stunnel [<filename>] | -fdn | -help | -version | -sockets

           stunnel [ [-install | -uninstall | -start | -stop] | -exit]
               [-quiet] [<filename>] ] | -help | -version | -sockets

       The stunnel program is designed to work as SSL encryption wrapper
       between remote clients and local (inetd-startable) or remote servers.
       The concept is that having non-SSL aware daemons running on your system
       you can easily set them up to communicate with clients over secure SSL

       stunnel can be used to add SSL functionality to commonly used Inetd
       daemons like POP-2, POP-3, and IMAP servers, to standalone daemons like
       NNTP, SMTP and HTTP, and in tunneling PPP over network sockets without
       changes to the source code.

       This product includes cryptographic software written by Eric Young

           Use specified configuration file

       -fd n (Unix only)
           Read the config file from specified file descriptor

           Print stunnel help menu

           Print stunnel version and compile time defaults

           Print default socket options

       -install (NT/2000/XP only)
           Install NT Service

       -uninstall (NT/2000/XP only)
           Uninstall NT Service

       -start (NT/2000/XP only)
           Start NT Service

       -stop (NT/2000/XP only)
           Stop NT Service

       -exit (Win32 only)
           Exit an already started stunnel

       o   '[service_name]' indicating a start of a service definition

       chroot = directory (Unix only)
           directory to chroot stunnel process

           chroot keeps stunnel in chrooted jail.  CApath, CRLpath, pid and
           exec are located inside the jail and the patches have to be
           relative to the directory specified with chroot.

       compression = zlib | rle
           select data compression algorithm

           default: no compression

           zlib compression of OpenSSL 0.9.8 or above is not backward
           compatible with OpenSSL 0.9.7.

           rle compression is currently not implemented by the OpenSSL

       debug = [facility.]level
           debugging level

           Level is a one of the syslog level names or numbers emerg (0),
           alert (1), crit (2), err (3), warning (4), notice (5), info (6), or
           debug (7).  All logs for the specified level and all levels
           numerically less than it will be shown.  Use debug = debug or debug
           = 7 for greatest debugging output.  The default is notice (5).

           The syslog facility 'daemon' will be used unless a facility name is
           supplied.  (Facilities are not supported on Win32.)

           Case is ignored for both facilities and levels.

       EGD = egd path (Unix only)
           path to Entropy Gathering Daemon socket

           Entropy Gathering Daemon socket to use to feed OpenSSL random
           number generator.  (Available only if compiled with OpenSSL 0.9.5a
           or higher)

       engine = auto | <engine id>
           select hardware engine

           default: software-only cryptography

           Here is an example of advanced engine configuration to read private
           key from an OpenSC engine


           Special commands "LOAD" and "INIT" can be used to load and
           initialize the engine cryptogaphic module.

       fips = yes | no
           Enable or disable FIPS 140-2 mode.

           This option allows to disable entering FIPS mode if stunnel was
           compiled with FIPS 140-2 support.

           default: yes

       foreground = yes | no (Unix only)
           foreground mode

           Stay in foreground (don't fork) and log to stderr instead of via
           syslog (unless output is specified).

           default: background in daemon mode

       output = file
           append log messages to a file instead of using syslog

           /dev/stdout device can be used to redirect log messages to the
           standard output (for example to log them with daemontools

       pid = file (Unix only)
           pid file location

           If the argument is empty, then no pid file will be created.

           pid path is relative to chroot directory if specified.

       RNDbytes = bytes
           bytes to read from random seed files

           Number of bytes of data read from random seed files.  With SSL
           versions less than 0.9.5a, also determines how many bytes of data
           are considered sufficient to seed the PRNG.  More recent OpenSSL
           versions have a builtin function to determine when sufficient
           randomness is available.

       RNDfile = file
           path to file with random seed data

           The SSL library will use data from this file first to seed the
           random number generator.

       RNDoverwrite = yes | no
           overwrite the random seed files with new random data

           default: yes

       service = servicename
       socket = a|l|r:option=value[:value]
           Set an option on accept/local/remote socket

           The values for linger option are l_onof:l_linger.  The values for
           time are tv_sec:tv_usec.


               socket = l:SO_LINGER=1:60
                   set one minute timeout for closing local socket
               socket = r:SO_OOBINLINE=yes
                   place out-of-band data directly into the
                   receive data stream for remote sockets
               socket = a:SO_REUSEADDR=no
                   disable address reuse (enabled by default)
               socket = a:SO_BINDTODEVICE=lo
                   only accept connections on loopback interface

       syslog = yes | no (Unix only)
           enable logging via syslog

           default: yes

       taskbar = yes | no (WIN32 only)
           enable the taskbar icon

           default: yes

       Each configuration section begins with service name in square brackets.
       The service name is used for libwrap (TCP Wrappers) access control and
       lets you distinguish stunnel services in your log files.

