sep 29

Olimex A20-OLinuXino-LIME2 – A review after 4 years in service

Posted on lørdag, september 29, 2018 in Hal9k, Planets, Sysadmin'ing

Last week my A20-OLinuXino-LIME2 one board Linux computer quit working, with a power supply issue. I looked up when it was purchased, and realised it had been in 24/7 service for almost 4 years. I guess that is a good excuse to do a little review. It even turned out that it the board was fine, but the AC-DC power supply brick could not supply enough current anymore.

The relevant specifications of the board, for my uses, are basically:

Dual core 1 GHz ARM Cortex-A7
1 GB memory, 1 Gbit ethernet, SATA connector
LiPo battery connector/charger for UPS functionality

The Lime2 has been tasked with running my home monitoring system, consisting of a Debian installation with a Graphite backend, a Grafana frontend, and a ZoneMinder installation. The Graphite database is running on a software RAID0 of two disks (one on SATA, one on USB): in the beginning it was two spinning disks, but after a few years the random 2.5″ laptop disk I was using crapped out, so it was upgraded to a Samsung SSD. The power budget is strained more or less to the max with two spinning harddrives: The system was only able to boot if the battery was connected, presumably because the voltage would otherwise drop for the startup torque. This problem went away after switching to a SSD.

Software wise the system started out with the Debian supplied by Olimex on a SD-card, a Debian pre-Jessie with a custom SunXi kernel. This system was reasonable, but did experience random hangs after some time of use (I belive I found a bugreport back in the day, but am unable to refind it now). The system was later upgraded to a Debian Stretch with a 4.9 kernel from stretch-backports, that supports the SunXi chipset enough for my uses. The upgrade was rather involved, requiring the correct kernel image, a custom U-boot script and the correct device tree file. Something did of course go wrong, at which point I got to be familiar with the serial console of the Lime2: there is a convenient 3 pin header, that gives access to a TTL serial. Using the serial console, I was able to identify the mistake and correct it. After the upgrade the system has been rock-stable.

The system has been handling the load reasonably: The 1GB of memory is constraining, there is not really any more free memory. The processor is only really strained by the motion detection in ZoneMinder, which uses more or less one core per camera. This will hopefully be optimized a bit, as ZoneMinder is being optimized for the ARM instruction set. Handling only the Graphite/Grafana load would be a breeze, even though the system is receiving ~650 metrics per minute.

All in all, I can recommend the Lime2 board for applications that need a little more umph than a Raspberry Pi, notably on the SATA and Ethernet side, and/or applications that need to be continuously available even after the power cuts out. For applications that need more than one SATA port, or more than one Ethernet port, or on-board Wifi, there are better — and more expensive — options. The price point of 45 EUR + VAT (which did not change from 4 years ago) puts the Lime2 slightly above the price of a RaspberryPi or BananaPi, but below boards like the Apu2. In addition, Olimex has announced that the Lime2 will be available “forever”, making any system designed using the Lime2 future proof — for the foreseeable future.

I ordered a new Lime2, before realising the problem was the power supply. I opted for the industrial variant that is now available. The only change, as far as I’m aware, is that the Allwinner A20 chip is rated for a larger temperature range, and it is 5 EUR more expensive.

Comments (3) |

okt 17

Reparation af DUKA/PAX Passad 30 Ventilator der kører uregelmæssigt

Posted on tirsdag, oktober 17, 2017 in Danish, Hal9k, Planets

Vores Duka Passad 30 ventilator var begyndt at køre noget uregelmæssigt. Ventilatoren er ellers ret smart styret af fugtighed og IR-bevægelse, men vi bruger den kun fugtighedsstyret. Den var imidlertid begyndt ikke at kunne starte ordentligt: den reagerede fint på fugt, men motoren stoppede efter få sekunder, for straks derefter at starte igen.

Der var jo ikke andet for end at prøve at åbne den og reparere den; en ny ventilator er relativt dyr, og den kunne jo ikke gå mere i stykker end den allerede var.

