grigoryvp's questions

I have latest clean Ubuntu 14.04.1 64-bit from official website installed in Virtualbox. I connect to a VPN network using vpnc that sets 2 DNS servers using DHCP:

user@virtual:~$ cat /etc/resolv.conf 
# Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)
#     DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN
nameserver 10.88.94.1
nameserver 8.8.8.8
nameserver 10.40.0.1

Where 10.88.94.1 and 8.8.8.8 are returned by vpn dhcp and 10.40.0.1 is returned by lan dhcp. The first DNS server returned by vpn dhcp is configured as authoritative, non-recursive name server for some internal names.

The problem is - Ubuntu somehow ignores the authoritative flag and discard valid response becouse it's non-recursive:

user@virtual:~$ nslookup
> video.something.com
;; Got recursion not available from 10.88.94.1, trying next server
Server:     8.8.8.8
Address:    8.8.8.8#53

Non-authoritative answer:
Name:   video.something.com
Address: 180.112.94.1

As tcpdump clearly shows the answer from first DNS server have 'authoritative' flag set, but somehow it is ignored ('*' in second response is for "authoritative", '-' is for "non-recursive"):

13:23:44.505098 IP 10.40.130.209.44159 > 10.88.94.1.domain: 63790+ A? video.something.com. (32)
13:23:44.506285 IP 10.88.94.1.domain > 10.40.130.209.44159: 63790*- 1/0/0 A 10.88.94.12 (48)
13:23:44.506390 IP 10.40.130.209.45437 > 8.8.8.8.domain: 63790+ A? video.something.com. (32)
13:23:44.608414 IP 8.8.8.8.domain > 10.40.130.209.45437: 63790 1/0/0 A 180.112.94.1 (48)

Same setup works as expected (first DNS result is used) on both Windows and OSX. But not on Ubuntu. Is it something i can fix in Ubuntu in order for authoritative responses to be processed crrectly regardless of "non-recursive" flag or it is completely broken and where is nothing i can do?

If i execute 'ps' command in shell, i can get some processes marked as '' - they are exited, but parent process don't receive they exit status yet. Sometimes, while debugging network apps, i need to get exit status of such process from shell - is it 0 or some error code like segmentation fault?

Is it possible to get this exit status from shell given PID, or only zombie's parent process can get this exit status?

P.S. I don't need to "kill" them, "close" them etc. I only need to check they exit status :)

I have a test VDS box with real IP. If i start web server on physical interface port 80, it can be opened from another computer via it's ip address (and default port 80):

python -m SimpleHTTPServer 80

But if i try to reditect port 80 from physical interface eth0 to loopback 127.0.0.1 port 8080 i can connect it from another computer on port 8080, but can't connect on port 80, it's just endless 'connecting'. Seems like no redirection occurs:

iptables -t nat -A PREROUTING -i eth0 -p tcp --dport 80 -j DNAT --to-destination 127.0.0.1:8080
python -m SimpleHTTPServer 8080

What i'm doing wrong? :(

P.S. Binding server on '127.0.0.1:8080' produce same result, but it does not matter since server running on '0.0.0.0:8080' will accept connection redirected to '127.0.0.1:8080'. AFAIK. :(

iptables -L result:

Chain INPUT (policy ACCEPT)
target     prot opt source               destination         

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination         

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination

iptables -t nat -L result:

Chain PREROUTING (policy ACCEPT)
target     prot opt source               destination         
DNAT       tcp  --  anywhere             anywhere             tcp dpt:http to:127.0.0.1:8080

Chain INPUT (policy ACCEPT)
target     prot opt source               destination         

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination         

Chain POSTROUTING (policy ACCEPT)
target     prot opt source               destination

netstat -nlp result:

Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name
tcp        0      0 0.0.0.0:22              0.0.0.0:*               LISTEN      676/sshd        
tcp6       0      0 :::22                   :::*                    LISTEN      676/sshd        
Active UNIX domain sockets (only servers)
Proto RefCnt Flags       Type       State         I-Node   PID/Program name    Path
unix  2      [ ACC ]     STREAM     LISTENING     7964     600/acpid           /var/run/acpid.socket
unix  2      [ ACC ]     STREAM     LISTENING     6590     1/init              @/com/ubuntu/upstart
unix  2      [ ACC ]     SEQPACKET  LISTENING     6760     231/udevd           /run/udev/control
unix  2      [ ACC ]     STREAM     LISTENING     7030     345/dbus-daemon     /var/run/dbus/system_bus_socket

ifconfig -a result:

eth0      Link encap:Ethernet  HWaddr 00:16:3e:da:1a:98  
          inet addr:5.14.223.181  Bcast:5.14.223.255  Mask:255.255.255.0
          inet6 addr: fe80::140:3eff:febe:201a/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:371264 errors:0 dropped:59 overruns:0 frame:0
          TX packets:2093 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:17377545 (17.3 MB)  TX bytes:214428 (214.4 KB)
          Interrupt:25 

lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:10 errors:0 dropped:0 overruns:0 frame:0
          TX packets:10 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:552 (552.0 B)  TX bytes:552 (552.0 B)

I have a Windows 7 computer and a MacOS X 10.6 computer that are connected to the same LAN using a 10$ hub. On MacOS I set the computer name to "mymac.local" in "preferences->sharing". The Windows computer has a static IP address of 192.168.0.10 and the Mac has the address 192.168.0.20. Both have a netmask of 255.255.255.0 and no gateway.

