Introduction to Stunnel

The Stunnel package contains a program that allows you to encrypt arbitrary TCP connections inside SSL (Secure Sockets Layer) so you can easily communicate with clients over secure channels. 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 server package source code.

Package Information

Stunnel Dependencies




TCP Wrapper-7.6

User Notes:

Installation of Stunnel

The stunnel daemon will be run in a chroot jail by an unprivileged user. Create the new user, group and chroot home directory structure using the following commands as the root user:

groupadd -g 51 stunnel &&
useradd -c "Stunnel Daemon" -d /var/lib/stunnel \
        -g stunnel -s /bin/false -u 51 stunnel &&
install -v -m 1770 -o stunnel -g stunnel -d /var/lib/stunnel/run


A signed SSL Certificate and a Private Key is necessary to run the stunnel daemon. If you own, or have already created a signed SSL Certificate you wish to use, copy it to /etc/stunnel/stunnel.pem before starting the build (ensure only root has read and write access), otherwise you will be prompted to create one during the installation process. The .pem file must be formatted as shown below:

<many encrypted lines of unencrypted key>
<many encrypted lines of certificate>

Install Stunnel by running the following commands:

sed -i -e 's|nogroup|stunnel|' \
       -e 's|$(prefix)/var/lib|$(localstatedir)|' \
sed -i 's|doc/stunnel|&-$(VERSION)|' {,doc/,tools/} &&

./configure --prefix=/usr --sysconfdir=/etc \
    --localstatedir=/var/lib --disable-libwrap &&

This package does not come with a test suite.

Now, as the root user:

make install

Command Explanations

sed -i -e '...' -e '...' tools/ This sed command modifies the group and directory used for the chroot jail to conform with the parameters created earlier.

sed -i '...' {,doc/,tools/} This sed command modifies the location of the installed docs to a versioned directory.

--sysconfdir=/etc: This parameter forces the configuration directory to /etc instead of /usr/etc.

--localstatedir=/var/lib: This parameter sets the installation to use /var/lib/stunnel instead of creating and using /usr/var/stunnel.

--disable-libwrap: This parameter is required if you don't have tcpwrappers installed. Remove the parameter if tcpwrappers is installed.

make install: This command installs the package and, if you did not copy an stunnel.pem file to the /etc/stunnel directory, prompts you for the necessary information to create one. Ensure you reply to the

Common Name (FQDN of your server) [localhost]:

prompt with the name or IP address you will be using to access the service(s).

Configuring Stunnel

Config Files


Configuration Information

Create a basic /etc/stunnel/stunnel.conf configuration file using the following commands:

cat >/etc/stunnel/stunnel.conf << "EOF" &&
# File: /etc/stunnel/stunnel.conf

pid = /run/
chroot = /var/lib/stunnel
client = no
setuid = stunnel
setgid = stunnel

chmod -v 644 /etc/stunnel/stunnel.conf

Next, you need to add the service(s) you wish to encrypt to the configuration file. The format is as follows:

accept  = <hostname:portnumber>
connect = <hostname:portnumber>

If you use Stunnel to encrypt a daemon started from [x]inetd, you may need to disable that daemon in the /etc/[x]inetd.conf file and enable a corresponding <service>_stunnel service. You may have to add an appropriate entry in /etc/services as well.

For a full explanation of the commands and syntax used in the configuration file, run man stunnel. To see a BLFS example of an actual setup of an stunnel encrypted service, read the the section called “Configuring SWAT” in the Samba instructions.

Boot Script

To automatically start the stunnel daemon when the system is rebooted, install the /etc/rc.d/init.d/stunnel bootscript from the blfs-bootscripts-20060910 package.

make install-stunnel


Installed Programs: stunnel and stunnel3
Installed Library:
Installed Directories: /etc/stunnel, /var/lib/stunnel and /usr/share/doc/stunnel-4.15

Short Descriptions


is a program designed to work as an SSL encryption wrapper between remote clients and local ({x}inetd-startable) or remote servers.


is a Perl wrapper script to use stunnel 3.x syntax with stunnel >=4.05.

contains the API functions required by Stunnel.

Last updated on 2007-01-18 13:38:19 -0600