Bladene kan hives af direkte ved at hive op i dem, og tragten kan tages af ved at dreje til siden. Der gemmer sig en enkelt skrue under mærkaten på bagsiden. Inden i er et relativt simpelt printkort:

Den eneste chip er desværre en micro-controller af en art, så hvis den er i stykker er der ikke rigtig noget at gøre. Jeg fik en hel del hjælp i Hal9k til at måle på printet, og det viste sig at strømforsyningen ikke var særlig stabil; ca. når problemet opstod steg spændingen. Vi endte med at lodde en ledning på microcontrollerens GND-ben, og kunne så se at VCC-benet faktisk lå ret lavt ved ca. 3V, og at spændingen der faldt når problemet opstod. Ved at måle tilbage i kredsløbet derfra endte vi helt tilbage ved den store kondensator (0,33 uF) der er næsten først i kredsløbet.

Det er dog ikke så nemt at måle kapacitet med kondensatoren i kredsløbet, men alligevel et forsøg værd: målingen var et godt stykke fra 0,33 uF. Med kondensatoren som hovedmistænkt blev den loddet af, og målt alene: værdien var nærmere et antal nF! Altså var kondensatoren gået i stykker. En erstatning blev fundet i en kaffemaskine fra Hal9k’s Limbo hylde, dog en 0,47 uF, men det burde virke:

Den nye kondensator blev loddet i, og problemet var nu væk! Spændingen ved micro-controlleren lå også stabilt, lige omkring 4,8V. Så var der kun tilbage at samle det hele igen, og sætte ventilatoren til, med lidt penge sparet, og en ventilator reddet fra skrotpladsen. Den eneste forskel synes at være at fugtigheds indstillingen nu skal stå lidt anderledes, men om det er pga. en lidt anden spænding eller bare er tilfældigt er jeg ikke sikker på.

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maj 25

Ford 3000 Tractor Instrument Voltage Stabilizer – Mechanical PWM!

Posted on torsdag, maj 25, 2017 in Hal9k, Planet Ubuntu-DK, Planets

Some time ago we bought a nice used Ford 3000 tractor (3 cylinder diesel, Chief frontloader). It needed some work, and one of the items was a new wiring harness. After replacing all the wiring everything seemed to work fine, until one day all the instruments just died; this being a mechanical beast everything else kept working. After quite some investigation, I found out that the instrument fuse (the only fuse in the entire system) had blown. Replacing it just blew it again, so something was clearly wrong. This lead to taking out the so-called “instrument voltage stabilizer”, and disassembling it.

Apparently I had connected it in such a way that the arm had raised itself, and was now short-circuiting to the case. I had already ordered a replacement, but only got what was essentially a very expensive connection:

So, what was the mechanism actually doing, and is it essential? After some headscratching at Hal9k the conclusion was that it was essentially a mechanical PWM, with something like this diagram

When the switch is touching the terminal current is flowing from the battery (B) to the instruments (I), but also to ground (E) through the resistor wrapped around the switch arm, causing the metal in the switch to heat up and lift. This breaks the connection, whereafter the switch cools down, and at some point makes contact again. Beautifully simple mechanism! Bending the arm back into position essentially fixed the device, and gave this waveform

I have seen the function described online as “pulsating DC”, which is actually quite accurate. So, I re-assembled the stabilizer with some sealant, inserted in the instrument cluster of the tractor, and it has worked perfectly ever since.

The only question is why it is done this way, if just giving a constant DC voltage from the battery also seems to work? I haven’t looked into it further, but my best guess is that the instruments are using coils to move the dials slowly, and that the PWM will heat up the coils less. In conclusion: If your voltage “stabilizer” is broken, you can probably do without it, or quite easily repair it.

For reference, here are the resistance readings between B-E, and I-E:

Comment (1) |

jan 29

Reverse engineering Aduro Smart Response

Posted on søndag, januar 29, 2017 in Hal9k

I have a fancy thermometer for my wood stove namely an Aduro Smart Response. The accompanying Android app basically shows a temperature graph, with guidelines as to whether the burning is optimal and when put in more wood. I have generally been content with the app: it is quite slow, but generally helps in more optimal burning. Recently however, the Android app has stopped working (something about connecting to a database), and this prompted me to start on a project I wanted to do for some time: get the data from the Smart Response unit into a database under my control.

