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203 lines
6.7 KiB
203 lines
6.7 KiB
.\" $Id$ |
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.\" |
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.\" Copyright 1998 by the Massachusetts Institute of Technology. |
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.\" Copyright (C) 2004-2010 by Daniel Stenberg |
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.\" |
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.\" Permission to use, copy, modify, and distribute this |
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.\" software and its documentation for any purpose and without |
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.\" fee is hereby granted, provided that the above copyright |
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.\" notice appear in all copies and that both that copyright |
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.\" notice and this permission notice appear in supporting |
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.\" documentation, and that the name of M.I.T. not be used in |
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.\" advertising or publicity pertaining to distribution of the |
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.\" software without specific, written prior permission. |
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.\" M.I.T. makes no representations about the suitability of |
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.\" this software for any purpose. It is provided "as is" |
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.\" without express or implied warranty. |
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.\" |
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.TH ARES_INIT 3 "5 March 2010" |
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.SH NAME |
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ares_init, ares_init_options \- Initialize a resolver channel |
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.SH SYNOPSIS |
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.nf |
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.B #include <ares.h> |
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.PP |
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.B int ares_init(ares_channel *\fIchannelptr\fP) |
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.B int ares_init_options(ares_channel *\fIchannelptr\fP, |
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.B struct ares_options *\fIoptions\fP, int \fIoptmask\fP) |
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.PP |
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.B cc file.c -lcares |
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.fi |
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.SH DESCRIPTION |
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The \fBares_init\fP function initializes a communications channel for name |
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service lookups. If it returns successfully, \fBares_init\fP will set the |
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variable pointed to by \fIchannelptr\fP to a handle used to identify the name |
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service channel. The caller should invoke |
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.BR ares_destroy (3) |
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on the handle when the channel is no longer needed. |
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.PP |
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The \fBares_init_options\fP function also initializes a name service channel, |
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with additional options useful for applications requiring more control over |
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name service configuration. The \fIoptmask\fP parameter specifies which fields |
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in the structure pointed to by \fIoptions\fP are set, as follows: |
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.TP 18 |
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.B ARES_OPT_FLAGS |
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.B int \fIflags\fP; |
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.br |
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Flags controlling the behavior of the resolver. See below for a |
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description of possible flag values. |
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.TP 18 |
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.B ARES_OPT_TIMEOUT |
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.B int \fItimeout\fP; |
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.br |
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The number of seconds each name server is given to respond to a query on the |
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first try. (After the first try, the timeout algorithm becomes more |
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complicated, but scales linearly with the value of \fItimeout\fP.) The |
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default is five seconds. This option is being deprecated by |
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\fIARES_OPT_TIMEOUTMS\fP starting in c-ares 1.5.2. |
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.TP 18 |
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.B ARES_OPT_TIMEOUTMS |
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.B int \fItimeout\fP; |
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.br |
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The number of milliseconds each name server is given to respond to a query on |
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the first try. (After the first try, the timeout algorithm becomes more |
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complicated, but scales linearly with the value of \fItimeout\fP.) The |
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default is five seconds. Note that this option is specified with the same |
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struct field as the former \fIARES_OPT_TIMEOUT\fP, it is but the option bits |
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that tell c-ares how to interpret the number. This option was added in c-ares |
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1.5.2. |
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.TP 18 |
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.B ARES_OPT_TRIES |
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.B int \fItries\fP; |
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.br |
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The number of tries the resolver will try contacting each name server |
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before giving up. The default is four tries. |
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.TP 18 |
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.B ARES_OPT_NDOTS |
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.B int \fIndots\fP; |
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.br |
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The number of dots which must be present in a domain name for it to be |
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queried for "as is" prior to querying for it with the default domain |
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extensions appended. The default value is 1 unless set otherwise by |
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resolv.conf or the RES_OPTIONS environment variable. |
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.TP 18 |
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.B ARES_OPT_PORT |
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.B unsigned short \fIport\fP; |
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.br |
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The port to use for queries (both TCP and UDP), in network byte order. |
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The default value is 53 (in network byte order), the standard name |
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service port. |
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.TP 18 |
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.B ARES_OPT_SERVERS |
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.B struct in_addr *\fIservers\fP; |
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.br |
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.B int \fInservers\fP; |
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.br |
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The list of IPv4 servers to contact, instead of the servers specified in |
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resolv.conf or the local named. In order to allow specification of either |
