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GNU Screen is a simple but at the same time flexible and programmable windows manager. It is often called terminal multiplexer, but the key functionality of screen is in the area of windows management: creation, destruction and resizing of windows. For example it can split the console screen horizontally and display two windows at the same time. Screen is a Unix program (Cygwin version exists and is quite usable). For good Windows terminal emulator see Teraterm
In addition to the ability to run many shell processes in a single terminal, screen provides classic windows management capabilities -- the ability to split terminal into regions (horizontal stripes of varying length, each containing its own session. What is also important is that like VNC screen provides the ability to detach the terminal emulator from the running programs and then reattach the same or new terminal to them.
This feature is enabled by default.
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An important feature of screen is that like VNC it provides the ability to detach the terminal emulator from the running programs and then reattach the same or new terminal to them. |
This means screen will keep shells and programs running in all windows that you opened even if you accidentally disconnected from the remote server or closed the terminal emulator. Like VNC screen also permits to share a terminal (in read-only mode) with someone else in real time. This permits to collaborate on a project by several remote users located in different places. It also frees administrator from waiting until a particular task ends. He/she can be connected to any number of servers, start a task, detatch from the task, and the task keeps running. Then reattach later, check the status and intervene of needed. That means that you can start a job at the office and check for it completion at home.
Screen has a certain architectural affinity to the orthodox file managers (OFM ), especially deco as well as orthodox editors like vi and THE (the power of command line).
Like in vi in screen you have to hit certain prefix to get to command line. The default prefix is Ctrl-A. For example Ctrl-A,C will open window.
This availability of command line operations and related scriptability via screenrc file makes screen attractive to system administrators who value blend of power and simplicity provided by "orthodox" tools. Like in all orthodox utilities there is an extensive set of commands (mini-language) that can used to modify the behavior of screen.
Ctrl-a is called attention/command key and is similar to Esc in vi (you also can change Ctrl-A to another sequence, if you wish). This sequence presuppose that you are using Sun keyboard (with Ctrl instead of Caps lop) or switched Ctrl and CapsLock keys (in Windows you can use Install RandyRants SharpKeys -- registry hack that permits remapping CapsLock to Alt. ).
If the colon (":") is entered after it, then screen switches to command mode and you'll see a highlighted colon prompt at the bottom of the screen. After that, like in vi, you can enter commands that change the behavior of the screen and modify its current configuration. For example you can open and close windows, change size of windows, etc. For example you open new window also by typing command
Ctrl-A: screen
which is equivalent to the shortcut Ctrl-A,C that we discussed above.
So shortcut Ctrl-A,C and command Ctrl-A: screen are synonyms. This is just an association that is defined in .screenrc file - screen's dotfile. File .screenrc is a list of commands which are executed at startup. While by default screen is using the name .screenrc you can start screen using arbitrary screen's dotfile using option -c, for example
screen -c ~myhome/.screenrc_`uname`
This example demonstrated that you can have multiple .screenrc files and use the one that suits current environment (for example Linux, AIX, Solaris, etc) and the task in hand.
You can also execute predefined sequences of screen commands stored in the files (screen scripts) using the command source. One common application is the execution of the set of command creating a particular combination of windows and loading particular applications into each window. For example, you can load Perl in debugging mode on one window, vi in another and Perl POD browser in the third creating poor man IDE environment. For example
source .screenrc_perl
or
source ~myhome/perl.screenrc
That provides you with the flexibility to have several predefined sets of windows working on a particular task, the capability that improves your productivity dramatically as you can polish the arrangement and gradually connect a set of useful shortcuts as you gain experience with the environment (in the example above, working with Perl). System administrators can (and should) have a custom part of configuration encoded for particular hosts (that's the way I use screen at work) :
source ${HOME}/${HOST}.screenrc
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Due to availability of command line interface and scriptability Screen can be considered to be a member of "orthodox" family of utilities which include orthodox file managers (mc, FAR, etc) and orthodox editors (vim, Xedit, THE, etc). Command line can be activated with Ctrl-A: after that you can enter any command from the screen command set to modify behavior of the screen or execute sets of commands (screen script) from particular file using command source. |
A typical and probably the simplest application of this capability is to launch a predefined set of windows at screen startup., for example:
source $HOME/.screenrc # read in your normal screenrc
screen top # now start opening windows
screen -t irc epic # with the -t option it's possible to set the window title
screen -t mail 8 mutt # you can also specify the window number to launch in
screen -t messages 9 tail -f /var/log/messages
In X-windows world screen inspired several minimalist windows managers which usually are bungled with linux mini-distributions. Classic example of this genre is ratpoison (the name suggest that it is one of the few that not support mouse "out of principle" ;-).
Screen is portable and is an almost a standard utility on all flavors of Unix. It is often preinstalled by default in Linux distributions (for example, Suse 10). And it is easily installed in Solaris, AIX and HP-UX. For example Solaris 10 package can be found on sunfreeware.com:
screen-4.0.2-sol10-intel-local.gz Screen provides an ANSI/vt100 terminal emulator, which can multiplex up to 10 pseudo-terminals - installs in /usr/local. There are further configuration steps in the /usr/local/doc/screen/INSTALL. The etc and terminfo directories containing other relevant files are in /usr/local/doc/screen. The screen package may also require that you install the ncurses package.
Using it, you can run any number of console-based applications -- interactive command shells, curses-based applications, text editors, etc. -- within a single terminal. Many administrators who use screen open a dozen or even more sessions.
