Imported knowledge from a private repository

2026-02-08 21:34:25 +00:00 · 2023-02-23 20:11:42 +01:00
parent e9a22db73b
commit fb83703ef9
12 changed files with 499 additions and 12 deletions
--- a/.vscode/settings.json
+++ b/.vscode/settings.json
@@ -21,6 +21,7 @@
        "fdupes",
        "firewalld",
        "flatpak",
+        "gcloud",
        "getfacl",
        "gpgtools",
        "growpart",
@@ -60,6 +61,7 @@
        "tmpfs",
        "tput",
        "usermod",
+        "userspace",
        "zstd"
    ]
 }
--- a/examples/.gitconfig
+++ b/examples/.gitconfig
@@ -0,0 +1,126 @@
+################################################################################
+## ~/.gitconfig
+##
+## Global git configuration file. Settings in here override the system's ones,
+## and are in turn overridden by the repositories' local ones.
+## Check the resolved configuration in full and its origins with the following:
+## `git config --list --show-origin`.
+##
+## Sources:
+## - https://git-scm.com/docs/git-config
+## - https://git-scm.com/book/en/v2/Customizing-Git-Git-Configuration
+################################################################################
+
+[alias]
+	branch-get-default = "!f() { \
+		git remote show origin \
+		| awk '/HEAD branch/ {print $NF}' \
+	;} && f"
+	branch-get-gone = "!f() { \
+		git fetch -p && \
+		git branch -vv \
+		| awk '/origin/&&/gone/{print $1}' \
+	;} && f"
+	branch-prune-gone = "!f() { \
+		git branch-get-gone \
+		| xargs \
+			git branch -D \
+	;} && f"
+	checkout-default-branch = "!f() { \
+		git checkout $(git branch-get-default) \
+	;} && f"
+	config-show-final = "!f() { \
+		git config --list \
+		| awk -F '=' '{print $1}' \
+		| sort -u \
+		| xargs -I {} \
+			sh -c 'printf \"{}=\" && git config --get {}' \
+	;} && f"
+	pull-from-all-remotes = "!f() { \
+		git remote show \
+		| xargs -I{} \
+			git pull {} ${1-$(git branch --show-current)} \
+	;} && f"
+	pull-from-all-remotes-once = "!f() { \
+		git remote-show-unique \
+		| xargs -I{} \
+			git pull {} ${1-$(git branch --show-current)} \
+	;} && f"
+	pull-from-reachable-remotes = "!f() { \
+		git remote show \
+		| xargs -I{} \
+			sh -c \"timeout 1 git ls-remote -hq {} HEAD >/dev/null 2>&1 && echo {}\" \
+		| xargs -I{} \
+			git pull {} ${1-$(git branch --show-current)} \
+	;} && f"
+	pull-from-reachable-remotes-once = "!f() { \
+		git remote-show-unique \
+		| xargs -I{} \
+			sh -c \"timeout 1 git ls-remote -hq {} HEAD >/dev/null 2>&1 && echo {}\" \
+		| xargs -I{} \
+			git pull {} ${1-$(git branch --show-current)} \
+	;} && f"
+	push-to-all-remotes = "!f() { \
+		git remote show \
+		| xargs -I{} \
+			git push {} ${1-$(git branch --show-current)} \
+	;} && f"
+	push-to-all-remotes-once = "!f() { \
+		git remote-show-unique \
+		| xargs -I{} \
+			git push {} ${1-$(git branch --show-current)} \
+	;} && f"
+	push-to-reachable-remotes = "!f() { \
+		git remote show \
+		| xargs -I{} \
+			sh -c \"timeout 1 git ls-remote -hq {} HEAD >/dev/null 2>&1 && echo {}\" \
+		| xargs -I{} \
+			git push {} ${1-$(git branch --show-current)} \
+	;} && f"
+	push-to-reachable-remotes-once = "!f() { \
+		git remote-show-unique \
+		| xargs -I{} \
+			sh -c \"timeout 1 git ls-remote -hq {} HEAD >/dev/null 2>&1 && echo {}\" \
+		| xargs -I{} \
+			git push {} ${1-$(git branch --show-current)} \
+	;} && f"
+	remote-show-unique = "!f() { \
+		git remote -v \
+		| sort -k2 -u \
+		| awk '{print $1}' \
+		| sort -u \
+	;} && f"
+	statis = status
+	statsu = status
+	switch-default-branch = "!f() { \
+		git switch $(git branch-get-default) \
+	;} && f"
+	top-level = "rev-parse --show-toplevel"
+[core]
+	# 'input' on unix, 'true' on windows
+	# 'false' only if you know what you are doing
+	autocrlf = input
+[diff]
+	wsErrorHighlight = all
+[init]
+	defaultBranch = main
+[pull]
+	rebase = false
+[submodule]
+	recurse = true
+[user]
+	email = name.surname@company.com
+	name = Name Surname
+
+# Enable LFS.
+[filter "lfs"]
+	clean = git-lfs clean -- %f
+	smudge = git-lfs smudge -- %f
+	process = git-lfs filter-process
+	required = true
+
+# Always sign commits.
+[commit]
+	gpgSign = true
+[user]
+	signingKey = 99C324BA
--- a/examples/git/configure.sh
+++ b/examples/git/configure.sh
@@ -0,0 +1,7 @@
+#!/bin/sh
+
+git config --local user.email name.surname@company.com
+git config --local user.name "Name Surname"
+git config --local user.signingkey 99C324BA
+git config --local commit.gpgsign true
+git config --local pull.rebase false
--- a/base/awk.md
+++ b/base/awk.md
@@ -0,0 +1,9 @@
+# `awk`
+
+## Further readings
+
+- [Print line only if number in third field is greater than X]
+- [Printing the last column of a line in a file]
+
+[print line only if number in third field is greater than x]: https://unix.stackexchange.com/questions/395588/print-line-only-if-number-in-third-field-is-greater-than-x#395593
+[Printing the last column of a line in a file]: https://stackoverflow.com/questions/13046167/printing-the-last-column-of-a-line-in-a-file#13046224
--- a/base/bash.md
+++ b/base/bash.md
@@ -1,8 +1,45 @@
 # Bourne Again SHell

