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knowledge base/kubernetes/README.md
View File

@@ -3,23 +3,32 @@
Open source container orchestration engine for containerized applications.<br />
Hosted by the [Cloud Native Computing Foundation][cncf].
1. [Basics](#basics)
1. [Control plane](#control-plane)
1. [Concepts](#concepts)
1. [Control plane](#control-plane)
1. [API server](#api-server)
1. [`kube-scheduler`](#kube-scheduler)
1. [`kube-controller-manager`](#kube-controller-manager)
1. [`cloud-controller-manager`](#cloud-controller-manager)
1. [Worker nodes](#worker-nodes)
1. [Worker nodes](#worker-nodes)
1. [`kubelet`](#kubelet)
1. [`kube-proxy`](#kube-proxy)
1. [Container runtime](#container-runtime)
1. [Addons](#addons)
1. [Workloads](#workloads)
1. [Workloads](#workloads)
1. [Pods](#pods)
1. [Best practices](#best-practices)
1. [Volumes](#volumes)
1. [hostPaths](#hostpaths)
1. [emptyDirs](#emptydirs)
1. [configMaps](#configmaps)
1. [secrets](#secrets)
1. [nfs](#nfs)
1. [downwardAPI](#downwardapi)
1. [PersistentVolumes](#persistentvolumes)
1. [Resize PersistentVolumes](#resize-persistentvolumes)
1. [Autoscaling](#autoscaling)
1. [Pod scaling](#pod-scaling)
1. [Node scaling](#node-scaling)
1. [Best practices](#best-practices)
1. [Quality of service](#quality-of-service)
1. [Containers with high privileges](#containers-with-high-privileges)
1. [Capabilities](#capabilities)
@@ -40,7 +49,7 @@ Hosted by the [Cloud Native Computing Foundation][cncf].
1. [Further readings](#further-readings)
1. [Sources](#sources)
## Basics
## Concepts
When using Kubernetes, one is using a cluster.
@@ -56,7 +65,7 @@ fault-tolerance and high availability.
![Cluster components](components.svg)
## Control plane
### Control plane
Makes global decisions about the cluster (like scheduling).<br/>
Detects and responds to cluster events (like starting up a new pod when a deployment has less replicas then it requests).
@@ -74,7 +83,7 @@ Control plane components run on one or more cluster nodes.<br/>
For ease of use, setup scripts typically start all control plane components on the **same** host and avoid **running**
other workloads on it.
### API server
#### API server
Exposes the Kubernetes API. It is the front end for, and the core of, the Kubernetes control plane.<br/>
`kube-apiserver` is the main implementation of the Kubernetes API server, and is designed to scale horizontally (by
@@ -108,7 +117,7 @@ The Kubernetes API can be extended:
- using _custom resources_ to declaratively define how the API server should provide your chosen resource API, or
- extending the Kubernetes API by implementing an aggregation layer.
### `kube-scheduler`
#### `kube-scheduler`
Detects newly created pods with no assigned node, and selects one for them to run on.
@@ -121,7 +130,7 @@ Scheduling decisions take into account:
- inter-workload interference;
- deadlines.
### `kube-controller-manager`
#### `kube-controller-manager`
Runs _controller_ processes.<br />
Each controller is a separate process logically speaking; they are all compiled into a single binary and run in a single
@@ -136,7 +145,7 @@ Examples of these controllers are:
- the EndpointSlice controller, which populates _EndpointSlice_ objects providing a link between services and pods;
- the ServiceAccount controller, which creates default ServiceAccounts for new namespaces.
### `cloud-controller-manager`
#### `cloud-controller-manager`
Embeds cloud-specific control logic, linking clusters to one's cloud provider's API and separating the components that
interact with that cloud platform from the components that only interact with clusters.
@@ -156,19 +165,19 @@ The following controllers can have cloud provider dependencies:
- the route controller, which sets up routes in the underlying cloud infrastructure;
- the service controller, which creates, updates and deletes cloud provider load balancers.
## Worker nodes
### Worker nodes
Each and every node runs components providing a runtime environment for the cluster, and syncing with the control plane
to maintain workloads running as requested.
### `kubelet`
#### `kubelet`
A `kubelet` runs as an agent on each and every node in the cluster, making sure that containers are run in a pod.
It takes a set of _PodSpecs_ and ensures that the containers described in them are running and healthy.<br/>
It only manages containers created by Kubernetes.
### `kube-proxy`
#### `kube-proxy`
Network proxy running on each node and implementing part of the Kubernetes Service concept.
@@ -178,21 +187,21 @@ or outside of one's cluster.
It uses the operating system's packet filtering layer, if there is one and it's available; if not, it just forwards the
traffic itself.
### Container runtime
#### Container runtime
The software responsible for running containers.
Kubernetes supports container runtimes like `containerd`, `CRI-O`, and any other implementation of the Kubernetes CRI
(Container Runtime Interface).
### Addons
#### Addons
Addons use Kubernetes resources (_DaemonSet_, _Deployment_, etc) to implement cluster features.<br/>
As such, namespaced resources for addons belong within the `kube-system` namespace.
See [addons] for an extended list of the available addons.
## Workloads
### Workloads
Workloads consist of groups of containers ([_pods_][pods]) and a specification for how to run them (_manifest_).<br/>
Configuration files are written in YAML (preferred) or JSON format and are composed of:
@@ -201,7 +210,7 @@ Configuration files are written in YAML (preferred) or JSON format and are compo
- resource specifications, with attributes specific to the kind of resource they are describing, and
- status, automatically generated and edited by the control plane.