Screen can be used in two ways (you can use both local and remote screen instances simultaneously by changing control character in local to say Ctrl-\ via .screenrc, see below):
A nested master-slave invocation of screen is also possible, but it is unclear how practical it is. See Jason White page and my screenrc and my slave screenrc by Tim Chambers. Here is how he explained this method in Slashdot post:
You run an "outer" screen session (the "slave" session) that in turn runs an "inner" (or "master") session. You use the regular escape sequence (Ctrl-A d) to detach from the master, and you map Ctrl-^ to be the control key for the slave session. If you press Ctrl-^ while using screen this way, you'll see one process in the slave session. It's running ssh-agent. That's the key to using ssh with screen. The slave's only purpose is to run ssh-agent. The master runs as a child of that. Consequently, all shells in the master session are running under the ssh-agent. Just run ssh-add from any master shell, and then all shells have your ssh identity.
As we mentioned above, after starting screen you need to open windows using the command Ctrl-a c. Every window in screen is identified by a unique number. The first window is usually numbered 0 (you can change this to one if you do not like counting from zero). For each created windows screen starts default shell. After that user for example can open remote session to a particular server and rename it to simplify recognition after switching to another (an optimal typical number of windows for one screen instance is around a dozen). You can use multiple screen instances each with its own set of servers to connect (DMZ servers, database servers, etc).
Minimum set of commands necessary to use screen productively includes just five commands:
- Ctrl-a c to create a new window (Ctrl-a N -- lists the number of the active windows)
- Ctrl-a <number> to switch between them (Ctrl-a n, Ctrl-a p or Ctrl-a Ctrl-a will work too providing previous and next windows, but are less convenient and there are two of them instead of one)
- Ctrl-a " (windows) Show a list of active windows. You can navigate this list with the arrow keys (or vi-style, with j and k), and pick a window to activate by pressing Enter when it's highlighted. As this is one of the most often used commands you will be better off redefining this command as Ctrl-a space (see .screenrc examples on how to do that).
- Ctrl-a d. detach from current session. You can also detach just by closing the terminal emulator that contains the session. Neither of these actually end your session. All they do is unbind your session from the current terminal. All of the programs you started running within screen are still running. To reattach type screen -r from the command prompt
- Ctrl-a Ctrl-\ (quit) Kill all windows and terminate screen. You can close individual window by exiting shell with command exit.
There are also several more advanced features that can improve your productivity. Among them I would like first of all mention regions.
Regions can dramatically improves your productivity in pure command line
environment. This feature turns screen in rudimentary windows manager able
to create "strips" non-overlapping horizontal zones each of which corresponds
to a separate shell window. To split the screen into two regions just press
C-a S. The current window will split into two separate areas
with the bottom area blank. To switch to the bottom part press
C-a [Tab]. If you need to create a new shell in the new window,
so press C-a c. If you want to see one of the existing sessions
press Ctrl-a " and select
the necessary session. You
can create more regions by pressing C-a S again: each time
the current "strip" will be split into two. Tabs display the active region
shell name in its title bar. You can also switch between tabs being in a
region, so e.g.: you have 4 tabs and 2 regions. Each region can display
one of these tabs. A nice trick is that upper region can react on the change
of the particular environment variable and display either file you are editing
or the listing of the current directory. This arrangement is close for the
OFM paradigm. You can change the size of each region by entering resize
[size], where size is the number of lines.
| The key additional feature of Screen that you need to master after mastring basic commands is split command. |
Here is slightly more elaborate set of commands, which we will call Level 1 command set. It includes regions-related commands:
- Ctrl-a ' (select)
- Prompt for a window name or number to switch to.
- Ctrl-a " (windowlist -b)
- Present a list of all windows for selection.
- Ctrl-a 0 (select 0)
- ... ...
- Ctrl-a 9 (select 9)
- Ctrl-a - (select -)
- Switch to window number 0 - 9, or to the blank window.
- Ctrl-a tab (focus)
- Switch the input focus to the next region.
- Ctrl-a Ctrl-a (other)
- Toggle to the window displayed previously.
Note that this binding defaults to the command character typed twice, unless overridden. For instance, if you use the option "-e]x", this command becomes "]]".- Ctrl-a a (meta)
- Send the command character (Ctrl-a) to window. See escape command.
- Ctrl-a A (title)
- Allow the user to enter a name for the current window (useful fo naming each window according to the purpose (for example each can represent a different directory).
- Ctrl-a b
- Ctrl-a Ctrl-b (break)
- Send a break to window.
- Ctrl-a B (pow_break)
- Reopen the terminal line and send a break.
- Ctrl-a c
- Ctrl-a Ctrl-c (screen)
- Create a new window with a shell and switch to that window.
- Ctrl-a C (clear)
- Clear the screen.
- Ctrl-a d
- Ctrl-a Ctrl-d (detach)
- Detach screen from this terminal.
- Ctrl-a D D (pow_detach)
- Detach and logout.
- Ctrl-a f
- Ctrl-a Ctrl-f (flow)
- Toggle flow on, off or auto.
- Ctrl-a F (fit)
- Resize the window to the current region size.
- Ctrl-a Ctrl-g (vbell)
- Toggles screen's visual bell mode.
- Ctrl-a h (hardcopy)
- Write a hardcopy of the current window to the file "hardcopy.n".
- Ctrl-a H (log)
- Begins/ends logging of the current window to the file "screenlog.n".
- Ctrl-a i
- Ctrl-a Ctrl-i (info)
- Show info about this window.
- Ctrl-a k
- Ctrl-a Ctrl-k (kill)
- Destroy current window.
