README.md added

README.md

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+Various monitoring plugins in golang
+=====================================
+
+This repository is meant to host various monitoring plugins for Nagios (or
+Centreon, or Icinga) written in golang. I will update it as I rewrite my old
+shell-based scripts or write new ones.
+
+Building
+---------
+
+Running the `build.sh` bash script will build the plugins for both the `amd64`
+and `386` architectures. It will create a `bin/` directory with
+architecture-specific subdirectories.
+
+Plugins
+--------
+
+### SSL certificate expiry
+
+The `check_ssl_certificate` plugin can be used to check that the certificate
+from a TLS service has not expired and is not going to expire shortly. It
+supports the following command-line flags:
+
+* `-H name`/`--hostname name`: the host name to connect to.
+* `-P port`/`--port port`: the TCP port to connect to.
+* `-W days`/`--warning days`: a threshold, in days, below which a warning will
+  be emitted for this service.
+* `-C days`/`--critical days`: a threshold, in days, below which the plugin will
+  indicate that the service is in a critical state.
+* `--ignore-cn-only`: do not cause errors if a certificate does not have SANs
+  and relies on the CN field.
+* `-a names`/`--additional-names names`: a comma-separated list of DNS names
+  that the certificate should also have.
+* `-s protocol`/`--start-tls protocol`: protocol to use before requesting a
+  switch to TLS. Supported protocols: `smtp`, `sieve`.