+1. [TL;DR](#tldr)
+2. [Startup files loading order](#startup-files-loading-order)
+3. [Functions](#functions)
+4. [Substitutions](#substitutions)
+   1. [!! (command substitution)](#-command-substitution)
+   2. [^^ (caret substitution)](#-caret-substitution)
+5. [Here documents](#here-documents)
+6. [Keys combinations](#keys-combinations)
+7. [Check if a script is sourced by another](#check-if-a-script-is-sourced-by-another)
+8. [Gotchas](#gotchas)
+   1. [Exist statuses of killed commands](#exist-statuses-of-killed-commands)
+   2. [Go incognito](#go-incognito)
+9. [Further readings](#further-readings)
+10. [Sources](#sources)
+
 ## TL;DR

 ```sh
+# Declare arrays. 
+ARRAY=(
+  "first_element"
+  "second_element" "nth_element"
+)
+
+# Get the length of arrays.
+# A.K.A. number of elements.
+ARRAY_LEN=${#ARRAY[@]}
+
+# Access all elements in arrays with referencing.
+echo ${ARRAY[@]}
+echo ${ARRAY[*]}
+
+# Access the last value of arrays.
+echo ${ARRAY[-1]}
+echo ${ARRAY: -1}
+
+# Get a slice of 4 elements from an array.
+# Start from the element with index number 2.
+echo ${ARRAY:2:4}
+
 # Declare functions.
 functionName () { … }
 function functionName { … }
@@ -10,6 +47,23 @@ function functionName { … }
 # Declare functions on a single line.
 functionName () { command1 ; … ; command N ; }

+# Get all the arguments in input.
+echo $@
+
+# Of all the arguments in input, return only those which are existing directories.
+DIRECTORIES=()
+for (( I = $# ; I >= 0 ; I-- )); do
+  if [[ -d ${@[$I]} ]]; then
+    DIRECTORIES+=${@[$I]}
+  else
+    local COMMAND="${@:1: 1-$I}"
+    break
+  fi
+done
+
+# Print all shell and environment variables.
+( set -o posix ; set )
+
 # Print exported variables only.
 export -p

@@ -68,10 +122,118 @@ Upon exit:

 A function automatically returns the exit code of the last command in it.

+## Substitutions
+
+### !! (command substitution)
+
+Substitutes `!!` with the last command in your history
+
+```sh
+$ echo 'hallo!'
+hallo!
+
+$ !!
+echo 'hallo!'
+hallo!
+
+$ sudo !!
+sudo echo 'hallo!'
+[sudo] password for user:
+hallo!
+```
+
+### ^^ (caret substitution)
+
+Re-runs a command replacing a string.
+
+```sh
+$ sudo apt search tmux
+…
+
+$ ^search^show
+sudo apt show tmux
+…
+```
+
+## Here documents
+
+A _Here document_ (_heredoc_) is a type of redirection that allows you to pass multiple lines of input to a command.
+
+```sh
+[COMMAND] <<[-] 'DELIMITER'
+  HERE-DOCUMENT
+DELIMITER
+```
+
+- the first line must start with an **optional command** followed by the special redirection operator `<<` and the **delimiting identifier**
+- one can use **any string** as a delimiting identifier, the most commonly used being `EOF` or `END`
+- if the delimiting identifier is **unquoted**, the shell will substitute all variables, commands and special characters before passing the here-document lines to the command
+- appending a **minus sign** to the redirection operator (`<<-`), will cause all leading tab characters to be **ignored**  
+  this allows one to use indentation when writing here-documents in shell scripts  
+  leading whitespace characters are not allowed, only tabs are
+- the here-document block can contain strings, variables, commands and any other type of input
+- the last line must end with the delimiting identifier  
+  white space in front of the delimiter is not allowed
+
+```sh
+$ cat << EOF
+The current working directory is: $PWD
+You are logged in as: $(whoami)
+EOF
+The current working directory is: /home/user
+You are logged in as: user
+```
+
+```sh
+$ cat <<-'EOF' | sed 's/l/e/g' > file.txt
+  Hello
+  World
+EOF
+$ cat file.txt
+Heeeo
+Wored
+```
+
+## Keys combinations
+
+- `Ctrl+L`: clear the screen (instead of typing `clear`)
+- `Ctrl+R`: reverse search your Bash history for a command that you have already run and wish to run again
+
 ## Check if a script is sourced by another

