Forem: nullity

Obsidian can't view pdf

nullity — Mon, 24 Mar 2025 04:40:13 +0000

OS: ubuntu 20.04

At the time, the latest Obsidian version is 1.8.9.

Problem

Using the latest Obsidian downloaded from snap, I find that I can't view some PDFs in obsidian vault. But those PDFs can be viewed normally in any other PDF viewers.

Solution

Step 1:

Remove the snap version of Obsidian.

snap remove obsidian

Step 2

Download the deb version of obsidian. (Downlaod page of Obsidian)

Run the following command to install it.

sudo apt install <the-deb-file-path>

For example, in the download folder,
run sudo apt install ./obsidian_1.8.9_amd64.deb

Result

All PDFs can be view normally in Obsidian.

在 Linux 上安裝與使用 Notion Desktop

nullity — Tue, 18 Feb 2025 14:47:04 +0000

Notion 官方並沒有推出 Desktop App for Linux
不過 GitHub 上有 unofficial desktop app 可以下載
https://github.com/xanmoy/notion-desktop
按照指示就可以安裝了

使用:
介面放大: 試試看 "Ctrl +" 或是 "Ctrl shift +" 或是 "按住 Ctrl + 滾動滑鼠"
介面縮小: 試試看 "Ctrl -" 或是 "Ctrl shift -" 或是 "按住 Ctrl + 滾動滑鼠"
都試試看

在我的電腦上 (Ubuntu 20.04)，是
介面放大: "Ctrl shift +"
介面縮小: "Ctrl -"
(我試了好久，才發現是這個組合，我也不懂為什麼要這樣設計)

gdb trick: automatically display local variables when stops

nullity — Tue, 12 Nov 2024 18:25:03 +0000

Add the following to ~/.gdbinit

define toggle-local
  if $toggle_hook_enabled == 0
    set $toggle_hook_enabled = 1
    define hook-stop
      info local
      printf "---------------------\n"
    end
    printf "display-local enabled.\n"
  else
    set $toggle_hook_enabled = 0
    define hook-stop
    end
    printf "display-local disabled.\n"
  end
end

set $toggle_hook_enabled = 0

Usage

When in gdb session, use "toggle-local" to toggle it.

Why not always turn it on? If there are too many local variables, gdb would use pagination to show all the infomation, sometimes it's kind of annoying to press an addition Enter.

gdb trick: automatically redirecct output to another terminal

nullity — Tue, 12 Nov 2024 17:35:39 +0000

tty command in gdb can direct output to another terminal.
Like https://stackoverflow.com/questions/8963208/gdb-display-output-of-target-application-in-a-separate-window

But I want it to be set automatically.

Method

Create a script ~/.gdbtty.sh
Its content

#!/bin/bash
gnome-terminal -- bash -c "tty > ~/.gdbtty.txt; exec bash" &
sleep 0.5  # Give it time to open
TTY=$(cat ~/.gdbtty.txt)
echo "set inferior-tty $TTY" > ~/.gdbtty.txt

And edit ~/.gdbinit as

shell ~/.gdbtty.sh
source ~/.gdbtty.txt

Some shortcomings

It's good but with some tiny shortcomings that I currently can't solve.

I cannot control where the output terminal would popup. (But even I can control, I have no idea where is the ideal position for me)
The output terminal may show a harmless warning "warning: GDB: Failed to set controlling terminal: Operation not permitted"

Install Ubuntu 20.04 on Virtualbox on Ubuntu 20.04

nullity — Mon, 20 May 2024 13:31:40 +0000

Problem: can't use sudo

When creating VM, check the option "Skip Unattached installation"

If you didn't check that and have completed the installation and find some problems, unfortunately, it's too late, you need to recreate VM and reinstall the OS. (If there is some easier way to fix it, please tell me, I would like to know)

Problem: Can't open terminal (worst thing ever)

Settings -> Language -> English (Canada)
reboot

Then you can open terminal. (I don't know why)
After that, even you switch to another language, the problem won't appear again.