- Ctrl-a l
- Ctrl-a Ctrl-l (redisplay)
- Fully refresh current window.
- Ctrl-a L (login)
- Toggle this windows login slot. Available only if screen is configured to update the utmp database.
- Ctrl-a m
- Ctrl-a Ctrl-m (lastmsg)
- Repeat the last message displayed in the message line.
- Ctrl-a M (monitor)
- Toggles monitoring of the current window.
- Ctrl-a space
- Ctrl-a n
- Ctrl-a Ctrl-n (next)
- Switch to the next window.
- Ctrl-a N (number)
- Show the number (and title) of the current window.
- Ctrl-a backspace
- Ctrl-a h
- Ctrl-a p
- Ctrl-a Ctrl-p (prev)
- Switch to the previous window (opposite of Ctrl-a n).
- Ctrl-a q
- Ctrl-a Ctrl-q (xon)
- Send a control-q to the current window.
- Ctrl-a Q (only)
- Delete all regions but the current one.
- Ctrl-a r
- Ctrl-a Ctrl-r (wrap)
- Toggle the current window's line-wrap setting (turn the current window's automatic margins on and off).
- Ctrl-a s
- Ctrl-a Ctrl-s (xoff)
- Send a control-s to the current window.
- Ctrl-a S (split)
- Split the current region into two new ones.
- Ctrl-a t
- Ctrl-a Ctrl-t (time)
- Show system information.
- Ctrl-a v (version)
- Display the version and compilation date.
- Ctrl-a Ctrl-v (digraph)
- Enter digraph.
- Ctrl-a w
- Ctrl-a Ctrl-w (windows)
- Show a list of window.
- Ctrl-a W (width)
- Toggle 80/132 columns.
- Ctrl-a x
- Ctrl-a Ctrl-x (lockscreen)
- Lock this terminal.
- Ctrl-a X (remove)
- Kill the current region.
- Ctrl-a z
- Ctrl-a Ctrl-z (suspend)
- Suspend screen. Your system must support BSD-style job-control.
- Ctrl-a Z (reset)
- Reset the virtual terminal to its "power-on" values.
- Ctrl-a . (dumptermcap)
- Write out a ".termcap" file.
- Ctrl-a ? (help)
- Show key bindings.
- Ctrl-a Ctrl-\ (quit)
- Kill all windows and terminate
screen.- Ctrl-a : (colon)
- Enter command line mode.
- Ctrl-a [
- Ctrl-a Ctrl-[
- Ctrl-a esc (copy)
- Enter copy/scrollback mode.
- Ctrl-a ] (paste .)
- Write the contents of the paste buffer to the stdin queue of the current window.
- Ctrl-a {
- Ctrl-a } (history)
- Copy and paste a previous (command) line.
- Ctrl-a > (writebuf)
- Write paste buffer to a file.
- Ctrl-a < (readbuf)
- Reads the screen-exchange file into the paste buffer.
- Ctrl-a = (removebuf)
- Removes the file used by Ctrl-a < and Ctrl-a >.
- Ctrl-a , (license)
- Shows where screen comes from, where it went to and why you can use it.
- Ctrl-a _ (silence)
- Start/stop monitoring the current window for inactivity.
- Ctrl-a * (displays)
- Show a listing of all currently attached displays.
Here are some examples of keyboard bindings:
bindkey -d # Show all of the default key bindings. The application mode entries are marked with [A].bindkey -k k1 select 1 # Makes the "F1" key switch to window one.bindkey -k F1 command # Makes the F11 (not F1!) key an alternative screen escape (besides `Ctrl-a').
You can also easily change Ctrl-A (the default attention/command key sequence) to another sequence. This can be done either via putting command escape into .screenrc or via a switch when you start screen.
If you invoked screen by using "screen
-e ^Ww" you can see that ^W
became attention/command key combination. So
^W-? gets the Help screen.
Ctrl-A and then ? no longer worked.
escape xy
Set the command character to x and the character generating a literal command character (by triggering the "meta" command) to y (similar to the -e option). Each argument is either a single character, a two-character sequence of the form "^x" (meaning "Ctrl-x"), a backslash followed by an octal number (specifying the ASCII code of the character), or a backslash followed by a second character, such as "\^" or "\\". The default is "^Aa".
For example if you add
escape ^\\
into the .screenrc you will see that ^\ became attention key sequence instead of default ^A.
It is also important to make screen more user friendly. In order better see what open windows you have you can do it by adding the following lines to .screenrc :
1 hardstatus alwayslastline
2 hardstatus string '%{= kG}[ %{G}%H %{g}][%= %{=
kw}%?%-Lw%?%{r}(%{W}%n*%f %t%?(%u)%?%{r})%{w}%?%+Lw%?%?%= %{g}][%{B}
%Y-%m-%d %{W}%c %{g}]'
In his paper Screen Tips & Tricks Łukasz Olender suggests several other variants:
But so as not to get lost in these windows, I suggest you create tabs similar to those found in web browsers. You can do this by writing to your configuration file
~/.screenrcone of the following codes:hardstatus alwayslastline hardstatus string '%{= mK}%-Lw%{= KW}%50>%n%f* %t%{= mK} %+Lw%< %{= kG}%-=%D %d %M %Y %c:%s%{-}'or
hardstatus alwayslastline hardstatus string '%{= kG}[ %{G}%H %{g}][%= %{= kw}%?%-Lw%?%{r} (%{W}%n*%f%t%?(%u)%?%{r})%{w}%?%+Lw%?%?%= %{g}][%{B} %d/%m %{W}%c %{g}]'or
hardstatus alwayslastline hardstatus string '%{gk}[ %{G}%H %{g}][%= %{wk}%?%-Lw%?%{=b kR} (%{W}%n*%f %t%?(%u)%?%{=b kR})%{= kw}%?%+Lw%?%?%= %{g}][%{Y}%l%{g}] %{=b C}[ %m/%d %c ]%{W}'With the first code each tab will have a number, a name plus time and date. The second one will give you tabs that will be created in the center and the active tab will be highlighted in red and also have the hostname displayed. The last code will additionally display the processor usage. You can create your own codes but it is a rather specialized task - I refer you to the system manuals for more information.
