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The dawn of 536801
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Today’s movie: Gravity
F*** classical mechanics.
I’ve finally seen Gravity by Alfonso Cuarón. I remember that this film was so praised for its visual effects and now I finally got to see it. That’s about time! The first fiften minutes or so were really thrilling. I really was under the impression that in space, no one can hear you scream. And I coud feel the relentless and terrifying apathy of cosmos.
But that was about everything there is to it as the rest of the movie lacked anything of substance and I wondered if this wasn’t just a demo for the use of 3D in cinema. It just seemed to me that the movie jumped to the end credits with nothing to tell. And I keep asking myself, what’s this movie all about?
Beside it was beautiful and visually stunning. I didn’t see it in 3D, and I’ve heard that it propels the movie to a whole new level. Also it is said that this is one of the few movie that is worth watching in 3D. But this fad is dying fast.
Although I never really believed in this trend, 3D brought far less to the cinema than the arrival of sound and color. It does not help to immerse the viewer deeper into the story. If you want this, perhaps you would need complete VR, but that is an entirely different medium.
Today’s movie: The Lobster
Would you like to dance?
The Lobster directed by Yorgos Lanthimos, Jury Prize at Cannes festival. I really wanted to see this movie although I didn’t really know what to expect. Now that we’ve seen it, it’s really hard to give it a specific genre. We came to the conclusion that it is just disturbingly horrible. The same feeling that you have when you are faced with something really horrible, yet totally real, but so horrible in fact that you don’t want to accept it. It was like a gigantic kick in the ass. A burdensome fable that still haunts me and makes me feel nauseous. Probably not everybody’s movie, but still a really great movie.
Rename interfaces on Linux
I just reinstalled a Debian stable on a laptop but messed with the interfaces so that an external USB WiFi card appeared as wlan0 while the main card appeared as wlan1. In case you wondered you can rename or reset interface names in /etc/udev/rules.d/70-persistent-net.rules. That’s on systemd though.
I wonder how we can change that on sysvinit? Nobody cares, probably, but I do.
According to what I read there, it is not consistent. Interfaces are named in the order in which they appear during the boot process. However it is possible to use ifrename from the wireless tools package. Why this tool that should work for all type of interface is part of the wireless tools package is beyond my comprehension. But hey whatever, Linux, and it just works.
If you are curious and want to know how ifrename actually does rename an interface, according to the code it uses a SIOCSIFNAME ioctl on a socket file descriptor. There it passes a struct ifreq in which you can provide a new name for the interface. Just man netdevice(7) for more info.
Use notify-send as root
The automount script is a neat devd based automounter for FreeBSD. Just pkg install automount and all your removable media will mount themselves automatically in /media when you plug them in. It’s very clean. You may also check vumount, a short script that I made to list all removable media and remove the mount point when you unmount them.
It’s possible to configure automount to send a notification to your desktop using notify-send from libnotify. What it does exactly is (as root):
env DISPLAY=:0 notify-send automount "Device '${1}' mounted on '${3}' directory."
Except that it doesn’t work… I started dbus-monitor and tried notify-send as root (from ttyv2) but didn’t receive anything and notify-send did not complain. So I tried to start dbus-monitor from root instead, in the hope that it would be a bit more verbose than notify-send. I got this error message:
Failed to open connection to session message bus: Did not receive a reply. Possible causes include: the remote application did not send a reply, the message bus security policy blocked the reply, the reply timeout expired, or the network connection was broken.
By default DBus sessions are private and don’t accept connections from other users than the one that own the bus, even root. The solution is to configure DBus to allow root on the session bus. Edit /usr/local/etc/dbus-1/session.conf and add this line to the default policy:
<allow user="root"/>
But you still need tell DBus how to connect to the session bus. To do so you have to specify the session bus address in DBUS_SESSION_BUS_ADDRESS. Fortunately automount is a shell script, so you can fetch and export the bus address from its configuration file. Just add this to /usr/local/etc/automount.conf:
# Load DBus session bus address
DBUS_USER=your-user
if [ -d /home/$DBUS_USER/.dbus/session-bus ]
then
dbus_file=$(ls -t1 /home/$DBUS_USER/.dbus/session-bus | head -n1)
export DBUS_SESSION_BUS_ADDRESS=$(cat /home/$DBUS_USER/.dbus/session-bus/$dbus_file | \
grep "DBUS_SESSION_BUS_ADDRESS=" | \
sed 's/[A-Z_]*=//')
fi
Data signing failed
I got the following error while trying to send a signed (GPG) e-mail using claws-mail:
Signature failed: Data signing failed, General error
Turns out it was a path problem. The GPG agent uses pinentry to ask for your private key password. The agent was configured with the absolute path to pinentry-gtk-2 on Linux. But this happened on FreeBSD and executables are located in /usr/local, not /usr.
So I changed in ~/.gnupg/gpg-agent.conf:
- pinentry-program /usr/bin/pinentry-gtk-2 + pinentry-program /usr/local/bin/pinentry-gtk-2
Today’s movie: The Martian
The Martian directed by Ridley Scott based on a novel by Andy Weir. Considering the last science fiction movie directed by Ridley Scott, I waited for this movie with a bit of anxiety. I still think Scott is a great director, but a butchered plot really can ruin everything.
Annnnnd… I really enjoyed it! It was like watching Prometheus again, except that the plot actually made sens. Damon Lindelof is an awful writer, some have gone so far as to call him an anti-Midas because it seems like everything that he touches just turns to shit. But this isn’t a Prometheus review…
Matt Damon already knows a thing or two about being stranded on a distant planet. But don’t get me wrong, this movie is entirely different.
