary image file, the
file checksum is looked up in the ‘[Parts]’ section of the jigdo file.
Any label in the corresponding entry is then expanded according to the
label definitions in the ‘[Servers]’ section and printed on standard
output. jigdo allows you to specify several alternative locations for
each label in this section, but print-missing will only output the
first one for each missing part.
If the checksum cannot be found in the ‘[Parts]’ section (this Should
Not Happen unless you deleted that section), a lookup is instead made
for ‘MD5Sum:<checksum>’, just like with jigdo. (Thus, if you want to
get rid of the ‘[Parts]’ section, you can do so if you rename each part
to its own checksum.)
--uri Label=http://some.server.org/
Override the entries in the ‘.jigdo’ file for any label with a
URI of your choice. With the example above, a ‘[Parts]’ entry of
‘Label:some/filename’ will cause the line
‘http://some.server.org/some/filename’ to be printed.
The supplied value is not quoted by the program; if it contains
characters such as space or any of the characters #"’\ then you
must quote it. (Under Unix, you may need to quote the value
twice to also protect it from the shell, e.g. \\\\ or ’\\’ to
get a single backslash in the URI.)
PRINT-MISSING-ALL, PMA
Just like print-missing, this command outputs a list of URIs still
needed to completely reassemble the image. However, all alternative
download locations are printed instead of just one. In the output, the
URIs for a file are separated from other files’ URIs with blank lines.
The --uri option has the same effect as for print-missing.
VERIFY, VER
Reads image (presumably generated with make-image) and ‘.template’,
checks for correct checksum of image.
The template data does not only contain checksums of the individual
parts, but also of the image as a whole. make-image already performs a
number of internal checks, but if you like, you can additionally check
the image with this command.
SCAN, SC
Reads all the FILES and enters them into the cache, unless they are
already cached. The --cache option must be present for this command.
--no-scan-whole-file
This is the default. This only causes the first --md5-block-size
bytes of each file to be read. If the cache is used later by
jigdo-file make-image, the rest of the file will be read once
these first bytes are recognized in the input image.
--scan-whole-file
Immediately read the entire file contents and store them in the
cache.
MD5SUM, MD5
Reads all the FILES and prints out MD5 checksums of their contents.
This command is quite similar to md5sum(1), except that the checksum is
output in the Base64-like encoding which is also used elsewhere by
jigdo-file.
The FILES arguments are processed in the same way as with the other
commands, which means that recursion automatically takes place for any
arguments that are directories, and that symbolic links are not listed
except when the file(s) they point to are not reachable directly.
In the checksum list printed on standard output, only the part of the
filename following any ‘//’ (or ‘\.\’ on Windows) is printed. Any
--cache will be used for querying files’ MD5 checksums and/or writing
the checksums of scanned files.
LIST-TEMPLATE, LS
Reads a ‘.template’ file and outputs low-level information about the
image and all parts contained in it, including offset, length and
checksum.
You can also use this command with temporary image files (by specifying
something like --template=imagename.tmp) - in that case, the output
also distinguishes between parts that have been written to the image
and parts that haven’t.
The exact output format may change incompatibly between different jigdo
releases. The following different types of lines can be output. ‘have-
file’ only occurs for ‘.tmp’ files, indicating a file that has already
been successfully written to the temporary file:
in-template offset-in-image length
need-file offset-in-image length file-md5sum filestart-rsyncsum
have-file offset-in-image length file-md5sum filestart-rsyncsum
image-info image-length image-md5sum rsyncsum-size
DETAILS
Jigsaw Download was created with the format of ISO9660 CD images in
mind - however, the following also applies to many other filesystem
formats, as well as to ‘tar’ archives and uncompressed ‘zip’ archives.
A CD image contains both information for organizing the filesystem
(header with disc name etc., ISO9660 directory data, data of extensions
such as Joliet or RockRidge, zero padding) and the files contained on
the CD. An important property that jigdo relies on is that each file is
stored in one contiguous section of the image; it is not split into two
or more parts.
When jigdo-file is given a number of files that might be contained in
an image, it detects whether any of the files are present using a
‘rolling checksum’ inspired by the one used by rsync(1). The resulting
data is written to the ‘.template’ file: If a section of the image
could not be matched (e.g. it was directory information), the data is
compressed and written directly to the template. However, if a matching
file was found, its data is omitted from the template. Instead, only a
reference (an MD5 checksum of the file) is inserted in the template.
Note that the template data only contains binary data, it does not
contain any filenames or URIs, since it cannot be easily edited in case
any of these values need to be changed. All that information is stored
in the ‘.jigdo’ file, a text file to which you can add URLs for your
server(s). The jigdo file provides a mapping for each MD5 checksum to
one or more alternative download locations for the corresponding part.