### Pods
#### Pods
The smallest deployable unit of computing that one can create and manage in Kubernetes.<br/>
Pods contain one or more relatively tightly coupled application containers; they are always co-located (executed on the
@@ -218,38 +227,6 @@ Gotchas:
- If a Container specifies a memory or CPU `limit` but does **not** specify a memory or CPU `request`, Kubernetes
automatically assigns it a resource `request` spec equal to the given `limit`.
## Autoscaling
Controllers are available to scale Pods or Nodes automatically, both in number or size.
Automatic scaling of Pods is done in number by the HorizontalPodAutoscaler, and in size by the VerticalPodAutoscaler.<br/>
Automatic scaling of Nodes is done in number by the Cluster Autoscaler, and in size by add-ons like [Karpenter].
> Be aware of mix-and-matching autoscalers for the same kind of resource.<br/>
> One can easily defy the work done by the other and make that resource behave unexpectedly.
K8S only comes with the HorizontalPodAutoscaler by default.<br/>
Managed K8S usually also comes with the [Cluster Autoscaler] if autoscaling is enabled on the cluster resource.
### Pod scaling
Autoscaling of Pods by number requires the use of the Horizontal Pod Autoscaler.<br/>
Autoscaling of Pods by size requires the use of the Vertical Pod Autoscaler.
### Node scaling
Autoscaling of Nodes by number requires the [Cluster Autoscaler].
1. The Cluster Autoscaler routinely checks for pending Pods.
1. Pods fill up the available Nodes.
1. When Pods start to fail for lack of available resources, Nodes are added to the cluster.
1. When Pods are not failing due to lack of available resources and one or more Nodes are underused, the Autoscaler
tries to fit the existing Pods in less Nodes.
1. If one or more Nodes can result unused from the previous step (DaemonSets are usually not taken into consideration),
the Autoscaler will terminate them.
Autoscaling of Nodes by size requires add-ons like [Karpenter].
## Best practices
Also see [configuration best practices] and the [production best practices checklist].
@@ -298,6 +275,374 @@ Also see [configuration best practices] and the [production best practices check
- Protect the cluster's ingress points.<br/>
Firewalls, web application firewalls, application gateways.
## Volumes
Refer [volumes].
Sources to mount directories from.
They go by the `volumes` key in Pods' `spec`.<br/>
E.g., in a Deployment they are declared in its `spec.template.spec.volumes`:
```yaml
apiVersion: apps/v1
kind: Deployment
spec:
template:
spec:
volumes:
- <volume source 1>
- <volume source N>
```
Mount volumes in containers by using the `volumesMount`:
```yaml
apiVersion: apps/v1
kind: Pod
spec:
containers:
- name: some-container
volumeMounts:
- name: my-volume-source
mountPath: /path/to/mount
readOnly: false
subPath: dir/in/volume
```
### hostPaths
Mount files or directories from the host node's filesystem into Pods.
**Not** something most Pods will need, but powerful escape hatches for some applications.
Use cases:
- Containers needing access to node-level system components<br/>
E.g., containers transferring system logs to a central location and needing access to those logs using a read-only
mount of `/var/log`.
- Making configuration files stored on the host system available read-only to _static_ Pods.
This because static Pods **cannot** access ConfigMaps.
If mounted files or directories on the host are only accessible to `root`:
- Either the process needs to run as `root` in a privileged container,
- Or the files' permissions on the host need to be changed to allow the process to read from (or write to) the volume.
```yaml
apiVersion: apps/v1
kind: Pod
volumes:
- name: example-volume
# Mount '/data/foo' only if that directory already exists
hostPath:
path: /data/foo # location on host
type: Directory # optional
```
### emptyDirs
Scrape disks for **temporary** Pod data.
**Not** shared between Pods.<br/>
All data is **destroyed** once the Pod is removed, but stays intact when Pods restart.
Use cases:
- Provide directories to create pid/lock or other special files for 3rd-party software when it's inconvenient or
impossible to disable them.<br/>
E.g., Java Hazelcast creates lockfiles in the user's home directory and there's no way to disable this behaviour.
- Store intermediate calculations which can be lost<br/>
E.g., external sorting, buffering of big responses to save memory.
- Improve startup time after application crashes if the application in question pre-computes something before or during
startup.</br>
E.g., compressed assets in the application's image, decompressing data into temporary directory.
```yaml
apiVersion: apps/v1
kind: Pod
volumes:
- name: my-emptydir
emptyDir:
# Omit the 'medium' field to use disk storage.
# The 'Memory' medium will create tmpfs to store data.
medium: Memory
sizeLimit: 1Gi
```
### configMaps
Inject configuration data into Pods.
When referencing a ConfigMap:
- Provide the name of the ConfigMap in the volume.
- Optionally customize the path to use for a specific entry in the ConfigMap.
```yaml
apiVersion: apps/v1
kind: Pod
spec:
containers:
- name: test
volumeMounts:
- name: config-vol
mountPath: /etc/config
volumes:
- name: config-vol
configMap:
name: log-config
items:
- key: log_level
path: log_level
- name: my-configmap-volume
configMap:
name: my-configmap
defaultMode: 0644 # posix access mode, set it to the most restricted value
optional: true # allow pods to start with this configmap missing, resulting in an empty directory
```
ConfigMaps **must** be created before they can be mounted.
