# screen.txt
# Huan Chen, 2/3/2017
# updated 3/11/2017, add an example of taxi project

Linux screen utility
can be used for pair programming and more.
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Example: use screen to proceed "human VS human" mode in the chess project
User 1 logins to the linux server, then:
$ screen 	# start a screen session

User 2 logins to the same account using another terminal or computer, do:
$ screen -x 	# join a screen session

Now the two users type in their own terminals and can see each other's moves immediately

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Example: use screen to run taxi project's server and client programs in two different windows
# After entering a screen session, go to the directory containing "server"
./server 2001   # run the server program with port 2001

Hit Control-a S # split the screen (ctrl-a Q: unsplit screen)
Control-a <TAB> # move to the new split
Control-a c     # create a new window within the split
# change directory to path of "client"
./client laguna 2001 # run the test client with port 2001
# check the output result of both splits

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Other helpful screen commands
$ screen -ls 	# list all screen sessions
$ screen -d 	# detach a screen session
$ screen -r 	# reattach a screen session

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Window session management (performed within the screen):
Hit Control-a ? # display help of screen's usage
Control-a c     # create a window session
Control-a n     # go to next window
Control-a p     # go to previous window
Control-a [0-9] # go to window x (0~9)
Control-a k     # kill a window session
Control-a "     # show a list of windows created 
Control-a w     # show current window's name
Control-a \     # quit screen

Control-a d     # detach current screen session

Control-a x     # lock your screen with password (linux account password)

$ exit			# terminate a screen session

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A screen session can be protected with a password (when the other user joins the session using "screen -x", then the password is needed). To accomplish it, you need to edit ~/.screenrc

# start a screen session
$ screen

# after entering the screen session (":" means command line mode)
Type ctrl + a then type ":passwd" 

# after inputing the password
Type ctrl + a + [ to copy the hash value of the password (or use "mkpasswd" utility to generate the hash of password)

# add the following line (containing the generated hash value) to ~/.srceenrc:
# xxxxxxx is a one-way hash value of the real screen utility password
password xxxxxxx 

$ exit          # exit screen and start a new screen session

# join this session from another terminal to verify the prompt of the password

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A good programmer does not initiate a screen session inside a screen session!