diff --git a/impermanence.pl b/impermanence.pl
index 40260ca..7ce616a 100755
--- a/impermanence.pl
+++ b/impermanence.pl
@@ -120,12 +120,13 @@ sub populate_ramdisk {
 # check if the mountpoint is already mounted with mfs
 sub is_mounted {
     my $impermanence_home = shift;
-    my $ret;
     my $mounted = 0;
+    my @output;
 
     # is this already mounted?
-    $ret = `df $impermanence_home | awk -v dest=$impermanence_home '/^mfs/ && \$NF == dest { print }'`;
-    if ( $ret =~ m/^mfs/ ) {
+    @output = split("\n", `/bin/df $impermanence_home`);
+    @output = split(" ", $output[$#output]);
+    if( $output[5] eq $impermanence_home && $output[0] =~ m/^mfs/ ) {
         $mounted = 1;
     }
     return $mounted;
@@ -135,15 +136,22 @@ sub is_mounted {
 sub mount_mfs {
     my ($user, $impermanence_home, $data) = @_;
     my $ret;
+    my $filesystem;
 
     saydebug("finding a ffs mountpoint to use for mfs");
     if( is_mounted($impermanence_home) ) {
         trap_error("ERROR: $impermanence_home is already mounted with MFS");
     }
-    my $fs = `swapctl | tail -n 1 | cut -d ' ' -f 1 | tr -d '\n'`;
+    my @fs = split("\n", `/sbin/swapctl`);
+    @fs = split(" ",$fs[$#fs]);
+    $filesystem = $fs[0];
 
-    saydebug("mount the destination using mount_mfs from $fs");
-    $ret = system("mount_mfs", "-s", $data->{size}, $fs, $impermanence_home);
+    if( $filesystem !~ m|^/dev/| ) {
+        trap_error("found swap device $filesystem doesn't start with /dev");
+    }
+
+    saydebug("mount the destination using mount_mfs from $filesystem");
+    $ret = system("/sbin/mount_mfs", "-s", $data->{size}, $filesystem, $impermanence_home);
     if( $ret != 0 ) {
         trap_error("ERROR: mounting the mfs filesystem errored with error $ret");
     } else {
@@ -259,7 +267,7 @@ sub main {
     }
 
     if( $stop && is_mounted($impermanence_home) ) {
-        my $status = system("umount", $impermanence_home);
+        my $status = system("/sbin/umount", $impermanence_home);
         if( $status != 0 ) {
             trap_error("umount did exit with status $status");
         }