Some general configuration after Ubuntu20.04 installation (memo + updating)

Replace with domestic sources
Configure vim
Configure oh-my-zsh
ToggleAgent
Refresh WiFi
Shut down
Completely remove/disable snap
Solve the problem of frequent wifi disconnection

Replace with domestic sources

# 查看系统是否为focal
lsb_release -a
# 换源
sudo vi /etc/apt/sources.list
# 先后用v、gg、dd命令清空原有源，再粘贴以下源
deb https://mirrors.ustc.edu.cn/ubuntu/ focal main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/ubuntu/ focal main restricted universe multiverse

deb https://mirrors.ustc.edu.cn/ubuntu/ focal-security main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/ubuntu/ focal-security main restricted universe multiverse

deb https://mirrors.ustc.edu.cn/ubuntu/ focal-updates main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/ubuntu/ focal-updates main restricted universe multiverse

deb https://mirrors.ustc.edu.cn/ubuntu/ focal-backports main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/ubuntu/ focal-backports main restricted universe multiverse

# 更新
sudo apt update
sudo apt upgrade

Configure vim

sudo apt install vim
export EDITOR=vim
# 美化vim界面
sudo vim /etc/vim/vimrc
filetype on                              " 开启文件类型检测
colorscheme desert

set encoding=utf-8                       " 编码设置
set number                               " 显示行号
set smartindent                          " 智能缩进
set autoindent                           " 自动对齐

set smarttab
set tabstop=4                            " tab缩进
set shiftwidth=4                         " 设定自动缩进为4个字符
set expandtab                            " 用space替代tab的输入
set splitright                           " 设置左右分割窗口时，新窗口出现在右侧
set splitbelow                           " 设置水平分割窗口时，新窗口出现在底部

set nobackup                             " 不需要备份
set noswapfile                           " 禁止生成临时文件
set autoread                             " 文件自动检测外部更改
set clipboard=unnamed                    " 共享剪切板

set nocompatible                         " 去除vi一致性
set ambiwidth=double                     " 解决中文标点显示的问题
set nowrap                               " 不自动折行
set mouse=a                              " 使用鼠标
set mousehide                            " 输入时隐藏光标
set sidescroll=10                        " 移动到看不见的字符时，自动向右滚动是个字符

set sm!                                  " 高亮显示匹配括号
set hlsearch                             " 高亮查找匹配
set cursorline                           " 高亮显示当前行
set termguicolors                        " 启用终端真色

set showmatch                            " 显示匹配
set ruler                                " 显示标尺，在右下角显示光标位置
set novisualbell                         " 不要闪烁
set showcmd                              " 显示输入的命令

set laststatus=2                         " always show statusline
set showtabline=2                        " always show tabline
set vb t_vb=

" 设置代码折叠---------------------------------
"  set nofoldenable             " 启动 vim 时关闭折叠代码
"  set foldmethod=indent        " 设置语法折叠
"  setlocal foldlevel=99        " 设置折叠层数
"  nnoremap <space> za          " 用空格键来开关折叠

" 设置光标样式-------------------------------
let &t_SI = "\<Esc>]50;CursorShape=1\x7"
let &t_SR = "\<Esc>]50;CursorShape=2\x7"
let &t_EI = "\<Esc>]50;CursorShape=0\x7"

set completeopt=longest,menu             " 自动补全配置让Vim补全菜单行为跟IDE一致
set backspace=indent,eol,start           " 允许用退格键删除字符
let g:markdown_fenced_languages =['c', 'cpp', 'python', 'javascript']
set guifont=Hack_Nerd_Font_Mono:h16      " 设置字体和字体大小, 只对gui客户端起作用，终端使用需要修改终端字体和大小
" 禁止显示滚动条
set guioptions-=l
set guioptions-=L
set guioptions-=r
set guioptions-=R
" 禁止显示菜单和工具条
set guioptions-=m
set guioptions-=T
" %{
    
    "[fenc=".(&fenc==""?&enc:&fenc).((exists("+bomb") && &bomb)?"+":"")."]"} 显示文件编码
" %{
    