Problem: The window is too small (like 800x800)

On the VM's top menu, select Devices -> Insert Guest Addition CD image
On the opened window's top right corner, click "Run software"
reboot
On the VM's top menu, select View -> Auto-resize Guest Display.

The time shown the top bar is in other langauges

edit /etc/default/locale to language you want

pyenv local is overrited by pyenv global in vscode's terminal

nullity — Fri, 10 May 2024 07:29:27 +0000

Problem

In termianl (outside vscode), pyenv local version overwrites pyenv global version, which is correct.

In vscode's terminal, the pyenv global version overwrites the pyenv local version, which is wrong.

Solution

In vscode's settings, search for "python environment"
Find "Python > Terminal: Activate Environment"

uncheck the box.
restart vscode.
It may show a warning in the vscode's terminal, follow that.

Ubuntu 20.04 Screen tearing

nullity — Mon, 15 Apr 2024 12:33:20 +0000

Screen tearing may happen when you change a display orientation to "Portrait Right" or "Portrait Left"

If you are using Intel's built-in graphic, you can try the combinations of following methods.

Method 1

Step 1. If you don't have the folder "/etc/X11/xorg.conf.d", create one.
Step 2. create the file 20-intel.confin the directory /etc/X11/xorg.conf.d/

content in 20-intel.conf

Section "Device"
    Identifier "Intel Graphics"
    Driver "intel"
    Option "TearFree" "true"
    Option "AccelMod"    "uxa"
    Option "DRI"         "3"
EndSection

and then reboot

Method 2

Try creating another file 20-intel-graphics.conf in the directory "/etc/X11/xorg.conf.d/"

content in the file

Section "Device"
    Identifier "Intel Graphics"
    Driver "intel"
    Option "TearFree" "true"
    Option "AccelMod"    "uxa"
    Option "DRI"         "3"
EndSection

and then reboot

Tips:
You can try playing the following options in method 1 and 2.

Try using either Option "AccelMod" "uxa" or Option "AccelMod" "sna" or none of them.
try using Option "TripleBuffer" "true" or not.
Try using Option "DRI" "3" or not

Remember to reboot after setting them.

Method 3

try removing the buggy package

sudo remove xserver-xorg-video-intel

and reboot

if that doesn't work, try reinstalling it.

sudo apt update
sudo install xserver-xorg-video-intel

My working settings (for your reference)

content in /etc/X11/xorg.conf.d/20-intel.conf and/etc/X11/xorg.conf.d/20-intel-graphics.conf

Section "Device"
    Identifier "Intel Graphics"
    Driver "intel"
    Option "TearFree" "true"
    Option "AccelMod"    "sna"
    Option "DRI"         "3"
    Option "TripleBuffer" "true"
EndSection

Reinstall xserver-xorg-video-intel

ref

CSS snippets for Obsidian

nullity — Fri, 22 Mar 2024 06:21:16 +0000

/* Make bold text bolder */
.cm-s-obsidian span.cm-formatting-strong,
.cm-s-obsidian span.cm-strong,
.cm-s-obsidian strong {
  /* --bold-weight is deprecated, use --bold-modifier instead */
  /* --bold-weight: 1000; */ 
  --bold-modifier: 250;
}

/* ref: https://www.reddit.com/r/ObsidianMD/comments/yunc56/how_to_make_bold_text_more_visible/ */


/* Make headers with different levels have different colors */
body {
  --h1-color: var(--color-red);
  --h2-color: var(--color-orange);
  --h3-color: var(--color-yellow);
  --h4-color: var(--color-green);
  --h5-color: var(--color-blue);
  --h6-color: var(--color-purple);
}

/* Make the vertical line besides a blockquote thinker */
body {
  --blockquote-border-thickness: 8px;
}

/* Make the first row in a table not bold by default because sometimes we don't want the first row to be the header */
/* If we do want to make the first row looks like a header, just surround each item in the first row with double asterisks to make them bold */
.cm-s-obsidian .cm-table-widget th {
  font-weight:normal;
}