You can combine ideas from those into you own status line that suits your need. But in any case it is important to improve visibility of windows by using this capability of screen.
Dr. Nikolai Bezroukov
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September 11, 2009 | ServerWatch.com
Monitor a window for output: Hit Ctrl-A Shift-M when in window 1, and then flip to window 2 (with Ctrl-A N), and you'll be notified in window 2 when there's output in window 1. This is useful if you're running a job that takes a long time; no need to keep flipping between windows. You can also monitor for silence with Ctrl-A _. This is useful if you're running a compile job or something else that outputs a lot of stuff when it's running successfully.
Selected comments
September 8, 2009 | ServerWatch.com
To enter copy mode in screen, hit Ctrl+A, then [. You can now use the arrow keys, or vim-like keybindings, to move around the screen. 0 gets you to the start of a line, and $ to the end of a line.
- When you've reached the point where you want to start the copy, hit Enter.
- Move the cursor to the end point of your selection (you'll see what you're copying highlighted), and then hit Enter again.
- Now move the cursor to wherever you want to paste the selection (you can move to another screen within your session), and hit Ctrl+A ] to paste the selection.
You can also use Ctrl+A > filename to paste the selection to a filename and Ctrl+A < filename to read a file into the selection buffer so you can then paste it out again using Ctrl+A ].
When in copy mode, you can also use screen's scrollback feature (i.e., you can scroll back upward past the top of the currently displayed text) and the search function.
Use ? to search backward. This is probably what you want initially, as you'll be starting by default from the bottom of the scrollback.
/ searches forward.
Bear in mind that the default scrollback is only 100 lines. To increase this, add a line to your ~/.screenrc:
defscrollback 1000
created by Eric Van DewoestineScreenshot: http://eclim.sourceforge.net/_images/screenshots/vim/gnu_screen_shell.png
Note: gvim is not supported. You must be running vim in a console.
Currently tested on Linux and cygwin, but should work on any unix based
platform where screen is supported (OSX, BSD, Solaris, etc.). Note that
in my testing of cygwin, invocations of screen were significantly slower
and less fluid than on Linux.
This plugin aims to simulate an embedded shell in vim by allowing you to
easily convert your current vim session into one running in gnu screen
with a split gnu screen window containing a shell, and to quickly send
statements/code to whatever program is running in that shell (bash,
python, irb, etc.).
Commands:
:ScreenShell [cmd] - Opens the split shell by doing the following:
1. save a session file from your currently running vim instance
(current tab only)
2. start gnu screen with vim running in it
3. load your saved session file
4. create a lower gnu screen split window and start a shell
5. if a command was supplied to :ScreenShell, run it
Ex. :ScreenShell ipython
Note: If you are already in a gnu screen session, then only steps
4 and 5 above will be run.
:ScreenSend - Send the visual selection or the entire buffer contents to
the running gnu screen shell window.
:ScreenQuit - Save all currently modified vim buffers and quit gnu
screen, returning you to your previous vim instance
running outside of gnu screen
Note: :ScreenQuit is not available if you where already in a gnu
screen session when you ran :ScreenShell.
Note: By default, if the gnu screen session was started by
:ScreenShell, then exiting vim will quit the gnu screen session
as well (configurable via g:ScreenShellQuitOnVimExit).
An example workflow may be:
Open a python file to work on:
$ vim something.py
Decide you want to run all or pieces of the code in an interactive
python shell:
:ScreenShell python
Send code from a vim buffer to the shell:
:ScreenSend
Quit the screen session and return to your original vim session:
:ScreenQuit
or
:qa
Gotchas:
- While running vim in gnu screen, if you detach the session instead of
quitting, then when returning to the non-screen vim, vim will complain
about swap files already existing. So try to avoid detaching.
- Not all vim plugins support saving state to or loading from vim
session files, so when running :ScreenShell some buffers may not load
correctly if they are backed by such a plugin.install details
Download the script and put it in your plugin directory (~/.vim/plugin).
screen is a very useful program which in effect gives you multiple console screens in the same window. It's handy if you're using a console rather than an xterm, or if you're connected to another machine, as it means you can do multiple things at once without having to move to another console or open another ssh connection. Even more useful if you're working remotely: If your connection falls over while you're still in a screen session, you can ssh back to the machine and reattach the screen (with screen -r) and get straight back to where you were, rather than having to start over.
You can also manually detach the screen, with screen -d (detach screen), or by hitting Ctrl-A then D while in a screen session. This leaves the screen running in the background, and it can be useful for running background jobs. Or you can leave a screen session connected to another machine: Run screen before you open the ssh session, then instead of logging out when you're done, detach the screen, and then just reattach it (screen -r) when you need to connect to that machine again. The downside of this is that it does have security implications!
» xclip: Command-Line Clipboard
» Make It Snappy With Vim
» Unicode Characters in Vim
Read All Tips of the TradeA final screen trick enables you to remotely look over a user's shoulder if you're trying to fix a problem.
