Operating systems

Is it just me, or has somebody at Microsoft really dropped the ball on network location setting? When a Windows computer detects a new network, which it has not be attached into earlier, it pops you the question and asks about how to profile the security in that particular case. If everything goes ok, there is no need to change anything. However, when you install your computer, you don't get to answer that. Also, there is commonly known that people make mistakes. What if you simply fumbled the question and clicked wrong.

In Windows 7 the setting is simple:

You go there, click the value and select a better one. In Windows 8, Windows 8.1, Windows Server 2012 and Windows Server 2012 R2 that is not the case. The setting cannot be changed. Period. Wtf?

There is a way to change the setting. I found this article with Google: How do I set my wireless network to be private instead of public? The "Easiest" and "Most direct" are crap, IMHO. The part with Local Security Policy seems to work:

That seems to be working from Windows 7 onwards. Whose bright idea it was to make the change that difficult?

This is a follow-up for my previous article about running IPv6 and WLAN access point. There I said "This was actually very easy to do into DD-WRT" and now I'd like to take that back.

It seemed to be easy, but ... Here are my settings in detail. Btw. I'm running DD-WRT v24-sp2 big
Release: 07/24/13 (SVN revision: 22118)

1. disable the autoconfiguration from the WLAN access-point and manually define a static IPv6-address

This is the part which I struggled the most. Sure it is easy to remove the manually assigned IPv6-address from an interface, just run:

ip -6 addr delete 2001::-da-IP-here-/64 dev br0

on a shell. It will drop the autoconfigured address and it will stay away. For a while. It surely won't survive a reboot.

To make this stick, go to web GUI Administration --> Commands and add a startup command:

echo 1 > /proc/sys/net/ipv6/conf/all/forwarding
echo 0 > /proc/sys/net/ipv6/conf/all/autoconf
echo 0 > /proc/sys/net/ipv6/conf/all/accept_ra
echo 0 > /proc/sys/net/ipv6/conf/all/accept_ra_pinfo

/usr/sbin/ip -6 addr add 2001:-da-IP-here-/64 dev br0

That makes the settings stick. Autoconfiguration will be gone and a static address will be assigned instead. I attempted at least 20 different combinations while looking the sysctl-settings list, but that was the 1st one I found to be actually functional for deactivating the autoconfig.

2. use a static default route from the WLAN access-point and confirm that it has proper IPv6-connectivity

4. make sure, that any incoming traffic from the mobile clients is properly routed to the real IPv6-router, and confirm that traffic flows both ways

Yet again, go to web GUI Administration --> Commands and add a startup command:

/usr/sbin/ip -6 route add default via 2001:-da-router-IP-here-::1 metric 1

That creates a static route which will work and fulfill the 2). To achieve 4) make sure to have the metric 1 at the end.

3. run router advertisement daemon (RADVD) to advertise the WLAN access-point as a proper router for any wireless clients

In the DD-WRT IPv6 article it said that RADVD configuration should be like this:

interface br0 {
   AdvSendAdvert on;
   prefix 0:0:0:1::/64 {
    AdvOnLink on;
    AdvAutonomous off;
   };
};

Don't do that! DON'T! It will royally fuck up your LAN. Nothing in IPv6-land will work if you literally copy/paste that like they suggest. The problem is with the prefix of 0:0:0:1::/64, it will assume that your network has that /64-prefix and assign route and IP-address for any IPv6-host with that prefix. I can bet you $1.000.000 dollars, that it will not be your IPv6-prefix. ... and win.

Just put the exactly same prefix your real IPv6-router has. The WLAN access point's RADVD should be configured pretty much exactly alike. For the configuration directives see radvd.conf manual-page. It literally says:

• AdvSendAdvert: do send advertisements, default is off
• AdvOnLink: use the prefix for link determination (meaning: yes you can get to The Net via this), it is on by default, you really don't need this line at all
  
• AdvAutonomous: do distribute new the IP-addresses from this RADVD to your wireless (and wired) clients, yet again it is on by default and you really don't need this
  

With these settings I succeeded a reboot and still had my wireless and wired clients working using either of the two IPv6-routers. On Windows the setup will display two default routes, like this:

PS C:\Windows\system32> netsh interface ipv6 show route

Publish  Type      Met  Prefix                    Idx  Gatewa
-------  --------  ---  ------------------------  ---  ------
No       Manual    256  ::/0                       18  fe80::
No       Manual    256  ::/0                       18  fe80::

On Linux:

# ip -6 route show | fgrep default
default via fe80:: dev eth0 metric 1024  expires 0sec mtu 1280 hoplimit 64
default via fe80:: dev eth0 metric 1024  expires 0sec mtu 1280 hoplimit 64

That's ok. IPv6 will support that ok. Just be aware, that your traffic may route either way.

