• 0 Posts
  • 39 Comments
Joined 1 year ago
Cake day: December 9th, 2023
  • bitcrafter@programming.devtoAsklemmy@lemmy.ml•How do the likes of JD Vance and Drumpf rationalise no more DEI when they have wives who are DEI? It makes no sense.
    5·
    1 month ago

    People are not generally as self-reflective as you might think; when someone settles upon a core belief, they tend to stick with it for the rest of their lives, with any challenge to it being treated as a threat rather than as a potential opportunity for growth. You might think that when a core belief is completely wrong and leads to disastrous negative consequences that this might at be enough to lead someone to give it up, but strangely the mind does not actually work this way.

    (I mean, I am not saying that these people are not also evil and/or oily snakes, but I think that there is value in observing the mental fallacies at work in others so that we can better spot them at work in ourselves, since our own mind is the one thing that we have at least some limited control over.)

  • bitcrafter@programming.devtoLinux@lemmy.ml•How do you backup?
    1·
    1 month ago

    I created a script that I dropped into /etc/cron.hourly which does the following:

    1. Use rsync to mirror my root partition to a btrfs partition on another hard drive (which only updates modified files).
    2. Use btrfs subvolume snapshot to create a snapshot of that mirror (which only uses additional storage for modified files).
    3. Moves “old” snapshots into a trash directory so I can delete them later if I want to save space.

    It is as follows:

    #!/usr/bin/env python
from datetime import datetime, timedelta
import os
import pathlib
import shutil
import subprocess
import sys

import portalocker

DATETIME_FORMAT = '%Y-%m-%d-%H%M'
BACKUP_DIRECTORY = pathlib.Path('/backups/internal')
MIRROR_DIRECTORY = BACKUP_DIRECTORY / 'mirror'
SNAPSHOT_DIRECTORY = BACKUP_DIRECTORY / 'snapshots'
TRASH_DIRECTORY = BACKUP_DIRECTORY / 'trash'

EXCLUDED = [
    '/backups',
    '/dev',
    '/media',
    '/lost+found',
    '/mnt',
    '/nix',
    '/proc',
    '/run',
    '/sys',
    '/tmp',
    '/var',

    '/home/*/.cache',
    '/home/*/.local/share/flatpak',
    '/home/*/.local/share/Trash',
    '/home/*/.steam',
    '/home/*/Downloads',
    '/home/*/Trash',
]

OPTIONS = [
    '-avAXH',
    '--delete',
    '--delete-excluded',
    '--numeric-ids',
    '--relative',
    '--progress',
]

def execute(command, *options):
    print('>', command, *options)
    subprocess.run((command,) + options).check_returncode()

execute(
    '/usr/bin/mount',
    '-o', 'rw,remount',
    BACKUP_DIRECTORY,
)

try:
    with portalocker.Lock(os.path.join(BACKUP_DIRECTORY,'lock')):
        execute(
            '/usr/bin/rsync',
            '/',
            MIRROR_DIRECTORY,
            *(
                OPTIONS
                +
                [f'--exclude={excluded_path}' for excluded_path in EXCLUDED]
            )
        )

        execute(
            '/usr/bin/btrfs',
            'subvolume',
            'snapshot',
            '-r',
            MIRROR_DIRECTORY,
            SNAPSHOT_DIRECTORY / datetime.now().strftime(DATETIME_FORMAT),
        )

        snapshot_datetimes = sorted(
            (
                datetime.strptime(filename, DATETIME_FORMAT)
                for filename in os.listdir(SNAPSHOT_DIRECTORY)
            ),
        )

        # Keep the last 24 hours of snapshot_datetimes
        one_day_ago = datetime.now() - timedelta(days=1)
        while snapshot_datetimes and snapshot_datetimes[-1] >= one_day_ago:
            snapshot_datetimes.pop()

        # Helper function for selecting all of the snapshot_datetimes for a given day/month
        def prune_all_with(get_metric):
            this = get_metric(snapshot_datetimes[-1])
            snapshot_datetimes.pop()
            while snapshot_datetimes and get_metric(snapshot_datetimes[-1]) == this:
                snapshot = SNAPSHOT_DIRECTORY / snapshot_datetimes[-1].strftime(DATETIME_FORMAT)
                snapshot_datetimes.pop()
                execute('/usr/bin/btrfs', 'property', 'set', '-ts', snapshot, 'ro', 'false')
                shutil.move(snapshot, TRASH_DIRECTORY)

        # Keep daily snapshot_datetimes for the last month
        last_daily_to_keep = datetime.now().date() - timedelta(days=30)
        while snapshot_datetimes and snapshot_datetimes[-1].date() >= last_daily_to_keep:
            prune_all_with(lambda x: x.date())

        # Keep weekly snapshot_datetimes for the last three month
        last_weekly_to_keep = datetime.now().date() - timedelta(days=90)
        while snapshot_datetimes and snapshot_datetimes[-1].date() >= last_weekly_to_keep:
            prune_all_with(lambda x: x.date().isocalendar().week)

        # Keep monthly snapshot_datetimes forever
        while snapshot_datetimes:
            prune_all_with(lambda x: x.date().month)
except portalocker.AlreadyLocked:
    sys.exit('Backup already in progress.')
finally:
    execute(
        '/usr/bin/mount',
        '-o', 'ro,remount',
        BACKUP_DIRECTORY,
    )
  • bitcrafter@programming.devtoScience@lemmy.ml•The quantum reason behind the solidity of matter
    2·
    5 months ago

    Which, in turn, is a consequence of the spin-statistics theorem.

    As for why the spin-statistics theorem is true, the answer is that, in a sense, we do not really know. This is because, although we have rigorous mathematical proofs that it is true, they rely on arguments that are very technical in nature, so they provide no real intuitive insight into why the theorem is true. (This theorem is actually really notorious for this; people have been trying for a long time to improve on the situation, but have yet to succeed in coming up with a satisfactory elementary proof of it.)