Thomas Vander Stichele's questions

Up to now, I've always configured my laptop with a wired and wireless interface, each of them being offered a different IP address from DHCP, and each of those IP addresses resolving to different host names. This has always felt kludgey but worked.

Our sysadmins made a configuration that for practical reasons doesn't work, which involves linking the same IP address to the two different MAC's. It doesn't work practically because of the tool they use to do so, but googling for this configuration tells me that this can in fact work.

I've also found posts that indicate that Windows wouldn't accept two interfaces having the same IP.

So, what are the best practices here, and the pros and cons of each approach ? In my particular case, I run Fedora Linux on the laptop. It sounds like using the same IP for both NIC's is in fact a nicer solution, since I would have the same hostname regardless of how I'm connected.

I thought DNS primary/secondary for redundancy purposes was straightforward. My understanding is that you should have a primary and at least one secondary, and that you should set up your secondary in a geographically different location, but also behind a different router (see for example https://serverfault.com/questions/48087/why-are-there-several-nameservers-for-my-domain)

Currently, we have two name servers both in our main data center. Recently, we've suffered some outages for various reasons that took out both name servers, and left us and our customers without working DNS for a few hours. I've asked my sysadmin team to finish setting up a DNS server in another data center and configure it as the secondary name server.

However, our sysadmins claim that this doesn't help much if the other data center is not at least as dependable as the primary data center. They claim that most clients will still fail to look up properly, or time out too long, when the primary data center is down.

Personally, I'm convinced we're not the only company with this kind of problem and that it most likely is already a solved problem. I can't imagine all those internet companies being affected by our kind of problem. However, I can't find good online docs that explain what happens in failure cases (for example, client timeouts) and how to work around them.

What arguments can I use to poke holes in our sysadmins' reasoning ? Any online resources I can consult to better understand the problems they claim exist ?

Some additional notes after reading the replies:

• we're on Linux
• we have additional complicated DNS needs; our DNS entries are managed by some custom software, with BIND currently slaving from a Twisted DNS implementation, and some views in the mix as well. However we're completely capable of setting up our own DNS servers at another data center.
• I'm talking about authoritative DNS for outsiders to find our servers, not recursive DNS servers for our local clients.

Sometimes I have two trees that used to have the same content, but have grown out of sync (because I moved disks around or whatever). A good example is a tree where I mirror upstream packages from Fedora.

I want to merge those two trees again by moving all of the files from tree1 into tree2.

Usually I do this with:

rsync -arv tree1/* tree2

Then delete tree1.

However, this takes an awful lot of time and disk space, and it would be much easier to be able to do:

mv -r tree1/* tree2

In other words, a recursive move. It would be faster because first of all it would not even copy, just move the inodes, and second I wouldn't need a delete at the end.

Does this exist ?

As a test case, consider the following sequence of commands:

$ mkdir -p a/b
$ touch a/b/c1
$ rsync -arv a/ a2
sending incremental file list
created directory
./
b/
b/c1
b/c2

sent 173 bytes  received 57 bytes  460.00 bytes/sec
total size is 0  speedup is 0.00
$ touch a/b/c2

What command would now have the effect of moving a/b/c2 to a2/b/c2 and then deleting the a subtree (since everything in it is already in the destination tree) ?

I want to be able to launch screen sessions on remote servers from a single ssh command on my desktop. However, screen seems to need a terminal, which is not available when running a command through ssh.

So the obvious

ssh [email protected] screen "tail -f /var/log/messages"

(as an example) does not work, and gives

Must be connected to a terminal.

I want ssh to launch the command under a screen so I can log in later and attach as I would to a screen session I would have launched manually.