News items for tag linux - Koos van den Hout

2018-01-25 Building a testing server for pppoe 10 months ago
The new homeserver will have to run the same pppoe client setup as the current server. But I want to get the whole setup tested before the migration to minimize disruption.

Since I'm not going to get a free extra vdsl line and vdsl modem to test with and the complicated part is in the pppoe and ppp client part I decided to use a test vlan and set up a pppoe-server and ppp server on that vlan.

The pppoe server part is started with
# pppoe-server -I eth0.99 -C kzdoos -L 172.16.19.1 -R 172.16.21.19
And it's indeed available from the client:
# pppoe-discovery -I eth2
Access-Concentrator: kzdoos
Got a cookie: 84 39 c6 51 13 fe 32 00 2c 06 2a b4 38 0e 30 87 46 7b 00 00
--------------------------------------------------
AC-Ethernet-Address: 00:1f:c6:59:76:f6
So that part works. Next is to get an actual ppp session working over it.

The server part was a bit of work as I want to get the whole configuration including password checks. Server configuration in /etc/ppp/pppoe-server-options on the server system:
require-pap
lcp-echo-interval 10
lcp-echo-failure 2
hide-password
noipx
ipv6 ,
And the client configuration in /etc/ppp/peers/dray-vdsl:
user testkees
password topsecret
+pap
noauth
noipdefault
ipv6 ,
ipv6cp-use-persistent
defaultroute
persist
maxfail 0
noproxyarp
ipparam xs4all
lcp-echo-interval 10
lcp-echo-failure 6
pty "pppoe -I eth2"
Lots of options to make the setup exactly the same as the current. It took a lot of tries before password authentication was working. I could not get the client-side password in /etc/ppp/pap-secrets to work, but as show above the password in the ppp configuration did work.

And the setup in /etc/network/interfaces on the client just the same as the known configuration:
iface pppdray inet ppp
        provider dray-vdsl

And it works!
# ifup pppdray
Plugin rp-pppoe.so loaded.
# ifconfig ppp0
ppp0: flags=4305<UP,POINTOPOINT,RUNNING,NOARP,MULTICAST>  mtu 1492
        inet 172.16.21.45  netmask 255.255.255.255  destination 172.16.19.1
        inet6 fe80::5254:ff:fe3c:2014  prefixlen 10  scopeid 0x20<link>
        ppp  txqueuelen 3  (Point-to-Point Protocol)
        RX packets 9  bytes 252 (252.0 B)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 9  bytes 202 (202.0 B)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0
# ping -c 3 172.16.19.1
PING 172.16.19.1 (172.16.19.1) 56(84) bytes of data.
64 bytes from 172.16.19.1: icmp_seq=1 ttl=64 time=0.721 ms
64 bytes from 172.16.19.1: icmp_seq=2 ttl=64 time=0.436 ms
64 bytes from 172.16.19.1: icmp_seq=3 ttl=64 time=0.449 ms

--- 172.16.19.1 ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2029ms
rtt min/avg/max/mdev = 0.436/0.535/0.721/0.132 ms
The mtu is not yet what I want, but the session is alive.

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2018-01-23 Avoiding the linux statefull firewall for some traffic 10 months ago
I was setting up a linux based firewall on a busy ntp server and to make sure everything worked as designed I added the usual:
iptables -A INPUT -j ACCEPT --protocol all -m state --state ESTABLISHED,RELATED
And after less than half an hour the system log started filling with
nf_conntrack: table full, dropping packet
nf_conntrack: table full, dropping packet
nf_conntrack: table full, dropping packet
nf_conntrack: table full, dropping packet
It is indeed a busy server. The solution is to exclude all the ntp traffic from the stateful firewall. Which means I have to allow all kinds of ntp traffic (outgoing and incoming) by itself.

