Skip to content

7th September 2023

Coding⚑

Languages⚑

Bash snippets⚑

  • New: How to deal with HostContextSwitching alertmanager alert.

    A context switch is described as the kernel suspending execution of one process on the CPU and resuming execution of some other process that had previously been suspended. A context switch is required for every interrupt and every task that the scheduler picks.

    Context switching can be due to multitasking, Interrupt handling , user & kernel mode switching. The interrupt rate will naturally go high, if there is higher network traffic, or higher disk traffic. Also it is dependent on the application which every now and then invoking system calls.

    If the cores/CPU's are not sufficient to handle load of threads created by application will also result in context switching.

    It is not a cause of concern until performance breaks down. This is expected that CPU will do context switching. One shouldn't verify these data at first place since there are many statistical data which should be analyzed prior to looking into kernel activities. Verify the CPU, memory and network usage during this time.

    You can see which process is causing issue with the next command:

    10:15:24 AM     UID     PID     cswch/s         nvcswch/s       Command
10:15:27 AM     0       1       162656.7        16656.7         systemd
10:15:27 AM     0       9       165451.04       15451.04        ksoftirqd/0
10:15:27 AM     0       10      158628.87       15828.87        rcu_sched
10:15:27 AM     0       11      156147.47       15647.47        migration/0
10:15:27 AM     0       17      150135.71       15035.71        ksoftirqd/1
10:15:27 AM     0       23      129769.61       12979.61        ksoftirqd/2
10:15:27 AM     0       29      2238.38         238.38          ksoftirqd/3
10:15:27 AM     0       43      1753            753             khugepaged
10:15:27 AM     0       443     1659            165             usb-storage
10:15:27 AM     0       456     1956.12         156.12          i915/signal:0
10:15:27 AM     0       465     29550           29550           kworker/3:1H-xfs-log/dm-3
10:15:27 AM     0       490     164700          14700           kworker/0:1H-kblockd
10:15:27 AM     0       506     163741.24       16741.24        kworker/1:1H-xfs-log/dm-3
10:15:27 AM     0       594     154742          154742          dmcrypt_write/2
10:15:27 AM     0       629     162021.65       16021.65        kworker/2:1H-kblockd
10:15:27 AM     0       715     147852.48       14852.48        xfsaild/dm-1
10:15:27 AM     0       886     150706.86       15706.86        irq/131-iwlwifi
10:15:27 AM     0       966     135597.92       13597.92        xfsaild/dm-3
10:15:27 AM     81      1037    2325.25         225.25          dbus-daemon
10:15:27 AM     998     1052    118755.1        11755.1         polkitd
10:15:27 AM     70      1056    158248.51       15848.51        avahi-daemon
10:15:27 AM     0       1061    133512.12       455.12          rngd
10:15:27 AM     0       1110    156230          16230           cupsd
10:15:27 AM     0       1192    152298.02       1598.02         sssd_nss
10:15:27 AM     0       1247    166132.99       16632.99        systemd-logind
10:15:27 AM     0       1265    165311.34       16511.34        cups-browsed
10:15:27 AM     0       1408    10556.57        1556.57         wpa_supplicant
10:15:27 AM     0       1687    3835            3835            splunkd
10:15:27 AM     42      1773    3728            3728            Xorg
10:15:27 AM     42      1996    3266.67         266.67          gsd-color
10:15:27 AM     0       3166    32036.36        3036.36         sssd_kcm
10:15:27 AM     119349  3194    151763.64       11763.64        dbus-daemon
10:15:27 AM     119349  3199    158306          18306           Xorg
10:15:27 AM     119349  3242    15.28           5.8             gnome-shell

pidstat -wt 3 10  > /tmp/pidstat-t.out

Linux 4.18.0-80.11.2.el8_0.x86_64 (hostname)    09/08/2020  _x86_64_    (4 CPU)

