Mac OS X Snow Leopard: permissions changed on /var results in dns lookup issues

domain-name-systememailmac-osxpermissionsvar

I was attempting to solve an issue ("/var/log/msmtp.log: permissions denied" error when attempting to send mail using msmtp) when I did this:

> chmod -R 770 /var

After that, my machine would not resolve domain names via cURL. (ping also fails) But, oddly, I can enter domain names into Safari and visit any web pages w/o a problem…

I'm actually not sure if the chmod command is the cause of the problem, but I suspect it is.

Also, if I ls -l on /var (or /private/var) it doesn't seem that any of the subdirectories or files there actually changed permission, but there are many, so I can't say that conclusively…

Incidentally, I fixed the original error (msmtp.log permission denied) by setting TMPDIR=/tmp in my local environment (bash). Now the error goes away, but I get this error:

msmtp: cannot locate host domainname.org: nodename nor servname provided, or not known

Any ideas about how to go about getting DNS working again?

Best Answer

Running chmod -R 700 /var will have made a bunch of important parts of the OS inaccessible to anything but root. You may be able to resurrect things with permissions repair: boot from the Install DVD, select a primary language, then select Disk Utility from the Utilities menu; in Disk Utility, select your HD from the sidebar, then the First Aid tab on the right, then Repair Disk Permissions under that. This may not fix everything back to the way it should be (it doesn't know what the perms should be on all files), but it'll probably get it back to the point where you can boot it.

If it reboots successfully after that, I'd actually run permissions repair again from the booted OS (it'll be using the version of Disk Utility that matches the running OS, and may have a slightly better idea of what the perms should be).

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DNS – Name Lookup Not Working After Snow Leopard Upgrade

I ran into the exact same problem and found a thread about a Mac mini having DNS issues on Apple's Discussions extremely helpful.

The crux of the issue: mDNSResponder seems to occasionally change the order of the DNS servers it queries and so if it queries your ISP's DNS servers first it won't get a proper record (or if you're using split DNS you'll get your public IP).

The best fix for this is to ensure (as you did) that only the required DNS servers are listed in your DNS settings. This may require removing the ISP DNS servers from your DHCP (as I had to do as well - all requests are forwarded through the local DNS server anyway).

The reason utilities like dig and nslookup will succeed as normal is they are using BIND and /etc/resolv.conf directly unlike the rest of the operating system.

For reference in Snow Leopard the DNS cache is now stored by mDNSResponder and in order to clear it you need to restart the process using sudo killall -HUP mDNSResponder. You can get more info (logging, dump internal state, etc.) by using different flags to the killall command.

"sudo killall -USR1 mDNSResponder" to enable operation logging.
"sudo killall -USR2 mDNSResponder" to enable packet logging.
"sudo killall -HUP mDNSResponder" to clear the DNS cache.
"sudo killall -INFO mDNSResponder" to dump mDNSRepsonder's internal state.

Source: Snoop Dogg on that same thread.

Mail server Mac OS X Snow leopard

See Apple's Mail Service Administration as well as their other Mac OS X 10.6 Snow Leopard Server documentation. Also, Topicdesk.com has excellent tutorials including one for tuning postfix and one for Making Virtual Mail Users in OS X 10.4/10.5 Server, but the latter hasn't been updated for Mac OS X 10.6 Snow Leopard Server yet and I haven't checked to see if Apple has improved that area of their Mail services. Worth a read though.

Best Answer

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