The specific ruleset:
iptables -t raw -A PREROUTING --protocol udp --dport 123 -j NOTRACK
iptables -t raw -A OUTPUT --protocol udp --sport 123 -j NOTRACK

iptables -A INPUT -j ACCEPT --protocol udp --destination-port 123
I also made sure the rules for the ntp traffic are the first rules.

Traffic at this server is somewhat over 1000 ntp request per second. So the counters of the NOTRACK rules go fast.
# iptables -t raw -L -v
Chain PREROUTING (policy ACCEPT 1652K packets, 126M bytes)
 pkts bytes target     prot opt in     out     source               destination 
9635K  732M CT         udp  --  any    any     anywhere             anywhere             udp dpt:ntp NOTRACK
1650K  125M CT         udp  --  any    any     anywhere             anywhere             udp dpt:ntp NOTRACK

Chain OUTPUT (policy ACCEPT 1522K packets, 117M bytes)
 pkts bytes target     prot opt in     out     source               destination 
9029K  686M CT         udp  --  any    any     anywhere             anywhere             udp spt:ntp NOTRACK
1520K  116M CT         udp  --  any    any     anywhere             anywhere             udp spt:ntp NOTRACK
But no packets are dropped, which is good as this server is supposed to be under a constant DDoS.

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2018-01-14 Recovering firmware on the Draytek Vigor 130 VDSL2 modem with linux / macosx 10 months ago
I needed the recovery procedure again: there was a new firmware 3.8.12 with newer VDSL modem driver and the standard update via the webinterface failed.

I just want to keep the notes from "OzCableguy" since his shop and blog have gone. I found the saved version via archive.org, Updating Draytek firmare using the MacOS X or UNIX command line and TFTP - OzCableguy.

Draytek modems have several methods available to update their firmware.

You can use the Firmware Upgrade Utility under Windows, load it from the web interface via HTTP, FTP the file to the modem or use the TFTP (Trivial File Transfer Protocol) service built into the box.

If your modem has been bricked you can’t use FTP or HTTP. If you don’t want to use Windows or go through the web interface, then this TFTP method is a viable alternative. Note that unlike a lot of other boxes using TFTP to load firmware, the Draytek is acting as a TFTP server, the UNIX/MacOS box as a client and you PUT the file onto the modem. It is normally the other way around, but that needs some extra setup steps that are conveniently avoided with this method.

The firmware comes in two pieces. Use the .rst version of the file if you want to change the modem settings back to factory defaults, use the .all file to keep the current settings (.all may not be a good option if the modem is bricked).

Secondly you need an ethernet interface on your Mac or UNIX box set to the subnet 192.168.1.0 (eg: with IP address 192.168.1.10) so that you can talk to the modem at its default IP address of 192.168.1.1.

If the modem is up and running (and not bricked), you should now be able to ping it ..
$ ping 192.168.1.1
PING 192.168.1.1 (192.168.1.1): 56 data bytes
64 bytes from 192.168.1.1: icmp_seq=0 ttl=255 time=0.309 ms
64 bytes from 192.168.1.1: icmp_seq=1 ttl=255 time=0.421 ms
64 bytes from 192.168.1.1: icmp_seq=2 ttl=255 time=0.409 ms
^C
—-192.168.1.1 PING Statistics—-
3 packets transmitted, 3 packets received, 0% packet loss
round-trip min/avg/max/stddev = 0.309/0.380/0.421/0.050 ms$ 
If your modem is really bricked then the ping will only work when the modem is actually in TFTP upload mode as below. You can ignore this step, it just demonstrates that the ethernet cable is working.

Now we can upload the firmware. With the modem powered off, press and hold the factory reset button, then power up the modem. Continue to hold the button down until ’some’ of the lights flash together. On the Vigor2820Vn ’some’ is the left column of three. On the 2800 and 2910 the left two LEDs flash.

Release the button and on your UNIX/MacOS box type the following commands (note that the modem only stays in TFTP mode for a short time, you can actually type right up to the end of the put command and just press return when the left-hand modem lights start flashing).

