98 lines
3.9 KiB
Plaintext
98 lines
3.9 KiB
Plaintext
# ----------------------------------------------------------------------------
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# "THE BEER-WARE LICENSE" (Revision 42):
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# <phk@login.dknet.dk> wrote this file. As long as you retain this notice you
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# can do whatever you want with this stuff. If we meet some day, and you think
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# this stuff is worth it, you can buy me a beer in return. Poul-Henning Kamp
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# ----------------------------------------------------------------------------
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#
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# $Id$
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#
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What will I not find in this file ?
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-----------------------------------
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Instructions on how to obtain FreeBSD via CTM.
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Contact <phk@freefall.cdrom.com> for that.
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What is CTM ?
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-------------
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CTM was originally "Cvs Through eMail", but has since changed scope to be
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much more general.
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CTM is now meant to be the definitive way to make and apply a delta between
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two versions of a directory tree.
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There are two parts to this, making the delta and applying it. These are two
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entirely different things. CTM concentrates the computation-burden on the
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generation og the deltas, as a delta very often is applied more times than
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it is made. Second CTM tries to make the minimal size delta.
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Why not use diff/patch ?
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------------------------
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Good question. Primarily because diff and patch doesn't do their job very
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well. They don't deal with binary files (in this case files with '\0' or
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'\0377' characters in them or files that doesn't end in '\n') which isn't
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a big surprise: they were made to deal with text-files only. As a second
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gripe, with patch you send the entire file to delete it. Not particular
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efficient.
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So what does CTM do exactly ?
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-----------------------------
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CTM will produce a file, (a delta) containing the instructions and data needed
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to take another copy of the tree from the old to the new status. CTM means to
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do this in the exact sense, and therefore the delta contains MD5 checksums to
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verify that the tree it is applied to is indeed in the state CTM expects.
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This means that if you have modified the tree locally, CTM might not be able
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to upgrade your copy.
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How do I make a CTM-delta ?
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---------------------------
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Don't. Send me email before you even try. This is yet not quite as trivial
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as I would like. This is not to discourage you from using CTM, it is merely
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to warn you that it is slightly tedious and takes much diskspace.
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How do I apply a CTM-delta ?
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----------------------------
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You pass it to the 'ctm' command. You can pass a CTM-delta on stdin, or
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you can give the filename as an argument. If you do the latter, you make
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life a lot easier for your self, since the program can accept gzip'ed files
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and since it will not have to make a temporary copy of your file. You can
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specify multiple deltas at one time, they will be proccessed one at a time.
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The ctm command runs in a number of passes. It will process the entire
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input file in each pass, before commencing with the next pass.
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Pass 1 will validate that the input file is OK. The syntax, the data and
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the global MD5 checksum will be checked. If any of these fail, ctm will
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never be able to do anything with the file, so it will simply reject it.
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Pass 2 will validate that the directory tree is in the state expected by
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the CTM-delta. This is done by looking for files and directories which
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should/should not exists and by checking the MD5 checksums of files.
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Pass 3 will actually apply the delta.
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Should I delete the delta when I have applied it ?
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--------------------------------------------------
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No. You might want to selectively reconstruct a file latter on.
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What features are are planned ?
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-------------------------------
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This list isn't exhaustive, and it isn't sorted in priority.
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Reconstruct subset of tree.
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Make tar-copy of things which will be affected.
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Verify.
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Internal editor instead of ed(1)
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Support for mode
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Support for uid/gid
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Support for hardlinks
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Support for symlinks
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Isn't this a bit thin yet ?
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---------------------------
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Yes.
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Can I say something ?
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---------------------
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Yes, email me: <phk@freefall.cdrom.com>
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Poul-Henning
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