207 lines
8.1 KiB
Plaintext
207 lines
8.1 KiB
Plaintext
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Hiding files on a CD
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=====================
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This document attempts to show how to hide files from being seen by an
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operating system accessing a CD as an ISO9660/Rock Ridge, Joliet or HFS
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CD. It also highlights some of the limitations ...
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Note: this document is about the various -hide options - not be confused with
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the -hidden options.
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The -hidden options set the 'EXISTENCE' bit in the directory entry which
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means the file or directory will be invisible - unless some special option
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is used to mount or view the CD - Linux has the 'unhide' mount option to
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make these files visible. i.e. the directory entry exists on the CD.
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With hindsight, to avoid confusion with the -hidden option, it would have
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been better to chose an option name like '-omit' instead of '-hide'...
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The various -hide options actually exclude the relevant directory entry
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from the directory tree. Therefore, it is not possible to access a file
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or directory that has be hidden with the -hide option when the ISO9600/Rock
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Ridge directory is mounted - because the directory entry does not exist on the
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CD (but the file data does). You would probably be able to access this file
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or directory when mounted as a Joliet or HFS CD (depending on other options
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used). Similarly, a directory entry hidden with the -hide-joliet option
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will not be accessible when mounted as an Joliet CD. Similarly for -hide-hfs
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etc.
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If you don't want a file or directory to appear on the CD at all, then use the
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-exclude options, not the -hide options (mkisofs completely ignores any
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file/directory excluded with the -exclude options).
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Using the hide options
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======================
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There are 6 hide options:
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-hide Hide a file/directory from the ISO9660/Rock Ridge directory
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-hide-list As above, but read file names from a file
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-hide-joliet Hide a file/directory from the Joliet directory
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-hide-joliet-list As above, but read file names from a file
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-hide-hfs Hide a file/directory from the HFS directory
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-hide-hfs-list As above, but read file names from a file
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You can use the -hide, -hide-joliet and/or -hide-hfs options as many times
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as you like on the command line, but if you have many files to hide, then
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it may be better to put your file names in a file (one per line) and use
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the corresponding 'list' option. You can also use the three -hide-list options
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as many times as you want.
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The arguments to the -hide options are either the 'basename' or the 'whole
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path name' of a file. That is, if you use the option:
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% mkisofs -hide ABC [-other-options] CD_directory
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then any file with the name ABC will be hidden. If you want to be more
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specific, then use the whole name - as seen by mkisofs e.g.:
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% mkisofs -hide CD_directory/XYZ/ABC [-other-options] CD_directory
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will hide just the file 'CD_directory/XYZ/ABC' - not any other file called
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'ABC' that might exist under 'CD_directory'. However, if your command line
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is like:
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% mkisofs -hide CD_directory/XYZ/ABC [-other-options] ./CD_directory
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Then the file 'CD_directory/XYZ/ABC' will not be hidden because as far as
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mkisofs is concerned. Its whole path is actually './CD_directory/XYZ/ABC'.
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You can use wild cards in the -hide arguments.
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If the file name to be hidden is a directory, then the directory and all
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its contents are hidden.
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The main use of the hide options is on a multi platform (hybrid CD) to hide
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various files/directories that are operating system specific from been seen
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on the CD when mounted on another OS. i.e. You may want to hide Macintosh
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executables from being seen when the CD is mounted as a Joliet CD on a PC etc.
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For example, say we want to create a ISO9660/Rock Ridge, Joliet, HFS hybrid
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CD from files/directories in the directory called 'cd_dir' - which are:
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MAC/
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MAC/app
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MAC/data/
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MAC/data/file1
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PC/
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PC/app
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PC/data/
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PC/data/file1
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UNIX/
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UNIX/app
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UNIX/data
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UNIX/data/file1
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COMMON/
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COMMON/some_files
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We could use the command line:
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% mkisofs -r -J -hfs -hide MAC -hide PC -hide-joliet MAC \
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-hide-joliet UNIX -hide-hfs PC -hide-hfs UNIX -o cd.iso cd_dir
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This will give a CD that when mounted as a Rock Ridge CD, you will only
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see the directories UNIX and COMMON, as a Joliet CD the directories
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PC and COMMON, and as an HFS CD the directories MAC and COMMON.
