Install printarena.
 [rsc] --rwxrwxr-x M 913078 rsc sys 550 Feb 13 09:00 sys/src/cmd/venti/dumpvacroots
	/n/sourcesdump/2006/0213/plan9/sys/src/cmd/venti/dumpvacroots:4,14 - 
	/n/sourcesdump/2006/0214/plan9/sys/src/cmd/venti/dumpvacroots:4,15
	  # if nothing else, this illustrates that you have to control access
	  # to the physical disks storing the archive!
	  
	- ventihttp=your-server:8000
	+ ventihttp=`{echo $venti | sed 's/^[a-z]+!([0-9\.]+)![a-z0-9]+$/\1/; s/^[a-z]+!([0-9\.]+)/\1/; s/$/:8000/'}
	+ 
	  hget http://$ventihttp/index | 
	  awk '
	   /^index=/ { blockSize=0+substr($3, 11); }
	   /^arena=/ { arena=substr($1, 7); }
	-  /^	arena=/ { start=0+substr($5, 2)-blockSize; printf("./8.printarena -o %d %s\n", start, $3); }' |
	+  /^	arena=/ { start=0+substr($5, 2)-blockSize; printf("venti/printarena -o %d %s\n", start, $3); }' |
	  rc |
	  sed -n 's/^(.*) 1$/vac:\1/p'
 [rsc] --rw-rw-r-- M 913078 glenda sys 1795 Feb 13 09:00 sys/src/cmd/venti/mkfile
	/n/sourcesdump/2006/0213/plan9/sys/src/cmd/venti/mkfile:63,68 - 
	/n/sourcesdump/2006/0214/plan9/sys/src/cmd/venti/mkfile:63,69
	  	write\
	  	copy\
	  	conf\
	+ 	printarena\
	  #	dumparena\
	  
	  CFILES=${TARG:%=%.c} $LIBCFILES