The Smart Response unit uses Bluetooth Low Energy, and is powered by 3xAAA batteries (my batteries lasted for a year before replacing). Connecting to a BLE unit from Linux is quite easy, at least from the command line:
$ sudo hcitool lescan LE Scan ... B4:99:4C:25:12:B2 (unknown) B4:99:4C:25:12:B2 Aduro demo $ sudo hcitool lecc B4:99:4C:25:12:B2 Connection handle 3585 $ sudo gatttool -b B4:99:4C:25:12:B2 --interactive [B4:99:4C:25:12:B2][LE]> connect Attempting to connect to B4:99:4C:25:12:B2 Connection successful
hcitool is used to create a connection/pairing. gatttool is used to query the device interactively. Thereafter the device can be explored, to see which “handles” are available:
[B4:99:4C:25:12:B2][LE]> primary attr handle: 0x0001, end grp handle: 0x000b uuid: 00001800-0000-1000-8000-00805f9b34fb #Generic Access attr handle: 0x000c, end grp handle: 0x000f uuid: 00001801-0000-1000-8000-00805f9b34fb #Generic Attribute attr handle: 0x0010, end grp handle: 0x0022 uuid: 0000180a-0000-1000-8000-00805f9b34fb #Device Information attr handle: 0x0023, end grp handle: 0x0027 uuid: 0000180f-0000-1000-8000-00805f9b34fb #Battery attr handle: 0x0028, end grp handle: 0xffff uuid: 0000ffb0-0000-1000-8000-00805f9b34fb # ???
The annotations on the right are mine; the UUIDs can be looked up under GATT services on the Bluetooth website.
For example, the battery status can be queried somewhere in the Battery handle group from 0x0023 to 0x0027:
[B4:99:4C:25:12:B2][LE]> characteristics 0x0023 0x0027 handle: 0x0024, char properties: 0x12, char value handle: 0x0025, uuid: 00002a19-0000-1000-8000-00805f9b34fb [B4:99:4C:25:12:B2][LE]> char-read-hnd 0x0025 Characteristic value/descriptor: 5d # Battery level 0x5d = 93%

Now, the only unknown primary is from handle 0x0028 and higher. Let’s query those:
[B4:99:4C:25:12:B2][LE]> characteristics 0x0028 0xffff handle: 0x0029, char properties: 0x0a, char value handle: 0x002a, uuid: 0000ffb6-0000-1000-8000-00805f9b34fb # 0x0a = R/W handle: 0x002c, char properties: 0x10, char value handle: 0x002d, uuid: 0000ffb7-0000-1000-8000-00805f9b34fb # 0x10 = notify handle: 0x0030, char properties: 0x10, char value handle: 0x0031, uuid: 0000ffb3-0000-1000-8000-00805f9b34fb # 0x10 = notify handle: 0x0033, char properties: 0x02, char value handle: 0x0034, uuid: 0000ffb4-0000-1000-8000-00805f9b34fb # 0x02 = Read handle: 0x0035, char properties: 0x08, char value handle: 0x0036, uuid: 0000ffb8-0000-1000-8000-00805f9b34fb # 0x08 = Write handle: 0x0037, char properties: 0x08, char value handle: 0x0038, uuid: 0000ffb9-0000-1000-8000-00805f9b34fb # 0x08 = Write handle: 0x0039, char properties: 0x0a, char value handle: 0x003a, uuid: 0000ffb5-0000-1000-8000-00805f9b34fb # 0x0a = R/W handle: 0x003b, char properties: 0x08, char value handle: 0x003c, uuid: 0000ffb2-0000-1000-8000-00805f9b34fb # 0x08 = Write
The annotations on the right are again mine: they specify the char properties as looked up under “Characteristic Declaration”. Querying the char value handles gives some uninteresting values (0x00 bytes, etc.), but also some interesting ones:
[B4:99:4C:25:12:B2][LE]> char-read-hnd 0x002d Characteristic value/descriptor: c4 01 03 01 fd 00 [B4:99:4C:25:12:B2][LE]> char-read-hnd 0x003a Characteristic value/descriptor: 44 65 6d 6f 20 20 20 00 # 'Demo \x00' [B4:99:4C:25:12:B2][LE]> char-read-hnd 0x0034 Characteristic value/descriptor: c3 01 ba 01 c4 01 27 00 c2 01 d1 01
Querying a bit outside also gives some very interesting strings:
[B4:99:4C:25:12:B2][LE]> char-read-hnd 0x002b Characteristic value/descriptor: 41 64 75 72 6f 20 47 65 74 4c 6f 67 # 'Aduro GetLog' [B4:99:4C:25:12:B2][LE]> char-read-hnd 0x002f Characteristic value/descriptor: 41 64 75 72 6f 20 4c 69 76 65 56 61 6c 75 65 # 'Aduro LiveValue'