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If you also had the three files in the current directory called README.hfs,
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README.joliet and README.unix - but you wanted to have each of these
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files appear as just 'README' when mounted, then you could use the above
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command line with the following:
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% mkisofs -r -J -hfs -graft-points -hide MAC -hide PC -hide-joliet MAC \
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-hide-joliet UNIX -hide-hfs PC -hide-hfs UNIX \
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-hide README.hfs -hide README.joliet -hide-joliet README.hfs \
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-hide-joliet README.uni -hide-hfs README.joliet -hide-hfs README.unix \
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README=README.hfs README=README.joliet README=README.unix \
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-o cd.iso cd_dir
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Note: we've used the -graft-points option as we're using the '=' syntax
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to insert the files called README.hfs, README.joliet and README.unix as
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'README'
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The resulting CD when mounted as a Rock Ridge CD, will have the directories
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UNIX and COMMON - with the file called README - which was originally
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called README.unix.
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However, in most circumstances, it would be better to have the contents
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of each of the OS specific directories (plus the contents of the COMMON
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directory) to appear at the top level of the CD. i.e. when the CD is mounted
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(as ISO9660/Rock Ridge, Joliet or HFS) it has the contents:
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README
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app
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data/file1
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some_files
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Unfortunately, this is not as straight forward as it may seem - i.e. doing
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the following may seem OK, but it won't work - for reasons I'll explain
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later:
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It gets a bit messy using the -graft-points syntax above, so we'll assume
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each of the MAC, UNIX and PC directories contain the correct README, We'll
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also change to the 'cd_dir' directory and use the command:
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mkisofs -r -J -hfs -hide MAC -hide PC -hide-joliet MAC \
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-hide-joliet UNIX -hide-hfs PC -hide-hfs UNIX \
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-o cd.iso MAC PC UNIX COMMON
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You will get errors like:
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mkisofs: Error: UNIX/README and MAC/README have the same Rock Ridge name
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...
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mkisofs: Unable to sort directory
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This is because you can not hide "pathspecs" that are directories ("pathspecs"
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are file names given on the command line, or in a path-list file). This a
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"feature" of mkisofs. In this case nothing is actually hidden at all.
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So you might think that the following may work:
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mkisofs -r -J -hfs -hide "MAC/*" -hide "PC/*" -hide-joliet "MAC/*" \
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-hide-joliet "UNIX/*" -hide-hfs "PC/*" -hide-hfs "UNIX/*" \
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-o cd.iso MAC PC UNIX COMMON
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which may appear to work - but when the CD is mounted as an ISO9660/Rock Ridge
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or Joliet CD, then the directory "data" is missing.
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Again this is a feature of mkisofs - the directories PC/data and UNIX/data
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are mapped by mkisofs to the same output directory called "/data" - the
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various "hide" flags are stored with this directory info - in this case as
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the output directory "/data" is first hidden from the ISO9660/Rock Ridge and
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then the Joliet directory, the net result is that "/data" gets hidden from
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both directories ... the way mkisofs hides HFS directories is slightly
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different, so in this case the directory "data" exists on the HFS volume
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and contains the correct contents.
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However, it is possible to obtain the required result, but we have to be
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careful about hiding multiple input directories that map to a single output
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directory.
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To do this we have to hide just the files in these directories (or more
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accurately, all the non-directories). This is best done by using lists of
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files to hide for example:
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find PC -type f -print > pc.list
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find UNIX -type f -print > unix.list
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find MAC -type f -print > mac.list
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mkisofs -r -J -hfs -hide-list pc.list -hide-list mac.list \
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-hide-joliet-list unix.list -hide-joliet-list mac.list \
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-hide-hfs-list pc.list -hide-hfs-list unix.list \
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-o cd.iso MAC PC UNIX COMMON
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i.e. instead of trying to hide a directory and letting mkisofs hide its
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contents, we explicitly hide all the files in the directory, but not the
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directory and any of its sub-directories.
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This will work for the above input files, but if your directory trees contain
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symbolic links and/or directories that will not get merged, then the hide lists
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will have to be tailored to get the required result.
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James Pearson 22-Nov-2001
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Any comments/problems to j.pearson@ge.ucl.ac.uk
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