One ConfigMap can be mounted into any number of Pods.
ConfigMaps are always mounted `readOnly`.
Containers using ConfigMaps as `subPath` volume mounts will **not** receive ConfigMap updates.
Text data is exposed as files using the UTF-8 character encoding.<br/>
Use `binaryData` For any other character encoding.
### secrets
Used to pass sensitive information to Pods.<br/>
E.g., passwords.
They behave like ConfigMaps but are backed by `tmpfs`, so they are never written to non-volatile storage.
Secrets **must** be created before they can be mounted.
Secrets are always mounted `readOnly`.
Containers using Secrets as `subPath` volume mounts will **not** receive Secret updates.
```yaml
apiVersion: apps/v1
kind: Pod
spec:
volumes:
- name: my-secret-volume
secret:
secretName: my-secret
defaultMode: 0644
optional: false
```
### nfs
mount **existing** NFS shares into Pods.
The contents of NFS volumes are preserved after Pods are removed and the volume is merely unmounted.<br/>
This means that NFS volumes can be pre-populated with data, and that data can be shared between Pods.
NFS can be mounted by multiple writers simultaneously.
One **cannot** specify NFS mount options in a Pod spec.<br/>
Either set mount options server-side or use `/etc/nfsmount.conf`.<br/>
Alternatively, mount NFS volumes via PersistentVolumes as they do allow to set mount options.
```yaml
apiVersion: v1
kind: Pod
spec:
containers:
- image: registry.k8s.io/test-webserver
name: test-container
volumeMounts:
- mountPath: /my-nfs-data
name: test-volume
volumes:
- name: test-volume
nfs:
server: my-nfs-server.example.com
path: /my-nfs-volume
readOnly: true
```
### downwardAPI
Downward APIs expose Pods' and containers' resource declaration or status field values.<br/>
Refer [Expose Pod information to Containers through files].
Downward API volumes make downward API data available to applications as read-only files in plain text format.
Containers using the downward API as `subPath` volume mounts will **not** receive updates when field values change.
```yaml
apiVersion: v1
kind: Pod
metadata:
labels:
cluster: test-cluster1
rack: rack-22
zone: us-east-coast
spec:
volumes:
- name: my-downwardapi-volume
downwardAPI:
defaultMode: 0644
items:
- path: labels
fieldRef:
fieldPath: metadata.labels
# Mounting this volume results in a file with contents similar to the following:
# ```plaintext
# cluster="test-cluster1"
# rack="rack-22"
# zone="us-east-coast"
# ```
```
### PersistentVolumes
#### Resize PersistentVolumes
1. Check the `StorageClass` is set with `allowVolumeExpansion: true`:
```sh
kubectl get storageClass 'storage-class-name' -o jsonpath='{.allowVolumeExpansion}'
```
1. Edit the PersistentVolumeClaim's `spec.resources.requests.storage` field.<br/>
This will take care of the underlying PersistentVolume's size automagically.
```sh
kubectl edit persistentVolumeClaim 'my-pvc'
```
1. Verify the change by checking the PVC's `status.capacity` field:
```sh
kubectl get pvc 'my-pvc' -o jsonpath='{.status}'
```
Should one see the message
> Waiting for user to (re-)start a pod to finish file system resize of volume on node
under the `status.conditions` field, just wait some time.<br/>
It should **not** be necessary to restart the Pods, and the capacity should change soon to the requested one.
Gotchas:
- It's possible to recreate StatefulSets **without** the need of killing the Pods it controls.<br/>
Reapply the STS' declaration with a new PersistentVolume size, and start new pods to resize the underlying filesystem.
<details>
<summary>If deploying the STS via Helm</summary>
1. Change the size of the PersistentVolumeClaims used by the STS:
```sh
kubectl edit persistentVolumeClaims 'my-pvc'
```
1. Delete the STS **without killing its pods**:
```sh
kubectl delete statefulsets.apps 'my-sts' --cascade 'orphan'
```
1. Redeploy the STS with the changed size.
It will retake ownership of existing Pods.
1. Delete the STS' pods one-by-one.<br/>
During Pod restart, the Kubelet will resize the filesystem to match new block device size.
```sh
kubectl delete pod 'my-sts-pod'
```
</details>
<details>
<summary>If managing the STS manually</summary>
1. Change the size of the PersistentVolumeClaims used by the STS:
```sh
kubectl edit persistentVolumeClaims 'my-pvc'
```
1. Note down the names of PVs for specific PVCs and their sizes:
```sh
kubectl get persistentVolume 'my-pv'
```
1. Dump the STS to disk:
```sh
kubectl get sts 'my-sts' -o yaml > 'my-sts.yaml'
```
1. Remove any extra field (like `metadata.{selfLink,resourceVersion,creationTimestamp,generation,uid}` and `status`)
and set the template's PVC size to the value you want.
1. Delete the STS **without killing its pods**:
```sh
kubectl delete sts 'my-sts' --cascade 'orphan'
```
1. Reapply the STS.<br/>
It will retake ownership of existing Pods.
```sh
kubectl apply -f 'my-sts.yaml'
```
1. Delete the STS' pods one-by-one.<br/>
During Pod restart, the Kubelet will resize the filesystem to match new block device size.
```sh
kubectl delete pod 'my-sts-pod'
```
</details>
## Autoscaling
Controllers are available to scale Pods or Nodes automatically, both in number or size.
