===== GNU Screen ===== * [[#Introduction]] * [[#Starting Screen, detaching and reattaching]] * [[#Multiple windows]] * [[#Multiple sessions]] * [[#Splitting windows]] * [[#Sharing screen sessions]] * [[#.screenrc]] * [[#Cheat sheet]] * [[#Resources]] ==== Introduction ==== [[http://savannah.gnu.org/projects/screen/|Screen]] is a //terminal multiplexer//, i.e., it will let you have multiple virtual terminals in a single window. You will also be able to 1) //detach// a screen session, and then detach it in a later moment; 2) share screen sessions. In this tutorial ">$" indicates a terminal prompt (just for visual convenience). A Screen command is usually of the form //CTRL-a KEY//, i.e., you'll have to press the //CTRL// key along with //a//, followed by a generic KEY. (Screen's default escape key is //CTRL-a//) You'll need to be a [[http://sdf.org/?join#meta|MetaARPA]] member in order to use Screen on SDF If you want a //screencast// tutorial, type: >$ ttyplay /ftp/pub/users/jecxjo/howto/screen on a terminal connected to SDF. Alternatively, you can watch the screencast online at [[http://playterm.org/r/brief-screen-tutorial-1307563176|PlayTerm]]. ==== Starting Screen, detaching and reattaching ==== You can run screen by typing: >$ screen When you run it, a window with some copyright and some other info will show up, with //[Press Space or Return to end.]// at the bottom. OK, as it says, you can now press //Space// or //Enter//. You will then see your shell prompt and nothing else. That's fine: you can now run your programs as usual, the difference is that they will run under a Screen session. You can //detach// it by typing //CTRL-a d//. Screen will keep your session running. Now if you logout, then log back in, and type: >$ screen -r you'll see your terminal as you left it when you detached Screen! If you lost connection, or simply forgot to detach Screen, and want to resume your session by typing: >$ screen -d -r The //-d// flag will detach Screen, while //-r// will reattach. There are various types of //detach// and //reattach// flags. For instance, if you type the previous command and there was no screen session to be resumed, you'll get a //There is no screen to be detached.// message. In this case you'll probably need: >$ screen -d -R which will first create a new session (or rettach an existing one). ==== Multiple windows ==== You can create various windows under your Screen session, each one running their own program. When you are in a Screen session, typing: >$ screen will create a new window, leaving the previous window untouched, though not visible. Instead of typing //screen//, you can use the shortcut //CTRL-a c//. You can create as many windows as you want. You can swith between windows with //CTRL-a n// (next window) and //CTRL-a p// (previous window). It's also possible to select windows by number. Typing //CTRL-a 1// will open window number 1, //CTRL-a 2//, to window 2, and so on. How do you know what's a window number? Well, you can type //CTRL-a "// (yeah, that's a double quote). In that case a menu with a windows list will open. You can select a number and press enter to go to that screen. An easier way is to have a //hard status line// that shows you each window number. For doing this in a permanent manner, you'll have to create a //.screenrc// (Screen's customization file) in your $HOME directory and write in it the following lines: hardstatus alwayslastline hardstatus string "%{WK}%-LW %{Y.}%n%f* %t%{-}%+LW" (We will see what that crazyness means later.) For your .screenrc file to be read by Screen, you'll have to start a new session. BTW, a Screen session ends when the last window is closed. ==== Multiple sessions ==== It's possible to have various Screen sessions running, each one with their own set of windows open. If you started Screen by just typing //screen//, a new session is created. If you detach and type //screen// again, a new session will start. If you now type: >$ screen -ls it will give you a list of Screen sessions like this: 3340.pts-6.HOST (Detached) 4522.pts-8.HOST (Attached) 2 Sockets in /tmp/screens/S-YOU where HOST is the hostname and YOU is your username. You can reattach a screen session by name. Say for instance that you want to resume the //4522.pts-8.HOST// session. In this case you'll have to type: >$ screen -r 4522.pts-8.HOST Obviously //4522.pts-8.HOST// is not a very userfriendly session name. You can give