我遇到了一个关于php curl的奇怪问题 .

它将连接到DNS服务器以解析，即使主机位于/ etc / hosts中！

软件版本：

Server :
    CentOS release 6.3 (Final)

Linux Curl version :
    curl --version
    curl 7.47.1 (x86_64-pc-linux-gnu) libcurl/7.47.1 OpenSSL/1.0.1e zlib/1.2.3   libidn/1.18
    Protocols: dict file ftp ftps gopher http https imap imaps ldap ldaps pop3    pop3s rtsp smb smbs smtp smtps telnet tftp
    Features: IDN IPv6 Largefile NTLM NTLM_WB SSL libz UnixSockets`

PHP version :
    php -v
    PHP 5.4.41 (cli) (built: Aug 11 2015 22:29:40)
    Copyright (c) 1997-2014 The PHP Group
    Zend Engine v2.4.0, Copyright (c) 1998-2014 Zend Technologies

PHP curl version : 
    php -r "var_export(curl_version());"
    array (
    'version_number' => 471040,
    'age' => 3,
    'features' => 952221,
    'ssl_version_number' => 0,
    'version' => '7.48.0',
    'host' => 'x86_64-redhat-linux-gnu',
    'ssl_version' => 'OpenSSL/1.0.1e',
    'libz_version' => '1.2.3',

服务器配置：

/etc/hosts : 
    127.0.0.1 lalala.examplekkk.com

/etc/resolv.conf : 
    nameserver 8.8.8.8

/etc/nsswitch.conf
    hosts:      files dns

命令执行结果：

PING lalala.examplekkk.com (127.0.0.1) 56(84) bytes of data.
    64 bytes from localhost (127.0.0.1): icmp_seq=1 ttl=64 time=0.041 ms
    64 bytes from localhost (127.0.0.1): icmp_seq=2 ttl=64 time=0.035 ms
    ....

strace php -r '$curl=curl_init();$url="http://lalala.examplekkk.com";curl_setopt($curl,CURLOPT_URL,$url);$content=curl_exec($curl);echo $content;'
    ...
    open("/etc/hosts", O_RDONLY)            = 3
    fstat(3, {st_mode=S_IFREG|0644, st_size=1308, ...}) = 0
    mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f85c7b5c000
    read(3, "127.0.0.1   localhost localhost."..., 4096) = 1308
    ...
    fcntl(3, F_SETFD, FD_CLOEXEC)           = 0
    connect(3, {sa_family=AF_INET, sin_port=htons(53), sin_addr=inet_addr("8.8.8.8")}, 16) = 0
    sendto(3, "\177{\1\0\0\1\0\0\0\0\0\0\6lalala\nexamplekkk\3c"..., 39, MSG_NOSIGNAL, NULL, 0) = 39
    poll([{fd=3, events=POLLIN|POLLRDNORM}], 1, 0) = 0 (Timeout)
    ...

我很困惑，为什么php curl需要连接到dns服务器来解析主机名？

我执行命令'strace curl'http：//lalala.examplekkk.com'，没有连接到8.8.8.8就可以了 .

它是php-curl中的一个错误吗？

php linux curl dns