Automatic scaling of Pods is done in number by the HorizontalPodAutoscaler, and in size by the VerticalPodAutoscaler.<br/>
Automatic scaling of Nodes is done in number by the Cluster Autoscaler, and in size by add-ons like [Karpenter].
> Be aware of mix-and-matching autoscalers for the same kind of resource.<br/>
> One can easily defy the work done by the other and make that resource behave unexpectedly.
K8S only comes with the HorizontalPodAutoscaler by default.<br/>
Managed K8S usually also comes with the [Cluster Autoscaler] if autoscaling is enabled on the cluster resource.
### Pod scaling
Autoscaling of Pods by number requires the use of the Horizontal Pod Autoscaler.<br/>
Autoscaling of Pods by size requires the use of the Vertical Pod Autoscaler.
### Node scaling
Autoscaling of Nodes by number requires the [Cluster Autoscaler].
1. The Cluster Autoscaler routinely checks for pending Pods.
1. Pods fill up the available Nodes.
1. When Pods start to fail for lack of available resources, Nodes are added to the cluster.
1. When Pods are not failing due to lack of available resources and one or more Nodes are underused, the Autoscaler
tries to fit the existing Pods in less Nodes.
1. If one or more Nodes can result unused from the previous step (DaemonSets are usually not taken into consideration),
the Autoscaler will terminate them.
Autoscaling of Nodes by size requires add-ons like [Karpenter].
## Quality of service
See [Configure Quality of Service for Pods] for more information.
@@ -694,6 +1039,7 @@ Others:
- [Common labels]
- [What is Kubernetes?]
- [Using RBAC Authorization]
- [Expose Pod information to Containers through files]
<!--
Reference
@@ -744,6 +1090,7 @@ Others:
[container hooks]: https://kubernetes.io/docs/concepts/containers/container-lifecycle-hooks/#container-hooks
[distribute credentials securely using secrets]: https://kubernetes.io/docs/tasks/inject-data-application/distribute-credentials-secure/
[documentation]: https://kubernetes.io/docs/home/
[expose pod information to containers through files]: https://kubernetes.io/docs/tasks/inject-data-application/downward-api-volume-expose-pod-information/
[labels and selectors]: https://kubernetes.io/docs/concepts/overview/working-with-objects/labels/
[namespaces]: https://kubernetes.io/docs/concepts/overview/working-with-objects/namespaces/
[no new privileges design proposal]: https://github.com/kubernetes/design-proposals-archive/blob/main/auth/no-new-privs.md
@@ -756,6 +1103,7 @@ Others:
[using rbac authorization]: https://kubernetes.io/docs/reference/access-authn-authz/rbac/
[using sysctls in a kubernetes cluster]: https://kubernetes.io/docs/tasks/administer-cluster/sysctl-cluster/
[version skew policy]: https://kubernetes.io/releases/version-skew-policy/
[volumes]: https://kubernetes.io/docs/concepts/storage/volumes/
<!-- Others -->
[best practices for pod security in azure kubernetes service (aks)]: https://learn.microsoft.com/en-us/azure/aks/developer-best-practices-pod-security

73
knowledge base/pandoc.md
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@@ -1,11 +1,54 @@
# Pandoc
Haskell library for converting from one markup format to another.<br/>
The command-line tool uses this library.
Pandoc's enhanced version of Markdown includes syntax for tables, definition lists, metadata blocks, footnotes,
citations, math, and more.
1. [TL;DR](#tldr)
1. [Further readings](#further-readings)
1. [Sources](#sources)
1. [Sources](#sources)
## TL;DR
Pandoc consists of a set of readers.<br/>
Those readers parse text in a given format, and produce:
- A native representation of the document (an abstract syntax tree or AST), and
- A set of writers.
The writers convert the document's native representation into the target format.
Adding an input or output format requires only adding a reader or writer.
Users can run custom pandoc filters to modify the intermediate AST.
> Pandoc's intermediate representation of a document is less expressive than many of the formats it converts
> between.<br/>
> As such, one should **not** expect perfect conversions between every format and every other.
>
> Pandoc attempts to preserve the structural elements of a document, but not formatting details such as margin
> size.<br/>
> Some document elements (i.e., complex tables) may **not** fit into pandoc's simple document model.
If no input files are specified, input is read from `stdin`.
The output goes to `stdout` by default.
If the input or output format is not specified explicitly, pandoc will attempt to guess it from the extensions of the
filenames.<br/>
If no input file is specified or if the input files' extensions are unknown, the input format will be assumed to be
Markdown.<br/>
If no output file is specified or if the output file's extension is unknown, the output format will default to HTML.
Pandoc uses the UTF-8 character encoding for both input and output.<br/>
If one's local character encoding is **not** UTF-8, one should pipe input and output through `iconv`:
```sh
iconv -t 'utf-8' 'input.txt' | pandoc | iconv -f 'utf-8'
```
```sh
# Install.
apt install 'pandoc'
@@ -14,6 +57,10 @@ dnf install 'pandoc'
yum install 'pandoc'
zypper install 'pandoc-cli'
# Print the lists of supported formats.
pandoc --list-input-formats
pandoc --list-output-formats
# Convert between formats.
# If the format is not specified, it will try to guess.
pandoc -f 'html' -t 'markdown' 'input.html'
@@ -21,33 +68,41 @@ pandoc -r 'html' -w 'markdown' 'https://www.fsf.org'
pandoc --from 'markdown' --write 'docx' 'input.md'
pandoc --read 'markdown' --to 'rtf' 'input.md'
pandoc -o 'output.tex' 'input.txt'
