This document describes how to examine a tape archive in an attempt to determine its archive type. Information in this document is valid for AIX 3.2.5 through 4.3.0.
Because there are many archive commands, each platform specific, and many syntaxes for each command, it is difficult to read an unlabeled tape. This document provides assistance in examining and determining if the archive tape is a "common" archive type and if the data is extractable.
NOTE: This document only addresses archives created and restored on
an AIX machine using AIX commands. All other platforms, cross-platforms, or
other command issues are not addressed in this document. For assistance, contact
your AIX support center.
http://www.rs6000.ibm.com/resource/
Be sure to label the tapes with information about how they were created in
order to restore them later. Some helpful things to include on the tape label
are:
In AIX, one method of archiving the system volume group is to create a
mksysb. The tape can be examined for the mksysb signature by doing the
following:
NOTE: If the above stated output is not displayed or if the tctl
fails, this is NOT a mksysb tape.
To find the tape block size, complete the following steps:
NOTE: Use bs=32k when using 1/4" tape drive. If it is still too big,
use bs=16k.
The size in bytes is the size of the physical blocks on the tape, assuming
the tape was written with a single physical block size.
This size can be used in the chdev command,
chdev -l rmt# -a block_size=0 to
configure the tape drive for the loaded tape.
In AIX, one method of archiving the system volume group and other volume
groups is by using an add-on product called SYSBACK 6000. To examine the tape
for the sysback signature, complete the steps outlined above for MKSYSB tapes,
but instead of checking the output for:
It should look like the following:
NOTE: If the stated output is not displayed or if the tctl fails,
this is NOT a SYSBACK 6000 tape.
The following assumes the tape was created on an AIX system, using standard
AIX archive commands, with only one image on the tape. For assistance with
multiple images or archive types, contact your AIX support center.
Each archive format contains a "signature". A listing of known AIX
signatures has been compiled into the /etc/magic file. The
following strings
are the latest for all known AIX archive commands.
NOTE: There are other signatures located in the /etc/magic
file other than known AIX archive commands. Do not delete them; they
will be used for other system purposes.
NOTE: When this is run it returns an archive command. If the
file command cannot determine the archive type, it displays
the following:
Once it is determined what archive command was used to create the tape, an
attempt to obtain a table of contents, or listing, of the archive can be made.
WARNING: Do not immediately extract the data unless you are VERY
certain of how it will be restored. Without obtaining a table of contents the
existing data may be overwritten.
NOTE: For assistance with the correct syntax for the specific
archive, contact your AIX support center.
NOTE: Because of the 10 block limit, some error messages may be seen.
The error messages may be ignored. If they are of concern, do NOT use the
dd syntax.
tar
cpio (ASCII format)
cpio (binary format)
backbyname
backbyinode
rdump
[ Doc Ref: 90605225214684 Publish Date: Oct. 02, 2000 4FAX Ref: 8177 ]
Related documentation
The product documentation library is also available:
Labeling
mksysb tapes
chdev -l rmt# -a block_size=512
tctl -f /dev/rmt#.1 fsf 2
dd if=/dev/rmt# bs=512 count=1
DUMMY TAPE TOC
Block size determination
chdev -l rmt# -a block_size=0
dd if=/dev/rmt# of=/tmp/block bs=128k count=1
wc -c /tmp/block
dd if=/dv/rmt# bs=128k count=1 | wc -c
Sysback 6000 tapes
DUMMY TAPE TOC
DUMMY SYSBACK TOC
Standard archive tapes
257 string ustar tar archive
0 short 070707 BIN cpio archive
0 string 070707 ASCII cpio archive
0 long 0x09006bea backbyname/restore format
2 long 0x0001332c backbyinode/rdump/restore format
0 short 0x1f9d compressed data
>2 byte &0x80>0 block compressed
chdev -l rmt# -a block_size=0
dd if=/dev/rmt# of=/tmp/block bs=128k count=1
wc -c /tmp/block
file /tmp/block
data or International Language text
chdev -l rmt# -a block_size=<bs from step in the previous section 3>
dd if=/dev/rmt# bs=<bs> count=10 | tar -tvf-
dd if=/dev/rmt# bs=<bs> count=10 | cpio -itcv
dd if=/dev/rmt# bs=<bs> count=10 | cpio -itv
dd if=/dev/rmt# bs=<bs> count=10 | restore -Tvqf-
dd if=/dev/rmt# bs=<bs> count=10 | restore -tvqf-
dd if=/dev/rmt# bs=<bs> count=10 | restore -tvqf