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default is
.B /etc/resolv.conf
.br
The message size to be advertized in EDNS; only takes effect if the
.B ARES_FLAG_EDNS
flag is set.
.br
.PP
The \fIoptmask\fP parameter also includes options without a corresponding
field in the
.B ares_options
structure, as follows:
.TP 23
.B ARES_OPT_ROTATE
Perform round-robin selection of the nameservers configured for the channel
for each resolution.
.TP 23
.B ARES_OPT_NOROTATE
Do not perform round-robin nameserver selection; always use the list of
nameservers in the same order.
.PP
The
.I flags
field should be the bitwise or of some subset of the following values:
.TP 23
.B ARES_FLAG_USEVC
Always use TCP queries (the "virtual circuit") instead of UDP
queries.  Normally, TCP is only used if a UDP query yields a truncated
result.
.TP 23
.B ARES_FLAG_PRIMARY
Only query the first server in the list of servers to query.
.TP 23
.B ARES_FLAG_IGNTC
If a truncated response to a UDP query is received, do not fall back
to TCP; simply continue on with the truncated response.
.TP 23
.B ARES_FLAG_NORECURSE
Do not set the "recursion desired" bit on outgoing queries, so that the name
server being contacted will not try to fetch the answer from other servers if
it doesn't know the answer locally. Be aware that ares will not do the
recursion for you.  Recursion must be handled by the application calling ares
if \fIARES_FLAG_NORECURSE\fP is set.
.TP 23
.B ARES_FLAG_STAYOPEN
Do not close communications sockets when the number of active queries
drops to zero.
.TP 23
.B ARES_FLAG_NOSEARCH
Do not use the default search domains; only query hostnames as-is or
as aliases.
.TP 23
.B ARES_FLAG_NOALIASES
Do not honor the HOSTALIASES environment variable, which normally
specifies a file of hostname translations.
.TP 23
.B ARES_FLAG_NOCHECKRESP
Do not discard responses with the SERVFAIL, NOTIMP, or REFUSED
response code or responses whose questions don't match the questions
in the request.  Primarily useful for writing clients which might be
used to test or debug name servers.
.TP 23
.B ARES_FLAG_EDNS
Include an EDNS pseudo-resource record (RFC 2671) in generated requests.
.SH RETURN VALUES
\fBares_init_options(3)\fP can return any of the following values:
.TP 14
.B ARES_SUCCESS
Initialization succeeded.
.TP 14
.B ARES_EFILE
A configuration file could not be read.
.TP 14
.B ARES_ENOMEM
The process's available memory was exhausted.
.TP 14
.B ARES_ENOTINITIALIZED
c-ares library initialization not yet performed.
.SH NOTES
When initializing from
.B /etc/resolv.conf,
(or, alternatively when specified by the
.I resolvconf_path
path location)
\fBares_init_options(3)\fP reads the \fIdomain\fP and \fIsearch\fP directives
to allow lookups of short names relative to the domains specified. The
\fIdomain\fP and \fIsearch\fP directives override one another. If more that
one instance of either \fIdomain\fP or \fIsearch\fP directives is specified,
the last occurrence wins. For more information, please see the
.BR resolv.conf (5)
manual page.
.SH SEE ALSO
.BR ares_init(3),
.BR ares_destroy(3),
.BR ares_dup(3),
.BR ares_library_init(3),
.BR ares_save_options(3),
.BR ares_set_servers(3),
.BR ares_set_sortlist(3)
.SH AUTHOR
Greg Hudson, MIT Information Systems
.br
Copyright 1998 by the Massachusetts Institute of Technology.
.br
Copyright (C) 2004-2010 by Daniel Stenberg.