At this point I tried to look for values that changed, and also manipulating the device (temperature, playing with the damper that is connected with a microswitch). It turns out that 0x002d and 0x0034 changes values, but 0x002d changes the most. Is there a pattern?
Characteristic value/descriptor: c4 01 08 01 fb 00 [B4:99:4C:25:12:B2][LE]> char-read-hnd 0x002d Characteristic value/descriptor: c4 01 1f 01 f3 00 [B4:99:4C:25:12:B2][LE]> char-read-hnd 0x002d Characteristic value/descriptor: c4 01 3c 01 ec 00 [B4:99:4C:25:12:B2][LE]> char-read-hnd 0x002d Characteristic value/descriptor: c4 01 5c 01 e2 00 [B4:99:4C:25:12:B2][LE]> char-read-hnd 0x002d Characteristic value/descriptor: c4 01 9f 01 c3 00 [B4:99:4C:25:12:B2][LE]> char-read-hnd 0x002d Characteristic value/descriptor: c4 01 0f 02 9d 00 #counting UP DOWN
Something is counting up, while something else seems to be counting down; this was while the temperature was cooling down. As 0x002d allows for notify, we can even ask for notifications by writing 0x0100 to 0x002d + 1:
[B4:99:4C:25:12:B2][LE]> char-write-cmd 0x002e 0100 Notification handle = 0x002d value: c5 01 43 00 2a 01 Notification handle = 0x002d value: c5 01 44 00 2a 01 Notification handle = 0x002d value: c5 01 45 00 2b 01 Notification handle = 0x002d value: c5 01 46 00 2c 01 ... Notification handle = 0x002d value: c5 01 f0 01 94 00 Notification handle = 0x002d value: c5 01 f1 01 94 00 Notification handle = 0x002d value: c6 01 00 00 93 00 Notification handle = 0x002d value: c6 01 01 00 93 00
In the end of the series I manipulated the damper. Trying to identify the temperature, the last 2 characters seems the most promising: values from 0x93 (147 C) to 0x012c (300 C) seem reasonable from what I have seen previously. The middle 2 characters always increase by 1, so it is probably a datapoint counter. The first 2 characters seems to increase by using the damper.

This was implemented in a small Python script, using the library Gattlib, pyAduroSmart.py.

I hooked this into my home monitoring system (more on that in a later blog post), and now have a nice graph of the number of firings, and the temperature:

Update 26/11-2022:

Gattlib seems to be more or less obsolete and not ported to Python3, so I had to port my script to Bleak. There were some stability problems, especially around not being notified about disconnects from the device, and if not explicitly disconnecting before exiting the script it is not possible to reconnect without restarting the bluetooth service. The updated script can be found here py3AduroSmart.py.

Comments (2) |

feb 19

Hvorfor korrelerer min DC-spænding med solen?

Posted on fredag, februar 19, 2016 in Danish, Hal9k

I mit home-monitoring setup har jeg en AC-DC strømforsyning der laver DC-strøm og lader UPS-batterierne. Denne spænding overvåger jeg, som beskrevet i sidste blogindlæg. Grafen set for en typisk dag ser ud som ovenover. Der er en tydelig stigning i spændingen om morgenen og et tydeligt fald sidst på eftermiddagen. Det korrelerer forbavsende godt med hvornår solen står og og går ned. Her er data for 3 forskellige dage, overlagt med sol op-/ned-tidspunkt:

6. september – ufiltreret

26. oktober – filtreret

21. december – filtreret

Der er ikke noget forbundet til DC-forsyningen der trækker væsentlig forskellig strøm efter belastning (det der er forbundet er switche, router og Arduinoer), og intet der tænder/slukker efter tidspunktet. Temperaturen varierer ikke væsentligt i rack-skabet, og korrelerer ikke med spændingen:

Temperatur og spænding, hele oktober. Spænding (grøn) på højre akse.

Temperatur og spænding, 26. oktober. Spænding (grøn) på højre akse.

Så det store spørgsmål er: Hvorfor korrelerer min DC-spænding med solen? Er det pga. solceller i nabolaget? Er det pga. gadebelysning der tænder/slukker? Gode bud modtages 🙂

Comments (0) |

aug 31

Measuring high DC supply voltage with an Arduino

Posted on mandag, august 31, 2015 in Hal9k, Ikke kategoriseret, Planets

For my home-monitoring setup I would like an Arduino to measure the supply voltage it is getting from a DC battery UPS (Uninteruptible Power Supply). Unfortunately (actually by design, but that’s another story), the power supply is 24V, which means it will put out anywhere from 21.3V-29.8V (according to the manufacturer), which is far too much to measure with the Arduino’s 0-5V input range. For simplicity’s sake, lets assume we want to measure a 20-30V voltage.

