When building on Gentoo Linux: ./configure --prefix=/usr --build=x86_64-pc-linux-gnu --host=x86_64-pc-linux-gnu --mandir=/usr/share/man --infodir=/usr/share/info --datadir=/usr/share --sysconfdir=/etc --localstatedir=/var/lib --libdir=/usr/lib64 --disable-dependency-tracking --without-mysql --without-ipv6 --with-ldap --without-radius --without-pgsql --without-openssl --with-gnutls=/usr --disable-nls --libexecdir=/usr/lib64/nagios/plugins --sysconfdir=/etc/nagios checking for libgnutls-config... no checking gnutls/openssl.h usability... yes checking gnutls/openssl.h presence... yes checking for gnutls/openssl.h... yes checking for main in -lgnutls-openssl... yes config.status: creating po/Makefile --with-apt-get-command: --with-ping6-command: --with-ping-command: /bin/ping -n -U -w %d -c %d %s --with-ipv6: no --with-mysql: no --with-openssl: no --with-gnutls: yes --enable-extra-opts: no --with-perl: /usr/bin/perl --enable-perl-modules: no --with-cgiurl: /nagios/cgi-bin --with-trusted-path: /bin:/sbin:/usr/bin:/usr/sbin --enable-libtap: no /bin/sh ../libtool --tag=CC --mode=link x86_64-pc-linux-gnu-gcc -DNP_VERSION='"1.5"' -mtune=native -O2 -pipe -Wl,-O1 -Wl,--as-needed -L. -o check_http check_http.o libnpcommon.a ../lib/libnagiosplug.a ../gl/libgnu.a libnpcommon.a ../lib/libnagiosplug.a ../gl/libgnu.a -lnsl -lresolv -lgnutls-openssl -lpthread -ldl libtool: link: x86_64-pc-linux-gnu-gcc -DNP_VERSION=\"1.5\" -mtune=native -O2 -pipe -Wl,-O1 -o check_http check_http.o -Wl,--as-needed -L. libnpcommon.a ../lib/libnagiosplug.a ../gl/libgnu.a -lnsl -lresolv -lgnutls-openssl -lpthread -ldl libnpcommon.a(sslutils.o): In function <code>np_net_ssl_init_with_hostname_version_and_cert': sslutils.c:(.text+0xa1): undefined reference to</code>SSL_CTX_check_private_key' collect2: error: ld returned 1 exit status Makefile:1983: recipe for target 'check_http' failed make[2]: *** [check_http] Error 1 make[2]: Leaving directory '/var/tmp/portage/net-analyzer/nagios-plugins-1.5-r1/work/nagios-plugins-1.5/plugins' Makefile:1510: recipe for target 'all-recursive' failed make[1]: *** [all-recursive] Error 1 make[1]: Leaving directory '/var/tmp/portage/net-analyzer/nagios-plugins-1.5-r1/work/nagios-plugins-1.5' Makefile:1435: recipe for target 'all' failed make: *** [all] Error 2 Commit: <a href="https://github.com/monitoring-plugins/monitoring-plugins/commit/2f92d0dab77a3f3b1005dae3401ea1316d6789b2" class="commit-link"><tt>2f92d0d</tt></a> Added: if (!SSL_CTX_check_private_key(c)) { printf ("%s\n", _("CRITICAL - Private key does not seem to match certificate!\n")); return STATE_CRITICAL; } However, SSL_CTX_check_private_key doesn't exist in Gnutls (checked in versions 2.12.23, 3.2.4, 3.3.0). People mentioning this: <a href="http://blog.nicolargo.com/2009/01/le-serveur-de-supervision-libre-part-2.html">http://blog.nicolargo.com/2009/01/le-serveur-de-supervision-libre-part-2.html</a> (comments): <a href="http://www.developpez.net/forums/d1384537/systemes/linux/administration-systeme/nagios-probleme-lancement/">http://www.developpez.net/forums/d1384537/systemes/linux/administration-systeme/nagios-probleme-lancement/</a> When mentioning gnutls, libgnutls-config seems to be missing in recent gnutls versions and is replaced with pkg-config: <a href="http://gnutls.org/manual/gnutls.html#Building-the-source">http://gnutls.org/manual/gnutls.html#Building-the-source</a> — <a href='https://github.com/monitoring-plugins/monitoring-plugins/issues/1254'>Reply to this email on GitHub</a>.<img src='https://github.com/notifications/beacon/5514713__eyJzY29wZSI6Ik5ld3NpZXM6QmVhY29uIiwiZXhwaXJlcyI6MTcxMzk0NjUyOSwiZGF0YSI6eyJpZCI6MzA2ODg0MTV9fQ==--9c62bc53d3cb6da984600cd973fba64368f29695.gif' height='1' width='1'>