Ciro Santilli @cirosantilli  40

Their crash system does not have an amazing user interface.

After something crashes, look under /var/crash for a crash file, which helps to determine which package to report under on Launchpad.

E.g. a file /var/crash/_usr_sbin_gdm3.0.crash makes you want to file the bug under gdm at: bugs.launchpad.net/ubuntu/+source/gdm/+filebug

Then, while reporting the bug, you want to give the developpers access to that .crash file. But you can't publicly upload it because it contains memory dumps and could contain secret information. The way to do it is to look at the ID under:

sudo cat /var/crash/_usr_sbin_gdm3.0.uploaded

Ubuntu's crash report system has already uploaded the .crash for you, so you just have to confirm it and give the ID on the ticket.

You can view a list of all your uploaded errors at:

xdg-open https://errors.ubuntu.com/user/$(sudo cat /var/lib/whoopsie/whoopsie-id)

and each of those contain a link to:

https://errors.ubuntu.com/oops/<.uloaded error id>

which you yourself cannot see.

askubuntu.com/questions/434431/how-can-i-read-a-crash-file-from-var-crash asks how to read the .crash files.

Running:

sudo apport-unpack /var/crash/_usr_sbin_gdm3.0.crash /tmp/app

splits it up into a few files, but does not make any major improvements.

apport-retrace

sudo apt install apport-retrace
sudo chmod 666 /var/crash/_usr_sbin_gdm3.0.crash
apport-retrace -g /var/crash/_usr_sbin_gdm3.0.crash

opens GDB with the core dump. Debug symbols are supplied as separate packages, which is a really cool idea: so you should be able to download them after the crash to see symbols. askubuntu.com/questions/487222/how-to-install-debug-symbols-for-installed-packages mentions how to install them. Official docs at: wiki.ubuntu.com/DebuggingProgramCrash#Debug_Symbol_Packages

Tried:

echo "deb http://ddebs.ubuntu.com $(lsb_release -cs) main restricted universe multiverse" | sudo tee -a /etc/apt/sources.list.d/ddebs.list
echo -e "deb http://ddebs.ubuntu.com $(lsb_release -cs)-updates main restricted universe multiverse\ndeb http://ddebs.ubuntu.com $(lsb_release -cs)-proposed main restricted universe multiverse" | sudo tee -a /etc/apt/sources.list.d/ddebs.list
sudo apt install ubuntu-dbgsym-keyring

but then sudo apt update fails with:

E: The repository 'http://ddebs.ubuntu.com impish-security Release' does not have a Release file.

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Ubuntu release Updated 2025-07-16

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Launchpad (website) Updated 2025-07-16

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Tangible asset Updated 2025-07-16

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Intangible asset Updated 2025-07-16

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DDR SDRAM Updated 2025-07-16

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Pros and cons of superconducting qubits Updated 2025-07-16

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Superconducting qubit type Updated 2025-07-16

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Stars nearest to the Sun Updated 2025-07-16

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Figure 2.
Distance of stars nearest to the Sun as function of time
. Source.

upload.wikimedia.org/wikipedia/commons/e/e9/Near-stars-past-future-en.svg

Some notable ones:

Proxima Centauri, the nearest one, at 4 ly. It is part of the Alpha Centauri star system, which contains two other stars at very similar distances as well, and their relative distances to earth will change positions in a few tens of thousands of years.
Sirius, the brightest star in the sky at 9 ly

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JTAG Updated 2025-07-16

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Covert Lab Updated 2025-07-16

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www.covert.stanford.edu/

Makes the E. Coli Whole Cell Model by Covert Lab.

Lead: Markus W. Covert.

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Closure table Updated 2025-07-16

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Nested set model Updated 2025-07-16

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This is particularly important in SQL: Nested set model in SQL, as it is an efficient way to transverse trees there, since querying parents every time would require multiple disk accesses.

The ASCII art visualizations from stackoverflow.com/questions/192220/what-is-the-most-efficient-elegant-way-to-parse-a-flat-table-into-a-tree/194031#194031 are worth reproducing.

As a tree:

Root 1
- Child 1.1
  - Child 1.1.1
  - Child 1.1.2
- Child 1.2
  - Child 1.2.1
  - Child 1.2.2

As the sets:

 __________________________________________________________________________
|  Root 1                                                                  |
|   ________________________________    ________________________________   |
|  |  Child 1.1                     |  |  Child 1.2                     |  |
|  |   ___________    ___________   |  |   ___________    ___________   |  |
|  |  |  C 1.1.1  |  |  C 1.1.2  |  |  |  |  C 1.2.1  |  |  C 1.2.2  |  |  |
1  2  3___________4  5___________6  7  8  9___________10 11__________12 13 14
|  |________________________________|  |________________________________|  |
|__________________________________________________________________________|

Consider the following nested set:

0, 8, root
  1, 7, mathematics
    2, 3, geometry
      3, 6, calculus
        4, 5, derivative
        5, 6, integral
      6, 7, algebra
  7, 8, physics

When we want to insert one element, e.g. limit, normally under calculus, we have to specify:

parent
index within parent

so we have a method:

insert(parent, previousSibling)

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SQL transaction isolation level Updated 2025-07-16

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Each transaction isolation level specifies what can or cannot happen when two queries are being run in parallel, i.e.: the memory semantics of the system.

Remember that queries can affects thousands of rows, and database systems like PostgreSQL can run multiple such queries at the same time.

Good summary on the PostgreSQL page: www.postgresql.org/docs/14/transaction-iso.html

Implementation specifics: