Hello I'm trying to pass the configuration file with option fd. However, I get the following errors when I do : echo my configuration | stunnel -fd 0 This is not related to echo since I get the same errors with: cat conf | stunnel -fd 0 stunnel is just filling my logs with : 2014-07-13 6:48:46.675 PM stunnel[1959]: LOG3[140735238959888]: local socket: Socket operation on non-socket (38) 2014-07-13 6:48:46.676 PM stunnel[1959]: LOG3[140735238959888]: local socket: Socket operation on non-socket (38) (...) stunnel ./conf works fine I found a reference to a bug that caused this same error message on OSX when run in inetd mode, but nothing else. Any help is appreciated I'm using stunnel 5.02 on x86_64-apple-darwin13.2.0 platform with the following in -sockets: Socket option defaults: Option Name | Accept | Local | Remote |OS default ----------------+----------+----------+----------+---------- SO_DEBUG | -- | -- | -- | no SO_DONTROUTE | -- | -- | -- | no SO_KEEPALIVE | -- | -- | -- | no SO_LINGER | -- | -- | -- | 0:0 SO_OOBINLINE | -- | -- | -- | no SO_RCVBUF | -- | -- | -- | 131072 SO_SNDBUF | -- | -- | -- | 131072 SO_RCVLOWAT | -- | -- | -- | 1 SO_SNDLOWAT | -- | -- | -- | 2048 SO_RCVTIMEO | -- | -- | -- | 0:0 SO_SNDTIMEO | -- | -- | -- | 0:0 SO_REUSEADDR | yes| -- | -- | no TCP_KEEPCNT | -- | -- | -- |write-only TCP_KEEPINTVL | -- | -- | -- |write-only IP_TOS | -- | -- | -- | 0 IP_TTL | -- | -- | -- | 64 TCP_NODELAY | -- | yes| yes| no My configuration is quite simple : I just echo CAfile=/path/to/file.pem verify = 3 fips = no options = NO_SSLv2 debug = 7 [test] client = yes accept = 127.0.0.1:4443 connect = remoteip:443