10:15:15 AM   UID      TGID       TID   cswch/s   nvcswch/s  Command
10:15:19 AM     0         1         -   152656.7   16656.7   systemd
10:15:19 AM     0         -         1   152656.7   16656.7   |__systemd
10:15:19 AM     0         9         -   165451.04  15451.04  ksoftirqd/0
10:15:19 AM     0         -         9   165451.04  15451.04  |__ksoftirqd/0
10:15:19 AM     0        10         -   158628.87  15828.87  rcu_sched
10:15:19 AM     0         -        10   158628.87  15828.87  |__rcu_sched
10:15:19 AM     0        23         -   129769.61  12979.61  ksoftirqd/2
10:15:19 AM     0         -        23   129769.61  12979.33  |__ksoftirqd/2
10:15:19 AM     0        29         -   32424.5    2445      ksoftirqd/3
10:15:19 AM     0         -        29   32424.5    2445      |__ksoftirqd/3
10:15:19 AM     0        43         -   334        34        khugepaged
10:15:19 AM     0         -        43   334        34        |__khugepaged
10:15:19 AM     0       443         -   11465      566       usb-storage
10:15:19 AM     0         -       443   6433       93        |__usb-storage
10:15:19 AM     0       456         -   15.41      0.00      i915/signal:0
10:15:19 AM     0         -       456   15.41      0.00      |__i915/signal:0
10:15:19 AM     0       715         -   19.34      0.00      xfsaild/dm-1
10:15:19 AM     0         -       715   19.34      0.00      |__xfsaild/dm-1
10:15:19 AM     0       886         -   23.28      0.00      irq/131-iwlwifi
10:15:19 AM     0         -       886   23.28      0.00      |__irq/131-iwlwifi
10:15:19 AM     0       966         -   19.67      0.00      xfsaild/dm-3
10:15:19 AM     0         -       966   19.67      0.00      |__xfsaild/dm-3
10:15:19 AM    81      1037         -   6.89       0.33      dbus-daemon
10:15:19 AM    81         -      1037   6.89       0.33      |__dbus-daemon
10:15:19 AM     0      1038         -   11567.31   4436      NetworkManager
10:15:19 AM     0         -      1038   1.31       0.00      |__NetworkManager
10:15:19 AM     0         -      1088   0.33       0.00      |__gmain
10:15:19 AM     0         -      1094   1340.66    0.00      |__gdbus
10:15:19 AM   998      1052         -   118755.1   11755.1   polkitd
10:15:19 AM   998         -      1052   32420.66   25545     |__polkitd
10:15:19 AM   998         -      1132   0.66       0.00      |__gdbus

    Then with help of PID which is causing issue, one can get all system calls details: Raw

    Let this command run for a few minutes while the load/context switch rates are high. It is safe to run this on a production system so you could run it on a good system as well to provide a comparative baseline. Through strace, one can debug & troubleshoot the issue, by looking at system calls the process has made.

  • New: Redirect stderr of all subsequent commands of a script to a file.

    {
    somecommand
    somecommand2
    somecommand3
} 2>&1 | tee -a $DEBUGLOG

DevOps⚑

Infrastructure as Code⚑

Ansible Snippets⚑

  • New: Ansible condition that uses a regexp.

    - name: Check if an instance name or hostname matches a regex pattern
  when: inventory_hostname is not match('molecule-.*')
  fail:
    msg: "not a molecule instance"

  • New: Ansible-lint doesn't find requirements.

    It may be because you're using requirements.yaml instead of requirements.yml. Create a temporal link from one file to the other, run the command and then remove the link.

    It will work from then on even if you remove the link. ¯\(°_o)/¯

  • New: Run task only once.

