February 9 2021 UMLet, Data Points, git-stash, Pico, IPFS, mariadb, IERS

As there were still problems with the sound on John’s new laptop, we started with a discussion of sound on chromium, whether it might worth trying Firefox, which did not recognise John’s external microphone, or whether it might be worth trying another microphone, without coming to any satisfactory conclusion.

David confessed that he had downloaded some AppImages for 3D slicing software and then

Darren demonstrated UMLet, a Java based program for producing diagrams aimed at arriving at a final specification using the Unified Modeling Language; he showed how elements could be linked and an interaction frame programmed to respond based on conditions; it looked a bit like an adult version of Scratch without the code generation though it can generate pseudo-code.

Bernard described how, not being able to get to the Raspberry Pi at the astronomy centre which transmits the temperature data, he had discovered that he could get a Python API from the Met Office to get weather data; this relies on getting a key from the Met Office. He can then read the data available from Bingley on one side of the astronomy centre and from a station in Lancashire on the other, average the readings and knock off ½° for altitude to work out the temperature at the astronomy centre for the time being.

He also mentioned coming across git-stash which allows you to store and retrieve work in progress without affecting the main working tree; git-stash is the equivalent of git-stash push while git-stash pop retrieves whatever has been stored.

He also mentioned the Raspberry Pi Pico, a micro-controller board for which others can make things.

Brian is exploring temperature and humidity sensors for use with Home assistant and also the InterPlanetary File System (IPFS), a peer to peer distributed file system which uses content addressing rather than being location based. There is a ten minute Youtube video, IPFS simply explained, which explains the rationale for it.

Among users are Filecoin, a decentralised cryptocurrency and digital payment system, Cloudflare, Microsoft’s self-sovereign identity system and the D.tube crypto-decentralised video platform.

John briefly mentioned some changes to mariadb’s authentication systems. Originally, with mysql, you had a root user and two anonymous users and you had to give a password to the root user and get rid of or secure the anonymous users. The details of all the users were stored in mysql.user which you could edit like any other table. This has all changed.

When installed on a Unix like system, any Unix users can log in directly using their Unix credentials and mysql.user is now a read only table showing the existing users in human readable form. User permissions are stored in mysql.global_privs.

If you update mariabd, it appears that mariadb simply says that the existing users are using legacy mysql authentication. However, if you try to copy an existing setup to a new device using mysqldump --all-databases, mariadb will refuse to import it because it contains a read-write version of mysql-user. So you have to recreate the user permissions, specifying the authentication system you intend to use with them, and import the other databases separately.

This change is part of allowing a variety of authentication systems to be used with mariadb — something which Bernard pointed out is already possible in PostgreSQL. John will research this more thoroughly and report back to a later meeting. In response to a question, he said that mysql and mariadb had remained in step until mysql 5.5 after which mariadb had diverged and become mariadb 10.

Bernard drew attention to the IERS data on the rotational speed of the earth which has to be taken into account in plotting astronomical data and David said he had seen various articles mentioning that melting ice was causing the earth to spin faster like a dancer rotating and that we might need a negative leap second!

Brian then mentioned that he had bought a pulse oximeter and David said he had one while John mentioned that there was a trial in Essex using pulse oximeters to monitor people with mild symptoms at home and then bring them into hospital if the readings on the oximeters fell too much.

We discussed options for a pay-as-you-go contract to enable Brian to send and receive text messages between the UK and Spain before lapsing into talking about the pandemic.

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