 ```sh
-(return 0 2>/dev/null) && echo "this script is not sourced" || echo "this script is sourced"
+(return 0 2>/dev/null) \
+&& echo "this script is not sourced" \
+|| echo "this script is sourced"
+```
+
+## Gotchas
+
+### Exist statuses of killed commands
+
+The exit status of a killed command is **128 + _n_** if the command was killed by signal _n_:
+
+```sh
+$ pgrep tryme.sh
+880
+$ kill -9 880
+$ echo $?
+137
+```
+
+### Go incognito
+
+See [How do I open an incognito bash session] on [unix.stackexchange.com]
+
+```sh
+HISTFILE=
+```
+
+You can also avoid recording a single command simply preceding it with space
+
+```shell
+echo $RECORDED
+ echo $NOT_RECORDED
 ```

 ## Further readings
@@ -93,3 +255,29 @@ A function automatically returns the exit code of the last command in it.
 [how to detect if a script is being sourced]: https://stackoverflow.com/questions/2683279/how-to-detect-if-a-script-is-being-sourced#28776166
 [the bash trap command]: https://www.linuxjournal.com/content/bash-trap-command
 [upper- or lower-casing strings]: https://scriptingosx.com/2019/12/upper-or-lower-casing-strings-in-bash-and-zsh/
+
+<!-- FIXME -->
+
+[add directory to $path if it's not already there]: https://superuser.com/questions/39751/add-directory-to-path-if-its-not-already-there
+[append elements to an array]: https://linuxhint.com/bash_append_array/
+[bash-heredoc]: https://linuxize.com/post/bash-heredoc
+[bashrc ps1 generator]: http://bashrcgenerator.com/
+[check if a string represents a valid path]: https://unix.stackexchange.com/questions/214886/check-if-string-represents-valid-path-in-bash
+[command line arguments in a shell script]: https://tecadmin.net/tutorial/bash-scripting/bash-command-arguments/
+[find out the exit codes of all piped commands]: https://www.cyberciti.biz/faq/unix-linux-bash-find-out-the-exit-codes-of-all-piped-commands
+[histsize vs histfilesize]: https://stackoverflow.com/questions/19454837/bash-histsize-vs-histfilesize#19454838
+[how do i open an incognito bash session]: https://unix.stackexchange.com/questions/158933/how-do-i-open-an-incognito-bash-session/158937#158937
+[how to find a bash shell array length]: https://www.cyberciti.biz/faq/finding-bash-shell-array-length-elements/
+[how to slice an array]: https://stackoverflow.com/questions/1335815/how-to-slice-an-array-in-bash#1336245
+[is there a way of reading the last element of an array?]: https://unix.stackexchange.com/questions/198787/is-there-a-way-of-reading-the-last-element-of-an-array-with-bash#198789
+[linux-terminal-trick]: https://opensource.com/article/20/1/linux-terminal-trick
+[printing array elements in reverse]: https://www.unix.com/shell-programming-and-scripting/267967-printing-array-elements-reverse.html
+[regular expressions in a case statement]: https://stackoverflow.com/questions/9631335/regular-expressions-in-a-bash-case-statement#9631449
+[reverse an array]: https://unix.stackexchange.com/questions/412868/bash-reverse-an-array
+[set]: https://ss64.com/bash/set.html
+[slice of positional parameters]: https://unix.stackexchange.com/questions/82060/bash-slice-of-positional-parameters#82061
