flush dns cache

[pAtwall]

Ho can I flush the DNS cache of my CentOS 7 server?

tried

Code: Select all

service nscd restart

and

Code: Select all

/etc/init.d/bind restart

to no avail ( got No such file or directory. type errors - so i imagine that the cache daemon is neither nscd nor bind, i guess a further question would be what is the default dns cache daemon in CentOS 7?)

cheers,
Pierre

[TrevorH]

Are you running your own DNS server? If not then there probably is no cache that you can flush. What do you have in /etc/resolv.conf?

[scottro]

On CentOS-7.x one uses systemctl restart <whatever>service.

As far as I can see from my own machine, it seems that the dnsmasq.service may be enabled by default. So, you can try

systemctl restart dnsmasq.service

To see what services are running you can use ls /etc/systemd/sysetem/*.wants


However, a lot of times it turns out to be an issue with your name servers, so, also answer Trevor's question. (If your nameserver is the one provided by your ISP, it may be doing something odd, and many people use google's name servers, opendns, or the like).

[pAtwall]

Not running my own DNS server.

Not much in /etc/resolv.conf:

Code: Select all

# Generated by NetworkManager
search {my company name}
nameserver 8.8.8.8
nameserver 8.8.4.4

and

Code: Select all

/etc/systemd/sysetem/*.wants

returns -bash: /etc/systemd/sysetem/*.wants: No such file or directory

I also tried what is recommended here:
http://serverfault.com/questions/500176 ... appen-then
and it looks like no caching is happening at all?

Code: Select all

[root@localhost ~]# dig ohdns.org | grep sec
;; Query time: 144 msec
[root@localhost ~]# dig ohdns.org | grep sec
;; Query time: 146 msec
[root@localhost ~]# dig ohdns.org | grep sec
;; Query time: 21 msec
[root@localhost ~]# dig ohdns.org | grep sec
;; Query time: 198 msec
[root@localhost ~]# dig ohdns.org | grep sec
;; Query time: 12 msec
[root@localhost ~]# dig ohdns.org | grep sec
;; Query time: 144 msec

If this is the case, then my problem lies somewhere else - do you think DNS is cached at all?

[TrevorH]

DNS is not cached except on the DNS server you talk to. There entries are looked up when required and then kept in cache for as long as the TTL on the dns record says to keep them cached for. Since you're using 8.8.8.8 there is no way that you can flush Google's cache for them.

[scottro]

Also, (though as Trevor says, it turns out to not be relevant), I said ls /etc/systemd/system/*.wants. That is, there's an ls, (lower case L) to list what services are expected to start by default.

[Metal3d]

You can flush google dns here: https://developers.google.com/speed/public-dns/cache