Re: tar - explicit spanning

[Joey Hess <joey@kitenet.net>]

Adam Blomberg wrote:
> Essentially, I want to archive a large directory into 2.2 Gbyte tarballs
> which are "spanning" in nature.  I have an 18 Gbyte directory tree that I
> want to compress into a set of 2.2 Gbyte archives so that I can copy the
> individual tarballs onto separate DVD-RAM media later.  It appears that
> the -M (multple) flag only works properly when you actually run out of
> space on the medium you are archiving to.  Is there a way to force tar to
> create iterative files in a specified size?


#!/bin/sh -e
# Kite short term backup script. Back up directories to a spare hard drive.
# This script is complicated a lot by having to ensure that the files arn't
# bigger than 2 gb. It uses multi-volume tar files.

# Configuration section.
DIRS="home var etc root usr/local"
BACKUPDIR=/mirror/kitenet/`hostname`
VERBOSE=""
# This is a bit smaller than 1 cd. It could be up to 2 gb.
VOLUME_SIZE=655360
NEXTFILE=.next

# If this is set, we are being called to change volumes.
if [ "$BACKUP_VOLUME" ]; then
	if [ -e $NEXTFILE ]; then
		n=`cat $NEXTFILE`
	else
		n=1
	fi
	mv -f $BACKUP_VOLUME $BACKUP_VOLUME.$n
	echo `expr 1 + $n` > $NEXTFILE
else
	# Paricular directories to backup can be speicifed, or the
	# whole list is used.
	if [ ! "$1" ]; then
		set -- $DIRS
	fi

	if [ "$VERBOSE" ]; then
		TAR_VERBOSE=-v
	fi
	
	if [ ! -x "$BACKUPDIR" ]; then
		echo "$0: $BACKUPDIR does not exist" >&2
		exit 1
	fi
	
	# Make sure that this script is on the path, even if it was called
	# relatively, before cding, so we can call ourselves later.
	PATH=$PATH:`pwd`
	cd $BACKUPDIR

	# Lock directory.
	if ! mkdir .backup_in_progress; then
		echo "$0: another backup is already in progress" >&2
		exit 2
	fi

	# Do the backups.
	for dir; do
		rm -f $NEXTFILE
		BACKUP_VOLUME=`echo $dir | sed s:/:_:g`.tar
		# So we can see this when asked to change volumes.
		export BACKUP_VOLUME

		# Move all old files out of the way.
		if [ ! -d old ]; then
	                mkdir old
		fi
		mv $BACKUP_VOLUME.* old 2>/dev/null || true
		
		# Use ourselves to change volumes.
		if tar cf $BACKUP_VOLUME /$dir --preserve $TAR_VERBOSE -L $VOLUME_SIZE -F $0; then
			# Move the last file.
			$0
			rm -rf old
		else
			echo "$0: error backing up $dir" >&2
		fi
		rm -f $NEXTFILE
	done
	rm -f $NEXTFILE
	
	rmdir .backup_in_progress
fi