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Manual Reference Pages  -  TLSDATE (1)


tlsdate - secure parasitic rdate replacement




tlsdate [-hnvVstlw] [-H [hostname]] [-p [port]] [-P [sslv23|sslv3|tlsv1]] [--certdir [dirname]] [-x [--proxy] proxy-type://proxyhost:proxyport]


tlsdate is a tool for setting the system clock by hand or by communication with the network. It does not set the Real Time Clock. It is designed to be as secure as TLS (RFC 2246) but of course the security of TLS is often reduced to whichever CA racket you believe is trustworthy. By default, tlsdate trusts your local CA root store - so any of these companies could assist in a MITM attack against you and you’d be screwed.

This tool is designed to be run by hand or as a system daemon. It must be run as root or otherwise have the proper caps; it will not be able to set the system time without running as root or another privileged user.


-h | --help Print the help message
-s | --skip-verification Skip certificate verification
-H | --host [hostname|ip] Set remote hostname (default: ’’)
-n | --dont-set-clock Do not set the system clock to the time of the remote server
-p | --port [port] Set remote port (default: ’443’)
-P | --protocol [sslv23|sslv3|tlsv1] Set protocol to use when communicating with server (default: ’tlsv1’)
-C | --certdir [dirname] Set the local directory where certificates are located (default: ’/etc/ssl/certs’) This allows for certificate or certificate authority (CA) pinning. To ensure that signatures are only valid if they are signed by a specific CA or certificate, set the path to a directory containing only the desired certificates.
-x | --proxy [proxy-type://proxyhost:proxyport] The proxy argument expects HTTP, SOCKS4A or SOCKS5 formatted as followed:

The proxy support should not leak DNS requests and is suitable for use with Tor.

-v | --verbose Provide verbose output
-V | --showtime [human|raw] Show the time retrieved from the remote server in a human-readable format or as a raw time_t.
-t | --timewarp If the local clock is before RECENT_COMPILE_DATE; we set the clock to the RECENT_COMPILE_DATE. If the local clock is after RECENT_COMPILE_DATE, we leave the clock alone. Clock setting is performed as the first operation and will impact certificate verification. Specifically, this option is helpful if on first boot, the local system clock is set back to the era of Disco and Terrible Hair. This should ensure that X509_V_ERR_CERT_NOT_YET_VALID or X509_V_ERR_CERT_HAS_EXPIRED are not encountered because of a broken RTC or the lack of a local RTC; we assume that tlsdate is recompiled yearly and that all certificates are otherwise considered valid.
-l | --leap Normally, the passing of time or time yet to come ensures that SSL verify functions will fail to validate certificates. Commonly, X509_V_ERR_CERT_NOT_YET_VALID and X509_V_ERR_CERT_HAS_EXPIRED are painfully annoying but still very important error states. When the only issue with the certificates in question is the timing information, this option allows you to trust the remote system’s time, as long as it is after RECENT_COMPILE_DATE and before MAX_REASONABLE_TIME. The connection will only be trusted if X509_V_ERR_CERT_NOT_YET_VALID and/or X509_V_OKX509_V_ERR_CERT_HAS_EXPIRED are the only errors encountered. The SSL verify function will not return X509_V_OK if there are any other issues, such as self-signed certificates or if the user pins to a CA that is not used by the remote server. This is useful if your RTC is broken on boot and you are unable to use DNSEC until you’ve at least had some kind of leap of cryptographically assured data.
-w | --http Run in web mode: look for the time in an HTTP "Date" header inside an HTTPS connection, rather than in the TLS connection itself. The provided hostname and port must support HTTPS.


It’s likely! Let us know by contacting

Note that tlsdate(1) is in Beta, and may not work as expected.


Jacob Appelbaum <jacob at appelbaum dot net>


tlsdate(1), tlsdate-helper(1), tlsdated(8), tlsdated.conf(5)
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Linux TLSDATE (1) OCTOBER 2012

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