    Add run_once: true on the task definition:

    - name: Do a thing on the first host in a group.
  debug:
    msg: "Yay only prints once"
  run_once: true

Gitea⚑

  • Correction: Using paths-filter custom action to skip job actions.

    jobs:
  test:
    if: "!startsWith(github.event.head_commit.message, 'bump:')"
    name: Test
    runs-on: ubuntu-latest
    steps:
      - name: Checkout the codebase
        uses: https://github.com/actions/checkout@v3

      - name: Check if we need to run the molecule tests
        uses: https://github.com/dorny/paths-filter@v2
        id: filter
        with:
          filters: |
            molecule:
              - 'defaults/**'
              - 'tasks/**'
              - 'handlers/**'
              - 'tasks/**'
              - 'templates/**'
              - 'molecule/**'
              - 'requirements.yaml'
              - '.github/workflows/tests.yaml'

      - name: Run Molecule tests
        if: steps.filter.outputs.molecule == 'true'
        run: make molecule

    You can find more examples on how to use paths-filter here.

  • New: Get variables from the environment.

    You can configure your molecule.yaml file to read variables from the environment with:

    provisioner:
  name: ansible
  inventory:
    group_vars:
      all:
        my_secret: ${MY_SECRET}

    It's useful to have a task that checks if this secret exists:

    - name: Verify that the secret is set
  fail:
    msg: 'Please export my_secret: export MY_SECRET=$(pass show my_secret)'
  run_once: true
  when: my_secret == None

    In the CI you can set it as a secret in the repository.

Infrastructure Solutions⚑

AWS Snippets⚑

  • New: [Remove the lock screen in ubuntu.](../aws_snippets.md#invalidate-a-cloudfront-distribution
aws-cloudfront-create-invalidation---paths-"/pages/about"---distribution-id-my-distribution-id

feat(bash_snippets)

Create the `/usr/share/glib-2.0/schemas/90_ubuntu-settings.gschema.override` file with the next content:

```ini
[org.gnome.desktop.screensaver]
lock-enabled = false
[org.gnome.settings-daemon.plugins.power]
idle-dim = false
```

Then reload the schemas with:

```bash
sudo glib-compile-schemas /usr/share/glib-2.0/schemas/
```

Operating Systems⚑

Linux⚑

aleph⚑

gitsigns⚑

  • New: Introduce gitsigns.

    Gitsigns is a neovim plugin to create git decorations similar to the vim plugin gitgutter but written purely in Lua.

    Installation:

    Add to your plugins.lua file:

      use {'lewis6991/gitsigns.nvim'}

    Install it with :PackerInstall.

    Configure it in your init.lua with:

    -- Configure gitsigns
require('gitsigns').setup({
  on_attach = function(bufnr)
    local gs = package.loaded.gitsigns

    local function map(mode, l, r, opts)
      opts = opts or {}
      opts.buffer = bufnr
      vim.keymap.set(mode, l, r, opts)
    end

    -- Navigation
    map('n', ']c', function()
      if vim.wo.diff then return ']c' end
      vim.schedule(function() gs.next_hunk() end)
      return '<Ignore>'
    end, {expr=true})

    map('n', '[c', function()
      if vim.wo.diff then return '[c' end
      vim.schedule(function() gs.prev_hunk() end)
      return '<Ignore>'
    end, {expr=true})

    -- Actions
    map('n', '<leader>gs', gs.stage_hunk)
    map('n', '<leader>gr', gs.reset_hunk)
    map('v', '<leader>gs', function() gs.stage_hunk {vim.fn.line('.'), vim.fn.line('v')} end)
    map('v', '<leader>gr', function() gs.reset_hunk {vim.fn.line('.'), vim.fn.line('v')} end)
    map('n', '<leader>gS', gs.stage_buffer)
    map('n', '<leader>gu', gs.undo_stage_hunk)
    map('n', '<leader>gR', gs.reset_buffer)
    map('n', '<leader>gp', gs.preview_hunk)
    map('n', '<leader>gb', function() gs.blame_line{full=true} end)
    map('n', '<leader>gb', gs.toggle_current_line_blame)
    map('n', '<leader>gd', gs.diffthis)
    map('n', '<leader>gD', function() gs.diffthis('~') end)
    map('n', '<leader>ge', gs.toggle_deleted)

