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options {
    listen-on port 53 { any; };
    directory       "/var/named";
};

logging {
    channel default_debug {
        file "data/named.run";
        print-time        yes;
        severity dynamic;
    };
    channel query_log {
        file "data/query.log" versions 3 size 20m;
        severity  info;
        print-time        yes;
        print-category  yes;
    };
    category queries {
        query_log;
    };
};

acl clients{
    192.168.1.0/24; 
};

view localhost {
    match-clients    { localhost; };
    allow-query      { localhost; };
    allow-query-cache { localhost; };
    recursion yes;  

};

view clients {
    match-clients    { clients; };
    allow-query      { clients; };
    allow-query-cache { clients; };

    zone "." {
        type forward;
        forwarders { 127.0.0.1 port 54;};
        forward only;
    };
};

view  external
{
    match-clients   { any; };
    allow-query     { any; };
    allow-query-cache { any; };
    recursion no; 
    allow-transfer  { none; }; 

    zone "." {
        type master;
        file "root.zone";
    };
};

拨号：

rasdial 宽带连接 user password

断开：

rasdial 宽带连接 /DISCONNECT

PDNS默认不支持bind view功能，通过PowerDNS Recursor加载Lua脚本判断再递归查询PowerDNS实现智能DNS。

#关闭数据包缓存，测试时开启查询时直接读缓存不经过lua preresolve()
disable-packetcache=yes
forward-zones=com=108.61.242.102
local-address=0.0.0.0
lua-dns-script=/tmp/b.lua
#转发所有域到pdns server
forward-zones=.=127.0.0.1:54

lua：

function preresolve ( remoteip, domain, qtype )
    pdnslog("a test message.. received query "..domain.." from "..remoteip.." on "..getlocaladdress());
    ret={}
    if qtype ~= pdns.A then return -1, ret end --非A记录查询跳过，后端查询
    local ips = {"192.168.1.1/32", "10.1.0.0/16", "127.0.0.0/24"}
    if matchnetmask(remoteip, ips) and domain == "www.example.com."
        then
            ret[1]= {qtype=pdns.A, content="85.17.220.215", ttl=86400}
            setvariable()
            return 0, ret
        else
            setvariable()
            return -1, ret 
        end
    end

packet cache:数据包缓存，优先级高
query cache：后台数据库查询缓存，packet cache无时查询
negquery-cache：无域名或域名无记录缓存
缓存操作：

PDNS Server:
pdns_control ccounts
pdns_control purge example.net
pdns_control purge

PDNS Recursor
rec_control get cache-entries packetcache-entries negcache-entries nsspeeds-entries
rec_control dump-cache /tmp/dns-cache
rec_control wipe-cache example.net

方法1：

if [ "$TERM" != "screen" ]; then
    WHOAMI=$(whoami)
    if tmux has-session -t $WHOAMI 2>/dev/null; then
        tmux -2 attach-session -t $WHOAMI
    else
        tmux -2 new-session -s $WHOAMI
        exit
    fi
fi

方法2：

if [ `which tmux 2> /dev/null` -a -z "$TMUX" ]; then
        tmux -2 attach || tmux -2 new; exit
fi

20220315更新：

[ -f /usr/bin/tmux ] && [ -z "$TMUX"  ] && { tmux attach || tmux new-session;}

20230211更新，更简单的方法：

tmux new -As0

参考：
http://bionicraptor.ca/2011/07/24/automatically-start-tmux/
https://coderwall.com/p/tgm2la