Setting the default monospace font on Raspberry Pi OS: An exercise in frustration

Many Linux distributions, including Debian GNU/Linux and Raspberry Pi OS (which is derived from Debian), use a system-wide font configuration framework called fontconfig. This uses a series of XML files to set default fonts, fine-tune font rendering, automatically detect new fonts, and more. By providing a centralized mechanism to manage fonts, fontconfig helps ensure a consistent look and feel across applications.

CUPS, the standard printing system on most Linux distributions as well as on Apple macOS, is among the numerous applications that use fontconfig. The configuration determines how CUPS renders documents that do not specify fonts, such as plain text files, for printing. For example, plain text files are printed using the default monospace font.

I followed the Arch Linux documentation for font configuration and Angelos Orfanakos's blog post on setting fonts in Debian to edit the font configuration manually. System-wide settings can be placed in ~/.config/fontconfig/fonts.conf, while per-user settings use ~/.config/fontconfig/fonts.conf.

On my Raspberry Pi 4, I was trying to change the default monospace font because the font it normally uses (Liberation Mono) looked very ugly when printed. Instead, I wanted it to use Courier New, from the Microsoft TTF Core Fonts, using the following configuration in /etc/fonts/local.conf:

<?xml version="1.0"?>
<!DOCTYPE fontconfig SYSTEM "fonts.dtd">
<fontconfig>
    <alias>
        <family>monospace</family>
        <prefer>
            <family>Courier New</family>
        </prefer>
    </alias>
</fontconfig>

However, the system wouldn't honor the setting, and it took a lot of fiddling to get it to work. I tried placing the configuration in both /etc/fonts/local.conf and ~/.config/fontconfig/fonts.conf and nothing worked. After extensive fiddling, it turns out that in Raspberry Pi OS, the monospace font is explicitly defined in /etc/fonts/conf.d/31-mono-substitute.conf. The way this is set up causes it to not accept manual changes to the monospace font in local configuration files. This is specific to Raspberry Pi OS, and is presumably there to match official documentation and educational materials released by the Raspberry Pi Foundation.

Renaming the 31-mono-substitute.conf file to disabled-31-mono-substitute.conf worked. I'd suspect it won't be kept during updates, so I subsequently created a file containing no configuration data (as above, but with nothing between the fontconfig tags) in its place to ensure that it's preserved during updates.

Now the system accepts the local font settings and plain text documents are printed with the much cleaner Courier New font. It took me two hours for me to sort this out and it frustrated me to no end.

Draco

Running a Raspberry Pi 4 from a USB portable SSD

I've been experimenting with the Raspberry Pi 4 as both a low-cost Linux desktop computer and a server. As inexpensive as it may be, there's lots of potential in the hardware and plenty of ways to make the most out of the miniature computer. One way of doing this is to use a portable SSD instead of a microSD card.

Newer Raspberry Pi boards, starting from revision 1.2 of the Raspberry Pi 2 Model B+, have the ability to boot directly from a USB storage device such as a flash drive or portable SSD, eliminating the need to use a microSD card. The use of an SSD can greatly increase storage performance, capacity, and reliability over a microSD card (more on this below).

There are a number of considerations to doing this, some of which are specific to the Pi 4:

• The process is relatively simple. Raspberry Pi OS ships with an "SD Card Copier" utility, listed under Accessories in the main menu, which can be used to copy the running system to another storage device.
• This process will erase all data on the target drive, so be sure you've selected the correct drive and backed up any important data on it.
• The target drive must use an MBR partition table. If it uses GPT partitioning, the copy process will fail, and the drive will need to be repartitioned and reformatted with an MBR.
  
• After copying, the target drive will contain both a small boot partition and a large Linux ext4 partition containing the full root filesystem outside of /boot. If you'd prefer to have a smaller root partition, run resize2fs on the second partition of the target drive (usually /dev/sda2) to shrink the ext4 filesystem to the desired size, then use cfdisk on the whole disk (usually /dev/sda) to shrink the partition to that same size.
  
• It should be noted that there is no snapshot functionality involved, so copies are inconsistent and will not reflect the system state at any one point in time. As a result, I'd recommend rebooting the Pi and having no other applications running before beginning this process. Any services that are particularly sensitive to data consistency, such as database servers, should be stopped as well.
  
• Enabling this feature on earlier generations of the Raspberry Pi may require writing to a one-time programmable memory on the board, a permanent and irreversible process. On the Raspberry Pi 4 Model B, an EEPROM firmware update may be required to enable USB booting. For more details, see the official documentation.
• Some SSDs can require too much power for the USB ports on a Raspberry Pi. In particular, if the drive internally uses NVMe technology, such as an M.2 NVMe drive inside a USB enclosure or a retail portable SSD rated at more than 600 MB/s, it may require large bursts of power, which can cause the drive to disconnect while in use. SATA-based drives are less likely to experience this issue.
• I learned this the hard way while trying to use a Plugable USB-C to NVMe enclosure containing a 1TB Samsung SSD 970 EVO Plus. The system simply could not finish copying the operating system without the drive disconnecting during the copy. This issue did not occur with a 500GB Samsung SSD 850 EVO in a StarTech USB 3.1 Gen 2 enclosure.
  
