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Chapter 15. How to use a wrapper

Bert de Ridder

Original text

Paul Bijnens

Original text

Stefan G. Weichinger

XML-conversion; Updates
AMANDA Core Team

Table of Contents

Bert de Ridder's suggestions
Paul Bijnens's suggestions

Note

Refer to http://www.amanda.org/docs/howto-wrapper.html for the current version of this document.

Note

The script used in this document is not part of the official Amanda release. The Amanda core team does not take any responsibility for this script.

Bert de Ridder's suggestions

This is a mini-howto explaining how to control other running tasks on a server where the Amanda software is used to backup data.

Problem : Lots of software is picky about their datafiles being backed up while the files are in use. It sometimes is even necessary to know the state of the datafiles at the moment of backup so that when restoring you know exactly *what* you are restoring. And most of the time there are dependencies between the datafiles as well (for instance, the pure datafiles and the controlfiles of an Oracle database.)

The solution is actually quite simple; you just use a custom made backupscript instead of the standard tar command. Inside this tar command, you do some necessary processing before executing the tar command and - if necessary - do some more processing. This way, you can easily stop an Oracle database, tar the files, send them to the tape server and restart the Oracle database. This of course is just an example, anything you can do in a shell script can be done.

  1. Create the script

    This is the most important step, this script is the work horse of the solution. I've called it /bin/amandatar. You can call it whatever you want though. It's a Perl script, it may not be very pretty code, but it does the job. In the script, an example is given for the backup of a Lotus Notes Domino server.

    #!/usr/bin/perl
    
    # Tar wrapper for Amanda's tar. 
    #
    
    use Getopt::Long qw(:config pass_through);
    
    # Obtain directory and file information from the command line.
    
    $result = GetOptions (
     'directory=s' => \$dir,
     'file=s' => \$file
    );
    
    # Check whether Amanda wants to do some administrative task (eg. indexinfo 
    # or obtain the number of bytes to be backed up) 
    # if file = /dev/null it's an administrative task and most of the time, no extra
    #   processing is necessary.
    
    # What you see here is just a log of the backup start time, and – more important
    #   the stopping of the domino server
    
    if ( $file ne '/dev/null' )
    {
      if ( $dir eq '/local/notesdata' )
      {
        system "echo 'Start backup notes at ' >> /var/lib/amanda/runtime" ;
        system "date >> /var/lib/amanda/runtime";
        system ( "/etc/init.d/domino stop >> /var/lib/amanda/runtime" );
      }
    }
    
    # The command line is being 'reconstructed'. Necessary because the GetOptions
    #   call above has stripped the file and directory information.
    # This is what I meant with 'ugly'  code ;-)
    
    while ( $ARGV[0] ne '' )
    {
      $val = $ARGV[0] ;
      unshift ( @NEWARGV, $val, ) ;
      shift @ARGV;
    }
    
    while ( $NEWARGV[0] ne '' )
    {
      $val = $NEWARGV[0] ;
      unshift ( @ARGV, $val ) ;
      shift @NEWARGV;
    }
    
    if ( $dir ne '' )
    {
      unshift ( @ARGV, '--directory', $dir );
    }
    if ( $file ne '' )
    {
      unshift ( @ARGV, '--file', $file );
    }
    
    if ( $file ne '/dev/null' )
    {
      system "echo 'Backing up directory ' $dir >> /var/lib/amanda/runtime" ;
    }
    
    # And finally make sure tar is called :-)
    #   (path may differ on your installation)
    unshift ( @ARGV , "/bin/tar" ) ;
    
    system ( @ARGV ) ;
    
    # Postprocessing
    #
    # If Notes backup was requested, restart the server.
    # Log the backup end time.
    #
    
    if ( $file ne '/dev/null' )
    {
      if ( $dir eq '/local/notesdata' )
      {
        system ( "/etc/init.d/domino start >> /var/lib/amanda/runtime" );
        system "echo 'End backup notes at ' >> /var/lib/amanda/runtime" ;
        system "date >> /var/lib/amanda/runtime";
      }
    }
    
    exit 0;
    
    # End script
    

    On some systems it may be necessary to setuid root the script.