Apart from the mapping of MD5 sums to URIs, the jigdo file also
contains an URI pointing to a download location for the template file.
This way, the jigdo download tool only needs to be given one URI (that
of the ‘.jigdo’ file) to be able to download and reassemble the
complete image.
FORMAT OF .JIGDO FILES
The overall format of ‘.jigdo’ files follows that of ‘.ini’ files, as
also used by the Gnome and KDE projects for some data. The file is
organized into sections, each of which is preceded by a line reading
‘[Sectionname]’. Within each section, lines have the form
‘Label=Value’. Such lines are also called ‘entries’ below. All ‘.jigdo’
files use UTF-8 as their character encoding.
Comments are introduced with the ‘#’ character and extend to the end of
the line. Whitespace is ignored at line start and end as well as to the
left and right of section names and the ‘=’ in entries. Furthermore,
the jigdo utilities split up the text of the entry value (i.e. the part
after the ‘=’) into whitespace-separated words, much like the Unix
shell. Single ’’ and double "" quotes can be used to prevent that e.g.
URIs containing whitespace are split apart. Similarly, characters with
special meaning (the characters ’"#\ and space/tab) must be quoted with
\ to appear in the value. As with the shell, there is a difference
between ’ ’ and " ": Within ’ ’, the characters "#\ and whitespace lose
their special meaning and become ordinary characters, whereas within
" ", only the characters ’# and whitespace lose their special meaning -
in other words, backslash escapes still work inside " ", but not ’ ’.
‘.jigdo’ files can optionally be compressed with gzip(1). jigdo-file
always outputs uncompressed files, which you can compress yourself.
jigdo-lite supports single uncompressed and compressed files.
(Behaviour which may change in the future and which should not be
relied upon: jigdo additionally supports any number of concatenated
plaintext and gzipped parts in the files - for example, you can
compress a ‘.jigdo’ file and then add a couple of lines of uncompressed
data to the end.)
In all cases, the ‘.gz’ extension should be removed from the filename -
the tools will determine automatically from the file contents whether a
file is compressed or not.
Below is a description of the individual section names used by jigdo.
JIGDO SECTION
[Jigdo]
Version=1.1
Generator=jigdo-file/1.0.0
Information about the version of the jigdo file format used, and the
program that generated it. There should be one such section per
‘.jigdo’ file.
IMAGE SECTION
[Image]
Filename="filename for saving on users disc"
Template="URI where to fetch template file"
Template-MD5Sum=OQ8riqT1BuyzsrT9964A7g
ShortInfo=single-line description of the image (200 characters max.)
Info=long description (5000 characters max.)
The value for the ‘Template’ entry can be either an URL (absolute or
relative to the URL of the jigdo file) or a string of the form
‘Label:pathname’ (UNIMPLEMENTED), as described below.
The ‘Template-MD5Sum’ entry is added by jigdo-file and specifies the
MD5 checksum of the generated ‘.template’ file. It is used by jigdo to
detect cases where the downloaded template data is corrupted or belongs
to a different image.
Unlike other entry values, the values of the ‘ShortInfo’ and ‘Info’
entries are not split up into words, instead all quoting is preserved.
The value of the ‘Info’ entry is special in that jigdo(1) can
optionally parse XML markup it contains. If the markup has errors such
as unbalanced/unsupported tags, the string is displayed literally,
without XML parsing. Supported tags are <b></b> (bold), <i></i>
(italic), <tt></tt> (typewriter font), <u></u> (underline), <big></big>
(larger font), <small></small> (smaller font) and <br/> (linebreak).
Supported entities include < (‘<’), > (‘>’) and & (‘&’). Note
that the whole ‘Info’ entry must be on one line in the jigdo file.
This section may occur multiple times, but all except the first one
will be ignored. This is useful e.g. when creating a ‘.jigdo’ file for
a DVD image when you already have ‘.jigdo’ files for CDs with the same
content: You can simply ‘[Include]’ (see below) the CDs’ jigdo files at
the end of the DVD jigdo file, after its ‘[Image]’ section.
PARTS SECTION
[Parts]
xJNkjrq8NYMraeGavUpllw=LabelA:part0
GoTResP2EC6Lb_2wTsqOoQ=LabelA:part1
kyfebwu6clbYqqWUdFIyaw=LabelB:some/path/part2
-J9UAimo0Bqg9c0oOXI1mQ=http://some.where.com/part3
All lines in the section, which provides the mapping from MD5 checksums
to URIs, have the same format: On the left side of the ‘=’ the checksum
(encoded with a Base64-like encoding) is given, and on the right a
string corresponding to the part with this checksum; either a complete
URI or a string of the form ‘Label:pathname’, which is expanded into
one or more URIs by looking up the definition(s) for the Label in the
‘[Servers]’ section.