a meaningful name by starting screen as: >$ screen -S mysession where //mysession// is the name you want to give to your session (e.g., //work//). ==== Splitting windows ==== It could be useful to split a window so that you can have two programs running on the viewport. In this case, type //CTRL-a S// and you'll see that the window will be split in two regions, with the one at the bottom blank. You can swith to it with //CTRL-a TAB// (TAB is the tab key) and then select a window by typing its number, or //p// (previous) or //n// (next), e.g., //CTRL-a 2//. You can always swith through regions with //CTRL-a TAB//. It's possible to split the window in more then two regions, each time by typing //CTRL-a S// If you want to split a window vertically, you'll have to either use a patch[1] or use a recent version of Screen. ==== Sharing screen sessions ==== The scenario is... ''HOSTUSER'' and ''SOMEUSER'' are both MetaARPA members logged into sverige. ''HOSTUSER'' wants to give ''SOMEUSER'' read only access to screen session of ''HOSTUSER''. ''HOSTUSER'' starts a screen session as normal. Only three commands are needed for basic read only access to the current active window. ''HOSTUSER'' types the following commands beginning with //CTRL-a :// each time (control and 'a' followed by a colon) CTRL-a:multiuser on CTRL-a:password none CTRL-a:aclchg SOMEUSER -w "#" ''SOMEUSER'' should exit screen first, then in the shell, type: >$ screen -r HOSTUSER/ ''SOMEUSER'' now has read only access to the active window in ''HOSTUSER'''s screen session at the time of attaching. ''HOSTUSER'' can verify ''SOMEUSER'' is attached by typing: //CTRL-a*// ''HOSTUSER'' can disconnect ''SOMEUSER'' by typing: //CTRL-a:acldel HOSTUSER// ''HOSTUSER'' can verify ''SOMEUSER'' is no longer attached by typing: //CTRL-a*// ''HOSTUSER'' can allow ''SOMEUSER'' access to additional commands. The following commands allow ''SOMEUSER'' to cycle backwards and forward through the windows and detach. ''HOSTUSER'' types: //CTRL-a:aclchg SOMEUSER +x next// //CTRL-a:aclchg SOMEUSER +x prev// //CTRL-a:aclchg SOMEUSER +x detach// === Some notes:=== - Screen version that was used "Screen version 4.00.03 (FAU) 23-Oct-06" - At the time of writing ( Tue Apr 17 23:01:50 IST 2012 ) all attempts at achieving the above read only functionality by editing .screenrc failed, usually resulting in SOMEUSER having FULL access to HOSTUSER's screen and shell account. - ''HOSTUSER'' might notice that screen resizes to fit the smaller of the two terminals. - After ''SOMEUSER'' is detached ''HOSTUSER'' might try //CTRL-aF//to resize the screen windows to fit the terminal. - For convenience and to reduce typing in screen ''HOSTUSER'' might want to have "multiuser on" and "password none" in .screenrc. ''HOSTUSER'''s screen is still private until a user is permitted to attach with aclchg. - ''HOSTUSER'' will hear/see lots of bells if ''SOMEUSER'' tries to type into the screen session. - ''HOSTUSER'' can check what window is being view by ''SOMEUSER'' by looking at the output of //CTRL-a*// - ''HOSTUSER'' might notice ''SOMEUSER'' appears to have rwx access in the output of //CTRL-a*// ...this is a bug or an undocumented feature. - ''SOMEUSER'' can remain attached even if ''HOSTUSER'' detachs. ==== .screenrc ==== As we previously saw, it is possible to customize Screen by writing settings in a file named //.screenrc// in your $HOME directory. We will now some useful Screen settings. === Avoiding the startup message == A full screen message with copyright and other stuff is usually displayed at startup. This can get annoying. In order to avoid it, you can put in your .screenrc the following: startup_message off === Keybindings === It's possible to bind keys so that when you type //CTRL-a KEY// Screen willl open a new window launching some program. For instance, if you write in your .screenrc file bind m screen -t mail 1 mutt each time you'll type //CTRL-a m// a new window (named //mail//) with mutt will be created. Be careful: when you bind a key, you'll overwrite Screen's defaults (e.g., we just lost the //lastmsg// key). ===== Cheat sheet ====== TODO ==== Resources ==== * http://aperiodic.net/screen/start * http://www.bangmoney.org/presentations/screen.html * SDF has some [[http://sdf.org/?tutorials/dotfiles|annotated dotfiles]]. ==== Notes ==== - http://fungi.yuggoth.org/vsp4s/ $Id: screen.html,v 1.8 2012/05/08 14:45:50 dickey Exp $