The name of the firmware and the number of bytes transmitted depend on the product you are trying to recover.
$ tftp 192.168.1.1
tftp> binary
tftp> put v2820_v03301_211011_A.rst
Sent 4973144 bytes in 13.1 seconds
tftp> quit
$ 
There will be a pause after the ‘put’ command, but your modem ethernet port light should be flashing madly. The transfer is done when you get the “Sent” message. Quit the TFTP client and perhaps your Terminal session, there’s nothing more to see.

What happens next isn’t really documented but we presume that the modem has to unpack the firmware and load it into flash. On our 2820Vn the column of 3 lights continued to flash, but gradually slowed down, speeded up, then slowed again. Eventually after a minute or two the modem rebooted in the normal fashion. Just be patient.
And this last bit is where the windows utility is better: it will tell you when the recovery is done and a success. With a commandline tool you'll just have to wait for the leds to blink right.

After all the recovery and the waiting the modem works again and the line is stable. I chose the 'modem6' version again. I may try the 'modem5' and 'modem4' version too to see whether I can get lower latency without losing stability. Although the improvement may be in the single digit millisecond range so it would be a lot of work for very little improvement.
Read the rest of Recovering firmware on the Draytek Vigor 130 VDSL2 modem with linux / macosx

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2017-12-28 Learning Apache 2.4 access control 11 months ago
Before I expose anything to the outside world I want the access controls to work as I expect, but things have changed a lot in Apache 2.4.

Standard for a site that's normally available is now in 2.4:
        <Directory "/home/httpd/idefix/html">
                Require all granted
        </Directory>
(and any other needed options). But for development systems I want a username/password request to access them. This part took a bit of work to get right. First I found Upgrading to 2.4 from 2.2 - Apache HTTP Server Version 2.4 has a repeating typo in the authorization samples:
AuthBasicProvider File
isn't going to work, giving
Unknown Authn provider: File
error messages. The right bit is:
AuthBasicProvider file
The difference one letter makes.

That also did not give me a working configuration, leading to interesting errors in the log of type:
AH00027: No authentication done but request not allowed without authentication for /. Authentication not configured?
Which turned out to be a missing bit in the samples in the same document: the AuthType is needed too.

The full now working access rule is:
    <Location "/">
        AuthType Basic
        AuthBasicProvider file
        AuthUserFile /home/httpd/data/sitemanagers
        AuthName "Koos z'n Doos beheer"
        <RequireAny>
            Require valid-user
        </RequireAny>
    </Location>
The use of RequireAny allows me to add trusted IP ranges so that the site is reachable from a trusted IP address or after using http basic authentication.

The good news is that the samples in Authentication and Authorization - Apache HTTP Server Version 2.4 are correct.

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2017-12-28 Getting haproxy to do what I want 11 months ago
In the new homeserver I want an haproxy running on the "router" so it can route http requests to the right backend. At the moment I am testing this and after the 'http' config I'm now testing the 'https' part. To keep things consistent things that come in via https also get requested via https from the backends.

For testing I have some ports on the main server forwarded to haproxy so I can test with all aspects of host-header based routing. After some searching I found out that when I visit http://developer.urlurl.org:8080/ the header is set to
Host: developer.urlurl.org:8080
And this wasn't routed to the 'development' server. The production server is the 'default' so I searched for the right incantation to test the domain name part and found:
acl devsite hdr_dom(host) -i developer.urlurl.org
And now it's a config that will test on developer.urlurl.org port 8080 and will run on port 80 too. I like configurations that I can test before bringing them into production.

