lock to avoid double execution

generate-rr.pl

@@ -6,6 +6,7 @@ use POSIX;
 use LWP;
 use Net::DNS;
 use Net::IPv6Addr;
+use Fcntl qw( :flock );
 
 #
 # setup: as root, use one of:
@@ -14,8 +15,11 @@ use Net::IPv6Addr;
 #           cpan LWP Net::DNS Net::IPv6Addr
 #
 
+open my $self, '<', $0;
+flock( $self, LOCK_EX | LOCK_NB ) or die "Already running, exit.\n";
+
 my $URL  = 'https://pkgmaster.devuan.org/mirror_list.txt';
-my $LOC  = '/etc/nsd';
+my $LOC  = './tmp/etc/nsd';
 my $ZONE = 'rr.devuan.org.zone';
 
 my $ua = LWP::UserAgent->new;