In case a particular MD5 checksum cannot be found in any ‘[Parts]’
section by jigdo, the program will perform a lookup for
‘MD5Sum:<checksum>’, e.g. for ‘MD5Sum:xJNkjrq8NYMraeGavUpllw’ if you
deleted the line for ‘part0’ above.
A checksum appearing multiple times in this section indicates
alternative download locations for the part.
There may be any number of ‘[Parts]’ sections in the file; they are all
considered when looking up MD5 checksums.
jigdo-file always puts the ‘[Parts]’ section at the end of the file,
and it even rearranges any file specified with --merge to have only one
such section at the end. This is done to allow jigdo to display the
information from the ‘[Image]’ section while the rest of that file is
still being downloaded.
SERVERS SECTION
[Servers]
LabelA=http://myserver.org/
LabelA=ftp://mirror.myserver.org/
LabelB=LabelC:subdirectory/
LabelC=http://some.where.com/jigdo/
All lines in the section, which provides the mapping from server labels
to server locations, have the same format: On the left side of the ‘=’
the label name is given, and on the right the value to expand the label
name to.
A label name appearing multiple times in this section indicates
alternative download locations for the parts that use the label in the
‘[Parts]’ section. This notation makes it very easy to add mirrors to
the jigdo file.
As shown by the example above, the label values may themselves
reference other labels. In this case, the entry
‘LabelB:some/path/part2’ in the ‘[Parts]’ section will expand to
‘http://some.where.com/jigdo/subdirectory/some/path/part2’. Loops in
the label definitions result in undefined behaviour and must be
avoided.
There may be any number of ‘[Servers]’ sections in the file; they are
all considered when looking up labels. Either of ‘[Parts]’ or
‘[Servers]’, but not both, can be omitted from the jigdo file.
COMMENT SECTION
[Comment]
Any text, except that lines must not begin with ‘[’.
All text following a ‘[Comment]’ or ‘[comment]’ line is ignored, up to
the next line with a section label.
INCLUDE DIRECTIVE
[Include http://some.url/file.jigdo]
Lines of this form cause the content of the specified jigdo file to be
downloaded and parsed just like the main jigdo file. The effect will be
the same as copying the included file’s contents into the file which
contains the include directive. (Exception: Any relative URLs are
always resolved using the URL of the ‘.jigdo’ file that contains that
relative URL.)
The URL argument can be an absolute or relative URL. Relative URLs are
assumed to be relative to the URL of the jigdo file which contains the
include directive. Includes can be nested, but it is an error to create
a loop of include directives. It is not possible to use URLs of the
form ‘Label:pathname’.
The URL cannot be quoted with "". Any ‘]’ characters in the argument
must be escaped as ‘%5D’, and any spaces as ‘%20’.
Include directives are only supported by jigdo, they are ignored by
jigdo-lite.
An include directive terminates any previous section, but it does not
start a new one. In other words, a new section must always be started
after the include line, jigdo does not allow normal entries to appear
below the ‘[Include]’.
CACHE FILES
Any file specified with the --cache option is used to store information
about the FILES presented to jigdo-file. When querying the cache, a
file is considered unchanged (and the cached data is used) only if
filename, file size and last modification time (mtime) match exactly.
For the filename match, not the entire file name is used, but only the
part following any ‘//’, so that any changes to the part before the
‘//’ will not invalidate the cache.
Old cache entries are removed from the cache if they have not been read
from or written to for the amount of time specified with --cache-
expiry. Entries are not immediately removed from the cache if the file
they refer to no longer exists - this makes it possible to cache
information about files on removable media.
Cache expiry only takes place after jigdo-file has done its main work -
if any old entries are accessed before expiry takes place, they will be
kept. For example, if the program is run using the default expiry time
of 30 days, but accesses a cache file with entries generated 2 months
ago, then entries in that cache will be considered, and only those
cache entries that were not needed during the program run will be
expired.
Due to a peculiarity of the underlying database library (libdb3), cache
files never shrink, they only grow. If a large number of entries was
expired from your cache file and you want it to shrink, you can either
just delete it (of course then everything will have to be regenerated)
or use the utilities accompanying libdb3 to dump and restore the
database, with a command like ‘db3_dump old-cache.db | db3_load new-
cache.db’. For Debian, these programs are supplied in the package
‘libdb3-util’.
If a different --md5-block-size is specified, the entire file needs to
be re-read to update its cache entry. If a different --min-length is
specified, only the first ‘md5-block-size’ bytes of the file need to be
re-read.
EXAMPLES
PREPARING YOUR CD IMAGE FOR DISTRIBUTION
You have created a CD image ‘image.iso’ from some of the files stored
in the directory ‘/home/ftp’ on your harddisc, which is also available
online as ‘ftp://mysite.org’. As you don’t want to waste space by
effectively hosting the same data twice (once as files on the FTP
server, once inside the image), and you are fed up with users’
downloads aborting after 200MB and their restarting the download dozens
of times, you decide to use jigdo. How do you prepare the image for
download?