       Note that if you wish to run stunnel in inetd mode (where it is
       provided a network socket by a server such as inetd, xinetd, or
       tcpserver) then you should read the section entitled INETD MODE below.

       accept = [host:]port
           accept connections on specified host:port

           If no host specified, defaults to all IP addresses for the local

       CApath = directory
           Certificate Authority directory

           This is the directory in which stunnel will look for certificates
           when using the verify.  Note that the certificates in this
           directory should be named XXXXXXXX.0 where XXXXXXXX is the hash
           value of the DER encoded subject of the cert.

           The hash algorithm has been changed in OpenSSL 1.0.0.  It is
           required to c_rehash the directory on upgrade from OpenSSL 0.x.x to
           OpenSSL 1.x.x.
           client mode will use this certificate chain as a client side
           certificate chain.  Using client side certs is optional.  The
           certificates must be in PEM format and must be sorted starting with
           the certificate to the highest level (root CA).

       ciphers = cipherlist
           Select permitted SSL ciphers

           A colon delimited list of the ciphers to allow in the SSL
           connection.  For example DES-CBC3-SHA:IDEA-CBC-MD5

       client = yes | no
           client mode (remote service uses SSL)

           default: no (server mode)

       connect = [host:]port
           connect to a remote host:port

           If no host is specified, the host defaults to localhost.

           Multiple connect options are allowed in a single service section.

           If host resolves to multiple addresses and/or if multiple connect
           options are specified, then the remote address is chosen using a
           round-robin algorithm.

       CRLpath = directory
           Certificate Revocation Lists directory

           This is the directory in which stunnel will look for CRLs when
           using the verify. Note that the CRLs in this directory should be
           named XXXXXXXX.r0 where XXXXXXXX is the hash value of the CRL.

           The hash algorithm has been changed in OpenSSL 1.0.0.  It is
           required to c_rehash the directory on upgrade from OpenSSL 0.x.x to
           OpenSSL 1.x.x.

           CRLpath path is relative to chroot directory if specified.

       CRLfile = certfile
           Certificate Revocation Lists file

           This file contains multiple CRLs, used with the verify.

       curve = nid
           specify ECDH curve name

           To get a list of supported cuves use:

               openssl ecparam -list_curves

           default: prime256v1

           execute local inetd-type program

           exec path is relative to chroot directory if specified.

       execargs = $0 $1 $2 ...
           arguments for exec including program name ($0)

           Quoting is currently not supported.  Arguments are separated with
           arbitrary number of whitespaces.

       failover = rr | prio
           Failover strategy for multiple "connect" targets.

               rr (round robin) - fair load distribution
               prio (priority) - use the order specified in config file

           default: rr

       ident = username
           use IDENT (RFC 1413) username checking

       key = keyfile
           private key for certificate specified with cert option

           Private key is needed to authenticate certificate owner.  Since
           this file should be kept secret it should only be readable to its
           owner.  On Unix systems you can use the following command:

               chmod 600 keyfile

           default: value of cert option

       libwrap = yes | no
           Enable or disable the use of /etc/hosts.allow and /etc/hosts.deny.

           default: yes

       local = host
           IP of the outgoing interface is used as source for remote
           connections.  Use this option to bind a static local IP address,

       sni = service_name:server_name
           Use the service as a slave service (a name-based virtual server)
           for Server Name Indication TLS extension (RFC 3546).

           service_name specifies the master service that accepts client
           connections with accept option.  server_name specifies the host
           name to be redirected.  Multiple slave services are normally
           specified for a single master service.  sni option can also be
           specified more than once within a single slave service.

           This service, as well as the master service, may not be configured
           in client mode.  connect option of the slave service is ignored
           specify OCSP server flag

           Several OCSPflag can be used to specify multiple flags.

           currently supported flags: NOCERTS, NOINTERN NOSIGS, NOCHAIN,

       options = SSL_options
           OpenSSL library options

           The parameter is the OpenSSL option name as described in the
           SSL_CTX_set_options(3ssl) manual, but without SSL_OP_ prefix.
           Several options can be used to specify multiple options.