+[how to list all variables names and their current values?]: https://askubuntu.com/questions/275965/how-to-list-all-variables-names-and-their-current-values#275972
+
+[linuxize.com]: https://linuxize.com
+[opensource.com]: https://opensource.com
+[unix.stackexchange.com]: https://unix.stackexchange.com
--- a/base/boinc.md
+++ b/base/boinc.md
@@ -3,9 +3,15 @@
 1. [TL;DR](#tldr)
 2. [Client management](#client-management)
   1. [Remote management](#remote-management)
-3. [Use the GPU for computation](#use-the-gpu-for-computation)
+3. [Use the GPU for computations](#use-the-gpu-for-computations)
   1. [On OpenSUSE](#on-opensuse)
-4. [Further readings](#further-readings)
+   2. [Check the GPU is OpenCL-enabled](#check-the-gpu-is-opencl-enabled)
+4. [Use VirtualBox for computations](#use-virtualbox-for-computations)
+5. [Gotchas](#gotchas)
+6. [Further readings](#further-readings)
+
+Files are located in `/var/lib/boinc` by default.  
+Some distribution (debian and derivate) use `/etc/boinc-client` for configuration files instead, and create links to the ones in the default location.

 ## TL;DR

@@ -26,8 +32,14 @@ Name            | Type         | Description
 [boinccmd]      | Command line |
 [boinctui]      | Text         |

+Local control RPCs are authenticated using the GUI RPC password. This password is located in the `gui_rpc_auth.cfg` configuration file, as the single first line, with a max length of 255 characters.
+
+A password is **required** from version FIXME, and is automatically generated if the file is not found or it is empty.
+
 ### Remote management

+All remote RPCs (both status and control) are authenticated using the GUI RPC password.
+
 Quick, dirty solution: use the `--allow_remote_gui_rpc` option when starting the client.<br/>
 This will make the BOINC client accept connections from **any** host (subject to password authentication) even if the client's configuration files are set otherwise.

@@ -42,12 +54,21 @@ Better solution:

 1. check the `gui_rpc_auth.cfg` file in the BOINC data directory to get the password for authentication

-## Use the GPU for computation
+## Use the GPU for computations

-Also see [AMD Linux drivers] and [Radeon™ Software for Linux® Installation].
+To use the GPU for projects you may need the proprietary nVidia or AMD drivers. See [AMD Linux drivers] and [Radeon™ Software for Linux® Installation].
+
+```sh
+amdgpu-install --usecase=workstation --opencl=rocr
+```

 The BOINC client seems to need to be added to the `video` group to be able to use the drivers correctly - this is something I still need to check.

+```sh
+gpasswd -a 'boinc' 'video'
+usermod --append --groups 'video' 'boinc'
+```
+
 ### On OpenSUSE

 Install the `amdgpu-install` package from [AMD's Linux drivers][amd linux drivers] page, then execute it.
@@ -65,11 +86,41 @@ At the next restart of the boinc-client, something similar to this line should a
 Oct 09 23:09:40 hostnameHere boinc[1709]: 09-Oct-2022 23:09:40 [---] OpenCL: AMD/ATI GPU 0: gfx90c:xnack- (driver version 3452.0 (HSA1.1,LC), device ve>
 ```