The immediate answer is to use a voltage divider, which will bring a voltage in the 0-30V range into the 0-5V range. The general formula for the resistor divider is:

$V_{out} = \frac{R_2}{R_1+R_2} \cdot V_{in}$

We want $V_{in} = 30$ to give $V_{out} = 5$ , so

$\frac{5}{30} = \frac{R_2}{R_1+R_2}$

Now, just as a sanity check we should calculate the current of the resistor divider, to make sure we’re not converting too much electricity into heat. Ohm’s law gives us

$I = \frac{U}{R}$

which in this cases gives

$I = \frac{30}{12000} = 0.0025 A = 2.5 mA$

No problems there.

This works okay, but we lose a lot of precision, as only ~1/3 of the Arduino’s range is actually used: the Arduino’s ADC has 1024 different readings between 0-5V, so when reading the 0-30V range the precision is just about
$30V / 1024 \approx 0.03 V$ over the range.

If only we could move the lower bound, so that 20V would map to 0V on the Arduino. A wild Zener Diode appears! One use of a Zener diode is as a voltage shifter.

Zener diode voltage shifter

The closest Zener diode I could find was an 18V of the BZX79 series. This resulted in the following circuit:

which I hacked into my Arduino box.

Now, theoretically the formula for translating an voltage at the Arduino to the supply voltage should be:

$Vcc = V_{in} / (4700/(4700+6800)) + 18 = V_{in} \cdot 2.4468 + 18$

I then did some quick measurements of various input voltages and the resulting voltage at the Arduino pin:

Input voltage	Arduino pin
18V	0.32V
20V	1.16V
26V	3.60V
28V	4.41V
29V	4.81V

Plot it into a spreadsheet, create a graph and add a linear regression gives:

Now, this formula is a bit different compared to the theoretical one, mainly in the Zener diode drop. However, the datasheet for the BZX79 actually has the 18V C-type ( $\plusminus 5\%$ ) as between 16.8-19.1V, so this is well within spec. Since this is just a one-off, I’m happy to just use the measured formula, as this will be more accurate.

The final precision should be $12V / 1024 = 0.012V$ . The current should be around $I = \frac{U}{R} = 30V/11500 Ohm \cdot 1000 \frac{mA}{A} = 2.6mA$ , which again is ok.

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jun 17

Roomba 500-series Easy Scheduling using an Arduino

Posted on onsdag, juni 17, 2015 in Hal9k, Planet Ubuntu-DK, Planets

I have a iRobot Roomba 500-series vacuum cleaner robot, but without any remote, or command center or anything; alas, I have to push a button everytime I want the cleaning revolution to start 🙁

But no more! It turns out the Roomba can be programmed, quite easily, to schedule automatically, and all you need is:

1 Arduino
2 wires

The Roomba actually supports a serial protocol, the iRobot Roomba 500 Open Interface Specification, that allows remote control, driving, sensoring, and scheduling.

Finding the serial port

Remove the plastic cover. It is easiest to remove the vacuum bin, and carefully pry it off with a screwdriver.

There should be a 7-pin plug, on the right side. It has the following pinout:

Roomba serial pinout

Program the Arduino

Use this sketch (download: roombaschedule.ino):

/* Set a schedule on an iRobot Roomba 500 series, using just an Arduino. Mads Chr. Olesen, 2015. */

const byte currentDay = 3;
// 0: Sunday, 1: Monday, 2: Tuesday, 3: Wednesday, 4: Thursday, 5: Friday, 6: Saturday
const byte currentHour = 2;
const byte currentMinute = 58;

// Schedule
const byte SUNDAY = 0x01, MONDAY = 0x02, TUESDAY = 0x04, WEDNESDAY = 0x08, THURSDAY = 0x10, FRIDAY = 0x20, SATURDAY = 0x40;

const byte daystorun = SUNDAY | MONDAY | WEDNESDAY | FRIDAY;
const byte times[14] = {
3, 0, // Sunday time
3, 0, // Monday time
3, 0, // Tuesday time
3, 0, // Wednesday time
3, 0, // Thursday time
3, 0, // Friday time
3, 0, // Saturday time
};

const int ledPin = 13;

void setup() {
Serial.begin(115200);
pinMode(ledPin, OUTPUT);
digitalWrite(ledPin, 0);