I've been using IPv6 on my own LAN for years. Most of the things I use on daily basis have IPv6 and it seems to work. For example a Sony television or iPhone 4S does not use IPv6, but iPad does.

On my router there is a Router Advertisement Damon to do stateless auto-configuration. On Windows 7 and 8 they have really weird things running out-of-the-box, but I'm in a habit of running (as admin):

netsh interface ipv6 set privacy state=disabled store=active
netsh interface ipv6 set privacy state=disabled store=persistent
netsh interface ipv6 set global randomizeidentifiers=disabled store=active
netsh interface ipv6 set global randomizeidentifiers=disabled store=persistent
netsh interface teredo set state disabled

That way I'm using fixed IPv6-addresses and disable the unnecessary Teredo-tunnel.

I don't exactly know why or how, but on one of my computers (running Windows 7), the IPv6-sockects started to not work properly. The symptoms include lot of reconnections and for example in SSH-client, the connection would simply drop. I did everything I knew, but nothing helped. A failing SSH-connection would look like this on the wire:

After 31 seconds of connection, there is a sporadic retransmission. That is not dangrous and it happens sometimes. My Windows 7 would respond with a duplicate ACK into it, waits 3 seconds and goes ballistic. It simply starts re-transmitting the already transmitted data with 1, 3 and 5 second intervals before determining that the connection has died. WTF?! The connection is not bad! It works on all other computers. The issue can be easily repeated and it works the same way every time. Windows thinks it needs to start a burst of re-transmissions and disconnects when they seem to fail.

During one of the Google-session for the fix, I found netsh interface ipv6 reset command. I tried it:

PS C:\Windows\system32> .\netsh.exe interface ipv6 reset
Reseting Global, OK!
Reseting Interface, OK!
Reseting Subinterface, OK!
Restart the computer to complete this action.

Did the Windows restart, ran the above commands to disable privacy, randomization and teredo-tunnel. Everything started to work! Whooo-hoo! Now my SSH-connections don't drop anymore. How cool is that!

The fix is very microsoft-ish. Some counter ticked into illegal value and in their mind the correct fix is to reset everything to the post-installation state. On *nix-world network-stack -code would be of much better quality and the entire issue would never happen!

In my Fedora 19 I've been wondering why my NTPd does not start on boot. It used to do so couple of Fedora installations ago. This is not a big deal, so I've been mostly ignoring it. Today I dug up some energy to investigate.

The reason was much simpler than I tought. On my very short checklist were:

1. Confirm that systemd has ntpd.service enabled, it was.
   
2. Confirm that ntpd.service has a dependency to start the service after network interfaces are up, it was chained to do a single ntpdate update and start the daemon after it.
3. Needed interfaces have not been blocked and/or needed interfaces have been enabled in config, everything was out-of-the-box: all network interfaces allowed.
   

The daemon even had the panic-threshold disabled in the config, so it wouldn't choke on startup if time was badly off for some reason. I found no reason for the daemon to start.

However, doing a search for ntpd in /usr/lib/systemd/system revealed what was going on. chronyd.service has Conflicts=ntpd.service in the service description. WTF?! What the hell is chronyd?

According to http://chrony.tuxfamily.org/ it is "a pair of programs which are used to maintain the accuracy of the system clock on a computer". Sounds like a NTPd to me. Running netstat confirmed the fact:

# netstat -nap | fgrep :123
udp        0      0 0.0.0.0:123             0.0.0.0:*                           666/chronyd        
udp6       0      0 :::123                  :::*                                666/chronyd        

The daemon does bind to NTP-ports. To get chronyd running properly, all I had to do was add proper time source and allowed updates from my LAN with allow-directives.

That's it!

My Fedora 19 failed to boot if I had an entry for an iSCSI-mount in /etc/fstab. During boot the system just fell to emergency mode. To get the box to boot, I simply did a "stupd man's solution", and commented the line out. This is what happens if I have the standard line in fstab:

My fstab line is:

/dev/qnap  /mnt/qnap  ext4  defaults  1 0

It took me a while to get back to the issue and investigate, it was that bad. This is the clue I found on Fedora project's documentation about iSCSI. They said, that any iSCSI-volumes should be mounted with a special flag _netdev. I changed to that, and hey presto! During bootup, it first does something and then mounts the iSCSI-drive. I merged those two occurrences into a single photo:

It works! I'm so happy about this. For clarity, the fstab-line is:

/dev/qnap  /mnt/qnap  ext4  _netdev  0 0

During my ventures in the Linux-land, I constantly package and re-package RPMs. Sometimes to introduce new functionality to existing package or to simply get a newer version that distro vendor is prepared to offer. Number of times I've created packaging to software that is not in the distro at all.