• Trim, which is needed to maintain optimal performance on SSDs, will not work without some manual configuration, even if the drive otherwise supports it. Jeff Geerling has a detailed blog post on how to enable it; it's a rather complicated procedure and I won't be repeating it here.

Why use an SSD instead of a microSD card?

Raspberry Pi computers are designed primarily to use inexpensive SD or microSD memory cards for system storage. However, most microSD cards are not designed to be used as the boot drive or primary storage device for a computer. Instead, they are typically optimized for sequential or streaming I/O where data is read from or written to the card in large chunks. This makes sense given that these memory cards are primarily used to store pictures, videos, music, and other media files on devices like smartphones and cameras.

But computer operating systems rely much more on random I/O, where small bits and pieces of data are read and written in many different places on the storage media. A typical SD card, with a low-power controller tuned for optimal sequential I/O performance, will often perform poorly when asked to process many small random reads and writes. SSDs can deliver much higher performance than memory cards, especially in random I/O.

An SSD will also be much more durable than a memory card when used as an operating system drive. I won't go into detail here, but suffice it to say that due to differences in flash memory controllers, firmware features and optimizations, storage capacities, and the underlying NAND flash memories themselves, an SSD will be much less prone to failure than a microSD card over extended usage in a Raspberry Pi. They also provide valuable S.M.A.R.T. information which can be used to monitor usage statistics and possibly detect imminent failure, making it easier to avoid data loss. (On Raspberry Pi OS, you'll need to install the smartmontools package to use the smartctl command and read S.M.A.R.T. data.) Of course, any storage device can fail without warning, so it's always important to maintain current backups.

Adventures with the Raspberry Pi 4

This is something I've been meaning to do for a while... but I finally got myself a Raspberry Pi 4 Model B 4GB, along with a few essential things to go with it. It's a tiny, inexpensive Arm-based computer, designed foremost for educational use, yet versatile enough to serve as a general-purpose Linux device.

As someone who's had a fair bit of experience with Linux over the years, particularly with openSUSE on both laptops and servers, the experience is both familiar and foreign. I installed Raspberry Pi OS (32-bit) onto a microSD card using the official Raspberry Pi Imager application on Windows, and everything loaded up and worked just as expected. But coming from an RPM-based Linux distribution, there was a bit of a learning curve as I had next to no experience with the apt package manager. The LXDE desktop also took some time for me to get used to.

While I can't say the Raspberry Pi 4 can fully replace a proper PC, it performs surprisingly well for such an inexpensive computer, and it can certainly serve as a basic web-browsing and productivity device. 4 GB of RAM has proven to be plenty for a low-power Arm-based device, even with multiple tabs open in Firefox (utilization typically sits just within 2 GB). You'll probably find desktop applications to be rather sluggish, and you may have to wait several seconds to do things that a modern laptop can do in a split-second, but it's certainly usable.

For the time being, I'm simply experimenting with the Pi as a Linux desktop microcomputer, though I do have a few project ideas for the future. While the starting price for the Raspberry Pi 4, a mere $35 for the 2GB base model ($55 for 4GB, $75 for 8GB), can be extremely tempting, the cost can rapidly balloon as you add essential supplies and accessories. Memory cards, keyboards and mice, displays, fans, cases, and other items can easily add up to well over a hundred dollars. Nonetheless, it's a worthwhile experience and you probably won't regret getting one.

I'll be sharing more about getting the most out of the Raspberry Pi 4 in later posts. Stay tuned.

Draco

Olympus BLH-1 battery and BCH-1 charger oddities

After using my Olympus OM-D E-M1 Mark III for some time, I've noticed some weirdness with the Olympus BLH-1 batteries that merited some experimentation. In particular, I found out why putting it on the BCH-1 charger at 97-99% would cause it to charge for a few moments then suddenly stop, claiming that it's full when it actually isn't.

From what I can tell, the charger is designed to drive a constant current (CC) of 1.1A to the battery at a variable voltage, up to 8.5V (as marked on the battery), for fast charging, before switching to a constant 8.4V (CV) and a gradually decreasing current to top off. This behavior is inferred from power measurements with the charger plugged into a Kill-A-Watt meter, as well as the fact that the battery is marked for 8.5V charging and not 8.4V despite having a normal 7.4V nominal voltage. (Higher-voltage Li-ion batteries rated at 3.8V per cell are typically charged to 4.35V per cell. With two cells, that would be 8.7V.)

