nvme smart-log does not show temps in Celsius

[Strykar]

Temps in Fahrenheit and Kelvin but not Celsius?

$ sudo nvme smart-log /dev/nvme0
Smart Log for NVME device:nvme0 namespace-id:ffffffff
critical_warning			: 0
temperature				: 91 °F (306 K)
available_spare				: 100%
available_spare_threshold		: 5%
percentage_used				: 1%
endurance group critical warning summary: 0
Data Units Read				: 42,210,392 (21.61 TB)
Data Units Written			: 20,246,705 (10.37 TB)
host_read_commands			: 2,247,662,721
host_write_commands			: 1,572,136,596
controller_busy_time			: 150
power_cycles				: 111
power_on_hours				: 5,221
unsafe_shutdowns			: 78
media_errors				: 0
num_err_log_entries			: 1,124
Warning Temperature Time		: 0
Critical Composite Temperature Time	: 0
Thermal Management T1 Trans Count	: 0
Thermal Management T2 Trans Count	: 0
Thermal Management T1 Total Time	: 0
Thermal Management T2 Total Time	: 0

$ sudo nvme version 
nvme version 2.10.2 (git 2.10.2)
libnvme version 1.10 (git 1.10)

$ uname -a
Linux r912 6.10.3-arch1-2 #1 SMP PREEMPT_DYNAMIC Tue, 06 Aug 2024 07:21:19 +0000 x86_64 GNU/Linux

[igaw]

The unit type is chosen depending of your locale settings, so if you use US locales you get Fahrenheit.

[Strykar]

The unit type is chosen depending of your locale settings, so if you use US locales you get Fahrenheit.

Thanks for clearing that up, setting LC_MEASUREMENT=metric in /etc/locale.conf works along side LANG=en_US.UTF-8,

[igaw]

Oh, we might also need to extend our check, though. I don't think we are actually looking at LC_MEASURMENT instead just on the country. This is wrong I think.

[wdoekes]

@Strykar : I'm not so sure LC_MEASUREMENT takes a metric argument. But it does take en_GB.UTF-8 for instance.

And the first hit on google for LC_MEASUREMENT=metric is the Arch Wiki which references this post!

The commit that was merged now narrows the affected locale scope from LC_ALL to LC_MEASUREMENT. Interestingly, it doesn't use setlocale() to set the category. Instead it uses it to get the current country. Which is non-standard. From there it uses custom is_fahrenheit_country() to check against e.g. the US in en_US. (Which is unreached code when you supply the value metric.) But see below, for proper usage of LC_MEASUREMENT.

If I look inside /usr/share/i18n/locales/i18n, I find:

LC_MEASUREMENT
% This is the ISO/IEC 14652 "i18n" definition for
% the LC_MEASUREMENT category.  It indicates metric.
measurement 1
END LC_MEASUREMENT

versus

LC_MEASUREMENT
% US customary units.
measurement 2
END LC_MEASUREMENT

which is in /usr/share/i18n/locales/en_US.

If nothing matches we will get C or ANSI_X3.4-1968 (default) locale, which happens to have measurement 1. So LC_MEASUREMENT=whatever will work to get metric, as will metric. But it's still wrong:

# LC_MEASUREMENT=metric locale -ck LC_MEASUREMENT
locale: Cannot set LC_ALL to default locale: No such file or directory
LC_MEASUREMENT
measurement=1
measurement-codeset="ANSI_X3.4-1968"

# LC_MEASUREMENT=en_US.UTF-8 locale -ck LC_MEASUREMENT
LC_MEASUREMENT
measurement=2
measurement-codeset="UTF-8"

Proper usage of LC_MEASUREMENT

In a modern system, one would use this:

#include <langinfo.h>
#include <locale.h>
#include <stdio.h>

int main(void) {
    // In nvme.c this is already called. Nothing more is needed.
    setlocale(LC_ALL, "");

    // At the appropriate place, you check for the correct measurement.
    const char *m = nl_langinfo(_NL_MEASUREMENT_MEASUREMENT);
    if (m && m[0] == 2) {
        printf("fahrenheit\n");
    } else {
        printf("celsius\n");
    }
    return 0;
}

Example where you see the precedence of LC_MEASUREMENT over LANG.

$ env -i ./a.out 
celsius

$ env -i LANG=en_US.UTF-8 ./a.out 
fahrenheit

$ env -i LANG=en_US.UTF-8 LC_MEASUREMENT=en_GB.UTF-8 ./a.out 
celsius

And how LC_ALL overrides all:

$ env -i LC_ALL=en_US.UTF-8 LC_MEASUREMENT=en_GB.UTF-8 ./a.out 
fahrenheit

TL;DR (1)

• ✅ LC_MEASUREMENT=en_GB.UTF-8
• 🚫 LC_MEASUREMENT=metric

TL;DR (2)

The code in question should prefer _NL_MEASUREMENT_MEASUREMENT over custom is_fahrenheit_country.

[martin-belanger]

Just my 2¢... 😏

We could also print all 3 units (°C, °F, K) and forget about the locale altogether.

temperature				: 33 °C, 91 °F, 306 K

[igaw]

As long we only print three different units I am fine with this solution. I swear my next open source project will only accept SI units.

[wdoekes]

Hehe, @martin-belanger's suggestion would've meant 0 change for my code that just used the first integer. So yeah, that could've been nice 😄

(Yes, you can point to -o json for programmatic readouts, but that didn't exist in version 0.2.12.g8c19-1~wheezy.)

[ell1e]

I tried LC_MEASUREMENT=metric nvme smart-log /dev/nvme0 but get Fahrenheit still, will this be fixed in an upcoming version? Is there any good way to do this with the older NVMe CLI 2.15?

[wdoekes]

Don't do metric in LC_MEASUREMENT 😩 -- see #2456 (comment)

And before decd39f you'll need LC_ALL=en_GB.UTF-8 or LC_ALL=C