Remembering TITR

So it’s now been 16 years since the end of TITR (This Is True, Really) News. I still occasionally listen to the old recordings of what we now know as ‘podcasts’ and have a giggle.

Scott, Tony, wherever you guys are, hope all is going well.

If you want to share in on the laughs, I’ve put up the small archive I have on soundcloud.

Central management of Lets Encrypt SSL certificates

Just wrote up a quick article on how I implemented centralised management of SSL Certificates issued via Lets Encrypt.

Yeah, its an article – its a bit big for a post 🙂

Adding a PPS source to ntpd

So I recently got given a Symmetricom TimeProvider 100 to have a bit of a play with – and was excited to see an ethernet port marked “NTP” on the front.

After firing it up and having no luck at all talking to it on this port other than ICMP ping packets, I trawled online to try and find the manual. That’s a challenge!

So, as a favour to Google and all others that try to find the manual for this damn thing, I’ve uploaded it here.

Symmetricom TimeProvider 100 User Manual

One thing that struck me is this little note:

Note: The NTP feature in the NTP port is currently not implemented.

Ok, so no NTP server running on it. A little bit of a shame, but we still have a PPS port. But its BNC?!

Linux has an entire API for PPS sources, but the main one seems to be using the DCD lines on a physical serial port. But how to convert a 50 ohm BNC connection to a RS232 serial port?!


It turns out that the PPS signal is compatible with the logic levels of the DCD line.

Now all that’s left is to set it up software wise. I’m using Scientific Linux 7 – so this should work across CentOS and RedHat Enterprise Linux.

$ yum install pps-tools
$ modprobe pps_ldisc
$ ldattach 18 /dev/ttyS0
$ $ ppstest /dev/pps0
trying PPS source "/dev/pps0"
found PPS source "/dev/pps0"
ok, found 1 source(s), now start fetching data...
source 0 - assert 1474704714.000005460, sequence: 4828 - clear 1474702748.000922784, sequence: 3229
source 0 - assert 1474704715.000005644, sequence: 4829 - clear 1474702748.000922784, sequence: 3229
source 0 - assert 1474704716.000002819, sequence: 4830 - clear 1474702748.000922784, sequence: 3229
source 0 - assert 1474704717.000002645, sequence: 4831 - clear 1474702748.000922784, sequence: 3229

If all of the above works, congratulations. Your PPS source works. Now you get to finalise the configuration.

Firstly, we need to set up udev to properly configure the serial port on boot, add the following to: /etc/udev/rules.d/pps-sources.rules:
KERNEL=="pps0", OWNER="root", GROUP="ntp", MODE="0660"
KERNEL=="ttyS0", RUN+="/bin/setserial -v /dev/%k low_latency irq 4"

Now we need to automatically load the pps_ldisc module on boot. Create /etc/modules-load.d/pps-source.conf and throw this in there:
## Load the PPS module on boot.

Next we need to configure systemd to attach the serial port to the PPS driver on boot. Create /etc/systemd/system/ldattach@.service and use this:
Description=Line Discipline for GPS Timekeeping for %i
ExecStart=/sbin/ldattach 18 /dev/%i

Enable this on boot and specify your serial port:
$ systemctl enable ldattach@ttyS0.service

The last step is to configure /etc/ntp.conf to use your PPS source. One thing to keep in mind is that the PPS source doesn’t contain an actual time – so you MUST have an NTP server set to a preferred time source. I use:
server minpoll 4 maxpoll 4
server iburst prefer
server iburst
server iburst

Restart ntpd now, and you should be done:
$ systemctl restart ntpd

After a while, you should see some good accuracy:
$ ntpstat -q
synchronised to atomic clock at stratum 1
time correct to within 1 ms
polling server every 16 s
$ ntptime
ntp_gettime() returns code 0 (OK)
time db90b5e4.76394f80 Sat, Sep 24 2016 18:20:52.461, (.461812146),
maximum error 5500 us, estimated error 1 us, TAI offset 0
ntp_adjtime() returns code 0 (OK)
modes 0x0 (),
offset -1.654 us, frequency -5.593 ppm, interval 1 s,
maximum error 5500 us, estimated error 1 us,
status 0x2001 (PLL,NANO),
time constant 4, precision 0.001 us, tolerance 500 ppm,

OpenWRT builds move to LEDE

Recently I’ve moved the builds for the WD MyNet systems to LEDE.