Serial.write(128); //Start
delay(1000);
Serial.write(131); //Safe mode, turns off Roomba light
delay(1000);
Serial.write(128); //Start, back to passive mode
delay(500);

//Set day time
Serial.write(168);
Serial.write(currentDay);
Serial.write(currentHour);
Serial.write(currentMinute);
delay(500);

//Set schedule
Serial.write(167);
Serial.write(daystorun);
for (int i = 0; i < 14; i++) {
Serial.write(times[i]);
}
}

void loop() {
digitalWrite(ledPin, 1);
delay(1000);
digitalWrite(ledPin, 0);
delay(1000);
}

You need to modify the variables at the top: set currentDay, currentHour, currentMinute according to the present time.
The pre-programmed schedule is to clean at 03:00 on Sunday, Monday, Wednesday and Friday. You can change this if you wish, by altering the daystorun and times variables.

If you don’t modify the schedule, the Roomba should start automatically after 2 minutes.

Put it all together

You should now have a partially undressed Roomba, and a programmed Arduino. Now it is time to connect them. With both unpowered, connect the following:

Arduino GND to Roomba ground (pin 6)
Arduino TX (pin 1 on e.g. Uno) to Roomba RX (pin 3)

It should look like this:

Now, the moment of truth. Press the “CLEAN” button on the Roomba, the light should go on. Plug in the USB for the Arduino. The Roomba light should turn off briefly, and after a few seconds the Arduino should blink it’s LED. The schedule is now programmed, all done!

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feb 3

Brother DS-620 on Linux

Posted on mandag, februar 3, 2014 in Planet Ubuntu-DK, Planets, Ubuntu

UPDATE: The drivers were temporarily unavailable; they seem to be up again, at least on the Brother US site: http://support.brother.com/g/b/downloadlist.aspx?c=us&lang=en&prod=ds620_all&os=128

I recently bought a Brother DS-620 document scanner that supposedly had support for Linux. It turns out it did, but only after a few quirks. I installed the official Linux drivers, and tried to scan a document using a GUI scanning application. Things were hanging and generally very unresponsive. I checked with the SANE command line tools, e.g. “sane-find-scanner”. It turns out things were indeed working, albeit very slowly. In dmesg I found a lot of messages like:
Jan 29 22:52:13 mchro-laptop kernel: [39172.165644] usb 2-1.3: reset high-speed USB device number 32 using ehci-pci Jan 29 22:52:13 mchro-laptop kernel: [39172.333832] usb 2-1.3: reset high-speed USB device number 32 using ehci-pci Jan 29 22:52:13 mchro-laptop kernel: [39172.501677] usb 2-1.3: reset high-speed USB device number 32 using ehci-pci Jan 29 22:52:13 mchro-laptop kernel: [39172.669712] usb 2-1.3: reset high-speed USB device number 32 using ehci-pci Jan 29 22:52:13 mchro-laptop kernel: [39172.837679] usb 2-1.3: reset high-speed USB device number 32 using ehci-pci
repeating several times every seconds. At this stage I was thinking that the Linux support was very crappy. After quite a lot of mucking around playing with capturing USB packets using Wireshark, it seemed the device itself was requesting a reset, and the Linux kernel was resetting it approximately 200ms later. Reading some Linux source code, and playing with USB quirks in Linux solved nothing.

Finally, I gave up and booted into Windows to check if the hardware had a defect. In Windows it worked without issues. I upgraded the firmware using the Windows utility to do so. After doing this the scanner worked without issue also in Linux.

So, all in all: There is official Linux support for this scanner, but it seems to require a firmware upgrade. This could definitely be better handled by the Brother documentation.

Comments (9) |

jan 31

Stupid sys-admin’ing, and hooray for LVM and unnecessary partitions

Posted on fredag, januar 31, 2014 in Planet Ubuntu-DK, Planets, Sysadmin'ing, Ubuntu

The scenario is: almost finished migrating from an old server to a new server. Only a few steps remain, namely

change DNS to point to new server
wipe disks on old server

Done in this order, one might be unlucky that ssh’ing in to wipe the disks lands you on the new server. If you don’t discover this and run the command
dd if=/dev/zero of=/dev/md2
to wipe the disks you might run it on the new server instead. BAM: you just wiped the data of your new server. Fortunately, I realised my mistake after a few seconds, and was able to recover from this with only unimportant data loss, and a little panic.

