amrestore - extract backup images from an AMANDA tape

Amrestore extracts backup images from the tape mounted on tapedevice or from the holding disk file holdingfile that match hostname, diskname and datestamp patterns given on the command line. The tape or holding file must be in a format written by the amdump or amflush program.

If diskname is not specified, all backups on the tape for the previous hostname are candidates. If datestamp is not specified, all backups on the tape for the previous hostname and diskname are candidates. If no hostname, diskname or datestamp are specified, every backup on the tape is a candidate.

Hostname and diskname are special expressions described in the "HOST & DISK EXPRESSION" section of amanda(8). Datestamp are special expression described in the "DATESTAMP EXPRESSION" section of amanda(8). For example, if diskname is "rz[23]a", it would match disks rz2a and rz3a.

Datestamp is useful if amflush writes multiple backup runs to a single tape.

Unless -p is used, candidate backup images are extracted to files in the current directory named:

hostname.diskname.datestamp.dumplevel

Amrestore doesn't use a changer, it restore from the tape already loaded in the tapedevice.

-b

Set the blocksize used to read the tape or holding file. All holding files must be read with a blocksize of 32 KBytes. Amrestore should normally be able to determine the blocksize for tapes on its own and not need this parameter.

The default is 32 KBytes.

-f

Do a rewind followed by a fsf <fileno> before trying to restore an image.

-l

Check if we restoring from the tape with the right label

-p

Pipe output. The first matching backup image is sent to standard output, which is normally a pipe to restore or tar, then amrestore quits. It may be run again to continue selecting backups to process. Make sure you specify the no-rewind tapedevice when doing this.

Note: restore may report "short read" errors when reading from a pipe. Most versions of restore support a blocking factor option to let you set the read block size, and you should set it to 2. See the example below.

-c

Compress output using the fastest method the compression program provides. Amrestore normally writes output files in a format understood by restore or tar, even if the backups on the tape are compressed. With the -c or -C option, amrestore writes all files in compressed format, even if the backups on the tape are not compressed. Output file names will have a .Z or .gz extension depending on whether compress or gzip is the preferred compression program. This option is useful when the current directory disk is small.

-C

Compress output using the best method the compression program provides (may be very CPU intensive). See the notes above about the -c option.

-r

Raw output. Backup images are output exactly as they are on the tape, including the amdump headers. Output file names will have a .RAW extension. This option is only useful for debugging and other strange circumstances.

-h

Header output. The tape header block is output at the beginning of each file. This is like -r except -c or -C may also be used to compress the result. Amrecover uses the header to determine the restore program to use.

If a header is written (-r or -h), only 32 KBytes are output regardless of the tape blocksize. This makes the resulting image usable as a holding file.

The following does an interactive restore of disk rz3g from host seine, to restore particular files. Note the use of the b option to restore, which causes it to read in units of two 512-byte blocks (1 Kbyte) at a time. This helps keep it from complaining about short reads.

% amrestore -p /dev/nrmt9 seine rz3g | restore -ivbf 2 -

The next example extracts all backup images for host seine. This is the usual way to extract all data for a host after a disk crash.

% amrestore /dev/nrmt9 seine

If the backup datestamp in the above example is 19910125 and seine has level 0 backups of disks rz1a and rz1g on the tape, these files will be created in the current directory:

seine.rz1a.19910125.0 seine.rz1g.19910125.0

You may also use amrestore to extract a backup image from a holding disk file that has not yet been flushed to tape:

% amrestore -p /amanda/20001119/seine.rz1a.2 | restore -ivbf 2 -

Amrestore may be used to generate a listing of images on a tape:

% mt -f /dev/nrmt9 rewind % amrestore -p /dev/nrmt9 no-such-host > /dev/null

This asks amrestore to find images for host no-such-host. It will not find any entries that match, but along the way will report each image it skips.

GNU-tar must be used to restore files from backup images created with the GNUTAR dumptype. Vendor tar programs sometimes fail to read GNU tar images.

James da Silva, <jds@amanda.org>, University of Maryland, College Park: Original text

Stefan G. Weichinger, <sgw@amanda.org>, maintainer of the AMANDA-documentation: XML-conversion

amanda(8), amdump(8), amflush(8), tar(1) restore(8)