OS - Oracle Linux 5.6 and 6.3 (Oracle Linux is based on Red Hat).
Background: I have several OL 5.6 virtual machines running under Virtual Box on my Win7 Pro desktop. Due to the way VBox handles networking through the network adapter it installs on the host OS, I build my vm's with 2 virtual NICs. The first is configured as NAT, becomes eth0 which is configured for DHCP. The second is configured as host-only, becomes eth1 and is configured with a fixed ip address. As soon as the vm goes through it's initial reboot, I configure a putty session on my desktop to access it, and continue my work from there, never again touching the 'console' inside the VBox window. I have done this scores of times with various updates of OL 5.x.
Now I'm trying to bring up a vm with OL 6.3, using all the same configuration. Whenever I try to log on from a putty session, it takes nearly a minute to get back the prompt for the password. This vm lives in the same network environment as any of my 5.x machines, who all behave as expected. I've been working with a friend on the Oracle OTN forum, but we're just about out of ideas. That discussion is at https://forums.oracle.com/forums/thr...7822� if you want to see what has already been tried.
I saw another thread on this forum that looked promising, but it seemed to involve a dns cache, as it reported a delay only on the first login after a period of inactivity, whereas my problem is consistent .. on every login.
The most recent test, and possibly the most telling, is this ... notice the time difference from the start to the finish of the 'hostname' command:
Code:
[root@vblnxsrv02 ~]# cat /etc/hosts
127.0.0.1 localhost localhost.localdomain localhost4 localhost4.localdomain4
::1 localhost localhost.localdomain localhost6 localhost6.localdomain6
[root@vblnxsrv02 ~]# date;hostname -f;date
Thu May 2 14:00:17 CDT 2013
hostname: Host name lookup failure
Thu May 2 14:01:13 CDT 2013
[root@vblnxsrv02 ~]#
[root@vblnxsrv02 ~]# date;dnsdomainname ;date
Thu May 2 14:05:16 CDT 2013
dnsdomainname: Host name lookup failure
Thu May 2 14:06:12 CDT 2013
Thanks for the response. Here is the requested info. In the resolv.conf, I have masked some of the IP addresses, because they are on my organization's net. I find that surprising, actually. I didn't directly configure this .. it was done by the OS installation. And I've always believed that between the NAT and the host-only adapters, my vm was effectively isolated from any direct knowledge of the environment outside of the host OS. Maybe there's stuff about NAT I don't fully understand.
By way of contrast, I ran the same on a OL 5.6 vm, also with no configuration beyond what is done by the installation procedure. I find the difference in the resolv.conf to be be interesting.
HTML Code:
[root@vblnxsrv03 ~]# cat /etc/resolv.conf
; generated by /sbin/dhclient-script
search ***myorganizationdomain***
nameserver ***.***.10.3
nameserver ***.***.20.1
nameserver ***.***.10.9
[root@vblnxsrv03 ~]# route -n
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
10.0.2.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0
192.168.56.0 0.0.0.0 255.255.255.0 U 0 0 0 eth1
169.254.0.0 0.0.0.0 255.255.0.0 U 0 0 0 eth1
0.0.0.0 10.0.2.2 0.0.0.0 UG 0 0 0 eth0
[root@vblnxsrv03 ~]# ifconfig -a
eth0 Link encap:Ethernet HWaddr 08:00:27:75:FB:5D
inet addr:10.0.2.15 Bcast:10.0.2.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:3 errors:0 dropped:0 overruns:0 frame:0
TX packets:17 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:794 (794.0 b) TX bytes:2838 (2.7 KiB)
eth1 Link encap:Ethernet HWaddr 08:00:27:94:37:86
inet addr:192.168.56.103 Bcast:192.168.56.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:102 errors:0 dropped:0 overruns:0 frame:0
TX packets:90 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:9984 (9.7 KiB) TX bytes:12063 (11.7 KiB)
lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:8 errors:0 dropped:0 overruns:0 frame:0
TX packets:8 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:560 (560.0 b) TX bytes:560 (560.0 b)
[root@vblnxsrv03 ~]# cat /etc/hosts
# Do not remove the following line, or various programs
# that require network functionality will fail.
127.0.0.1 vblnxsrv03.vbdomain vblnxsrv03 localhost.localdomain localhost
::1 localhost6.localdomain6 localhost6
Make two modification:-
(1) comment everything in /etc/resolve.conf
(2) Make UseDNS=no in /etc/sshd/sshd_config
If any of the ethernet adapter are configured to use DHCP, DNS, /etc/resolve.conf will be generated by Network Manager when you reboot the VM. In that case you need to comment everything in /etc/resolve.conf every time.
Make two modification:-
(1) comment everything in /etc/resolve.conf
Interesting. That change alone fixed it. So I tried copying resolv.conf from one of my OL 5.6 machines, but that did *NOT* fix it. And of course, that alone is not a viable solution because resolve.conf gets regenerated at every boot up.
Quote:
Originally Posted by hiten.r.chauhan
(2) Make UseDNS=no in /etc/sshd/sshd_config
I take it there is a typo there, as there is no file by that exact name:
So I went with the second, and made made this change:
HTML Code:
[root@vblnxsrv02 etc]# grep UseDNS ./ssh/sshd_config
UseDNS no
That worked *after* a reboot - which of course reset the resolv.conf. So either of the two is sufficient independent of the other, and of course the second (sshd_config) is the only one that is persistent.
Which then led me back to compare with my OL 5.6 installation. It had the same setting as we started with on the 6.3 :
Code:
[root@vblnxsrv03 etc]# grep DNS ./ssh/sshd_config
#UseDNS yes
So at this point I have a workable solution, but no explanation of why it is *different* on the 6.3 machine - why it *needs* to be different. I suspect the answer is in the output of the 'route -n' commands I posted earlier but I'm not enough of a net admin to understand what we're looking at there.
Quote:
Originally Posted by hiten.r.chauhan
If any of the ethernet adapter are configured to use DHCP, DNS, /etc/resolve.conf will be generated by Network Manager when you reboot the VM. In that case you need to comment everything in /etc/resolve.conf every time.
Commenting out everything in /etc/resolv.conf will deny you access to all DNS, pretty much cutting your guest from accessing the internet outside.
Quote:
So at this point I have a workable solution, but no explanation of why it is *different* on the 6.3 machine - why it *needs* to be different. I suspect the answer is in the output of the 'route -n' commands I posted earlier but I'm not enough of a net admin to understand what we're looking at there.
It's showing what IP ranges get routed into what interfaces, and which gateway it uses as a catchall, which seems to be 192.168.56.1.
It's trying to do a DNS lookup on you when you login and failing to do so. Which are you logging into, eth0 or eth1?
Hi guys.
You'd have to excuse me a bit, as I'm a noob. I really try to avoid asking questions and do research for whatever linux issues that may arise.
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