  2. Rebuild Amanda so that it uses your newly created script.

    Download the sources, untar them to a directory. I'm sure there are lots of documents already available on how to do this, so I won't go into too much detail. (Refer to Amanda Installation Notes).

    fast path :

    /usr/local/src # tar -xvzf amanda-source.tar.gz
    /usr/local/src # cd amanda-version
    /usr/local/src/amanda-version # ./configure \
      --with-user=amanda \
      --prefix=/usr/local \
      --exec-prefix=/usr \
      --bindir=/usr/bin \
      --sbindir=/usr/sbin \
      --libexecdir=/usr/lib/amanda \
      --with-configdir=/etc/amanda \
      --with-group=disk \
      --with-gnutar=/bin/amandatar \
      --with-gnutar-listdir=/var/lib/amanda/gnutar-lists \
      --with-tmpdir=/tmp/amanda \
      --with-smbclient=/usr/bin/smbclient \
      --mandir=/usr/local/man
    

    Here, it may be necessary to adjust some paths to match your installation. This setup works on SuSE Linux (also SLES) and MacOSX although you may have to use another binary tar.

    As you see, you may also "replace" the smbclient if necessary. I haven't yet tested it though. I'll leave it as an exercise for the reader <g>.

    /usr/local/src/amanda-version # make 
    /usr/local/src/amanda-version # make install

    Now proceed as with a "normal" installation.

Paul Bijnens's suggestions

How do I run pre- and post dump programs, e.g. database stop/start?

Currently (Amanda 2.4.5) there is no direct support to run a program before or after a backup on a client. But there is an easy workaround by using a wrapper for GNU-tar that does the additional tasks.

Let's suppose you want to stop a database before the backup, and start it up again when the backup is finished. You have already two scripts "shutdb" and "startdb" to shutdown and startup the database.

First you have to configure Amanda on the client to use the gnutar-wrapper instead of the real GNU-tar:

./configure ... --with-gnutar=/usr/local/bin/amgtar ...

and re-compile Amanda. The program "amgtar" can be a simple link to the real GNU-tar-binary on clients that don't need special handling, or it can be a script.

Amanda expects that the bytestream on stdout is the backup image, and the bytestream on stderr are messages. The stderr messages are filtered against a known set of strings, and anything unexpected is flagged as "STRANGE" in the Amanda report. The return-codes of the program should be the same as the return-codes of GNU-tar:

  • 0 = ok (backup image will be put on tape)

  • 1 = not ok (backup image will not be put on tape, same level will be tried next time).

The arguments passed to the program are pretty static (see in the sources client-src/sendbackup-gnutar.c, line 483). To decide if you need to stop/start the database you have to check if:

  • this run makes a backup and not a restore: look for "--create"

  • this it is not an estimate run: look for "--file /dev/null" (estimate) or "--file -" (real run)

  • this run is for the database directory: look for "--directory /my/data/base"

In all other cases, we just pass the args and run the real GNU-tar.

Here is an example script in Bourne shell:

Example 15.1. 

#!/bin/sh

# # uncomment next block to follow the flow
# LOG=/tmp/amanda/mytar.debug
# date >> $LOG
# echo "$@" >> $LOG
# if [ "$3" = "/dev/null" ]
# then echo "Estimate only" >> $LOG
# else echo "Real backup" >> $LOG
# fi

# - Avoid output to stdout! (the backup stream by tar)
# - Any output to stderr is flagged as "strange" by amanda
#   and may be used to pass error messages into the report

if [ "$1" = "--create"  -a  "$3" = "-"  -a  "$5" = "/my/dir" ]
then
    # echo "/my/dir: want to execute some progs first" >>$LOG
    /usr/local/bin/shutdb thedb >&2
    /usr/local/bin/gtar "$@"
    rc=$?
    # echo "Finished the real backup; some postprocessing" >>$LOG
    /usr/local/bin/startdb thedb >&2
    exit $rc
else
    /usr/local/bin/gtar "$@"
fi

Here is an example script in perl:

Example 15.2. 

#!/usr/bin/perl -w

use Getopt::Long qw(:config pass_through);

my @saveopts = @ARGV;
GetOptions (
        'create' => \$create,
        'directory=s' => \$dir,
        'file=s' => \$file,
);
@ARGV = @saveopts;

my $postproc = 0;
if ($create  &&  $dir eq '/my/data/base' &&  $file ne '/dev/null') {
    system '/usr/local/bin/dbshut thedb >/tmp/amanda/dbshut.debug 2>&1';
    $postproc = 1;
}

unshift(@ARGV, "/usr/local/bin/gtar");
system @ARGV;

my $rc = $? >> 8;

if ($postproc) {
    system '/usr/local/bin/dbstart thedb >/tmp/amanda/dbstart.debug 2>&1';
}

exit $rc;