User Management

• Add group sudo groupadd groupname
• Add user and specify group and home folder sudo useradd username -g groupname -d path_to_home_folder
• Add user home folder mkdir /path/to/home_folder && sudo chmod -R groupname:username /path/to/home_folder
• Set password for user sudo passwd username
• Add existing user to exising group sudo usermod -a -G groupname username
• Check user information id will show up username, primary group name and all group names
• Switch user su [username] if no username specified, default switch to supersuer
• Switch user and load simimar environment as if it’s a direct user login su - username
• Add user to sudoer list sudo adduser username sudo

Terminal/Console

• Delete one words before cursor <CTRL+w>
• Delete all words after cursor <CTRL+k>
• Move to head of line <CTRL+a>
• Move to end of line <CTRL+e>
• Clean line <CTRL+u>

• Clean screen <CTRL+l>

• Paste last parameter of last command <ESC+.>

• Generate random number echo $RANDOM

• Show full path ls -d $PWD/*

Network

• MAC refresh DNS sudo dscacheutil -flushcache or sudo discoveryutil udnsflushcaches
• Windows refresh DNS ipconfig /flushdns
• Linux refresh DNS sudo /etc/init.d/networking restart
• show public IP curl ifconfig.me
• show local DNS cat /etc/resolv.conf
• Resolve Agent admitted failure to sign using the key
  • generate private key and public key on machine ssh-keygen
  • (ssh-add ~/.ssh/id_dsa.pub) add content of local public key to remote machine’s ~/.ssh/authorized_keys
  • specify location of private key on local machine ssh-add ~/.ssh/id_dsa

File System

• Check total size of a folder du -shm
  • -s — summarize the sizes of all available files in a folder
  • -h — show resulted value in Human readable format
  • -m — show the result in Megabytes

VIM

• save read-only file :w !sudo tee %

• Change to uppercase visual + U

• Change to lowercase visual + u
• Toggle case visual + ~

Gnome

• Fix the problem that title bar dispear on ubuntu　compiz-decorator --replace

File Operation

• Batch moZipve files mv src_folder1 src_folder2 src_folder3 -t dest_folder
• Compress a folder into zip file zip -r filename.zip folder_name