Log on to the user's machine as him, then type
Then, get him to type
and he'll join your screen session. After this, whatever he does will be replicated on your screen (and vice versa). ('debug' is the identifier; any other name would also be fine.) This can save a lot of time when trying to track down a problem or to explain a solution!
tmux is a "terminal multiplexer". It allows a number of terminals (or windows) to be accessed and controlled from a single terminal. It is intended to be a simple, modern, BSD-licensed alternative to programs... such as GNU screen
Customizing the configuration file
Screen keeps its configuration file in the same vein that many applications do: in a dot file in your user’s home directory. This file is aptly named .screenrc. In my experience, most people use ~/.screenrc to do two things:
- Make a hardstatus line. This is basically a line at the bottom of the screen that lists your current terminal and all opened ones. It can also display the system clock and the hostname.
- Default screens on startup. It’s quite nice to have your IRC connection, mail client, and default SSH connections auto-start for you!
The lines below are numbered for reference. Your config file should not have numbered lines.
1 hardstatus alwayslastline 2 hardstatus string '%{= kG}[ %{G}%H %{g}][%= %{=kw}%?%-Lw%?%{r}(%{W}%n*%f%t%?(%u)%?%{r})%{w}%?%+Lw%?%?%= %{g}][%{B}%Y-%m-%d %{W}%c %{g}]' 3 4 # Default screens 5 screen -t shell1 0 6 screen -t shell2 1 7 screen -t server 2 ssh me@myserverOn lines 1 and 2, you are setting the hardstatus. Line 1 makes the hardstatus always show up as the last line. Line 2 is about what will be shown in the hardstatus line. In this case you will see something like so at the bottom:
Using Screen
From your ssh login prompt enter the following command
screen
or
screen -S 1
and select your profile option.
-S sessionname – When creating a new session, this option can be used to specify a meaningful name for the session. This name identifies the session for “screen -list” and “screen -r” actions.
... ... ...
Customise Screen-profiles
If you look in the bottom right corner you’ll see there’s an “F9 Menu” you can press F9 to reconfigure your screen profiles. Once it opens you should see similar to the following screen here you can see list of changes you can do
Sample screenshots for screen-profile options
[Feb 12, 2004] Curiosity is bliss Essential utility screen
Screen is a command line utility that comes with lots of Unix variants (including Linux). It is a bit hard to describe and to discover. It provides two main features: multiplexing a terminal and detaching/re-attaching sessions.
I originally got shown this by my "System programming" TA, when I asked him if I could disconnect X11 application from one terminal and have them re-open (in the same state) onto another terminal. It turns out this is possible for X11 applications (see xmove or xmx, proxy-based redirections, or guiEvict <via sweetcode>, described in this paper). But "screen" although limited to text applications is so useful that I dropped my search for its X11 equivalent.
Multiplexing: If you start a remote shell (say SSH) but want to do more than one thing at a time, you may want to open more sessions, but you can also use screen. It allows you to switch between multiple shells on the same connection.
You need to first run "screen", then use "Ctrl-A Ctrl-C" (control A, control C) to create a new shell, and you now can switch between shells with "Ctrl-A Ctrl-*" where * is the number for you shell (for ex, use "Ctrl-A Ctrl-1" to switch to shell 1).Session migration: Let's say you need to disconnect from that session, but you want to continue it from another computer. You can use "Ctrl-A Ctrl-D" to detach screen. All the shells will be maintained, and you can reconnect to the remote machine again and type "screen -R" to re-attach to the original session. This is also very useful in can the connection is lost by accident.
macosxhints.com - Use 'screen' as a serial terminal emulator
I often have to do router configuration via a console port, so I use a Keyspan Serial Adapter to get access. Two problems then present themselves:Solution: Use screen, Terminal, and a little AppleScripting.
- ZTerm is a horrible Mac OS X app. It hasn't been updated in five years or so, and isn't a Universal Binary. The developer doesn't seem in any hurry to rectify the situation. It is not worth the shareware fee in its current form.
- Minicom requires installation of Fink or MacPorts and is overly complex.
First, launch Script Editor and type/paste in the following code:Compile and save as an app from within Script Editor, and you have a double-clickable application to launch a serial Terminal session. You may want to customize this slightly -- you can change the screen colors or number of columns or rows. You may also need to customize the screen command with a different device name if you are using something other than the Keyspan Serial Adapter (do an ls tty* of the /dev/ directory to get the right name).tell application "Terminal" do script with command "screen /dev/tty.KeySerial1" set number of rows of window 1 to 100 set number of columns of window 1 to 80 set background color of window 1 to "black" set normal text color of window 1 to "green" set custom title of window 1 to "SerialOut" end tell
screen uses Control-A to take commands directed to it. So type Control-A followed by Control-\ to exit your screen session. If you fail to do this and exit a Terminal session, you'll leave the screen session alive and the serial resource unavailable until you kill the screen session manually. man screen will show you further commands to send to a screen session.
If anyone can reply with a link to a tutorial on how to wrap an interactive Unix App in Cocoa, that would be the next step -- it would be nice to do this without involving Terminal. If you prefer to use Minicom, you could still use the AppleScript to wrap it into a nice launchable app -- use this older hint to find the right command line commands.
Solaris Packages
Solaris Package Archive -- GNU screen 3.9.4
GNU screen 3.9.4 provides you with an ANSI/vt100 terminal emulator, which can multiplex up to 10 pseudo-terminals. On startup, it executes $SHELL in window 0. Then it reads $HOME/.screenrc to learn configuration, keybindings, and possibly open more windows. GNU screen has the ability to detach from your virtual screens and re-attach at a later time.