If I issue the command ping mymac.local from my Windows computer it will successfully ping 192.168.0.20. How did Windows determine that IP 192.168.0.20 is associated with "mymac.local" since there's no DNS on my network? Is it some broadcast? What protocol is used?

I have a network problem on my MacOS that i need to troubleshoot. I know that TCP socket has internal timeout that will close connection if remote party is not responding (but no graceful disconnect either). Is it any command/tool i can use to check exact value of this timeout(s)?

I have Ubuntu 9.10 installed with sshd and I can successfully connect to it using login and password. I have configured an RSA key login and now have "Server refused our key" as expected. Ok, now I want to check sshd log in order to figure out a problem. I have examined /etc/ssh/sshd_config and it have

SyslogFacility AUTH
LogLevel INFO

Ok. I'm looking at /var/log/auth.log and... it's empty O_O. Changing Loglevel to VERBOSE helps nothing - auth.log is still empty. Any hints how I can check sshd log?

Is it a way to create a VHD virtual drive image from files in existing folder? I know that it can be done programmatically via .NET framework API, but maybe it's already exists a tool that can be run like

create my.vhd c:\my

As a developer, i frequently need to perform complex searches for files. For example, search for file that starts with 'buf' and ends with '.c' or '.h' in a c:\sdk and c:\project\include. Windows search in vista+ is good, but for a lrage amount of sources it will search VERY long time if not index, and it's not possible to specify a number of folders to search in.

Is it any good and freeware tool available that allows to perform complex file search on windows platform? Google desktop requires indexing too and regexp support is very limited.

Currently i'm working on some NAT traversal code (that allows to computers each behind it's own NAT to communicate with each other). But, surprisingly, i can't find any symmetric NAT's! (it's the most hard case). Anyone knows where can i find one, wither in software or hardware? It seems that windows 'internet connection sharing' is not symmetric :(.

A task has emerged to install latest subversion for a group of mac os x users (latest mac os version). I have tried first to install it manually from subversion.tigris.org, 'opencollabnet binary' (http://downloads.open.collab.net/binaries.html, "Universal Subversion 1.6.3 Binaries for MAC OS X (32 and 64 bit)"). It installed ok via .pkg installer, but after using 'svn' command I was surprised to see an old 1.4.4 version bundled with macos.

It seems, that installing new subversion does not replace an old one. What is a 'correct' way to ensure that 'svn' command always uses newly installed subversion? I can create a symlink or add /opt/bla-bla-bla/subversion to path, but I'm afraid that such crude hacking can break something.

I need a script that can be run on freshly installed windows xp+ and download specified files from internet, like http://www.python.org/ftp/python/2.6.2/python-2.6.2.msi Is it any easy way to do it without hand-crafting HTTP/FTP requests or using third-party programs like wget? I can suggest that WScript.CreateObject("internetexplorer.application") will do the magic, but documentation on it is extremely huge and Google is silent, as always :).

Is it any cross-platform way to check that my python script is executed under admin rights? Unfortunately, os.getuid() is UNIX-only and is not available under windows :(.

If editing some script in vim, a file with .py or .sh extension, is it any build-in vim command that allows to run such file? I know it's a lot of IDE-like addons for VIM that allows to execute files vim edit, but is it possible without addons?

Is there any way in Mac OS X 10.5.x to create a .dmg image from existing physical DVD, without a third-party tools installation? I have carefully examined "disk utility" and searched Google, but it seems that all people just write .dmg files, no information on how to create them from physical DVD disks.

Many machines i need to work with have basic NIX installation with vim as text editor. But vim's way to select text is kind of unusual to me :). Is it any easy way to re-configure vim so it will use shift in order to select text and ctrl+c / ctrl+v for copy and paste?

I have an .app executable generated for MacOSX. Is it any easy way to install this app into Applications so it can be used by end users, via script? (need to install on multiple computers and really don't want to create intermediate .pkg installer for it)

How to check that my python script is running under Administrator rights (sudo) under BSD-like OS? Need to display user-friendly warning in order it is executed without admin rights.

It's a common task to check network 'quality' - latency, number of dropped packets etc. But 'ping' has a number of drawbacks: - It uses ICMP. Many ISP has different shapers for ICMP and TCP traffic, so 'ping' will show 10ms latency, but TCP connections will experience 1000ms+. - It sends very small amount of packets. By default, one packet every second. Since TCP protocol tolerates packets loss (it can operate very well is half packets are lost - it's normal), it's absolutely unclear if ping's "30% packet loss" killing connection or if it's absolutely normal.

So, is it any alternative for ping that use TCP connection instead of ICMP and checks internet connection quality?

I have a .dmg MacOS package (with 'continue' buttons, EULA etc) that i need to install on multiple computers. Is it a way to do so silently via a bash/python/ruby/etc script just like silent MSI installation in Windows? I can automate installation writing script that will click buttons for me, but that looks kinda unnatural :).

Is it possible to get a file name of a process using PID? ps displays a lot of useful information about a process, but not a hint about a process executable file location.