:: Re: [DNG] how to clear DNS cache
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著者: Rowland Penny
日付:  
To: dng
題目: Re: [DNG] how to clear DNS cache
On Sun, 1 Jan 2017 14:11:27 -0800
Rick Moen <rick@???> wrote:

> Quoting Simon Hobson (linux@???):
>
> > What do /etc/resolv.conf and /etc/nssswitch.conf have in them ?
> > Though to be honest, other than the systems I have BIND running on,
> > DNS resolution is something of a black box to me.
>
> On Linux systems, there is a DNS 'stub resolver' librery 'libresolv'
> included in the glibc package, that furnishes the system's
> res_query(), res_search(), res_mkquery(), res_send(), res_init(),
> dn_comp(), dn_expand() functions, plus higher-level functions such as
> gethostbyname() and gethostbyaddr(). See:
> https://linux.die.net/man/3/resolver
>
> This is distressingly ancient and crufty code, going all the way back
> to 1980s BSD UNIX. After that, it was inside BIND4, BIND8, and all
> BIND9 versions until 9.6.0 as 'libbind'. It was removed from BIND
> itself starting BIND 9.6.0. glibc borrowed as 'libresolv' the
> version of this code during the long BIND8 era, and kept in sync with
> the BIND8 module through BIND 8.2.3-T5B in July 2000, from which
> point it has continued to evolve independently in glibc.
>
> The purpose of a 'stub resolver' is to originate outgoing DNS queries
> to a separate _real_ recursive nameserver[1] on- or off-system (e.g.,
> Unbound, BIND9's recursive functions, MaraDNS, PowerDNS Recursor,
> dnscache, Deadwood).
>
> libresolv is used as a generic glibc interface to all DNS name
> resolution methods - from using /etc/hosts file to DNS/NIS/LDAP
> services, and system its behaviour is controlled
> by /etc/nsswitch.conf and /etc/resolv.conf.
>
> It should be noted that many programs presume to cache DNS, e.g., Web
> browsers do, as does the Java runtime. Also, some systems such as
> ones on NIS or LDAP and NFS tend to run dedicated system caching
> daemons like GNU's nscd[2] for performance purposes (i.e., to make
> performance suck less).
>
> Possibly of assistance:
> http://linuxmafia.com/faq/Network_Other/dns-servers.html
>
>
> [1] Or to a forwarder such as Dnsmasq, DNRD, CurveDNS, dproxy, or
> pdnsd, which in turn would need to relay the query to a real
> recursive nameserver.
>


He is probably running dnsmasq (well part of it), is there a line
in /etc/hosts that starts '127.0.1.1' ?

Rowland