Another thing I love using are symlinks. I can have newer and older package of a software and can simply switch with updating the symlink into correct version. When I combined those two, it bit me in the ass.

I had quite simple script-blocks to handle the symlink:

%post
cd /my/package/directory/
%{__rm} -f my.cool.symlink-name
ln -s package/library/my.cool my.cool.symlink-name

%preun
%{__rm} -f /my/package/directory/my.cool.symlink-name

On install, that worked, but on update/freshen there was no symlink left. I was puzzled, why is that? Little bit of googling revealed two pieces of information: RPM spec-file documentation about scripts, especially the Install/Erase-time Scripts -part and 2nd the Fedora Project's packaging information, especially the scriptlet ordering. I'll abbreviate the Fedora's ordering here omitting the non-interesting parts:

1. %pre of new package
   This is the part where my script confirms that the symlink exists.
   
2. (package install)
3. %post of new package
4. %preun of old package
   During update/freshen, this is the part where my script removes the symlink created in 1.)
   Crap!
   
5. (removal of old package)
6. %postun of old package

Further reading of RPM spec-docs said "the argument passed to version 1.0's scripts is 1". Ok, nice to how, but now what? How can I utilize the information? What is the exact syntax for the script? The only usable information I found was in the Fedora packaging instructions, there was an example:

%preun
if [ $1 = 0 ] ; then
  /sbin/install-info --delete %{_infodir}/%{name}.info %{_infodir}/dir || :
fi

So this was the thing I had to try. My solution is to change the %preun-block:

%preun
if [ $1 -lt 1 ] ; then
  # This is really an un-install, not deleting previous version on update
  %{__rm} -f /my/package/directory/my.cool.symlink-name
fi

I did that and upgraded the package. Poooof! The symlink was gone like there was no change at all. WHY? I upgraded the revision number of the package and upgraded again. NOW it worked! Nice.

There is a simple explanation what happened. It says in the Fedora project's order-list that "%preun of old package". OLD package! It works starting from the next update, but not on the first one.

Anyway I was delighted to get that one sorted.

Previously I've studied the init.d replacement systemd.
Update 4th Jun 2017: See the new version

To my surprise, my contraption from the previous article didn't survive a reboot. WTF?! It turned out that in Fedora 19 the /var/run/ is a symlink into /run/ which has been turned into tmpfs. Goddamnit! It literally means, that it is pointless to create /var/run/<the daemon name here>/ with correct permissions in RPM spec-file. Everything will be wiped clean on next reboot anyway.

So, I just had to study the systemd some more.

This is my version 2 (the Unit and Install -parts are unchanged):

[Service]
Type=forking
PrivateTmp=yes
User=nobody
Group=nobody
# Run ExecStartPre with root-permissions
PermissionsStartOnly=true
ExecStartPre=-/usr/bin/mkdir /var/run/dhis
ExecStartPre=/usr/bin/chown -R nobody:nobody /var/run/dhis/
# Run ExecStart with User=nobody / Group=nobody
ExecStart=/usr/sbin/dhid -P /var/run/dhis/dhid.pid
PIDFile=/var/run/dhis/dhid.pid

The solution is two-fold. First an ExecStartPre-directive is required. It allows to run stuff before actually executing the deamon. My first thing to do is create a directory, the minus sign before the command says to ignore any possible errors during creation. The target is mainly to ignore any errors from the fact that creation would fail due to the directory already existing. Anyway, all errors are ignored regardless of the reason.

The second command to run is to make sure that permissions are set correctly for my daemon to create a PID-file into the directory created earlier. That must succeed or there will be no attempt to start the daemon. chowning the directory will fail if the directory does not exist, or any other possible reason.

Sounds nice, huh? Initially I couldn't get that working. It was simply due to reason, that the entire Service-part is run as the user pointed by the User=nobody and Group=nobody -directives. That user was intentionally chosen, because it has very limited permission anywhere or anything. Now it cannot create any new directories into/var/run/. Darn!

This where the solution's 2nd part comes in. Somebody designing the systemd thought about this. Using the PermissionsStartOnly-directive does the security context switch at the last moment before starting the daemon. This effectively changes the default behavior to allow running Service-part as root, except for the daemon. Exactly what I was looking for! Now my daemon starts each and every time. Even during boot.

Another thing which I noticed, is that when I edit a systemd service-file, the changes really don't affect before I do a systemctl --system daemon-reload. It was a big surprise to me, after all in traditional init.d everything was effective immediately.

PS.
Why cronie does not create a PID-file? I had an issue in CentOS where I had not one, but two cron-daemons running at the same time. This is yet another reason to go systemd, it simply works better with ill-behaving deamons like cronie.