# By default, pandoc produces document fragments.
# Use the '-s', '--standalone' option to produce a standalone document.
pandoc -s --output 'output.pdf' 'input.html'
# If multiple input files are given at once, pandoc will concatenate them all with blank lines between them before
# parsing.
# Use `--file-scope` to parse files individually.
# Convert to PDF.
# The default way leverages LaTeX, requiring a LaTeX engine to be installed.
# Alternative engines allow ConTeXt, roff ms or HTML as intermediate formats.
# Alternative engines allow 'ConTeXt', 'roff ms' or 'HTML' as intermediate formats.
pandoc … 'input.html'
pandoc … --pdf-engine 'context' 'https://www.fsf.org'
pandoc … --pdf-engine 'html' -c 'style.css' 'input.html'
# Render markdown documents and show them in `links`.
pandoc --standalone 'docs/pandoc.md' | links
```
## Further readings
- [Website]
- [Manual]
## Sources
All the references in the [further readings] section, plus the following:
### Sources
- [Creating a PDF]
<!--
References
Reference
═╬═Time══
-->
<!-- In-article sections -->
[further readings]: #further-readings
<!-- Upstream -->
[creating a pdf]: https://pandoc.org/MANUAL.html#creating-a-pdf
[manual]: https://pandoc.org/MANUAL.html
[website]: https://pandoc.org/

43
knowledge base/polkit.md Normal file
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@@ -0,0 +1,43 @@
# Polkit
Provides an authorization API<br/>.
Those are intended to be used by privileged programs (A.K.A. _mechanisms_) that offer services to unprivileged programs
(A.K.A. _subjects_).
Mechanisms typically treat subjects as **untrusted**.<br/>
For every request from subjects, mechanisms need to determine if the request is authorized or if they should refuse
to service the subject; mechanisms can offload this decision to **the polkit authority** using the polkit APIs.
The system architecture of polkit is comprised of the _Authority_ and an _Authentication Agent_ per user session.<br/>
_Actions_ are defined by applications. Vendors, sites and system administrators can control the authorization policy
using _Authorization Rules_.
The Authentication Agent provided and started by the user's graphical environment
The Authority is implemented as a system daemon (`polkitd`)<br/>
The daemon itself runs as the `polkitd` system user to have little privilege.
Mechanisms, subjects and authentication agents communicate with the authority using the system message bus.
In addition to acting as an authority, polkit allows users to obtain temporary authorization through authenticating
either an administrative user or the owner of the session the client belongs to.<br/>
This is useful for scenarios where mechanisms needs to verify that the operator of the system really is the user or an
administrative user.
## Sources
- Arch Linux's [Wiki page][arch wiki page]
- Polkit's [documentation]
- Polkit's [`man` page][man page]
<!--
Reference
═╬═Time══
-->
<!-- Upstream -->
[documentation]: https://www.freedesktop.org/software/polkit/docs/latest/
[man page]: https://www.freedesktop.org/software/polkit/docs/latest/polkit.8.html
<!-- Others -->
[arch wiki page]: https://wiki.archlinux.org/index.php/Polkit

29
knowledge base/prometheus.md
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@@ -21,7 +21,7 @@ security policy.
1. [Management API](#management-api)
1. [Take snapshots of the data](#take-snapshots-of-the-data)
1. [Further readings](#further-readings)
1. [Sources](#sources)
1. [Sources](#sources)
## TL;DR
@@ -201,6 +201,20 @@ calculates the **per-second rate of change** based on the last two data points o
To calculate the overall CPU usage, the idle mode of the metric is used. Since idle percent of a processor is the
opposite of a busy processor, the irate value is subtracted from 1. To make it a percentage, it is multiplied by 100.
<details>
<summary>Examples</summary>
```promql
# Get all allocatable CPU cores where the 'node' attribute matches regex ".*-runners-.*" grouped by node
sum(kube_node_status_allocatable_cpu_cores{node=~".*-runners-.*"}) BY (node)
# FIXME
sum(rate(container_cpu_usage_seconds_total{namespace="gitlab-runners",container="build",pod_name=~"runner.*"}[30s])) by (pod_name,container) /
sum(container_spec_cpu_quota{namespace="gitlab-runners",pod_name=~"runner.*"}/container_spec_cpu_period{namespace="gitlab-runners",pod_name=~"runner.*"}) by (pod_name,container)
```
</details>
## Storage
Refer [Storage].