           For example for compatibility with erroneous Eudora SSL
           implementation the following option can be used:

               options = DONT_INSERT_EMPTY_FRAGMENTS

       protocol = proto
           application protocol to negotiate SSL (e.g. starttls or stls)

           protocol option should not be used with SSL encryption on a
           separate port.

           Currently supported protocols:

               Proprietary (undocummented) extension of CIFS protocol
               implemented in Samba.  Support for this extension was dropped
               in Samba 3.0.0.

               Based on RFC 2817 - Upgrading to TLS Within HTTP/1.1, section
               5.2 - Requesting a Tunnel with CONNECT

               This protocol is only supported in client mode.

               Based on RFC 2595 - Using TLS with IMAP, POP3 and ACAP

               Based on RFC 4642 - Using Transport Layer Security (TLS) with
               Network News Transfer Protocol (NNTP)

               This protocol is only supported in client mode.

               Based on RFC 2449 - POP3 Extension Mechanism

               Based on RFC 2487 - SMTP Service Extension for Secure SMTP over

           default: basic

       protocolHost = host:port
           destination address for protocol negotiations

       protocolPassword = password
           password for protocol negotiations

       protocolUsername = username
           username for protocol negotiations

       pty = yes | no (Unix only)
           allocate pseudo terminal for 'exec' option

       retry = yes | no (Unix only)
           reconnect a connect+exec section after it's disconnected

           default: no

       session = timeout
           session cache timeout

       sessiond = host:port
           address of sessiond SSL cache server

       sslVersion = version
           select version of SSL protocol

           Allowed options: all, SSLv2, SSLv3, TLSv1

       stack = bytes (except for FORK model)
           thread stack size

       TIMEOUTbusy = seconds
           time to wait for expected data

       TIMEOUTclose = seconds
           time to wait for close_notify (set to 0 for buggy MSIE)

       TIMEOUTconnect = seconds
           time to wait to connect a remote host

       TIMEOUTidle = seconds
           time to keep an idle connection

       transparent = none | source | destination | both (Unix only)
           enable transparent proxy support on selected platforms

           Supported values:

               Disable transparent proxy support.  This is the default.

                   equivalent file):

                       iptables -t mangle -N DIVERT
                       iptables -t mangle -A PREROUTING -p tcp -m socket -j DIVERT
                       iptables -t mangle -A DIVERT -j MARK --set-mark 1
                       iptables -t mangle -A DIVERT -j ACCEPT
                       ip rule add fwmark 1 lookup 100
                       ip route add local dev lo table 100
                       echo 0 >/proc/sys/net/ipv4/conf/lo/rp_filter

                   stunnel must also to be executed as root and without setuid

               Remote mode (connect option) on Linux 2.2.x
                   This configuration requires kernel to be compiled with
                   transparent proxy option.  Connected service must be
                   installed on a separate host.  Routing towards the clients
                   has to go through the stunnel box.

                   stunnel must also to be executed as root and without setuid

               Remote mode (connect option) on FreeBSD >=8.0
                   This configuration requires additional firewall and routing
                   setup.  stunnel must also to be executed as root and
                   without setuid option.

               Local mode (exec option)
                   This configuration works by pre-loading
                   shared library.  _RLD_LIST environment variable is used on
                   Tru64, and LD_PRELOAD variable on other platforms.

               Original destination is used instead of connect option.

               A service section for transparent destination may look like


               This configuration requires the following setup for iptables
               (possibly in /etc/rc.local or equivalent file):

                   /sbin/iptables -I INPUT -i eth0 -p tcp --dport <stunnel_port> -j ACCEPT
                   /sbin/iptables -t nat -I PREROUTING -i eth0 -p tcp --dport <redirected_port> -j DNAT --to-destination <local_ip>:<stunnel_port>

               Transparent destination option is currently only supported on

               Use both source and destination transparent proxy.

           level 2 - verify peer certificate
           level 3 - verify peer with locally installed certificate
           default - no verify

           It is important to understand, that this option was solely designed
           for access control and not for authorization.  Specifically for
           level 2 every non-revoked certificate is accepted regardless of its
           Common Name.  For this reason a dedicated CA should be used with
           level 2, and not a generic CA commonly used for webservers.  Level
           3 is preferred for point-to-point connections.

       stunnel returns zero on success, non-zero on error.