Under normal conditions, the switchover from constant-current to constant-voltage mode can be detected as a sharp drop from about 12W on the meter to anywhere between 4W to 8W, depending on the battery's state of charge (the fuller the battery, the lower the resulting wattage). If the battery is lower, it'll charge in the faster CC mode for some time, then switch to CV mode when it reaches 80% or so. If there's more than that when the battery's put on the charger, it'll charge in CC mode for a minimum of about 20 or so seconds before switching to CV mode.

Apparently, if the battery is near full (~97% to 99% as reported by the camera), that 20-second minimum in CC mode may involve the charger pushing more than 8.5V to the battery at 1.1A and triggering the over-voltage protection on the battery before it can switch to CV mode. When OVP is triggered, the battery goes high-impedance to reject further charging, and the voltage at the terminals will be about 8.00 volts. (The battery will switch back to normal once a load is placed on it. The actual battery voltage should be about 8.30V to 8.40V.) Because of this high-impedance state, the charger immediately signals that the battery is full and stops charging (the light turns green and the meter reads zero watts).

Under normal conditions, when OVP is not triggered, by the time the charger light turns green, there is still some topping off happening: 2-3W load may be measurable on the meter, gradually decreasing to 1W before it actually stops charging. This sudden drop from 12W (CC mode charging, maximum voltage) to 0W indicates that OVP has been triggered.

I was able to confirm this after some experimentation with a jury-rigged variable-voltage supply: if I drive about 8.6V to the battery, it'll charge at an estimated 0.5A to 1.0A for some time, then suddenly reject power and read out 8.00V on the meter. If I put the battery in the camera briefly and remove it for measurement, I'll get something like 8.39V. This means the battery has detected over-voltage and rejected further charging. Now I can say that the stock charger can trigger this behavior if you put a battery on it when almost full.

Not too sure if the charger's fast-charging algorithm is a good idea, but given what I'm seeing, it's probably doing 8.6V and hitting OVP. That kind of charging regime is quite hard on the battery...

Draco

Some random info about the Olympus OM-D E-M1 Mark III

Last updated on April 12, 2020.

I recently purchased an Olympus OM-D E-M1 Mark III with the M.Zuiko 12-100mm f/4 PRO lens, and have additionally purchased an M.Zuiko 25mm f/1.8 lens to go with it. I've been shooting a lot with this camera, even in the midst of this coronavirus pandemic (before New York essentially went into lockdown) and have been thoroughly enjoying it.

This post is just to serve as a space for random notes and information about the camera. It isn't going to be as polished as my usual content, but perhaps some of this information will be useful to others. I'll be updating it as needed.

• Sensor readout speed is normally about 1/60s. If the ISO sensitivity is set to 8000 or higher, it is about 1/30s. This is reflected in the flash sync speeds when shooting in silent mode (♥ heart symbol), which are 1/50s at ISO 6400 and below and 1/20s at ISO 8000 and above. In comparison, the flash sync speed of the mechanical shutter is 1/250s. (Note that flash is disabled by default in silent mode but can be enabled in the menu, under Shooting Menu 2, Anti-Shock[♦️]/Silent[♥].)
• Accessing the camera's hidden service menu, including the shutter count, is actually simpler than what some online guides may state, e.g. this article. To do this, hold the Menu button when turning on the camera, then open the menu, open the brightness settings (Setup Menu, fourth item), and press OK. (There is no need to press Right or Info on this screen.) Then press Up, Down, Left, Right, and the shutter button, in that order. From here, pressing Right will show the camera's internal counters:
• MS is the number of mechanical shutter actuations. This does not include shots taken with the electronic shutter, and does account for operations like pixel mapping (which requires four shutter actuations) which use the mechanical shutter. This means that the value displayed here can be relied on as an accurate shutter count. (Older Olympus cameras used R for shutter releases, which wasn't an accurate shutter count because it included electronic shutter usage.)
• S (strobe) is the number of times the camera has fired a flash (there's no pop-up flash but the camera does count shoe-mounted flashgun usage).
• U is the number of times the camera has activated the Supersonic Wave Filter, which removes dust from the sensor. This can be used to estimate the number of power cycles because the camera activates the SSWF every time it is turned on; however, the SSWF is also activated during pixel mapping (Custom Menu J1) so it won't be an exact value.
  

Using Wi-Fi on Panasonic LUMIX cameras to send photos directly to your PC as you take them

An underappreciated feature of many newer Panasonic LUMIX cameras is the ability to connect to a computer via Wi-Fi and send pictures directly to a shared folder. Essentially, the camera can log onto your computer, connect to an SMB share, and write photos to it. However, depending on your setup, it can take some finesse to get it to do what you want. In this blog post, I'll describe how to set up your camera to send photos directly to your PC, even when you're away from a Wi-Fi network.