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2017-12-28 Non-predictable interface names biting me 11 months ago
While doing some upgrades on new homeserver I ran into a problem with the tun/tap network driver which is needed for virtual machines, giving the error message
Dec 27 21:41:51 conway kernel: [  266.832675] tun: Unknown symbol dev_get_valid_name (err 0)
Since virtual machines are the main thing to run in this machine I needed this driver to work. Searching for solutions found the suggestion to reinstall the linux kernel image, which I did:
# apt-get install --reinstall linux-image-$(uname -r)
# apt-mark auto linux-image-$(uname -r)
After which the system came up fine but without a network connection it seemed. This is irritating as the homeserver is in the attic and I found out the VGA screen up there does not cooperate with the new server. So another VGA screen got dragged up there to fix it.

Some searching later I found the eth2 and eth3 interfaces got swapped from what I expected. These are the two mainboard interfaces, both Intel interfaces but with different chipsets. There is a /etc/udev/rules.d/70-persistent-net.rules which sets this up but it isn't working at the moment:

In the system logs:
[    2.833442] udevd[542]: Error changing net interface name eth2 to eth3: File exists
[    2.834309] udevd[542]: could not rename interface '4' from 'eth2' to 'eth3': File exists
[    2.866356] udevd[538]: Error changing net interface name eth3 to eth2: File exists
[    2.868197] udevd[538]: could not rename interface '5' from 'eth3' to 'eth2': File exists
Maybe different names that don't start with eth will work better to get truely persistant names as the current situation isn't very stable and reliable.

After all the work the tun/tap driver works again so the virtual machines now start fine.

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2017-11-13 Linux and enabling NFSv4 name mapping 1 year ago
Note: even with full name mapping enabled you will still have problems. To get this mapping fully working you will need to establish trust relations via kerberos.

When I shared my article on NFSv4 on the synology I noticed I left out the fundamentals about Linux and NFSv4 with name mapping. All kernels I nowadays run into have the same preference to disable using names over NFSv4 because somewhere the decision was made to assume most Linux systems will be in an environment with centralized UID/GID management.

In any environment with devices with their own UID/GID management (such as synology devices without central LDAP) this will not be true. So the defaults need an override.

The runtime way to change this is, for the nfs client kernel process:
# echo N > /sys/module/nfs/parameters/nfs4_disable_idmapping
And for the nfsd server kernel process:
# echo N > /sys/module/nfsd/parameters/nfs4_disable_idmapping
Notice the one letter difference.

To make this change more permanent, set up a file with a name like /etc/modprobe.d/local-config.conf with
options nfs nfs4_disable_idmapping=0
options nfsd nfs4_disable_idmapping=0
And you still need to set /etc/idmapd.conf on all systems involved (both clients and servers) with the same value for the 'Domain'. I obviously have:
[General]

Verbosity = 0
Pipefs-Directory = /run/rpc_pipefs
# set your own domain here, if id differs from FQDN minus hostname
Domain = idefix.net

[Mapping]

Nobody-User = nobody
Nobody-Group = nogroup
And enable idmapd. How you enable this depends on your Linux distribution. In ubuntu server it's in /etc/default/nfs-common with
# Do you want to start the idmapd daemon? It is only needed for NFSv4.
NEED_IDMAPD=yes

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2017-11-10 Really disabling framebuffer on a modern linux 1 year ago
Framebuffer is nice but I want it really disabled on my new homeserver 2017 because that will end up in the attic where I don't want a repeat of the earlier Linux-related radio interference problem. And for virtual machines it's a bit of overkill too.

To disable framebuffer in both grub and the running Linux it has to be disabled twice. Both in /etc/default/grub which now has these two lines:
GRUB_CMDLINE_LINUX_DEFAULT="nomodeset"

GRUB_TERMINAL=console

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2017-11-10 NFSv4 on the synology isn't complete NFSv4 until you do some special configuration 1 year ago
This solution fails at the moment I start using rsync to sync directories to the Synology. Update when I find out where that goes wrong.

I am now using a synology for storage in the home network. Linux clients use NFS to access the Synology, and nowadays the default NFS version is version 4, which does things quite differently from version 3. NFS version 4 is supposed to use user names with NFS domain names and rpc.idmapd instead of numeric user and group IDs.