@@ -377,9 +391,7 @@ The snapshot now exists at `<data-dir>/snapshots/20171210T211224Z-2be650b6d019eb
- [`ordaa/boinc_exporter`][ordaa/boinc_exporter]
- [Grafana]
## Sources
All the references in the [further readings] section, plus the following:
### Sources
- [Getting started with Prometheus]
- [Node exporter guide]
@@ -395,15 +407,15 @@ All the references in the [further readings] section, plus the following:
- [How to integrate Prometheus and Grafana on Kubernetes using Helm]
- [node-exporter's helm chart's values]
- [How to set up and experiment with Prometheus remote-write]
- [Install Prometheus and Grafana by Helm]
- [Prometheus and Grafana setup in Minikube]
- [I need to know about the below kube_state_metrics description. Exactly looking is what the particular metrics doing]
<!--
Reference
═╬═Time══
-->
<!-- In-article sections -->
[further readings]: #further-readings
<!-- Knowledge base -->
[grafana]: grafana.md
[node exporter]: node%20exporter.md
@@ -434,8 +446,11 @@ All the references in the [further readings] section, plus the following:
[how relabeling in prometheus works]: https://grafana.com/blog/2022/03/21/how-relabeling-in-prometheus-works/
[how to integrate prometheus and grafana on kubernetes using helm]: https://semaphoreci.com/blog/prometheus-grafana-kubernetes-helm
[how to set up and experiment with prometheus remote-write]: https://developers.redhat.com/articles/2023/11/30/how-set-and-experiment-prometheus-remote-write
[i need to know about the below kube_state_metrics description. exactly looking is what the particular metrics doing]: https://stackoverflow.com/questions/60440847/i-need-to-know-about-the-below-kube-state-metrics-description-exactly-looking-i#60449570
[install prometheus and grafana by helm]: https://medium.com/@at_ishikawa/install-prometheus-and-grafana-by-helm-9784c73a3e97
[install prometheus and grafana with helm 3 on a local machine vm]: https://dev.to/ko_kamlesh/install-prometheus-grafana-with-helm-3-on-local-machine-vm-1kgj
[ordaa/boinc_exporter]: https://gitlab.com/ordaa/boinc_exporter
[prometheus and grafana setup in minikube]: http://blog.marcnuri.com/prometheus-grafana-setup-minikube/
[scrape selective metrics in prometheus]: https://docs.last9.io/docs/how-to-scrape-only-selective-metrics-in-prometheus
[set up prometheus and ingress on kubernetes]: https://blog.gojekengineering.com/diy-how-to-set-up-prometheus-and-ingress-on-kubernetes-d395248e2ba
[snmp monitoring and easing it with prometheus]: https://medium.com/@openmohan/snmp-monitoring-and-easing-it-with-prometheus-b157c0a42c0c

68
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@@ -3,6 +3,8 @@
## Table of contents <!-- omit in toc -->
1. [First boot](#first-boot)
1. [Boot from USB](#boot-from-usb)
1. [Raspberry Pi 4B](#raspberry-pi-4b)
1. [Repositories](#repositories)
1. [Privilege escalation](#privilege-escalation)
1. [Disable WiFi and Bluetooth](#disable-wifi-and-bluetooth)
@@ -30,12 +32,37 @@
1. [LED warning flash codes](#led-warning-flash-codes)
1. [Issues connecting to WiFi network using roaming features or WPA3](#issues-connecting-to-wifi-network-using-roaming-features-or-wpa3)
1. [Further readings](#further-readings)
1. [Sources](#sources)
1. [Sources](#sources)
## First boot
Unless manually set from the Imager, on first boot the system will ask to create a new initial user.
## Boot from USB
Available on Raspberry Pi 2B v1.2, 3A+, 3B, 3B+, 4B, 400, Compute Module 3, Compute Module 3+ and Compute Module 4 only.
### Raspberry Pi 4B
The bootloader EEPROM may need to be updated to enable booting from USB mass storage devices.
To check this, power the Pi up with no SD card inserted and a display attached to one of the HDMI ports.<br/>
It will display a diagnostic screen which includes the bootloader EEPROM version at the top.
The bootloader must be dated **_Sep 3 2020_** or later to support USB mass storage boot.<br/>
If the diagnostic screen reports a date earlier than _Sep 3 2020_, or there is no diagnostic screen shown, one will need
to update the bootloader EEPROM first to enable USB mass storage boot.
To update it:
1. use the _Misc Utility Images_ option in Raspberry Pi Imager to create an SD card with the latest
_Raspberry Pi 4 EEPROM boot recovery_ image
1. boot the Pi using this SD card
1. the bootloader EEPROM will be updated to the latest factory version
1. the Pi will flash its green ACT light rapidly and display green on the HDMI outputs to indicate success
USB mass storage boot on the Pi 4B requires Raspberry Pi OS 2020-08-20 or later.
## Repositories
[Repositories], [Mirrors].
@@ -239,6 +266,11 @@ sudo nano '/etc/init.d/raspi-config'
See [Timely tips for speeding up your Raspberry Pi].
```sh
# Run benchmarks.
curl -L https://raw.githubusercontent.com/aikoncwd/rpi-benchmark/master/rpi-benchmark.sh | sudo bash
```
## Headless boot
Manual procedure:
@@ -296,7 +328,7 @@ network={
Use `wpa_passphrase`:
```
```plaintext
usage: wpa_passphrase <ssid> [passphrase]
If passphrase is left out, it will be read from stdin
```
@@ -404,10 +436,9 @@ Long term solution: none currently known.