    -- Text object
    map({'o', 'x'}, 'ih', ':<C-U>Gitsigns select_hunk<CR>')
  end
})

    Usage:

    Some interesting bindings:

    • ]c: Go to next diff chunk
    • [c: Go to previous diff chunk
    • <leader>gs: Stage chunk, it works both in normal and visual mode
    • <leader>gr: Restore chunk from index, it works both in normal and visual mode
    • <leader>gp: Preview diff, you can use it with ]c and [c to see all the chunk diffs
    • <leader>gb: Show the git blame of the line as a shadowed comment

Diffview⚑

Grafana⚑

  • Correction: Install grafana.

    ---
version: "3.8"
services:
  grafana:
    image: grafana/grafana-oss:${GRAFANA_VERSION:-latest}
    container_name: grafana
    restart: unless-stopped
    volumes:
      - data:/var/lib/grafana
    networks:
      - grafana
      - monitorization
      - swag
    env_file:
      - .env
    depends_on:
      - db
  db:
    image: postgres:${DATABASE_VERSION:-15}
    restart: unless-stopped
    container_name: grafana-db
    environment:
      - POSTGRES_DB=${GF_DATABASE_NAME:-grafana}
      - POSTGRES_USER=${GF_DATABASE_USER:-grafana}
      - POSTGRES_PASSWORD=${GF_DATABASE_PASSWORD:?database password required}
    networks:
      - grafana
    volumes:
      - db-data:/var/lib/postgresql/data
    env_file:
      - .env

networks:
  grafana:
    external:
      name: grafana
  monitorization:
    external:
      name: monitorization
  swag:
    external:
      name: swag

volumes:
  data:
    driver: local
    driver_opts:
      type: none
      o: bind
      device: /data/grafana/app
  db-data:
    driver: local
    driver_opts:
      type: none
      o: bind
      device: /data/grafana/database

    Where the monitorization network is where prometheus and the rest of the stack listens, and swag the network to the gateway proxy.

    It uses the .env file to store the required configuration, to connect grafana with authentik you need to add the next variables:

    GF_AUTH_GENERIC_OAUTH_ENABLED="true"
GF_AUTH_GENERIC_OAUTH_NAME="authentik"
GF_AUTH_GENERIC_OAUTH_CLIENT_ID="<Client ID from above>"
GF_AUTH_GENERIC_OAUTH_CLIENT_SECRET="<Client Secret from above>"
GF_AUTH_GENERIC_OAUTH_SCOPES="openid profile email"
GF_AUTH_GENERIC_OAUTH_AUTH_URL="https://authentik.company/application/o/authorize/"
GF_AUTH_GENERIC_OAUTH_TOKEN_URL="https://authentik.company/application/o/token/"
GF_AUTH_GENERIC_OAUTH_API_URL="https://authentik.company/application/o/userinfo/"
GF_AUTH_SIGNOUT_REDIRECT_URL="https://authentik.company/application/o/<Slug of the application from above>/end-session/"
GF_AUTH_OAUTH_AUTO_LOGIN="true"
GF_AUTH_GENERIC_OAUTH_ROLE_ATTRIBUTE_PATH="contains(groups[*], 'Grafana Admins') && 'Admin' || contains(groups[*], 'Grafana Editors') && 'Editor' || 'Viewer'"

    In the configuration above you can see an example of a role mapping. Upon login, this configuration looks at the groups of which the current user is a member. If any of the specified group names are found, the user will be granted the resulting role in Grafana.

    In the example shown above, one of the specified group names is "Grafana Admins". If the user is a member of this group, they will be granted the "Admin" role in Grafana. If the user is not a member of the "Grafana Admins" group, it moves on to see if the user is a member of the "Grafana Editors" group. If they are, they are granted the "Editor" role. Finally, if the user is not found to be a member of either of these groups, it fails back to granting the "Viewer" role.