After serious debugging I found out NFSv4 with the synology doesn't use names as I expected. I kept looking at nfs client settings but eventually I used tcpdump, wireshark and tshark to find out owner names aren't used at all. Numerical UIDs are used as text in the NFSv4 answers, even for files that have an owner that is known in the synology. As if the nfs4_disable_idmapping=0 is never set for the NFS server.

I confirmed this with capturing the NFS traffic with tcpdump and analyzing the pcap files with wireshark and tshark. I indeed see:
                        reco_attr: Owner (36)
                            fattr4_owner: 1026
                                length: 4
                                contents: 1026

A lot of google searching confirms this, including anyone have nfsv4 actually working? - Synology Forum. The next step is to adjust the idmapping in the running kernel on the synology, using:
# echo N > /sys/module/nfsd/parameters/nfs4_disable_idmapping
Now I indeed see the right strings in the NFSv4 traffic, but the idmapd on the client doesn't translate for some reason. Fixing the /etc/idmapd.conf file helped.

The next step is to make this change permanent on the synology. Adding a file /etc/modules.local.conf with
module_nfsd_args="nfs4_disable_idmapping=0"
does the trick. This I learned from reading the startup file /etc/rc.subr which loads the kernel modules.

And now I see the right data in the NFS traffic:
                        reco_attr: Owner (36)
                            fattr4_owner: koos@idefix.net
                                length: 15
                                contents: koos@idefix.net
And the user mapping works. On an older system I have UID 501, on the synology I have UID 1026 and on a new system I have UID 1000, and I'm owner of the files everywhere.

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2017-10-15 Getting to play VIC-20 games again 1 year ago
VIC-20 startscreen Ages ago my first homecomputer was a Commodore VIC-20. I did basic programming on it and played some games. I remember the game Centipede and loading games from audio cassette.

These days games seem to be enormously complex and expensive or filled with advertisments. I don't like these, the last time I seriously invested time in a game was Pinball Dreams.

I found out about the VIC-20 emulator xvic, part of the vice package. I even bought a cheap USB joystick to use. I never had a joystick with my VIC-20 so it was about time to get one. This joystick is a DragonRise Inc. Generic USB Joystick (yes, including the spaces) and I noticed today it wasn't working right: up and down on the joystick did not work. I found out eventually the left and right on the second stick mapped to up and down, thanks to a simple joystick tester from Joystick - Denialwiki in 7 lines of Basic.

Some searching found DragonRise USB Driver Issue - RetroPie which mentions this issue in hid-dr.ko happened in Linux 4.4 - 4.9.

I did not feel like going back to compiling my own kernels for this laptop, but there is a simple solution in Ubuntu 16.04: use hwe (hardware enablement) kernels. These seem to be aimed at the long term support server versions, but they fix my joystick problem and I can play centipede.

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2017-10-11 Haproxy on the new home server and devuan upgrades 1 year ago
I got around again to working on the new homeserver 2017 and I worked on the installation of a 'testing' virtual machine with virt-install. This test machine also runs devuan linux. The first application I was testing on there is haproxy.

haproxy I noticed some defaults I did not expect (such as preferring IPv4 over IPv6). It seems the 'stable' devuan has the same age issues as 'stable' debian. Otherwise haproxy does what it is supposed to and I may standardize on it.

Upgrading was easy, I looked at Upgrading Devuan Jessie to Ascii and just changed jessie to ascii in /etc/apt/sources.list and did an apt-get dist-upgrade. The only minor issue afterwards is that the system now insists on using framebuffer video, which I find overkill for a virtual machine. VGA 80x25 is fine.

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2017-10-09 Interesting NFS exports problem 1 year ago
I am used to being unable to unmount filesystems as long as they are NFS exported. It took me a while to find out how to correctly unexport filesystems before trying to unmount them. The easy solution would be to unexport everything and just export the other filesystems, but I'd rather not interrupt NFS availability of other filesystems.