In fact, only one command is necessary:
jigdo-file make-template --image=image.iso
--jigdo=/home/ftp/image.jigdo
--template=/home/ftp/image.template /home/ftp// --label
Mysite=/home/ftp --uri Mysite=ftp://mysite.org/
People can now point jigdo at ‘ftp://mysite.org/image.jigdo’ to
download your image. The template file needs to be accessible as
‘ftp://mysite.org/image.template’.
Note that nothing prevents you from doing the same for an FTP server
that isn’t administrated by you - in that case, you only need to host
the ‘.jigdo’ and ‘.template’ files on your own server/homepage.
PREPARING AN ARBITRARY LARGE FILE FOR DISTRIBUTION
We assume that you have a large file that is not a filesystem, e.g.
‘movie.mpeg’. Because of space problems, you want to distribute the
data on two servers.
In this case, the parts of the image need to be generated artificially
with the split command. For example, to create chunks of 4MB each, use
‘split -b 4m movie.mpeg part’. Copy the resulting files ‘partXX’ into
two directories ‘1’ and ‘2’ that you create, according to how you want
the files distributed between the servers. Next, create the jigdo and
template files with ‘jigdo-file make-template --image=movie.mpeg 1//
2//’. You will need to edit the ‘.jigdo’ file and provide the right
URIs for the two servers that you are going to upload the ‘partXX’
files to.
CUSTOMIZED VERSIONS OF IMAGES
Because it is possible to assign a different URI for each part of an
image if necessary, jigdo is very flexible. Only one example is the
possibility of customized versions of images: Suppose that someone is
distributing a CD image, and that you want to make a few small changes
to it and redistribute your own version. You download the
‘official.iso’ CD image with jigdo (passing it the URL of
‘official.jigdo’), write it to CD-R, make your changes (say, adding
files from the ‘myfiles’ directory on your harddisc) and produce your
own version, ‘myversion.iso’. Next, you instruct jigdo-file to create
the jigdo and template files for your modified image, using the command
jigdo-file make-template --image=myversion.iso /mnt/cdrom/
myfiles// --label My=myfiles/ --uri My=http://my.homepage.net/
--merge=official.jigdo
while ‘official.iso’ is mounted under ‘/mnt/cdrom’. By using --merge,
you have told jigdo-file to take the contents of ‘official.jigdo’, add
to it a new ‘[Image]’ section for ‘myversion.iso’ and write the
resulting jigdo file to ‘myversion.jigdo’ - so now ‘myversion.jigdo’
offers two images for download, the original version and your modified
version. (If you do not want it to offer the official version, edit it
and remove the ‘[Image]’ section that lists ‘official.iso’.)
Now you can upload the ‘.jigdo’ file, the ‘.template’ file and also the
files in ‘myfiles’ to ‘http://my.homepage.net/’. Thus, for people to
download your modified image, you do not need to upload the complete
image contents to your web space, but only the changes you made!
(In case you only made very few changes, you could also omit the
‘myfiles’ parameter in the command above, then all your changes end up
in the new template file.)
COMBINING MANY JIGDO-MANAGED IMAGES INTO ONE
It is also no problem to combine data from several sources that use
jigdo. For example, if of five different and unrelated servers each one
distributes a different CD image via jigdo, you can create a customized
DVD image that contains the data from all these CDs. When people use
jigdo to download your image, the individual files on the DVD are
fetched from the same sources as the original CDs.
Consequently, even though you will be distributing a 3.2GB file via
your web space, the actual amount of data that is stored on your server
will only be in the order of several MBs.
BUGS
For certain contents of one of the input files, most notably a sequence
of zero bytes longer than --min-length at the start of the file and an
area of zeros preceding the file data in the image, jigdo-file make-
template may fail to find the file in the image. Unfortunately, this
restriction cannot be avoided because the program could become very
slow otherwise. If you use the --debug option, all instances of jigdo-
file discarding possible matches are indicated by lines containing the
word ‘DROPPED’.
In fact, not only all-zeroes files trigger this behaviour, but also
files which contain at their start a long sequence of short identical
strings. For example, both a file containing only ‘a’ characters and
one containing ‘abcabcabcabc...’ are problematic.
SEE ALSO
jigdo(1) (NOT YET IMPLEMENTED), jigdo-lite(1), jigdo-mirror(1),
split(1) (or ‘info split’), find(1) (or ‘info find’), mkisofs(1),
md5sum(1)
AUTHOR
Jigsaw Download <URL:http://atterer.net/jigdo/> was written by Richard
Atterer <jigdo atterer.net>, to make downloading of CD ROM images for
the Debian Linux distribution more convenient.
19 May 2006