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QBall
Asked: 2015-03-11 03:10:41 +0800 CST

How to postition within magnetic tape in rescue mode of the installer image

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I'm trying to get data from magnetic tape in the ubuntu installer environment respectively the rescue mode of the ubuntu installer image.

To do so, i need to position on a distinct filespace/filemark within the magnetic tape. During normal operation the mt-st package is used for this.

So i have gone through all the *.udeb packages available in the /cdrom/pool/main tree of in the rescue mode of the ubuntu 14.04 installer image but didn't find a suitable package.

What are the possibilities?

debian-installer

1 Answers

  1. As the tape devices /dev/st0 (rewinding tape drive) and /dev/nst0 (non-rewinding tape drive) are discovered, the following workaround worked for me:

    dd if=/dev/st0 of=/dev/zero count=0

    rewinds the tape (equals "mt -f /dev/st0 rewind").

    dd if=/dev/nst0 of=/dev/zero [bs=<block size>]

    "fast forwards" to the next file space (equals "mt -f /dev/nst0 fsf 1"). But be aware: I saw some "out of memory"-messages from the dd command when the tape was created with large "block size" (i used 1MiB) and the was not specified. So you should generally know the "block size" when restoring from tapes in the installer environment.

    dd if=/dev/[n]st0 [bs=<block size>] | tar [<tar options>] -f - [<file spec>]

    Finally retrieves the data (the "-f -" tells tar to read from STDIN). Also here it is a very good idea to know the "block size" the tape was created with.

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