+### Check the GPU is OpenCL-enabled
+
+Just install and run `clinfo`:
+
+```sh
+$ clinfo
+Number of platforms     1
+  Platform Name         NVIDIA CUDA
+  Platform Vendor       NVIDIA Corporation
+  Platform Version      OpenCL 1.2 CUDA 10.0.132
+…
+```
+
+## Use VirtualBox for computations
+
+Install VirtualBox, then add the `boinc` user to the `vboxusers` group:
+
+```sh
+usermod --append --groups 'vboxusers' 'boinc'
+```
+
+## Gotchas
+
+- it seems to work much better on debian-based distribution
+- In order to suspend computing when the computer is in use, the `boinc` user should have access to your X session so that mouse and keyboard input can be communicated to the client:
+
+  ```sh
+  xhost +SI:localuser:boinc
+  ```
+
 ## Further readings

 - [BOINC Manager]
- [boinccmd]
- [boinctui]
+- [boinccmd] for the bare CLI utility
+- [boinctui] for a TUI manager
 - [GUI RPC bind to port 31416 failed: 98]

 <!-- internal references -->
@@ -83,3 +134,11 @@ Oct 09 23:09:40 hostnameHere boinc[1709]: 09-Oct-2022 23:09:40 [---] OpenCL: AMD
 [radeon™ software for linux® installation]: https://amdgpu-install.readthedocs.io/en/latest/

 [gui rpc bind to port 31416 failed: 98]: https://boinc.mundayweb.com/wiki/index.php?title=GUI_RPC_bind_to_port_31416_failed:_98
+
+<!-- FIXME -->
+
+[boinc on arch wiki]: https://wiki.archlinux.org/title/BOINC
+[client configuration]: https://boinc.berkeley.edu/wiki/Client_configuration
+[controlling boinc remotely]: https://boinc.berkeley.edu/wiki/Controlling_BOINC_remotely
+[installing or uninstalling the amdgpu stack]: https://amdgpu-install.readthedocs.io/en/latest/install-installing.html
+[linux suspend when computer is in use bug]: https://boinc.berkeley.edu/dev/forum_thread.php?id=14019&postid=101146#101146
--- a/base/gcloud.md
+++ b/base/gcloud.md
@@ -1,8 +1,8 @@
 # Google cloud platform CLI <!-- omit in toc -->

- [TL;DR](#tldr)
- [Further readings](#further-readings)
- [Sources](#sources)
+1. [TL;DR](#tldr)
+2. [Further readings](#further-readings)
+3. [Sources](#sources)