    Also make sure in your configuration that root_url is set correctly, otherwise your redirect url might get processed incorrectly. For example, if your grafana instance is running on the default configuration and is accessible behind a reverse proxy at https://grafana.company, your redirect url will end up looking like this, https://grafana.company/. If you get user does not belong to org error when trying to log into grafana for the first time via OAuth, check if you have an organization with the ID of 1, if not, then you have to add the following to your grafana config:

    [users]
auto_assign_org = true
auto_assign_org_id = <id-of-your-default-organization>

    Once you've made sure that the oauth works, go to /admin/users and remove the admin user.

  • New: Configure grafana.

    Grafana has default and custom configuration files. You can customize your Grafana instance by modifying the custom configuration file or by using environment variables. To see the list of settings for a Grafana instance, refer to View server settings.

    To override an option use GF_<SectionName>_<KeyName>. Where the section name is the text within the brackets. Everything should be uppercase, . and - should be replaced by _. For example, if you have these configuration settings:

    instance_name = ${HOSTNAME}

[security]
admin_user = admin

[auth.google]
client_secret = 0ldS3cretKey

[plugin.grafana-image-renderer]
rendering_ignore_https_errors = true

[feature_toggles]
enable = newNavigation

    You can override variables on Linux machines with:

    export GF_DEFAULT_INSTANCE_NAME=my-instance
export GF_SECURITY_ADMIN_USER=owner
export GF_AUTH_GOOGLE_CLIENT_SECRET=newS3cretKey
export GF_PLUGIN_GRAFANA_IMAGE_RENDERER_RENDERING_IGNORE_HTTPS_ERRORS=true
export GF_FEATURE_TOGGLES_ENABLE=newNavigation

    And in the docker compose you can edit the .env file. Mine looks similar to:

    GRAFANA_VERSION=latest
GF_DEFAULT_INSTANCE_NAME="production"
GF_SERVER_ROOT_URL="https://your.domain.org"

GF_DATABASE_TYPE=postgres
DATABASE_VERSION=15
GF_DATABASE_HOST=grafana-db:5432
GF_DATABASE_NAME=grafana
GF_DATABASE_USER=grafana
GF_DATABASE_PASSWORD="change-for-a-long-password"
GF_DATABASE_SSL_MODE=disable

GF_AUTH_GENERIC_OAUTH_ENABLED="true"
GF_AUTH_GENERIC_OAUTH_NAME="authentik"
GF_AUTH_GENERIC_OAUTH_CLIENT_ID="<Client ID from above>"
GF_AUTH_GENERIC_OAUTH_CLIENT_SECRET="<Client Secret from above>"
GF_AUTH_GENERIC_OAUTH_SCOPES="openid profile email"
GF_AUTH_GENERIC_OAUTH_AUTH_URL="https://authentik.company/application/o/authorize/"
GF_AUTH_GENERIC_OAUTH_TOKEN_URL="https://authentik.company/application/o/token/"
GF_AUTH_GENERIC_OAUTH_API_URL="https://authentik.company/application/o/userinfo/"
GF_AUTH_SIGNOUT_REDIRECT_URL="https://authentik.company/application/o/<Slug of the application from above>/end-session/"
GF_AUTH_OAUTH_AUTO_LOGIN="true"
GF_AUTH_GENERIC_OAUTH_ROLE_ATTRIBUTE_PATH="contains(groups[*], 'Grafana Admins') && 'Admin' || contains(groups[*], 'Grafana Editors') && 'Editor' || 'Viewer'"

  • New: Configure datasources.

    You can manage data sources in Grafana by adding YAML configuration files in the provisioning/datasources directory. Each config file can contain a list of datasources to add or update during startup. If the data source already exists, Grafana reconfigures it to match the provisioned configuration file.

    The configuration file can also list data sources to automatically delete, called deleteDatasources. Grafana deletes the data sources listed in deleteDatasources before adding or updating those in the datasources list.