/* Hide the blank line above a table to save space */
.cm-line:has(+ .cm-embed-block.cm-table-widget) br {
  display: none;
}

/* Make math equations bigger */
mjx-math {
  font-size: 140% !important;
}

/* Make horizontal lines thinker */
hr {
  border: 2px solid;
}

/* Indent headers */
h2, .HyperMD-header-2 { left: -56px; }
h3, .HyperMD-header-3 { left: -30px; }
h4, .HyperMD-header-4 { left: -15px; }
h5, .HyperMD-header-5 { left: -7.5px; }
h6, .HyperMD-header-6 { left: 0px; }
div.markdown-preview-view,
div.markdown-source-view div.cm-content { 
  /* Shift note right to spare space for headers */
  padding-left: 30px !important;
  margin-right: -20px !important;  /* more characters in one line */
}
/* ref: https://forum.obsidian.md/t/heading-and-text-after-it-indentation/53086/4 */

/* Prevent mermaid images being cropped */
.mermaid svg { 
  max-width: 100%; 
  height: auto;
}

/* Make math blocks align left */
mjx-container {
  text-align: left !important;
}

.internal-embed.markdown-embed.inline-embed.is-loaded {
  border: 2px dashed gray;
  /* background-color: rgb(240, 255, 255); */
}

/* Enable text wrapping in file sidebar */
.nav-file-title-content, .nav-folder-title-content {
  white-space: normal;
}

/* Automically display horizontal line before header 2 */
.HyperMD-header-2::before {
  content: '';
  position: absolute;
  width: 100%;
  height: 3px;
  left: 0;
  top: 4px;
  display: block;
  clear: both;
  background-color: black;
}

/* Surrond mermaid graph with rectangle boder */
.mermaid {
  border: 1px solid black;
}

reference:

Make math equations in Obidian bigger

nullity — Wed, 20 Mar 2024 04:49:23 +0000

I find that math equations in Obsidian are too small to see clearly.

Here are the solutions,

Change `\frac` to `\dfrac`

"d" means "display"

This is a inline fraction $\frac{x^2-3x+2}{x^2-1}$ in the middle

This is a inline fraction $\dfrac{x^2-3x+2}{x^2-1}$ in the middle

Change `\binom` to `\dbinom`

This is a inline binomial $\binom{n}{m}$ in the middle

This is a inline binomial $\dbinom{n}{m}$ in the middle

General method (applicable to all functions)

Just add \displaystyle to the front of each function

note: it's also ok to add \displaystyle to \frac or \binom.
The effect of \displaystyle\frac equals to \drac
The effect of \displaystyle\binom equals to \dbinom

This is a inline sum $\sum_{k=1}^n \frac{1}{k+\frac{1}{k + \frac{1}{k}}}$ in the middle

Add \displaystyle before \sum

This is a inline sum $\displaystyle \sum_{k=1}^n \frac{1}{k+\frac{1}{k + \frac{1}{k}}}$ in the middle

Add \displaystyle before \sum and change each \frac to dfrac

This is a inline sum $\displaystyle\sum_{k=1}^n \dfrac{1}{k+\dfrac{1}{k + \dfrac{1}{k}}}$ in the middle

Edit CSS snippet

mjx-math {
  font-size: 140% !important;
}

Make it even bigger

Use \Huge, \huge, \LARGE, \Large or \large in front of the function that you want to enlarge.

This is a inline binomial $\huge \dbinom{n}{m}$ in the middle

Note:
Obsidian use MathJax to display math equations.
You can see MathJax - Supported TeX/LaTeX commands for more information.

