# with "keyserver hkp://keys.gnupg.net"
[my-pc]/home/me/.gnupg$ gpg --refresh-keys
  gpg: refreshing 7 keys from hkp://keys.gnupg.net
  gpg: key D7E69871: "asdf asdf <blah@blah.org>" not changed
  gpg: key 17A4CD9C: "asdf asdf <blah@blah.org>" not changed
  gpg: key 9741E8AC: "blah alh <fauno@endefensadelsl.org>" 1 new signature
  gpg: Total number processed: 3
  gpg:              unchanged: 2
  gpg:         new signatures: 1
  gpg: 3 marginal(s) needed, 1 complete(s) needed, PGP trust model
  gpg: depth: 0  valid:   2  signed:   0  trust: 0-, 0q, 0n, 0m, 0f, 2u
  gpg: next trustdb check due at 2018-03-03

# with "keyserver hkps://hkps.pool.sks-keyservers.net":
[my-pc]/home/me/.gnupg$ gpg --refresh-keys
  gpg: refreshing 7 keys from hkps://hkps.pool.sks-keyservers.net
  gpg: keyserver refresh failed: General error

[my-pc]/home/me$ ps aux | grep dirmng
me    17695  0.0  0.0 311016  7240 ?        Ssl  Dec30   0:01 dirmngr --daemon --homedir /home/me/.gnupg
me    27366  0.0  0.0  10732  2376 pts/41   S+   14:35   0:00 grep --color=auto dirmng

[my-pc]/home/me$ dirmngr --debug-level guru
  dirmngr[27054.0]: enabled debug flags: x509 crypto memory cache memstat hashing ipc lookup
  dirmngr[27054.0]: permanently loaded certificates: 0
  dirmngr[27054.0]:     runtime cached certificates: 0
  dirmngr[27054.0]: DBG: chan_4 -> # Home: ~/.gnupg
  # Home: ~/.gnupg
  dirmngr[27054.0]: DBG: chan_4 -> # Config: /home/me/.gnupg/dirmngr.conf
  # Config: /home/lucas/.gnupg/dirmngr.conf
  dirmngr[27054.0]: DBG: chan_4 -> OK Dirmngr 2.1.10 at your service
  OK Dirmngr 2.1.10 at your service

[my-pc]/home/me$ gpg --refresh-keys
gpg: key 0xD605848ED7E69871: "asdf asdf <blah@blah.org>" not changed
gpg: key 0x456032D717A4CD9C: "asdf asdf <blah@blah.org>" not changed
gpg: key 0x7F2D434B9741E8AC: "asdf asdf <blah@blah.org>" not changed
gpg: Total number processed: 3
gpg:              unchanged: 3

keyserver hkps://hkps.pool.sks-keyservers.net
hkp-cacert /home/me/.cert/sks-keyservers.netCA.pem