Dr. Mann, I presume? [Interstellar]
The Martian [xkcd]
No more corruption on the RPi
I talked in a preceding post about corruption problems on my RPi’s SD-Card. I was told that 4.65V is very low for the RPi and that was probably the cause for the frequent corruptions of the SD-Card. Unfortunately new peripherals drop the voltage rather quickly on the RPi. Here are the voltage after each plugin in (cumulative):
- None: 4.80V
- Ethernet (internal – smsc95xx): 4.77V
- Ethernet (external – asix): 4.66V
So my first solution was to limit the stress on the SD-Card. I measured the IO bandwidth of various task with iotop -aoP. Turns out that most tasks accounted for only a handful to a hundred of kylobytes. These tasks are sporadic (dhcpd, rsyslogd and jbd for the most part) and in the end of the day accounted for less than 20MB read/write on the SD-Card.
On the other end an update (apt-get) account for around 80MB of writes. That’s a lot combined to increased CPU usage that further contributed to the voltage drop. With apticron running an update at least once a day, it’s not a wonder that the SD-Card got corrupted so quickly.
So my first solution was to put apt into a tmpfs. That is in /etc/fstab:
tmpfs /var/lib/apt tmpfs noatime,nosuid,nodev,noexec,mode=755 0 0 tmpfs /var/cache/apt tmpfs noatime,nosuid,nodev,noexec,mode=755 0 0
And we don’t want packages to fill the cache. So we specify that the cache should be emptied after each package installation / upgrade. That is in /etc/apt/apt.conf.d/70no-cache:
DPkg::Post-Invoke { "/bin/rm -f /var/cache/apt/archives/*.deb || true"; };
This way an apt-get update does not solicit the SD-Card anymore. On the plus point updates are also faster. However there are two disadvantages with this solution:
- You cannot upgrade after the system just rebooted. You need to rebuild the cache with
apt-get updatefirst. But that is not a problem as apticron does so automatically once a day. - The number of packages you can install / upgrade at once depends on their size and the size of the tmpfs. But it is OK if you frequently upgrade your system on stable.
But that is probably not enough to avoid corruption on the SD-Card. Or at least this is what I thought. So the other solution was to find a way to raise the voltage from 4.66V to a reasonable value. The F3 polyfuse that protects the board has a noticeable resistance causing a voltage drop of ~0.2V.
The F3 polyfuse (green) is located at the back bottom right of the board.
I soldered the polyfuse and the voltage raised to 4.85V. Did not have any corruption problem since more than a month. Fantastic!
However remember that the fuse is there for a reason. It limits the maximum amount of current powering the board. Without the polyfuse the RPi can ask more current than the PSU is rated for (which can happen for example if you short the GPIOs). So it might be a better idea to try another power supply or USB cable. I just like to live dangerously. I also protected those RPi with a case. Note that the RPi B+ and newer have a new power supply circuitry with a lower voltage drop. So all of this may not be needed.
Today’s movie: Cafard
It’s been a long time since I last posted about a movie. Truth is, there are so many movies that I’ve seen since then that I wanted to talk about, but finally didn’t seem to find the time. So I postponed to the next week, and then to some week-end eventually and finally I didn’t post anything.
Actually it’s been so long that I’ll probably have to watch all those movies again before I can post about them. I don’t mind this though, and will probably watch them again anyway. But I really think I should post ASAP and try my best to keep it short.
That was for the short update. Now for the movie…
Я люблю тебя
Cafard by Jan Bultheel inspired by the true story of the Belgian ACM corps sent to Russia to fight the German army in 1915. Not a movie about war, if you ask me, or not only. But a great and colorful animation for adult.
Constant SD-Card corruption on the RPi
Our home servers broke. Here we are again.
I spent weeks of my time, countless evenings up to 4AM, entire weekends since months trying to design and configure our reborn home-servers and gateways.
And it was neat.
- DNSSEC all the way down
- RPC accross the nodes
- Easy configuration
- Caching and stuff
- Automatic tests
- …
It took me a lot of time to assemble all of this in something that I liked. And to document everything so that we could easily install a new node from scratch.
I installed two nodes and it worked well for several weeks. Until a week ago or so I started to see corruption on the first node. And by corruption I mean random garbage in a lot of binaries and libraries. Exec format error at every corner. At this point it was completely broken and useless so the only option was to reinstall it.
So I used a new SD-Card, changed the power supply and reinstalled everything last weekend. Just finished today and also fixed bugs in some of our scripts. Had to search for a package on the second node which at this point was still in a pretty good shape.
$ apt-cache zsh: exec format error: apt-cache $ su zsh: exec format error: su
Dang! So there goes another weekend I will spend to reinstall the thing. And who knows how long until the first node gets corrupted again.
Checked the TP1-TP2 voltage, 4.65V, probably because of the second USB Ethernet adapter. I tried to limit the amount of writes on the SD-Card. No heavy writers, no swapping, no overclocking.
So I must be doing something wrong, right? Right?! The RaspberryPi can be that unreliable. I wonder how many power supplies and SD-Cards I will have to buy and try until, by sheer luck, I do not have to reinstall everything in the following three months or so.
I ran into this problem years ago. And now it seems that I will run in the same problem over and over again. Any recommendation is welcome of course. Though to be honest, for now, I just want to fly the damn thing across the room.