/dev/md2 is actually a LVM physical partition, of which the first part now only contains zeroes; hereunder all the meta-data. LVM reported no volumes of any kind:
root@server# pvs -v Scanning for physical volume names root@server# lvs -v Finding all logical volumes No volume groups found root@server # vgs -v Finding all volume groups No volume groups found
After a bit of Google’ing while panicking I found out LVM keeps a backup of all its metadata in /etc/lvm/backup, and that it could be rewritten to the physical volume using:
pvcreate -ff -u XXXXXX-XXXX-XXXX-XXXX-XXXX-XXXX-XXXXXX --restorefile /etc/lvm/backup/vg0 /dev/md2
where XXXXXX-XXXX-XXXX-XXXX-XXXX-XXXX-XXXXXX is the physical UUID from the backup file:
... physical_volumes { pv0 { id = "XXXXXX-XXXX-XXXX-XXXX-XXXX-XXXX-XXXXXX" device = "/dev/md2" # Hint only ...
Unfortunately, I got an error:
root@server# pvcreate -ff -u XXXXXX-XXXX-XXXX-XXXX-XXXX-XXXX-XXXXXX --restorefile /etc/lvm/backup/vg0 /dev/md2 Couldn't find device with uuid XXXXXX-XXXX-XXXX-XXXX-XXXX-XXXX-XXXXXX. Can't open /dev/md2 exclusively. Mounted filesystem?
lsof showed nothing accessing md2, but I guess something still had references to the logical volumes. I was unable to get it to work, so I decided to reboot (while making sure the system would come up, and nothing would try to mount the (non-existent) LVM volumes). After a reboot the command worked, but still no logical volumes:
root@server # pvcreate -ff -u XXXXXX-XXXX-XXXX-XXXX-XXXX-XXXX-XXXXXX --restorefile /etc/lvm/backup/vg0 /dev/md2 Couldn't find device with uuid XXXXXX-XXXX-XXXX-XXXX-XXXX-XXXX-XXXXXX. Physical volume "/dev/md2" successfully created root@server # sudo pvs PV VG Fmt Attr PSize PFree /dev/md2 lvm2 a- 648.51g 648.51g root@server # sudo lvs No volume groups found
Now I had a physical volume, and could use the vgcfgrestore command:
root@server # vgcfgrestore -f /etc/lvm/backup/vg0 /dev/vg0 Restored volume group vg0 root@server # sudo lvs LV VG Attr LSize Origin Snap% Move Log Copy% Convert ... home vg0 -wi-a- 20.00g
I now had my logical volumes back! Now to assess the data loss… The backup file /etc/lvm/backup/vg0 lists which order the logical volumes are stored. The first volume in my case was the “home” volume. Sure enough, it would no longer mount:
root@server # mount /dev/vg0/home /home mount: wrong fs type, bad option, bad superblock on /dev/mapper/vg0-home, missing codepage or helper program, or other error In some cases useful info is found in syslog - try dmesg | tail or so
I actually had no important information on that file system, so I re-created it. Luckily the next volume was intact, and I could bring up the rest of the system without problems.

So to sum up: LVM keeps a backup of all it’s metadata that can be restored (after a reboot), but if your keyboard is faster than your brain it can be a good idea to keep an unused volume as the first logical volume 🙂

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jun 18

Making objdump -S find your source code

Posted on mandag, juni 18, 2012 in Planet Ubuntu-DK, Ubuntu, University

We all know the situation: We want to disassemble the most awesome pre-compiled object file, with accompanying sources, using objdump and we would like to view the assembly and C-code interleaved, so we use -S. Unfortunately, objdump fails to find the sources, and we are sad 🙁

How does objdump look for the sources? Normally the paths are hardcoded in the object file in the DWARF information. To inspect the DWARF debug info:
$ objdump --dwarf myobject.o | less
and look for DW_TAG_compile_unit sections, where the paths should exist like:
<25> DW_AT_name : C:/ARM/myfile.c

Of course, this might not be the path you have on your machine, and thus objdump gives up.

However, we can use an undocumented option to objdump: the -I or –include:
$ objdump -I ../mysources -S myobject.o | less
and voila, objdump finds the sources, inlines the C-code, and everything is awesome!

Comment (1) |

blog.smartere // Ramblings of Mads Chr. Olesen

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