So it was time to check some large filesystems again and I'd rather not do that during boot as it can delay booting for up to an hour. Currently those filesystems are exported via IPv4 and IPv6. Removing the export for IPv4 is easy:
# exportfs -u 192.168.1.0/255.255.255.0:/export
But for IPv6 it gets harder:
# exportfs -u 2001:db8:a::/64:/export
exportfs: Invalid unexporting option: 2001
So it is still exported via IPv6. And next thing I try to unmount it and notice it's ok to unmount a filesystem that is only exported via IPv6. I guess this shows some interesting bug.

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2017-08-24 Uploading FT8 contacts to LoTW from CQRLOG 1 year ago
Other people from my radioclub were reporting they uploaded FT8 contacts to LoTW so I wanted to try this too. I uploaded earlier contacts as 'DATA' (and got some confirmations) but FT8 is the correct mode so I wanted to re-upload them.

After my earlier experiences uploading FT8 contacts to eQSL I expected some database work to be able to upload those contacts again. Finding the right field to set to the right value was a bit of work since I expected the approach to be similar but it wasn't. In the end:
$ mysql -S /home/koos/.config/cqrlog/database/sock cqrlog002
mysql> update cqrlog_main set lotw_qsls = '' where mode='FT8';
Query OK, 77 rows affected (0.01 sec)
Rows matched: 78  Changed: 77  Warnings: 0
That's after trying most lotw related fields and values.

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2017-07-24 Last night receiving ISS SSTV images 1 year ago
And a third night. I used the timed recording option of audacity, which in the current linux version does not offer the option to set in advance how to save the project. This time I 'only' recorded for 7 hours, and was able to save the project afterwards without needing a recover. But on reloading the saved project audacity complained about some internal error in it, and it still had the problem of assuming 44.1 kHz sampling while showing the project sample rate as 48 kHz. Anyway, images decoded from the audio and I even recieved a few new ones.

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2017-07-24 Getting a lot more entropy from the Raspberry Pi 1 year ago
Entropy graph of a Raspberry Pi On doing some research on randomness in Linux I found out about the rng-tools package which includes rngd which can get randomness from hardware random generators to linux /dev/random.

On the main homeserver greenblatt there was no hardware randomness source available, I already use randomsound to generate randomness from audio noise. I found out the Raspberry Pi has a hardware randomness source so I installed rng-tools and rngd was able to use it. The impact on the measured available entropy is quite visible.

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2017-07-21 Received slow scan TV images from ISS while I was sleeping 1 year ago
I read about the current ARISS Celebrates it’s 20th Anniversary through SSTV Event and noticed the planned times weren't really compatible with my day/night cyclus. I know, as a hardcore radio amateur I should be up at the weirdest hours for rare events but I also like my sleep a lot and my wife really dislikes alarms at weird hours.

Automation to the rescue: I decided to record all of a night of ISS signals on the computer with audacity and decode images from it later. The computer adjusted the radio for doppler using gpredict. Since I don't have an automatic rotor for satellite antennas I used the VHF/UHF vertical. This may seem strange but the weakest signals from ISS are when it is right above the horizon (which is when the vertical has the best reception). And as noticed on earlier SSTV events that compared to other amateur satellites the ISS has a strong signal.

So I left it running for a night and checked the results afterwards. The result was a 9 hour recording and audacity decided to hang after stopping the recording. I made a backup copy of the audio data just to be safe and restarted audacity. Luckily it recovered the project fine after restarting.

With a recent version of qsstv I decoded the recorded audio and searched for ISS passes in the recording.

The result is 13 decodes in one night. It turns out it received audio from a number of low passes that I did not see in gpredict because I have gpredict set up to skip low passes (those that don't come above a 20 degree angle above the horizon). But the strong signals from ISS make those show up in my radio anyway.