    For example to configure a Prometheus datasource use:

    apiVersion: 1

datasources:
  - name: Prometheus
    type: prometheus
    access: proxy
    # Access mode - proxy (server in the UI) or direct (browser in the UI).
    url: http://prometheus:9090
    jsonData:
      httpMethod: POST
      manageAlerts: true
      prometheusType: Prometheus
      prometheusVersion: 2.44.0
      cacheLevel: 'High'
      disableRecordingRules: false
      incrementalQueryOverlapWindow: 10m
      exemplarTraceIdDestinations: []

  • New: Configure dashboards.

    You can manage dashboards in Grafana by adding one or more YAML config files in the provisioning/dashboards directory. Each config file can contain a list of dashboards providers that load dashboards into Grafana from the local filesystem.

    Create one file called dashboards.yaml with the next contents:

    ---
apiVersion: 1
providers:
  - name: default # A uniquely identifiable name for the provider
    type: file
    options:
      path: /etc/grafana/provisioning/dashboards/definitions

    Then inside the config directory of your docker compose create the directory provisioning/dashboards/definitions and add the json of the dashboards themselves. You can download them from the dashboard pages. For example:

  • New: Configure the plugins.

    To install plugins in the Docker container, complete the following steps:

    • Pass the plugins you want to be installed to Docker with the GF_INSTALL_PLUGINS environment variable as a comma-separated list.
    • This sends each plugin name to grafana-cli plugins install ${plugin} and installs them when Grafana starts.

    For example:

    docker run -d -p 3000:3000 --name=grafana \
  -e "GF_INSTALL_PLUGINS=grafana-clock-panel, grafana-simple-json-datasource" \
  grafana/grafana-oss

    To specify the version of a plugin, add the version number to the GF_INSTALL_PLUGINS environment variable. For example: GF_INSTALL_PLUGINS=grafana-clock-panel 1.0.1.

    To install a plugin from a custom URL, use the following convention to specify the URL: <url to plugin zip>;<plugin install folder name>. For example: GF_INSTALL_PLUGINS=https://github.com/VolkovLabs/custom-plugin.zip;custom-plugin.

Jellyfin⚑

Matrix⚑

  • New: How to install matrix.

    sudo apt install -y wget apt-transport-https
sudo wget -O /usr/share/keyrings/element-io-archive-keyring.gpg https://packages.element.io/debian/element-io-archive-keyring.gpg
echo "deb [signed-by=/usr/share/keyrings/element-io-archive-keyring.gpg] https://packages.element.io/debian/ default main" | sudo tee /etc/apt/sources.list.d/element-io.list
sudo apt update
sudo apt install element-desktop

Mediatracker⚑

retroarch⚑

  • New: Install retroarch instructions.

    To add the stable branch to your system type:

    sudo add-apt-repository ppa:libretro/stable
sudo apt-get update
sudo apt-get install retroarch

    Go to Main Menu/Online Updater and then update everything you can:

    • Update Core Info Files
    • Update Assets
    • Update controller Profiles
    • Update Databases
    • Update Overlays
    • Update GLSL Shaders

Vim⚑

  • New: Update treesitter language definitions.

    To do so you need to run:

    :TSInstall <language>

    To update the parsers run

    :TSUpdate

  • New: Telescope changes working directory when opening a file.

    In my case was due to a snippet I have to remember the folds:

    vim.cmd[[
  augroup remember_folds
    autocmd!
    autocmd BufWinLeave * silent! mkview
    autocmd BufWinEnter * silent! loadview
  augroup END
]]

    It looks that it had saved a view with the other working directory so when a file was loaded the cwd changed. To solve it I created a new mkview in the correct directory.

Arts⚑

Dancing⚑

Lindy Hop⚑

Video Gaming⚑

Age of Empires⚑

  • New: How to fight Vietnamese with Mongols.

    Gain early map control with scouts, then switch into steppe lancers and front siege, finally castle in the face when you clicked to imperial.