 ## TL;DR

--- a/base/history.md
+++ b/base/history.md
@@ -0,0 +1,10 @@
+# History
+
+1. [TL;DR](#tldr)
+
+## TL;DR
+
+```sh
+# Delete everything.
+history -c
+```
--- a/base/http
+++ b/base/http
@@ -0,0 +1,9 @@
+# HTTP response status codes
+
+## Further readings
+
+- [MDN]
+- [http.cat]
+
+[mdn]: https://developer.mozilla.org/nl/docs/Web/HTTP/Status
+[http.cat]: https://http.cat/
--- a/base/jsonpath.md
+++ b/base/jsonpath.md
@@ -3,8 +3,8 @@
 ## TL;DR

 ```sh
-# filter elements
-# only works on arrays, not on maps
+# Filter elements.
+# Only works on arrays, not on maps.
 kubectl get serviceaccounts \
  -o jsonpath="{.items[?(@.metadata.name!='default')].metadata.name}"
 ```
@@ -12,5 +12,7 @@ kubectl get serviceaccounts \
 ## Further readings

 - [JSONPath Syntax]
+- [Live editor]

 [jsonpath syntax]: https://support.smartbear.com/alertsite/docs/monitors/api/endpoint/jsonpath.html
+[live editor]: https://json8.github.io/patch/demos/apply/
--- a/base/nilfs.md
+++ b/base/nilfs.md
@@ -0,0 +1,10 @@
+# NilFS
+
+* -O _feature_: set feature
+* -m _percentage_: set percentage of segments reserved to garbage collection (default: 5)
+* -n: dry run
+* -v: verbose
+
+```sh
+sudo mkfs -t 'nilfs2' -L 'label' -O 'block_count' -v '/dev/sdb1'
+```
--- a/base/optimize
+++ b/base/optimize
@@ -0,0 +1,65 @@
+# Optimize battery on a linux system
+
+1. [TL;DR](#tldr)
+2. [Disable unused services](#disable-unused-services)
+3. [Improve battery performance](#improve-battery-performance)
+4. [Further readings](#further-readings)
+
+## TL;DR
+
+```sh
+# Summarize performance of the last boot.
+sudo systemd-analyze
+
+# Show last boot performance.
+# Also shows the process tree.
+sudo systemd-analyze critical-chain
+
+# Check power stats.
+sudo 'powertop'
+```
+
+## Disable unused services
+
+```sh
+$ sudo systemd-analyze
+Startup finished in 13.129s (firmware) + 5.413s (loader) + 1.746s (kernel) + 7.903s (userspace) = 28.192s 
+graphical.target reached after 1.239s in userspace
+
+$ sudo systemd-analyze critical-chain
+The time when unit became active or started is printed after the "@" character.
+The time the unit took to start is printed after the "+" character.
+
+graphical.target @1.239s
+└─multi-user.target @1.239s
+  └─ModemManager.service @1.154s +84ms
+    └─polkit.service @937ms +215ms
+      └─basic.target @928ms
+        └─sockets.target @928ms
+          └─dbus.socket @928ms
+            └─sysinit.target @924ms
+              └─systemd-backlight@backlight:acpi_video0.service @2.273s +8ms
+                └─system-systemd\x2dbacklight.slice @2.272s
+                  └─system.slice @197ms
+                    └─-.slice @197ms
+```
+
+## Improve battery performance
+
+```sh
+# Enable automatic power management.
+# See `tlpui` on GitHub for UI.
+sudo systemctl enable --now 'tlp.service'
+sudo vim '/etc/tlp.conf'
+
+# Check power stats.
+sudo 'powertop'
+```
+
+## Further readings
+
+- [laptop-mode-tools]
+- [laptop-mode-tools in the Arch Wiki]
+
+[laptop-mode-tools]: https://www.unixmen.com/laptop-mode-tools-extend-laptop-battery-life/
+[laptop-mode-tools in the arch wiki]: https://wiki.archlinux.org/title/Laptop_Mode_Tools