Misc Records

• connect to another tty

  # Print the file name of the terminal connected  to  standard input.
  tty
  # connect to it
  script -f /dev/tty1
  

• tar

  # sudo to keep permission
  # pack
  sudo tar -cvf mysql.tar mysql
  # unpack
  sudo tar -xvf www.tar -C .
  

• manually update zsh completion cache

  rehash
  

• zsh completion

  rm  ~/.zcompdump; compinit
  

• Generate random password

  # use package pwgen
  pwgen 8 # generate with length 8
  

• find file in a certain day

  # more to see option `-newerXY` in `man find`
  sudo find /var -type d -newermt 2019-08-30 ! -newermt 2019-08-31 -print 2>/dev/null
  

• find dhcp server

  sudo nmap --script broadcast-dhcp-discover -e eth0
  # for dhcpv6
  sudo nmap -6 --script broadcast-dhcp6-discover -e eth0
  

• find out the MAC of a given IP

  sudo arping -I enp4s0 -c1 172.24.68.179

• find hostname by IP

  # netbios names
  nmblookup -A <ip>
  # from dns server
  nslookup <ip>
  

• Using the KDE Wallet to store ssh key passphrases ssh-add

• zip文件名乱码

  unzip -O cp936 filename
  

• run as root in Gui

  # in .desktop
  # see https://wiki.archlinux.org/index.php/Sudo#kdesu
  X-KDE-SubstituteUID=true
  

• visudo导致sudo无法使用时

  # 前提是你已经安装相应的 policykit-1-gnome 或者 polkit-kde-agent
  /usr/lib/policykit-1-gnome/polkit-gnome-authentication-agent-1 &
  pkexec visudo
  # 否则就只能重启进入recovery或者livecd修复
  

• Clean journal

  journalctl --rotate --vacuum-time=1d
  

• rsync with root

  rsync -avPpr -e "ssh" --rsync-path="sudo rsync"  fancy@172.24.71.53:/opt/cudnn/cudnn-10.1-linux-x64-v7.5.0.56   /opt/cudnn/
  

• runtime path

  # refer https://en.wikipedia.org/wiki/Rpath
  # see RPATH or RUNPATH
  readelf -d binary-or-library
  # see `man chrpath`
  chrpath -l binary-or-library
  

• iptables LOG in netns

  sysctl -w net.netfilter.nf_log_all_netns=1
  

Server

• List human users

  cut -d: -f1,3 /etc/passwd | egrep ':[0-9]{4}$' | cut -d: -f1
  

• disable or enable users

  # disable
  chage -E 0 <user>
  # enable
  chage -E -1 <user>
  

Video related

• You-Get

  # bilibili, 下载  		
  you-get <url>
  # bilibili, 批量下载  
  you-get --playlist <url>
  

• video info

  ffprobe -hide_banner <video>
  

• show videos codec

  ffprobe -v error  -select_streams v:0   -show_entries stream=codec_name <url>
    
  find . -type f -print  -exec sh -c "ffprobe -v error  -select_streams v:0   -show_entries stream=codec_name '{}' |grep codec|sed -e 's/codec_name=//'" \;
  

• flv to mp4 with loss

  # single
  ffmpeg -i input.flv -codec copy output.mp4
  # loop way
  for f in *.flv
  do
  ffmpeg -i "$f" -codec copy "${f/.flv/.mp4}"
  done
  

NeoVIM

显示行号，显示空白字符

:set nu # show line number
:set list # show space
:noh # turn off highlighting until the next search

Vim < 8.1.1365， Neovim < 0.3.6 中存在漏洞，modeline 在root情况下默认关闭

/etc/xdg/nvim/sysinit.vim
-------------------------------
set modeline

ZSH

^left ^right Backward or forward one word

^u Clear whole line

^k Clear to end of line

^w Delete one word backward

^l Clear screen

^x u Undo last change

^y Yank

pacman

• Remove orphan package, repeat the cmd multi times

  sudo pacman -Ru $(pacman -Qdtq)
  

cgroup

systemd-cgls systemd-cgtop

journal

journalctl -f -u <service>

journalctl -b <boot_number>

Exit stuck sessions

ssh includes the escape character ~ by default. The command ~. closes an open connection and brings you back to the terminal.