REMCTL_OPEN

Section: remctl Library Reference (3) Updated: 2010-05-02 Local index Up

NAME

remctl_open - Connect to a remote remctl server

SYNOPSIS

#include <remctl.h>

int remctl_open(struct remctl *r, const char *host,
unsigned short port,
const char *principal);

DESCRIPTION

remctl_open() opens a TCP connection to the given host on the given port and then authenticates using the remctl protocol and the service principal principal. r is a remctl struct created via remctl_new(). host must not be NULL. If port is 0, the library first attempts to connect to the registered port of 4373 and then tries the legacy port of 4444 if that fails. Future versions of the library will drop this fallback to 4444. If principal is NULL, a service principal of "host/host" is used, with the realm determined by domain-realm mapping.

If no principal is specified and the default is used, the underlying GSS-API library may canonicalize host via DNS before determining the service principal, depending on your library configuration. Specifying a principal disables this behavior.

The remctl protocol uses Kerberos v5 via GSS-API for authentication. The underlying GSS-API library will use the default ticket cache for authentication, so to successfully use remctl_open(), the caller should already have Kerberos tickets for an appropriate realm stored in its default ticket cache. The environment variable KRB5CCNAME can be used to control which ticket cache is used.

RETURN VALUE

remctl_open() returns true on success and false on failure. On failure, the caller should call remctl_error() to retrieve the error message.

CAVEATS

If the principal argument to remctl_open() is NULL, most GSS-API libraries will canonicalize the host using DNS before deriving the principal name from it. This means that when connecting to a remctl server via a CNAME, remctl_open() will normally authenticate using a principal based on the canonical name of the host instead of the specified host parameter. This behavior may cause problems if two consecutive DNS lookups of host may return two different results, such as with some DNS-based load-balancing systems.

The canonicalization behavior is controlled by the GSS-API library; with the MIT Kerberos GSS-API library, canonicalization can be disabled by setting "rdns" to false in the [libdefaults] section of krb5.conf. It can also be disabled by passing an explicit Kerberos principal name via the principal argument, which will then be used without changes. If canonicalization is desired, the caller may wish to canonicalize host before calling remctl_open() to avoid problems with multiple DNS calls returning different results.

The default behavior, when a port of 0 is given, of trying 4373 and falling back to 4444 will be removed in a future version of this library in favor of using the "remctl" service in /etc/services if set and then falling back on only 4373. 4444 was the poorly-chosen original remctl port and should be phased out.

NOTES

The remctl port number, 4373, was derived by tracing the diagonals of a QWERTY keyboard up from the letters "remc" to the number row.

AUTHOR

Russ Allbery <rra@stanford.edu>

This document was created by man2html, using the manual pages.
Time: 21:54:03 GMT, April 16, 2011