I’ve also started building for more than just the MyNet N750 – and now *all* ar71xx systems will get a nightly build.

The build directories now follow the date of the build, not the revision number. The new builds are available at:

Why people hate #systemd

So yeah, I’ve been forced into using SystemD for just about everything now that the entire community has taken the koolaid.

I recently had a question where if a ConditionFileIsExecutable fails in the [Unit] section, the logs say that the service was started – but in fact the service won’t attempt to be started. No errors, no warnings, but a message of success. This seemed strange, so I jumped onto #systemd on Freenode and ended up with the following conversation:

17:37 -!- Irssi: Join to #systemd was synced in 5 secs
17:38 < CRCinAU> ok – so if the start of a service fails because ConditionFileIsExecutable fails, is it expected to be a silent failure?
17:38 < CRCinAU> ie nothing in the journal or logged to state why a service failed? just a “Started” then nothing further?
17:39 < grawity> CRCinAU: yeah, it’s supposed to be mostly silent
17:39 < grawity> unlike AssertFileIsExecutable=, by the way
17:39 < CRCinAU> logic behind that?
17:39 < grawity> its primary purpose is in filtering units which should or shouldn’t auto-start
17:40 < grawity> logging failures at default level would result in too much logspam on most systems
17:40 < CRCinAU> o_O
17:40 < grawity> e.g. there’s ssh-keygen.service with Condition= that at least one ssh_host_key is missing
17:41 < grawity> if you want things to be logged loudly, use Assert=
17:41 < CRCinAU> I don’t see a problem with that?
17:41 < grawity> with what
17:41 < CRCinAU> a message that a file doesn’t exist…..
17:41 < grawity> with users seeing “warning: ssh-keygen not started because EVERYTHING IS FINE” on every reboot?
17:42 < grawity> some programs install units with ConditionVirtualization=, which would either log warnings on every VM, or on every bare metal system
17:42 < grawity> if you want things to be logged loudly, use Assert=
17:42 < CRCinAU> wait……..
17:42 < CRCinAU> what the hell is systemd doing thinking about virtualisation?
17:43 < grawity> there are daemons which are only needed in VMs, or aren’t needed in VMs
17:43 < CRCinAU> urrrmmmm…….
17:43 < grawity> e.g. systemd’s own udev has no business running in a container
17:43 < CRCinAU> holy crap… so what you’re telling me is systemd is still hungry and needs to be fed more?
17:44 < michich> another example: vmtoolsd.service:ConditionVirtualization=vmware
17:44 < CRCinAU> I think I just died a little inside in that level of retardation.
17:45 < grawity> so by your own logic, a few minutes ago you were telling me systemd should be checking for your config files, instead of your own daemons doing that themselves?
17:46 < CRCinAU> no – the unit failed to start, and had no warning. if there was a problem and the unit failed, I’d expect to see something that says “blah.service failed because ConditionFileIsExecutable failed” or similar.
17:46 < CRCinAU> not just “Unit blah.service started”
17:46 < CRCinAU> when it fact it wasn’t
17:46 < CRCinAU> it *attempted* to start
17:46 < CRCinAU> but failed.
17:49 < CRCinAU> on another note, now I’m hearing that systemd is becoming virtualisation aware because users are too stupid to do “systemctl enable vmtoolsd.service” when they do a virtualised install?
17:49 -!- mode/#systemd [+b $a:CRCinAU] by evilgrawity
17:49 < CRCinAU> well, not even that… as I guess you’d have to install the VMWare tools in that situation to even have the service file in the first place – so it could even be part of the package install.
17:50 -!- #systemd Cannot send to channel
17:50 -!- CRCinAU was kicked from #systemd by evilgrawity [CRCinAU]

I’m kinda speechless now.

Load more