Email To
Send bug reports or queries to screen@uni-erlangen.de.
Upgrading Packages
When upgrading from an earlier GNU screen package, remember to pkgrm GNUscreen before you pkgadd the new version.
Solaris Issues
Click here to read about 32 bit and 64 bit packages.
Source Code
You can ftp the source code from ftp://ftp.gnu.org/pub/gnu/screen/screen-3.9.4.tar.gz
Special Issues
You may need to configure your terminal definitiosn to get the most out of GNU screen. See the files in the /usr/local/share/screen directory for more information.
See the main packages README for installation information.
Screen User's Manual - Table of Contents
Each window in a screen session emulates a VT100 terminal, with some extra functions added. The VT100 emulator is hardcoded; no other terminal types can be emulated.
Usually screen tries to emulate as much of the VT100/ANSI standard as possible. But if your terminal lacks certain capabilities, the emulation may not be complete. In these cases screen has to tell the applications that some of the features are missing. This is no problem on machines using termcap, because screen can use the $TERMCAP variable to customize the standard screen termcap.
But if you do a rlogin on another machine or your machine supports only terminfo this method fails. Because of this, screen offers a way to deal with these cases. Here is how it works:
When screen tries to figure out a terminal name for itself, it first looks for an entry named “screen.<term>”, where <term> is the contents of your $TERM variable. If no such entry exists, screen tries “screen” (or “screen-w” if the terminal is wide (132 cols or more)). If even this entry cannot be found, “vt100” is used as a substitute.
The idea is that if you have a terminal which doesn’t support an important feature (e.g. delete char or clear to EOS) you can build a new termcap/terminfo entry for screen (named “screen.<dumbterm>”) in which this capability has been disabled. If this entry is installed on your machines you are able to do a rlogin and still keep the correct termcap/terminfo entry. The terminal name is put in the $TERM variable of all new windows. Screen also sets the $TERMCAP variable reflecting the capabilities of the virtual terminal emulated. Notice that, however, on machines using the terminfo database this variable has no effect. Furthermore, the variable $WINDOW is set to the window number of each window.
The actual set of capabilities supported by the virtual
terminal depends on the capabilities supported
by the physical terminal. If, for instance,
the physical terminal does not support underscore
mode, screen does not put the us
and ue capabilities into the window’s $TERMCAP variable, accordingly.
However, a minimum number of capabilities must be supported by a
terminal in order to run
screen; namely scrolling, clear
screen, and direct cursor addressing (in
addition, screen does not run on hardcopy
terminals or on
terminals that overstrike).
Also, you can customize the $TERMCAP value used by screen by using the “termcap” .screenrc command, or by defining the variable $SCREENCAP prior to startup. When the is latter defined, its value will be copied verbatim into each window’s $TERMCAP variable. This can either be the full terminal definition, or a filename where the terminal “screen” (and/or “screen-w”) is defined.
Note that screen honors the “terminfo” .screenrc command if the system uses the terminfo database rather than termcap.
When the boolean ‘G0’ capability is present in the termcap entry for
the terminal on which
screen has been called, the
terminal emulation of
screen supports multiple character sets.
This allows an application to make use of, for instance, the VT100 graphics
character set or national character sets. The following control functions
from ISO
2022 are supported: lock shift G0 (SI), lock shift G1 (SO),
lock shift G2, lock shift G3, single shift G2, and single shift G3. When
a virtual terminal is created or reset,
the
ASCII character set is designated as G0 through G3. When the
G0 capability is present, screen
evaluates the capabilities S0, E0, and C0
if present. S0 is the sequence the
terminal uses to enable and start the graphics character set rather
than SI. E0 is the corresponding replacement for
SO. C0 gives a character by character translation
string that is used during semi-graphics mode. This string is built like
the acsc terminfo capability.
When the po and pf capabilities are present
in the terminal’s termcap entry, applications
running in a screen window can send output
to the printer port of the terminal. This
allows a user to have an application in one window sending output to a printer
connected to the terminal, while all other
windows are still active (the printer port is enabled and disabled again
for each chunk of output). As a side-effect, programs running in different
windows can send output to the printer simultaneously. Data sent to the
printer is not displayed in the window. The info command displays a line
starting ‘PRIN’ while the printer is active.
Screen maintains a hardstatus line for
every window. If a window gets selected, the display’s hardstatus will be
updated to match the window’s hardstatus line. If the display has no hardstatus
the line will be displayed as a standard screen
message. The hardstatus line can be changed with the ANSI Application Program
Command (APC): ESC_<string>ESC\. As a convenience
for xterm users the sequence ESC]0..2;<string>^G is
also accepted.
Some capabilities are only put into the $TERMCAP variable of the virtual
terminal if they can be efficiently implemented
by the physical terminal. For instance,
dl (delete line) is only put into the $TERMCAP variable if
the terminal supports either delete line
itself or scrolling regions. Note that this may provoke confusion, when
the session is reattached on a different terminal,
as the value of $TERMCAP cannot be modified by parent processes.
The “alternate screen” capability is
not enabled by default. Set the altscreen
.screenrc command to enable it.
The following is a list of control sequences recognized by screen. “(V)” and “(A)” indicate VT100-specific and ANSI- or ISO-specific functions, respectively.