Decoded and seen the numbers sofar: 11 (partially), 12, 9, 10, 9, 10, 9 (partially), 9, 7, 8.

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2017-07-17 Now NetworkManager generates resolv.conf .. and starts with legacy IP 1 year ago
I removed rdnssd and resolvconf and fixed the symlink linking /var/run/NetworkManager/resolv.conf and /etc/resolv.conf by hand. The file /etc/NetworkManager/NetworkManager.conf now says:
dns=none
rc-manager=file
But now I run into the 'NetworkManager prefers IPv4 resolvers' again, leaving me with the resolvers from the DHCP answer before those from the IPv6 route advertisment. The search domains are fine now.

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2017-07-16 Uploading FT8 contacts to eQSL 1 year ago
This evening I noticed incoming FT8 QSO's in eQSL, so the mode is now recognized there. But I needed to retry uploading all FT8 contacts to get them to upload. It took a bit of experimenting, but finally the right SQL command to mark the contacts as not uploaded was:
$ mysql -S /home/koos/.config/cqrlog/database/sock cqrlog002
mysql> update cqrlog_main set eqsl_qslsdate = NULL where mode='FT8';
Query OK, 24 rows affected (0.02 sec)
Rows matched: 26  Changed: 24  Warnings: 0
And now they are all uploaded.

That is about a week between first seeing mentions of FT8 in radio amateur news and the first confirmed contacts.

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2017-07-16 SSH attacks by Java 1 year ago
Jul 16 04:17:01 greenblatt sshd[9365]: reverse mapping checking getaddrinfo for 121-124-124-73.youiwe.co.kr [121.124.124.73] failed - POSSIBLE BREAK-IN ATTEMPT!
Jul 16 04:17:01 greenblatt sshd[9365]: Invalid user 1234 from 121.124.124.73
Jul 16 04:17:01 greenblatt sshd[9365]: input_userauth_request: invalid user 1234 [preauth]
Jul 16 04:17:01 greenblatt sshd[9365]: Received disconnect from 121.124.124.73: 3: com.jcraft.jsch.JSchException: Auth fail [preauth]
That last bit is not from my sshd but an error message related to a java library for ssh, as noted in Reasons for com.jcraft.jsch.JSchException: Auth fail | Maximilian Bhm which correctly notes that attacks are a reason.

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2017-07-15 More resolving via IPv6 1 year ago
I was reading Debian Stretch - Het Lab Henk van de Kamer (in Dutch) which mentions removing package rdnssd to avoid a dependency problem. But I like rdnssd as it helps use the nameservers available via IPv6 in a network with only SLAAC and no DHCPv6.

Right away I had to check on my own laptop with Ubuntu 16.04 and noticed all traffic was going to the IPv4 address of the local resolver. Which is not what I want, I want to prefer IPv6 when possible. Searching found Bug #936712 “NetworkManager should put IPv6 DNS servers before I...” : Bugs : network-manager package : Ubuntu which is indeed what I saw, and it's still showing in Ubuntu 16.04 Xenial.

My solution was to stop using dnsmasq, and switch to a generated resolv.conf from NetworkManager. To do that I had to update /etc/NetworkManager/NetworkManager.conf to have:
#dns=dnsmasq
dns=none
rc-manager=file
And now I have a resolv.conf with only 3 IPv6 nameservers and no search domains. Not exactly what I want, but at least IPv6 is preferred. I considered something using only the first three resolvers because that is a maximum somewhere but just advertising two resolvers via radvd also makes two show up in the generated resolv.conf. This is not perfect. The generated resolv.conf has comments that it is generated by resolvconf so maybe this is a conflict between resolvconf and NetworkManager not in 'use resolvconf' mode.

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, reachable as koos+website@idefix.net. PGP encrypted e-mail preferred.

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Other webprojects: Camp Wireless, wireless Internet access at campsites, The Virtual Bookcase, book reviews