- [Country code search]
- [`k3s`][k3s]
- [Configuration]
- [os documentation]
## Sources
All the references in the [further readings] section, plus the following:
### Sources
- [Prepare SD card for WiFi on headless Pi]
- [Run Kubernetes on a Raspberry Pi with k3s]
@@ -416,27 +447,43 @@ All the references in the [further readings] section, plus the following:
- [Timely tips for speeding up your Raspberry Pi]
- [Repositories]
- [Mirrors]
- [disabling bluetooth on raspberry pi]
- [ghollingworth/overlayfs]
- [how to disable onboard wifi and bluetooth on raspberry pi 3]
- [how to disable wi-fi on raspberry pi]
- [how to disable your raspberry pi's wi-fi]
- [how to make your raspberry pi 4 faster with a 64 bit kernel]
- [re: raspbian jessie linux 4.4.9 severe performance degradati]
- [rp automatic updates]
- [sd card power failure resilience ideas]
- [alpine linux headless installation]
- [alpine linux]
- [benchmark]
- [preventing filesystem corruption in embedded linux]
- [usb mass storage boot]
<!--
References
Reference
═╬═Time══
-->
<!-- Upstream -->
[/boot/config.txt]: https://www.raspberrypi.org/documentation/configuration/config-txt/README.md
[configuration]: https://www.raspberrypi.com/documentation/computers/configuration.html
[mirrors]: https://www.raspbian.org/RaspbianMirrors
[os documentation]: https://www.raspberrypi.org/documentation/computers/os.html
[overclocking]: https://www.raspberrypi.org/documentation/configuration/config-txt/overclocking.md
[repositories]: https://www.raspbian.org/RaspbianRepository
[vcgencmd]: https://www.raspberrypi.com/documentation/computers/os.html#vcgencmd
<!-- In-article sections -->
[further readings]: #further-readings
<!-- Knowledge base -->
[k3s]: kubernetes/k3s.md
[rfkill]: rfkill.md
<!-- Others -->
[alpine linux headless installation]: https://wiki.alpinelinux.org/wiki/Raspberry_Pi_-_Headless_Installation
[alpine linux]: https://wiki.alpinelinux.org/wiki/Raspberry_Pi
[benchmark]: https://github.com/aikoncwd/rpi-benchmark
[country code search]: https://www.iso.org/obp/ui/#search/code/
[disabling bluetooth on raspberry pi]: https://di-marco.net/blog/it/2020-04-18-tips-disabling_bluetooth_on_raspberry_pi/
[ghollingworth/overlayfs]: https://github.com/ghollingworth/overlayfs
@@ -445,8 +492,8 @@ All the references in the [further readings] section, plus the following:
[how to disable your raspberry pi's wi-fi]: https://pimylifeup.com/raspberry-pi-disable-wifi/
[how to make your raspberry pi 4 faster with a 64 bit kernel]: https://medium.com/for-linux-users/how-to-make-your-raspberry-pi-4-faster-with-a-64-bit-kernel-77028c47d653
[issue 2067]: https://github.com/k3s-io/k3s/issues/2067#issuecomment-664052806
[os documentation]: https://www.raspberrypi.org/documentation/computers/os.html
[prepare sd card for wifi on headless pi]: https://raspberrypi.stackexchange.com/questions/10251/prepare-sd-card-for-wifi-on-headless-pi
[preventing filesystem corruption in embedded linux]: https://www.embeddedarm.com/assets/preventing-filesystem-corruption-in-embedded-linux
[raspbian bug 1929746]: https://bugs.launchpad.net/raspbian/+bug/1929746
[re: how to make sure the rpi cpu is not throttled down?]: https://www.raspberrypi.org/forums/viewtopic.php?t=152549#p999931
[re: raspbian jessie linux 4.4.9 severe performance degradati]: https://www.raspberrypi.org/forums/viewtopic.php?f=63&t=147781&start=50#p972790
@@ -454,3 +501,4 @@ All the references in the [further readings] section, plus the following:
[run kubernetes on a raspberry pi with k3s]: https://opensource.com/article/20/3/kubernetes-raspberry-pi-k3s
[sd card power failure resilience ideas]: https://www.raspberrypi.org/forums/viewtopic.php?f=63&t=253104&p=1549229#p1549117
[timely tips for speeding up your raspberry pi]: https://www.raspberry-pi-geek.com/Archive/2013/01/Timely-tips-for-speeding-up-your-Raspberry-Pi
[usb mass storage boot]: https://www.raspberrypi.org/documentation/hardware/raspberrypi/bootmodes/msd.md

45
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@@ -0,0 +1,45 @@
# Shell
```shell
$ cat /etc/locale.conf
LANG=en_US.UTF-8
LC_NUMERIC=en_GB.UTF-8
LC_TIME=en_GB.UTF-8
LC_MONETARY=en_GB.UTF-8
LC_PAPER=en_GB.UTF-8
LC_MEASUREMENT=en_GB.UTF-8
$ locale
LANG=en_US.UTF-8
LC_CTYPE="en_US.UTF-8"
LC_NUMERIC=en_GB.UTF-8
LC_TIME=en_GB.UTF-8
LC_COLLATE="en_US.UTF-8"
LC_MONETARY=en_GB.UTF-8
LC_MESSAGES="en_US.UTF-8"
LC_PAPER=en_GB.UTF-8
LC_NAME="en_US.UTF-8"
LC_ADDRESS="en_US.UTF-8"
LC_TELEPHONE="en_US.UTF-8"
LC_MEASUREMENT=en_GB.UTF-8
LC_IDENTIFICATION="en_US.UTF-8"
LC_ALL=
```
## See also
- [Shellcheck]
[shellcheck]: https://www.shellcheck.net/
## Further readings
- [How can I declare and use boolean variables in a shell script]?
- [What does LC_ALL=C do]?
- [Exit Codes With Special Meanings]
- [How to check if running as root in a bash script]
[exit codes with special meanings]: https://tldp.org/LDP/abs/html/exitcodes.html
[how can i declare and use boolean variables in a shell script]: https://stackoverflow.com/questions/2953646/how-can-i-declare-and-use-boolean-variables-in-a-shell-script#21210966
[how to check if running as root in a bash script]: https://stackoverflow.com/questions/18215973/how-to-check-if-running-as-root-in-a-bash-script#21622456
[what does lc_all=c do]: https://unix.stackexchange.com/questions/87745/what-does-lc-all-c-do#87763

14
knowledge base/tmux.md
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@@ -28,7 +28,15 @@ See usage for details.
