(SOLVED) DNS cache flush

[Yankee]

Recently am having problems staying connected to the internet
with AT&T.    The tech suggested I perform a DNS cache flush
just like they do on Windows.   Could resolve the whole problem.

Well the Linux command I found doesn't work as the daemon is
not installed or available thru Synaptic.

Would help eliminating the computer as the source of the problem
and focus on the modem, which usually starts the internet up when
reset and the connection reinstalled, reconnecting the DNS server
and the Configuration server again thru the reset modem process.

Any help with the DNS cache flush command would be appreciated.

Thanks,

Patrick

[Just17]

I know little of this ....  but always assumed that unless I was running a DNS server I would not either have DNS cache or the need to purge it .....  and we all know what assumptions do 

What is the package name you referred to above?

[menotu]

I found  this

To flush the DNS cache in Linux, restart the nscd daemon:-

    - To restart the nscd daemon, type /etc/rc.d/init.d/nscd restart in your terminal

    - Once you run the command your linux DNS cache will flush.

===================

I think this will need to be done as root

[muungwana]

Recently am having problems staying connected to the internet
with AT&T.    The tech suggested I perform a DNS cache flush
just like they do on Windows.   Could resolve the whole problem.

you can tell if the problem is DNS related by trying to go online using an IP address vs going online using a name addresses.

If using name fail but using ip pass,then the problem is DNS related.If using IP addresses fail, then the problem is connectivity.

Test to make sure you can go online and DNS is working

ping -c 1 google.com

expected result:

PING google.com (74.125.226.232) 56(84) bytes of data.
64 bytes from lga15s29-in-f8.1e100.net (74.125.226.232): icmp_req=1 ttl=53 time=55.5 ms

--- google.com ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 55.540/55.540/55.540/0.000 ms

Test to make sure you can go online(not using dns)

ping -c 1 8.8.8.8

expected result:

PING 8.8.8.8 (8.8.8. 56(84) bytes of data.
64 bytes from 8.8.8.8: icmp_req=1 ttl=50 time=50.1 ms

--- 8.8.8.8 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 50.154/50.154/50.154/0.000 ms

The line to look for is in red, If 100% of packets are lost then the test fail

[Yankee]

The nscd daemon doesn't appear to exist, the other commands run
give 0% packet loss.   So, I'll make a copy of this thread and run the
commands to tell the AT&T tech the results.     Thank You.

The good news is I've had to reset the modem several times to
reconfigure the connection and the tech said one more time
and he's pretty sure a new modem will be req'd.    But, he wanted to
see the DNS test results or what happens after a DNS cache flush to make sure, 
so not my motherboard, but the AT&T modem losing the connection info
is the direct cause of the problem reoccurring, and that would be confirmed.

He didn't know the Linux command, just the Windows command for the
info you provided and needed to be provided for that.

Much obliged.

THX.

Patrick

[phd7]

what modem are you using?
I had the same problem with a sierra. Recently bought a Huawei E353 and problem disappeared.

Curiously, this only happened with gnome network manager or nm applet...never with KDE network manager.

have you tried it with a KDE distro?

[Yankee]

what modem are you using?
I had the same problem with a sierra. Recently bought a Huawei E353 and problem disappeared.

Curiously, this only happened with gnome network manager or nm applet...never with KDE network manager.

have you tried it with a KDE distro?

The modem is an AT&T 2WIRE on an LXDE2010 which I use primarily.
Don't have KDE presently installed, just a couple LXDE's and a couple
OpenBox's.

Off a phone line I'm expecting it to work for 2 or 3 weeks and need
another modem reset, which takes a hour to do with waiting for
the connections all to reset then.    Don't know.    The DNS flush
doesn't seem to be how the computer is working.   I'll probably
need a new modem from AT&T eventually.    Have had it for over
a year and a half now.

Patrick

[phd7]

The modem is an AT&T 2WIRE on an LXDE2010 which I use primarily.
Don't have KDE presently installed, just a couple LXDE's and a couple
OpenBox's.

Off a phone line I'm expecting it to work for 2 or 3 weeks and need
another modem reset, which takes a hour to do with waiting for
the connections all to reset then.    Don't know.    The DNS flush
doesn't seem to be how the computer is working.   I'll probably
need a new modem from AT&T eventually.    Have had it for over
a year and a half now.

Patrick

have you had a look at syslog after a crash for more info?

[Yankee]

have you had a look at syslog after a crash for more info?

Today it says I'm connected to the modem Gateway and another IP address I
recognize, but doesn't mention the AT&T DNS server or the AT&T Configuration
server.    They have to receive my ping signal from the modem and sometimes they don't. 
They have IP adresses also, so the ping commands in this thread should help
to confirm or not confirm that.   Today it works OK.