To begin, press the Wi-Fi button on the camera and select New Connection > Send Images While Recording > PC. The Via Network option connects to a wireless network and is for sending images with the computer connected to that network, which works if you're at home or in a studio with a wireless router. The Direct > Manual Connection option shows the camera's SSID (network name) and password to use for the computer to connect to the camera; the computer will connect directly to the camera, independently of any wireless network. However, this is where things get tricky.

Using an SSD as a Linux swap device isn't (usually) as destructive as you thought it would be

It's been a while since I've posted something on this blog but there's something I'd really like to get out of my head.

I've read, and continue to read, claims from others on the Internet that putting swap space on an SSD is bad for it and will quickly kill it. However, these statements rest on the assumption that the swap space will be used heavily or that the SSD's endurance is low enough that this would cause it to fail well before the end of its designed service life. In the vast majority of situations, neither of these are true. Even on bottom-bin hardware like Bifrons (a cheap Lenovo netbook with 2 GB of memory and 64 GB of eMMC flash storage), where endurance is more likely to be an issue, it's still very likely that the flash memory will last the intended life of the system.

Several months back, I took an old 64 GB Plextor M5M mSATA SSD previously used in one of my old laptops, put it in a StarTech USB 3.1 Gen 2 enclosure, and plugged it into the USB 3.0 port on this laptop. I then secure-erased it, partitioned 8 GB of that drive as a swap partition, and enabled it as swap space. Using the Linux iostat command, I monitored the amount of data written to the drive over time as I used the system for everyday web browsing and productivity. The worst I saw was 170 GB of writes to the drive over just shy of nine days of usage, or about 20 GB of writes per day from swapping. Remember that this system has just 2 GB of memory so some swapping is likely to be unavoidable. It's also noteworthy that swappiness was set to 100, which makes the system swap more aggressively than normal (the default is 60).

20 GB per day is well within the endurance limits of most modern SSDs. A good name-brand SSD like the Samsung SSD 860 EVO will be rated for far more than that over its warranty period; the 250 GB version of the 860 EVO is warranted for five years or 150 TBW (total terabytes written). That's 84 GB per day over five years, and 20 GB is less than a quarter of this value. Even if you add another 10 GB per day (because a typical user would put the system/boot partition and the swap partition on the same disk), you're still not using even half of the drive's rated endurance within its warranty period. Even cheaper SATA SSDs with lower endurance ratings are unlikely to fail under this kind of workload.

This does not mean that swap is completely harmless, as endurance problems can still occur if you're swapping to a low-cost, low-capacity flash memory device. The eMMC flash module on Bifrons is rated by its manufacturer (SanDisk) for 44 TBW of endurance. This is 40 GB per day over three years, or 24 GB per day over five years, which should be enough to last the service life of the device. However, eMMC modules are permanently installed in the device and cannot be replaced without highly-specialized equipment (they are soldered onto the motherboard). Furthermore, the limited capacity of the device means that the typical consumer will use most of its capacity, which increases write amplification and reduces the effective endurance of the NAND, possibly below its specifications, and many netbooks of this kind have just 32 GB of storage which further compounds the endurance issue. (The same also applies to low-cost external flash memory devices like SD cards or USB flash drives.) This is, in fact, the reason I put the swap onto an external SSD and not on the system's onboard flash memory.

But this isn't the case for the vast majority of system configurations, where the benefits of placing swap on an SSD outweigh the risks. Most flash memory devices are far faster than any electromechanical hard drive; even if swapping significantly degrades system performance, the performance impact of swapping to an SSD is much lower than swapping to spinning rust. The above endurance issues only truly apply if 1) you're swapping to a cheap and small flash memory device like an eMMC chip or USB flash drive; and 2) your system has low memory and your usage patterns are such that you need to swap more than occasionally. Most systems have enough memory that swapping only happens rarely, if at all, rendering the whole endurance issue moot. And even when swapping is necessary, the drive isn't going to be written to so much that it'll exhaust the endurance of the drive and cause it to fail prematurely. Swapping isn't going to cause the drive to get hundreds of gigabytes or terabytes of writes per day. The 20 GB per day figure is the highest that one might encounter in a typical day of usage, and most users aren't going to see this much swapping.

If endurance is still a concern, there are solutions like zram which can effectively compress the contents of system memory and therefore allow more data to be stored in RAM before the system needs to swap to disk. While this comes at the cost of increased CPU usage, you'll still get better performance than if you're swapping to disk, and fitting more data into memory means that less data needs to be swapped out and written to the flash memory.

Ultimately, for the vast majority of use cases, putting swap on your SSD isn't going to kill it.