<summary>Installation and configuration</summary>
```sh
# Install.
brew install 'tmux'
# Get the default settings.
# Might need to run from inside a sessions.
# Specify a null configuration file so that tmux ends up printing whatever is hard-coded in its source.
tmux -f '/dev/null' show-options -s
tmux -f '/dev/null' show-options -g
tmux -f '/dev/null' list-keys
```
The configuration file is `$HOME/.tmux.conf` or `$XDG_CONFIG_HOME/tmux/tmux.conf`.
@@ -120,6 +128,9 @@ tmux kill-session -t 'session-name'
- [Tmux has forever changed the way I write code]
- [Sending simulated keystrokes in Bash]
- [Is it possible to send input to a tmux session without connecting to it?]
- [devhints.io]
- [hamvocke/dotfiles]
- [Default Tmux config]
<!--
Reference
@@ -135,6 +146,9 @@ tmux kill-session -t 'session-name'
[tmux plugin manager]: https://github.com/tmux-plugins/tpm
<!-- Others -->
[default tmux config]: https://unix.stackexchange.com/questions/175421/default-tmux-config#342975
[devhints.io]: https://devhints.io/tmux
[hamvocke/dotfiles]: https://github.com/hamvocke/dotfiles/blob/master/tmux/.tmux.conf
[is it possible to send input to a tmux session without connecting to it?]: https://unix.stackexchange.com/questions/409861/is-it-possible-to-send-input-to-a-tmux-session-without-connecting-to-it#409863
[sending simulated keystrokes in bash]: https://superuser.com/questions/585398/sending-simulated-keystrokes-in-bash#1606615
[tmux cheat sheet & quick reference]: https://tmuxcheatsheet.com/

84
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@@ -0,0 +1,84 @@
# VSCodium
## Troubleshooting
### Zsh terminal icons are not getting displayed in the terminal
Change font to `NotoSansMono Nerd Font` in the _Terminal_ > _Integrated_ > _Font Family_ settings.
See [Why Zsh terminal icons are not getting displayed in Atom Platformio Ide Terminal?]
## Flatpak version
In case you missed, the README file is at `/app/share/codium/README.md`
### FAQ
This version is running inside a _container_ and is therefore __not able__
to access SDKs on your host system!
#### To execute commands on the host system, run inside the sandbox
```bash
flatpak-spawn --host <COMMAND>
```
#### Host Shell
To make the Integrated Terminal automatically use the host system's shell,
you can add this to the settings of vscodium:
```json
{
"terminal.integrated.shell.linux": "/usr/bin/env",
"terminal.integrated.shellArgs.linux": ["--", "flatpak-spawn", "--host", "bash"]
}
```
#### SDKs
This flatpak provides a standard development environment (gcc, python, etc).
To see what's available:
```bash
flatpak run --command=sh com.vscodium.codium
ls /usr/bin (shared runtime)
ls /app/bin (bundled with this flatpak)
```
To get support for additional languages, you have to install SDK extensions, e.g.
```bash
flatpak install flathub org.freedesktop.Sdk.Extension.dotnet
flatpak install flathub org.freedesktop.Sdk.Extension.golang
FLATPAK_ENABLE_SDK_EXT=dotnet,golang flatpak run com.vscodium.codium
```
You can use
```bash
flatpak search <TEXT>
```
to find others.
#### Run flatpak codium from host terminal
If you want to run `codium /path/to/file` from the host terminal just add this to your shell's rc file
```bash
alias codium="flatpak run com.vscodium.codium"
```
then reload sources, now you could try:
```bash
$ codium /path/to/
# or
$ FLATPAK_ENABLE_SDK_EXT=dotnet,golang codium /path/to/
```
## Sources
- [Why Zsh terminal icons are not getting displayed in Atom Platformio Ide Terminal?]
[why zsh terminal icons are not getting displayed in atom platformio ide terminal?]: https://forum.manjaro.org/t/why-zsh-terminal-icons-are-not-getting-displayed-in-atom-platformio-ide-terminal/64885/2

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@@ -0,0 +1,44 @@
# ZRAM
TODO
1. [TL;DR](#tldr)
1. [Further readings](#further-readings)
1. [Sources](#sources)
## TL;DR
```sh
$ grep 'swap' /etc/fstab
/dev/zram0 none swap sw 0 0
$ cat /etc/modules-load.d/zram.conf
zram
# Create a zram block device with total capacity of 2x the total RAM.
# Size is determined by the 'echo ...' part.
$ cat /etc/udev/rules.d/10-zram.rules
KERNEL=="zram0", \
SUBSYSTEM=="block", \
ACTION=="add", \
ATTR{initstate}=="0", \
PROGRAM="/bin/sh -c 'echo $(($(LANG=C free --kilo | sed --silent --regexp-extended s/^Mem:\ (0-9+)\ +.$/\1/p)*2))KiB'", \
ATTR{disksize}="$result", \
RUN+="/sbin/mkswap $env{DEVNAME}", \
TAG+="systemd"
```
## Further readings
### Sources
<!--
Reference
═╬═Time══
-->
<!-- In-article sections -->
<!-- Knowledge base -->
<!-- Files -->
<!-- Upstream -->
<!-- Others -->