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IPv4 or IPv6 name servers, function |
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.BR ares_set_servers(3) |
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must be used instead. |
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.TP 18 |
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.B ARES_OPT_DOMAINS |
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.B char **\fIdomains\fP; |
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.br |
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.B int \fIndomains\fP; |
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.br |
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The domains to search, instead of the domains specified in resolv.conf |
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or the domain derived from the kernel hostname variable. |
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.TP 18 |
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.B ARES_OPT_LOOKUPS |
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.B char *\fIlookups\fP; |
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.br |
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The lookups to perform for host queries. |
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.I lookups |
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should be set to a string of the characters "b" or "f", where "b" |
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indicates a DNS lookup and "f" indicates a lookup in the hosts file. |
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.TP 18 |
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.B ARES_OPT_SOCK_STATE_CB |
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.B void (*\fIsock_state_cb\fP)(void *data, int s, int read, int write); |
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.br |
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.B void *\fIsock_state_cb_data\fP; |
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.br |
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A callback function to be invoked when a socket changes state. |
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.I s |
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will be passed the socket whose state has changed; |
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.I read |
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will be set to true if the socket should listen for read events, and |
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.I write |
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will be set to true if the socket should listen for write events. |
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The value of |
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.I sock_state_cb_data |
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will be passed as the |
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.I data |
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argument. |
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.PP |
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The |
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.I flags |
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field should be the bitwise or of some subset of the following values: |
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.TP 23 |
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.B ARES_FLAG_USEVC |
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Always use TCP queries (the "virtual circuit") instead of UDP |
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queries. Normally, TCP is only used if a UDP query yields a truncated |
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result. |
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.TP 23 |
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.B ARES_FLAG_PRIMARY |
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Only query the first server in the list of servers to query. |
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.TP 23 |
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.B ARES_FLAG_IGNTC |
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If a truncated response to a UDP query is received, do not fall back |
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to TCP; simply continue on with the truncated response. |
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.TP 23 |
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.B ARES_FLAG_NORECURSE |
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Do not set the "recursion desired" bit on outgoing queries, so that the name |
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server being contacted will not try to fetch the answer from other servers if |
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it doesn't know the answer locally. Be aware that ares will not do the |
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recursion for you. Recursion must be handled by the application calling ares |
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if \fIARES_FLAG_NORECURSE\fP is set. |
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.TP 23 |
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.B ARES_FLAG_STAYOPEN |
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Do not close communications sockets when the number of active queries |
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drops to zero. |
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.TP 23 |
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.B ARES_FLAG_NOSEARCH |
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Do not use the default search domains; only query hostnames as-is or |
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as aliases. |
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.TP 23 |
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.B ARES_FLAG_NOALIASES |
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Do not honor the HOSTALIASES environment variable, which normally |
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specifies a file of hostname translations. |
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.TP 23 |
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.B ARES_FLAG_NOCHECKRESP |
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Do not discard responses with the SERVFAIL, NOTIMP, or REFUSED |
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response code or responses whose questions don't match the questions |
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in the request. Primarily useful for writing clients which might be |
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used to test or debug name servers. |
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.SH RETURN VALUES |
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.I ares_init |
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or |
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.I ares_init_options |
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can return any of the following values: |
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.TP 14 |
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.B ARES_SUCCESS |
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Initialization succeeded. |
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.TP 14 |
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.B ARES_EFILE |
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A configuration file could not be read. |
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.TP 14 |
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.B ARES_ENOMEM |
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The process's available memory was exhausted. |
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.TP 14 |
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.B ARES_ENOTINITIALIZED |
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c-ares library initialization not yet performed. |
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.SH SEE ALSO |
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.BR ares_destroy(3), |
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.BR ares_dup(3), |
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.BR ares_library_init(3), |
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.BR ares_set_servers(3) |
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.SH AUTHOR |
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Greg Hudson, MIT Information Systems |
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.br |
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Copyright 1998 by the Massachusetts Institute of Technology. |
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.br |
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Copyright (C) 2004-2010 by Daniel Stenberg.
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