Successful System Cloning using Ignite-UX

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Over time, patches to pax have removed some of its limitations. This has allowed pax to increase
its support for both cpio and ustar formats to the maximums that the formats allow (file size,
maximum uid and gid values). Information is provided here about what those maximums are, as
they are less than what file systems on HP-UX support. This section does not discuss the patch
history of pax. It assumes that pax has been patched up to a level that addresses those limitations
to the extent possible.
When using pax format archives, it is important to understand that the pax format has no practical
limitations compared to ustar and cpio interchange formats. There are no restrictions on file size,
path length, file name length, or uid/gid values allowed by the format. This means if you previously
used ustar format archives and relied on it to not archive large files (files 8GB or larger), they will
be included in an archive if you use pax format archives.
Path Name Length Limitations in ustar Format
The full path to a file in ustar format can be split between the different fields in the header record
describing a file in the archive. The two fields have the following names and length (and they occur
in different parts of the header describing the file):
Name
4
Length
name 100
prefix 155
Standards
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control how a file name is placed into these two fields. If the name of the file is less than
or equal to 100 octets then the file name will be contained within the name field. If the name of the
file is more than 100 octets long the name must be split between the name and prefix field.
When the name of the file is split between the two fields it is not allowed to be split in the middle of
a path component. That means you can only split the file name where a '/' occurs. To put the file
name back together, as required by standards, you take the prefix field (if not NULL) followed by a
'/', then place the name field at the end. The way that the file name is put back together controls
how it can be split between the two fields.
For example, the following file name 'afilename', will not fit into a ustar format archive because
the path cannot be split leaving whole path components and still fit within the prefix and name
fields so it will not be added to the archive:
4
The names used here are the field names used in the Single Unix Specification Version 2.
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. The Open Group’s Single Unix Specification Version 2 can be viewed online by registering at
http://www.opengroup.org/. Viewing the standard online enables you to identify the limitations discussed in this section
more clearly.