Unix dump

Revision as of 17:18, 29 January 2019

dump is an archive format that is written by Unix dump, which is a backup program that was popular in the '90s (reference?). Dump files were often written to tape. Dump files can be read using the restore tool. It appears that no specifications exist.

Variants

There are a number of variants to the Unix dump format.

The file(1) magic definition of the format makes a distiction between 'old' and 'new' filesystem variants. Each of these can be big-endian or little endian. In addition a 16-bit subtype of the 'old' variant exists. Finally there is also a ufs2 variant (which again can be big-endian or little endian). In total this results in 7 variants of the format. According to the restore documentation, the dump file format changed in version 4.4 (of the dump tool?).

Software

• Dump / restore utilities

Documentation

• Linux man page for dump
• Linux man page for restore

Sample files

• Unix dump format - includes some minimal sample files, created for testing magic patterns

Restoring the contents of a dump file

To restore the contents of a dump file on a Unix system, first the install the "restore" tool. On Debian-based systems:

sudo apt install dump

Then go through the following steps:

1. Create an empty directory, and go to that directory in the command terminal:

   mkdir extracted

   cd extracted

2. Run restore in interactive mode on the dump file you want to extract^[1]:

   sudo restore -if ../../tapes-DDS/1/file000002.dd

3. Inspect the contents of the dump file:

   restore > ls

   Result:

    5bin/        diag/        kvm/         mdec         share/       ucbinclude 
    5include/    dict/        lddrv/       net          spool        ucblib 
    5lib/        etc/         lib/         nserve       src          xpg2bin/
    adm          export/      local        old/         stand        xpg2include/
    bin/         games/       local-/      openwin/     sys          xpg2lib/
    boot         hosts/       lost+found/  pub          tmp 
    demo/        include/     man          sccs/        ucb/

4. Use the addcommand to add directories that are to be extracted to the directory list. To extract everything:

   restore > add .

5. Run the extract command:

   restore > extract

   This results in the following prompt:

    You have not read any volumes yet.
    Unless you know which volume your file(s) are on you should start
    with the last volume and work towards the first.
    Specify next volume # (none if no more volumes):

6. Now enter 1. Response:

   set owner/mode for '.'? [yn]

7. Enter n ^[2]

8. When the extraction is finished, exit the interactive restore session:

   restore > q

References

• Wikipedia:Dump_(program)
• Is dump really deprecated?
• Using Dump for Linux/Unix data backup
• Restore Linux Commands
• How to Restore UFS Files Interactively
• file(1) magic for dump file format (also includes patterns for extraction of header fields)

1. ↑

   If you don't run restore as sudo, extraction results in a flood of chown: Operation not permitted messages (the files are extracted though).

2. ↑

   This needs further investigation, as the implications of this setting are not 100% clear to me.