ESC E |
Next Line | |||
ESC D |
Index | |||
ESC M |
Reverse Index | |||
ESC H |
Horizontal Tab Set | |||
ESC Z |
Send VT100 Identification String | |||
ESC 7 |
(V) | Save Cursor and Attributes | ||
ESC 8 |
(V) | Restore Cursor and Attributes | ||
ESC [s |
(A) | Save Cursor and Attributes | ||
ESC [u |
(A) | Restore Cursor and Attributes | ||
ESC c |
Reset to Initial State | |||
ESC g |
Visual Bell | |||
ESC Pn p
|
Cursor Visibility (97801) | |||
Pn = |
6 | Invisible | ||
| 7 | Visible | |||
ESC = |
(V) | Application Keypad Mode | ||
ESC > |
(V) | Numeric Keypad Mode | ||
ESC # 8 |
(V) | Fill Screen with Es | ||
ESC \ |
(A) | String Terminator | ||
ESC ^ |
(A) | Privacy Message String (Message Line) | ||
ESC ! |
Global Message String (Message Line) | |||
ESC k |
A.k.a. Definition String | |||
ESC P |
(A) | Device Control String. Outputs a string directly to the host terminal without interpretation. | ||
ESC _ |
(A) | Application Program Command (Hardstatus) | ||
ESC ] 0 ; string
^G |
(A) | Operating System Command (Hardstatus, xterm title hack) | ||
ESC ] 83 ; cmd
^G |
(A) | Execute screen command. This
only works if multi-user support is compiled into
screen. The pseudo-user “:window:”
is used to check the access control list. Use aclchg :window:
-rwx #? to create a user with no rights and allow only the
needed commands. |
||
Control-N |
(A) | Lock Shift G1(SO) | ||
Control-O |
(A) | Lock Shift G0 (SI) | ||
ESC n |
(A) | Lock Shift G2 | ||
ESC o |
(A) | Lock Shift G3 | ||
ESC N |
(A) | Single Shift G2 | ||
ESC O |
(A) | Single Shift G3 | ||
ESC ( Pcs
|
(A) | Designate character set as G0 | ||
ESC ) Pcs
|
(A) | Designate character set as G1 | ||
ESC * Pcs
|
(A) | Designate character set as G2 | ||
ESC + Pcs
|
(A) | Designate character set as G3 | ||
ESC [ Pn ;
Pn H |
Direct Cursor Addressing | |||
ESC [ Pn ;
Pn f |
same as above | |||
ESC [ Pn J
|
Erase in Display | |||
Pn = |
None or 0 | From Cursor to End of Screen | ||
| 1 | From Beginning of Screen to Cursor | |||
| 2 | Entire Screen | |||
ESC [ Pn K
|
Erase in Line | |||
Pn = |
None or 0 | From Cursor to End of Line | ||
| 1 | From Beginning of Line to Cursor | |||
| 2 | Entire Line | |||
ESC [ Pn X
|
Erase character | |||
ESC [ Pn A
|
Cursor Up | |||
ESC [ Pn B
|
Cursor Down | |||
ESC [ Pn C
|
Cursor Right | |||
ESC [ Pn D
|
Cursor Left | |||
ESC [ Pn E
|
Cursor next line | |||
ESC [ Pn F
|
Cursor previous line | |||
ESC [ Pn G
|
Cursor horizontal position | |||
ESC [ Pn '
|
same as above | |||
ESC [ Pn d
|
Cursor vertical position | |||
ESC [ Ps ;...;
Ps m |
Select Graphic Rendition | |||
Ps = |
None or 0 | Default Rendition | ||
| 1 | Bold | |||
| 2 | (A) | Faint | ||
| 3 | (A) | Standout Mode (ANSI: Italicized) | ||
| 4 | Underlined | |||
| 5 | Blinking | |||
| 7 | Negative Image | |||
| 22 | (A) | Normal Intensity | ||
| 23 | (A) | Standout Mode off (ANSI: Italicized off) | ||
| 24 | (A) | Not Underlined | ||
| 25 | (A) | Not Blinking | ||
| 27 | (A) | Positive Image | ||
| 30 | (A) | Foreground Black | ||
| 31 | (A) | Foreground Red | ||
| 32 | (A) | Foreground Green | ||
| 33 | (A) | Foreground Yellow | ||
| 34 | (A) | Foreground Blue | ||
| 35 | (A) | Foreground Magenta | ||
| 36 | (A) | Foreground Cyan | ||
| 37 | (A) | Foreground White | ||
| 39 | (A) | Foreground Default | ||
| 40 | (A) | Background Black | ||
| ... | ||||
| 49 | (A) | Background Default | ||
ESC [ Pn g
|
Tab Clear | |||
Pn = |
None or 0 | Clear Tab at Current Position | ||
| 3 | Clear All Tabs | |||
ESC [ Pn ;
Pn r |
(V) | Set Scrolling Region | ||
ESC [ Pn I
|
(A) | Horizontal Tab | ||
ESC [ Pn Z
|
(A) | Backward Tab | ||
ESC [ Pn L
|
(A) | Insert Line | ||
ESC [ Pn M
|
(A) | Delete Line | ||
ESC [ Pn @
|
(A) | Insert Character | ||
ESC [ Pn P
|
(A) | Delete Character | ||
ESC [ Pn S
|
Scroll Scrolling Region Up | |||
ESC [ Pn T
|
Scroll Scrolling Region Down | |||
ESC [ Pn ^
|
same as above | |||
ESC [ Ps ;...;
Ps h |
Set Mode | |||
ESC [ Ps ;...;
Ps l |
Reset Mode | |||
Ps = |
4 | (A) | Insert Mode | |
| 20 | (A) | Automatic Linefeed Mode | ||
| 34 | Normal Cursor Visibility | |||
| ?1 | (V) | Application Cursor Keys | ||
| ?3 | (V) | Change Terminal Width to 132 columns | ||
| ?5 | (V) | Reverse Video | ||
| ?6 | (V) | Origin Mode | ||
| ?7 | (V) | Wrap Mode | ||
| ?9 | X10 mouse tracking | |||
| ?25 | (V) | Visible Cursor | ||
| ?47 | Alternate Screen (old xterm code) | |||
| ?1000 | (V) | VT200 mouse tracking | ||
| ?1047 | Alternate Screen (new xterm code) | |||
| ?1049 | Alternate Screen (new xterm code) | |||
ESC [ 5 i |
(A) | Start relay to printer (ANSI Media Copy) | ||
ESC [ 4 i |
(A) | Stop relay to printer (ANSI Media Copy) | ||
ESC [ 8 ; Ph ;
Pw t |
Resize the window to Ph lines and Pw columns (SunView special) | |||
ESC [ c |
Send VT100 Identification String | |||
ESC [ x |
Send Terminal Parameter Report | |||
ESC [ > c |
Send VT220 Secondary Device Attributes String | |||
ESC [ 6 n |
Send Cursor Position Report | |||
Screen has the following command-line options:
dtach is a tiny program that emulates the detach feature of screen, allowing you to run a program in an environment that is protected from the controlling terminal and attach to it later. dtach does not keep track of the contents of the screen, and thus works best with programs that know how to redraw themselves.dtach does not, however, have the other features of screen, such as its support of multiple terminals or its terminal emulation support. This makes dtach extremely tiny compared to screen, making it more easily audited for bugs and security holes, and also allows it to fit in environments where space is limited, such as on rescue disks.
