title: node_exporter unable to export specific volume/mount point metrics - err="permission denied"
body: <p>We have 3 disks on the server</p>
  <ol>
  <li>/dev/nvme2n1p1  for root</li>
  <li>/dev/nvme0n1  for /data</li>
  <li>/dev/nvme1n1 for /data/postgresql/12/main/pg_wal</li>
  </ol>
  <p>The node-exporter can export all the metrics to Prometheus server for the first 2 mount points but for the 3rd one (nvme1n1) few metrics, it won't be able to export.</p>
  <p>It can still export the following metrics for 3rd one</p>
  <pre><code>curl &quot;http://localhost:9100/metrics&quot;|grep nvme1n1
    % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                   Dload  Upload   Total   Spent    Left  Speed
    0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0node_disk_discard_time_seconds_total{device=&quot;nvme1n1&quot;} 0
  node_disk_discarded_sectors_total{device=&quot;nvme1n1&quot;} 0
  node_disk_discards_completed_total{device=&quot;nvme1n1&quot;} 0
  node_disk_discards_merged_total{device=&quot;nvme1n1&quot;} 0
  node_disk_io_now{device=&quot;nvme1n1&quot;} 0
  node_disk_io_time_seconds_total{device=&quot;nvme1n1&quot;} 21338.728
  node_disk_io_time_weighted_seconds_total{device=&quot;nvme1n1&quot;} 56694.8
  node_disk_read_bytes_total{device=&quot;nvme1n1&quot;} 8.1892795904e+11
  node_disk_read_time_seconds_total{device=&quot;nvme1n1&quot;} 4943.992
  node_disk_reads_completed_total{device=&quot;nvme1n1&quot;} 3.130765e+06
  node_disk_reads_merged_total{device=&quot;nvme1n1&quot;} 1948
  node_disk_write_time_seconds_total{device=&quot;nvme1n1&quot;} 83561.291
  node_disk_writes_completed_total{device=&quot;nvme1n1&quot;} 1.5033066e+07
  node_disk_writes_merged_total{device=&quot;nvme1n1&quot;} 2.85686e+06
  node_disk_written_bytes_total{device=&quot;nvme1n1&quot;} 3.1148191744e+12
  node_filesystem_device_error{device=&quot;/dev/nvme1n1&quot;,fstype=&quot;ext4&quot;,mountpoint=&quot;/data/postgresql/12/main/pg_wal&quot;} 1
  100 84365    0 84365    0     0  13.4M      0 --:--:-- --:--:-- --:--:-- 13.4M
  </code></pre>
  <p>But it won't be able to ship the following metrics</p>
  <pre><code>node_filesystem_size_bytes
  node_filesystem_avail_bytes
  node_filesystem_free_bytes
  </code></pre>
  <p>This is the error from the debug logs:</p>
  <pre><code>Nov 12 14:39:10 host1 node_exporter[20020]: level=debug ts=2020-11-12T09:09:10.701Z caller=filesystem_linux.go:94 collector=filesystem msg=&quot;Error on statfs() system call&quot; rootfs=/data/postgresql/12/main/pg_wal err=&quot;permission denied&quot;
  </code></pre>
  <p>Kindly advise what's wrong here. Thanks</p>