    &ff} 显示文件类型
set statusline=%1*%F%m%r%h%w%=\ 
set statusline+=%2*\ %Y\ \|\  
set statusline+=%3*%{\"\".(\"\"?&enc:&fenc).((exists(\"+bomb\")\ &&\ &bomb)?\"+\":\"\").\"\"}\ 
set statusline+=%4*[%l:%v]\ 
set statusline+=%5*%p%%\ \|\ 
set statusline+=%6*%LL\ 

hi User1 cterm=none ctermfg=gray ctermbg=darkgray
hi User2 cterm=none ctermfg=darkgrey ctermbg=gray
hi User3 cterm=bold ctermfg=darkgrey ctermbg=gray
hi User4 cterm=bold ctermfg=yellow ctermbg=gray
hi User5 cterm=none ctermfg=darkgrey ctermbg=gray
hi User6 cterm=none ctermfg=darkgrey ctermbg=gray

" 设置tab栏-------------------------------------------------
" 选中的tab颜色
hi SelectTabLine term=Bold cterm=Bold ctermfg=DarkYellow ctermbg=LightGray
hi SelectPageNum cterm=None ctermfg=DarkRed ctermbg=LightGray
hi SelectWindowsNum cterm=None ctermfg=DarkCyan ctermbg=LightGray
" 未选中状态的tab
hi NormalTabLine cterm=None ctermfg=Gray ctermbg=DarkGray
hi NormalPageNum cterm=None ctermfg=Gray ctermbg=DarkGray
hi NormalWindowsNum cterm=None ctermfg=Gray ctermbg=DarkGray
" tab栏背景色
hi TabLineFill term=reverse ctermfg=5 ctermbg=7 guibg=#6c6c6c

function MyTabLine()
    let s = ''
    for i in range(tabpagenr('$'))
        " select the highlighting
        let hlTab = ''
        let select = 0
        if i + 1 == tabpagenr()
            let hlTab = '%#SelectTabLine#'
            let s ..= hlTab . '⎡%#SelectPageNum#%T' . (i + 1) . hlTab
            let select = 1
        else
            let hlTab = '%#NormalTabLine#'
            let s ..= hlTab . "⎡%#NormalTabLine#%T" . (i + 1) . hlTab
        endif

        " the label is made by MyTabLabel()
        let s .= ' %<%{MyTabLabel(' . (i + 1) . ', ' . select . ')} '
        "追加窗口数量
        let wincount = tabpagewinnr(i + 1, '$')
        if wincount > 1
            if select == 1
                let s .= "%#SelectWindowsNum#" . wincount
            else
                let s .= "%#NormalWindowsNum#" . wincount
            endif
        endif
        let s .= hlTab . "⎦"
    endfor

    " after the last tab fill with TabLineFill and reset tab page nr
    let s ..= '%#TabLineFill#%T'

    " right-align the label to close the current tab page
    if tabpagenr('$') > 1
      let s ..= '%=%#TabLine#%999X░❨X❩'
    endif

    return s
endfunction

" Now the MyTabLabel() function is called for each tab page to get its label. >
function MyTabLabel(n, select)
    let label = ''
    let buflist = tabpagebuflist(a:n)

    for bufnr in buflist
        if getbufvar(bufnr, "&modified")
            let label = '+'
            break
        endif
    endfor

    let winnr = tabpagewinnr(a:n)
    let name = bufname(buflist[winnr - 1])

    if name == ''
        if &buftype == 'quickfix'
            let name = '[Quickfix List]'
        else
            let name = '[No Name]'
        endif
    else
        let name = fnamemodify(name, ':t')
    endif

    let label .= name
    return label
endfunction
set tabline=%!MyTabLine()
" 设置netrw-------------------------------------
let g:netrw_banner = 0         " 设置是否显示横幅
let g:netrw_liststyle = 3      " 设置目录列表样式：树形
let g:netrw_browse_split = 4   " 在之前的窗口编辑文件
let g:netrw_altv = 1           " 水平分割时，文件浏览器始终显示在左边
let g:netrw_winsize = 20       " 设置文件浏览器窗口宽度为25%
let g:netrw_list_hide= '^\..*' " 不显示隐藏文件 用 a 键就可以显示所有文件、 隐藏匹配文件或只显示匹配文件
" 自动打开文件浏览器
" augroup ProjectDrawer
"     autocmd!
"     autocmd VimEnter * :Vexplore
" augroup END
nnoremap <SPACE>ft :Lexplore<CR>    " 打开或关闭目录树
" 来源：知乎