dtach has many possible uses, even though it is tiny. With dtach, you can:
- Attach multiple times to the same program. Access to the dtach session is controlled through the Unix filesystem permissions; thus, you can trivially allow other people to watch your session.
- Run a program in an environment that is protected from the controlling terminal. This means that, for instance, the program running under dtach would not be affected by the terminal being disconnected for some reason.
- Run programs such as emacs, which tend to want full control over the terminal. dtach mostly acts as a relay, and does not mangle the text between the application and your terminal.
- Suspend dtach without suspending the running program. dtach can handle the suspend key itself instead of passing it to the running program, which may be useful for certain programs such as ircII.
The latest version of dtach is version 0.7, which you can fetch here. Other download formats may be available at the sourceforge download area for dtach.The changes in version 0.7 are:
The changes in version 0.6 are:
- The redraw method can now be explicitly specified on the command line (either no redraw at all, the old ^L character method, and the new WINCH signal method), since many programs only handle one or the other properly.
- Changed the default redraw method back to the old ^L character method.
- Changed the attach code to check the return value of select more carefully.
- Changed the SIGWINCH handler to reinstall itself, to handle systems that always reset the handler.
- Added more proper process group handling.
The changes in version 0.5 are:
- Redraws are now handled by sending the child process a WINCH signal instead of by sending a ^L character. This should help prevent line-oriented programs (such as bash) from clearing the screen excessively.
- Flow control is now disabled when setting raw mode on the terminal.
- Switched to using select instead of poll.
- Changed some exits to exit succesfully instead of non-sucessfully.
- Updated my email address.
- Updated to Autoconf 2.59, renaming some files in the process.
The changes in version 0.4 are:
- Fix fd leakage.
- Prevent atexit from being called twice on dtach -A.
The changes in version 0.3 are:
- Slightly improved README and dtach.1
- Portability updates thanks to sourceforge's compile farm. dtach should now work on: FreeBSD, Debian/alpha, Debian/sparc, Debian/PPC, and Solaris.
You can also obtain information on how to access the CVS tree here, and access the sourceforge project page here.
- Fixed a typo in dtach.1
- Changed the attach code so that it tells the master when a suspend occurs.
- Decreased the client <-> master packet size.
- Changed the master to send a stream of text to attaching clients instead of sending a huge packet all the time.
- Use getrlimit and dynamically allocate the data structures, if possible.
- Added some more autoconf checks.
- Initial sourceforge release.
You can send any comments or questions about dtach to the author. Comments and suggestions are welcome.
Copyright © 1996-2009 by Dr. Nikolai Bezroukov. www.softpanorama.org was created as a service to the UN Sustainable Development Networking Programme (SDNP) in the author free time. Submit comments This document is an industrial compilation designed and created exclusively for educational use and is placed under the copyright of the Open Content License(OPL). Site uses AdSense so you need to be aware of Google privacy policy. Original materials copyright belong to respective owners. Quotes are made for educational purposes only in compliance with the fair use doctrine.
Disclaimer:
Last modified: September 15, 2009
the one i use ;)
@bertocasa (amelgar) ~ :: cat .screenrc
#kill startup message
startup_message off
defscrollback 1024
hardstatus on
hardstatus alwayslastline
#hardstatus string "%{.bW}%-w%{.rW}%n %t%{-}% w %=%{..G} %H %{..Y} %m/%d %C%a "
hardstatus string '%{= kg}[ %{G}%H %{g}][%= %{= kw}%?%-Lw%?%{=b kR}(%{W}%n*%f %t%?(%u)%?%{=b kR})%{= kw}%?% Lw%?%?%= %{g}]%{=b C}[ %d %M %c ]%{W}'
screen -t rOOt 0 su -
screen -t ncmpc 1 bash
screen -t terminal 2 bash
screen -t MComander 3 mc
screen -t vimTerm 4 bash
screen -t terminal 5 bash
screen -t dropbox 6 bash