Katex's syntax is very similar, the above methods apply to Katex too.

ref:

Install or uninstall gcc 13 on Ubuntu 20.04

nullity — Tue, 12 Mar 2024 10:30:57 +0000

Testing date: Mar 14, 2024

Install gcc-13, g++-13

sudo apt update
sudo apt install software-properties-common

sudo add-apt-repository ppa:ubuntu-toolchain-r/test
sudo apt update
sudo apt install gcc-13 g++-13

Add gcc-13 to gcc's alternatives

並設定 "切換 gcc 版本時會同時切換 g++, gcov 的版本"
At the time, the latest gcc provided by this ppa is 13.1

sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-13 131 --slave /usr/bin/g++ g++ /usr/bin/g++-13 --slave /usr/bin/gcov gcov /usr/bin/gcov-13

若之前沒有設定過 priority 大於 131 的 gcc 版本，則此時的 gcc 版本會自動切換至 gcc-13

Check gcc's version

At the time, the latest gcc provided by this ppa is 13.1

gcc -v

Uninstall gcc 13

sudo update-alternatives --remove gcc /usr/bin/gcc-13
sudo apt purge gcc-13 g++-13

ref

vlc 打不開影片 (Ubuntu 20.04)

nullity — Sat, 02 Mar 2024 08:30:02 +0000

Testing date: Mar 1, 2024
OS: Ubuntu 20.04

Problem

vlc 打開一個影片後，把影片關掉。接下來就再也打不開其他影片了。
但這時 vlc 還是在 background 執行。
這時只能下指令把 vlc kill 掉，才能再打開影片。

Solution

先把 background 的 vlc kill 掉。
打開 vlc，
Tools -> Preferences -> Video
把 Output 的 value，改成 XVideo output (XCB)
再點選 Save，就完成了

Ref

解法是從 Stack Exchange 找到的

Google Chrome 畫面會抖動跳動 (Ubuntu 20.04)

nullity — Sat, 02 Mar 2024 08:15:13 +0000

測試日期: Feb 20, 2024
OS: Ubuntu 20.04.3

網路上查了老半天都找不到有人遇過這種問題，這邊紀錄一下怎麼解決的

Problem

Google chrome 或是其他 browser (例如 Brave)，browser 畫面有時就會瘋狂抖動 (or 跳動 or 閃爍 or 抽動 or 左右橫跳) (多打一些關鍵字讓大家比較好 google 到)
尤其是在安裝 extension 的時候，更是瘋狂，讓你什麼 UI 都按不到
刪掉所有 extension，重裝 browser 都無法解決這個問題

Solution

打開 Tweaks，Fonts -> Scaling Factor 設為 1.00

但這樣 Ubuntu 的界面變得好小怎麼辦阿 (會遇到這個問題的人應該都覺得吧)
替代方案是把 Fonts 上面的 Text size 都調大一點
例如:
"Interface Text" 從 12 調到 14
"Document Text" 從 12 調到 14
"Monospace Text" 從 14 調到 16
"Legacy Window Titles" 從 12 調到 14

Forem: nullity

Obsidian can't view pdf

Problem

Solution

Step 1:

Step 2

Result

在 Linux 上安裝與使用 Notion Desktop

gdb trick: automatically display local variables when stops

Usage

gdb trick: automatically redirecct output to another terminal

Method

Some shortcomings

Install Ubuntu 20.04 on Virtualbox on Ubuntu 20.04

Problem: can't use sudo

Problem: Can't open terminal (worst thing ever)

Problem: The window is too small (like 800x800)

The time shown the top bar is in other langauges

pyenv local is overrited by pyenv global in vscode's terminal

Problem

Solution

Ubuntu 20.04 Screen tearing

Method 1

Method 2

Method 3

My working settings (for your reference)

ref

CSS snippets for Obsidian

Make math equations in Obidian bigger

Change \frac to \dfrac

Change \binom to \dbinom

General method (applicable to all functions)

Edit CSS snippet

Make it even bigger

Install or uninstall gcc 13 on Ubuntu 20.04

Install gcc-13, g++-13

Add gcc-13 to gcc's alternatives

Check gcc's version

Uninstall gcc 13

ref

vlc 打不開 影片 (Ubuntu 20.04)

Problem

Solution

Ref

Google Chrome 畫面會抖動跳動 (Ubuntu 20.04)

Problem

Solution

Change `\frac` to `\dfrac`

Change `\binom` to `\dbinom`

vlc 打不開影片 (Ubuntu 20.04)