       The following signals can be used to control stunnel in Unix

           Force a reload of the configuration file.

           Some global options will not be reloaded:

           o   chroot

           o   fips

           o   foreground

           o   pid

           o   setgid

           o   setuid

           The use of 'setuid' option will also prevent stunnel from binding
           privileged (<1024) ports during configuration reloading.

           When 'chroot' option is used, stunnel will look for all its files
           (including configuration file, certificates, log file and pid file)
           within the chroot jail.

           Close and reopen stunnel log file.  This function can be used for
           log rotation.

           Shut stunnel down.

       The result of sending any other signals to the server is undefined.

       In order to provide SSL encapsulation to your local imapd service, use

           pty = yes

       If you want to use stunnel in inetd mode to launch your imapd process,
       you'd use this stunnel.conf.  Note there must be no [service_name]

           exec = /usr/sbin/imapd
           execargs = imapd

       stunnel cannot be used for the FTP daemon because of the nature of the
       FTP protocol which utilizes multiple ports for data transfers.  There
       are available SSL enabled versions of FTP and telnet daemons, however.

       The most common use of stunnel is to listen on a network port and
       establish communication with either a new port via the connect option,
       or a new program via the exec option.  However there is a special case
       when you wish to have some other program accept incoming connections
       and launch stunnel, for example with inetd, xinetd, or tcpserver.

       For example, if you have the following line in inetd.conf:

           imaps stream tcp nowait root /usr/bin/stunnel stunnel /etc/stunnel/imaps.conf

       In these cases, the inetd-style program is responsible for binding a
       network socket (imaps above) and handing it to stunnel when a
       connection is received.  Thus you do not want stunnel to have any
       accept option.  All the Service Level Options should be placed in the
       global options section, and no [service_name] section will be present.
       See the EXAMPLES section for example configurations.

       Each SSL enabled daemon needs to present a valid X.509 certificate to
       the peer. It also needs a private key to decrypt the incoming data. The
       easiest way to obtain a certificate and a key is to generate them with
       the free OpenSSL package. You can find more information on certificates
       generation on pages listed below.

       The order of contents of the .pem file is important.  It should contain
       the unencrypted private key first, then a signed certificate (not
       certificate request).  There should be also empty lines after
       certificate and private key.  Plaintext certificate information
       appended on the top of generated certificate should be discarded. So
       the file should look like this:

           -----BEGIN RSA PRIVATE KEY-----
           [encoded key]
           -----END RSA PRIVATE KEY-----
           [empty line]
           -----BEGIN CERTIFICATE-----
           [encoded certificate]
           -----END CERTIFICATE-----

       o   The file specified with '--with-random' at compile time.

       o   The contents of the screen if running on Windows.

       o   The egd socket specified with the EGD flag.

       o   The egd socket specified with '--with-egd-sock' at compile time.

       o   The /dev/urandom device.

       With recent (>=OpenSSL 0.9.5a) version of SSL it will stop loading
       random data automatically when sufficient entropy has been gathered.
       With previous versions it will continue to gather from all the above
       sources since no SSL function exists to tell when enough data is

       Note that on Windows machines that do not have console user interaction
       (mouse movements, creating windows, etc.) the screen contents are not
       variable enough to be sufficient, and you should provide a random file
       for use with the RNDfile flag.

       Note that the file specified with the RNDfile flag should contain
       random data -- that means it should contain different information each
       time stunnel is run.  This is handled automatically unless the
       RNDoverwrite flag is used.  If you wish to update this file manually,
       the openssl rand command in recent versions of OpenSSL, would be

       One important note -- if /dev/urandom is available, OpenSSL has a habit
       of seeding the PRNG with it even when checking the random state, so on
       systems with /dev/urandom you're likely to use it even though it's
       listed at the very bottom of the list above.  This isn't stunnel's
       behaviour, it's OpenSSLs.

       Stunnel 4.40 and later contains hardcoded 2048-bit DH parameters.

       It is also possible to specify DH parameters in the certificate file:

           openssl dhparam 2048 >> stunnel.pem

       DH parameter generation may take several minutes.

           stunnel configuration file

       Option execargs does not support quoting.

           access control facility for internet services

4.42                              2011.08.18                        STUNNEL(8)
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