In this example, the foo.html page is being requested from the www.example.com web server over HTTPS.
And the following is displayed, which, in laymen terms, means the certificate being used by the www.example.com web server for HTTPS is not trusted by a certification authority (CA). This is common when a web server is using a self-signed certificate.
curl: (60) Peer certificate cannot be authenticated with known CA certificates More details here: http://curl.haxx.se/docs/sslcerts.html curl performs SSL certificate verification by default, using a "bundle" of Certificate Authority (CA) public keys (CA certs). If the default bundle file isn't adequate, you can specify an alternate file using the --cacert option. If this HTTPS server uses a certificate signed by a CA represented in the bundle, the certificate verification probably failed due to a problem with the certificate (it might be expired, or the name might not match the domain name in the URL). If you'd like to turn off curl's verification of the certificate, use the -k (or --insecure) option.
The -k or --insecure flag can be used to tell curl to ignore this warning and the content of foo.html is returned.
~]# curl --insecure https://www.example.com/foo.html <html> <body> Hello World </body> </html>