Configure oh-my-zsh

sudo apt install zsh
chsh -s zsh
reboot
sudo apt install git
sh -c "$(curl -fsSL https://raw.github.com/robbyrussell/oh-my-zsh/master/tools/install.sh)"
git clone https://github.com/zsh-users/zsh-autosuggestions ${ZSH_CUSTOM:-~/.oh-my-zsh/custom}/plugins/zsh-autosuggestions
git clone https://github.com/zsh-users/zsh-syntax-highlighting.git ${ZSH_CUSTOM:-~/.oh-my-zsh/custom}/plugins/zsh-syntax-highlighting
plugins=(
  git
  extract
  zsh-autosuggestions
  zsh-syntax-highlighting
)
# theme half-life

ToggleAgent

( [ $(gsettings get org.gnome.system.proxy mode) != "'manual'" ] && gsettings set org.gnome.system.proxy mode "manual" && notify-send "代理已开启" ) || ( gsettings set org.gnome.system.proxy mode "none" && notify-send "代理已关闭" )
sh -c ~/.toggle_Proxy.sh

Refresh WiFi

sh -c 'nmcli radio wifi off && nmcli radio wifi on'

Shut down

gnome-session-quit --power-off

Completely remove/disable snap

Stop startup Snap service

sudo systemctl disable snapd.service
sudo systemctl disable snapd.socket
sudo systemctl disable snapd.seeded.service

Query and remove software installed by Snap

# 查询
snap list
#移除snap-store
sudo snap remove snap-store
#移除firefox
sudo snap remove firefox
#移除gnome-3-38-2004
sudo snap remove gnome-3-38-2004
#移除其他软件
#移除core20以及bare
sudo snap remove core20
sudo snap remove bare
#使用apt移除snapd
sudo apt autoremove --purge snapd
#移除snapd的一些目录
rm -rf ~/snap
sudo rm -rf /snap
sudo rm -rf /var/snap
sudo rm -rf /var/lib/snapd
sudo rm -rf /var/cache/snapd

Disable reinstallation of Snap

sudo sh -c "cat > /etc/apt/preferences.d/no-snapd.pref" << EOL
Package: snapd
Pin: release a=*
Pin-Priority: -10
EOL

Disable snap Firefox updates

sudo sh -c "cat > /etc/apt/preferences.d/no-firefox.pref" << EOL
Package: firefox
Pin: release a=*
Pin-Priority: -10
EOL

(Attachment) How to restore Snap

sudo rm /etc/apt/preferences.d/no-snap.pref
sudo rm /etc/apt/preferences.d/no-firefox.pref
sudo rm /etc/apt/preferences.d/mozillateam-firefox.pref
sudo apt update
sudo snap install snap-store
sudo apt install firefox

Solve the problem of frequent wifi disconnection

Kill nameserver 127.0.0.53 loopback

sudo apt install unbound
sudo systemctl stop systemd-resolved
sudo systemctl disable systemd-resolved
sudo rm -rf /etc/resolv.conf
sudo vim  /etc/NetworkManager/NetworkManager.conf

Add under [main]

dns=unbound

Set up custom DNS

Turn off power management

sudo vim /etc/NetworkManager/conf.d/default-wifi-powersave-on.conf
# 将3改2
wifi.powersave = 2
iwconfig #查看wifi power management是否为off状态，并记下当前网卡名
sudo iwconfig 此处替换成当前网卡名 power off

Increase lcp-echo-failure time

sudo vim /etc/ppp/options
# 把默认的lcp-echo-failure 4改为lcp-echo-failure 30
lcp-echo-failure 30

Turn off connection check.
Go to Settings - Privacy - Connection Status - (Turn off) Connection Check.

Conclusion: Go through the above four steps in one round. After restarting the computer, the connection will not be dropped for the time being. Check the effect again after a while.