GNU Screen is a program that enables the user to create sessions and have several virtual consoles.
- 1 Installation
- 2 Configuration
- 3 Usage
- 4 Hardstatus Customization
- 5 Solutions to Common Problems
- 6 TTY Autologin with a GNU Screen Session
- 7 Enable 256 Colors
- 8 See also
|debug||No||No||Enable extra debug codepaths, like asserts and extra output. If you want to get meaningful backtraces see http://www.gentoo.org/proj/en/qa/backtraces.xml|
|nethack||No||Express error messages in nethack style|
|pam||No||Adds support for PAM (Pluggable Authentication Modules) - DANGEROUS to arbitrarily flip|
|selinux||No||!!internal use only!! Security Enhanced Linux support, this must be set by the selinux profile or breakage will occur|
|multiuser||No||Enable multiuser support (by setting correct permissions)|
The configuration files are located in /etc/screenrc and ~/.screenrc.
General usage of Screen.
Screen can be started with the following command:
Once started is will create a socket for the session in /var/run/screen/S-<username>
You can use any key combination within the session except of Ctrl+a which initiates the Command-Mode.
Give the session a reasonable name on startup:
Start a command in a screen session without attaching to it (like a daemon):
In Command Mode (after pressing Ctrl+a) the following key combinations can be used:
- ? = show quick help
- d = detach from the current session, all windows will continue running in the background
- c = create another window
- n or Space = switch to the next window
- p or Backspace = switch to the previous window
- 0 = switch to window 0 (similar for 1-9)
- ', then a number or title = switch to window with given number or title, used to reach windows numbered above 9
- Ctrl+a = switch to last used window
- Shift+a = set title for window
- " = display a list of windows, which can be navigated with arrow keys and selected with Enter or Space
- w = display a non-interactive list of windows at the bottom of screen (see Hardstatus Customization)
Copy, Paste and Scroll operations
- Esc = begin "copy mode", which allows scrolling and copying of window contents with following keys
- Ctrl+B = scroll up in copy mode
- Ctrl+F = scroll down in copy mode
- arrow keys = move the curser in copy mode
- Space or Enter = begin/end copying
- ] = paste the text copied in copy mode
- Shift+h = start/stop logging everything displayed on current window. log will be saved as a file "screenlog.X" under the directory in which screen was run
- h = (disabled in default configuration) dump the current contents of the current window to a file named "hardcopy.X" under the directory in which screen was run
- Shift+m = start/stop monitoring current window for activity, any output produced by a program will cause an alert
- _ = start/stop monitoring for inactivity (i.e. a long and output producing command finishes runnning)
After the session is detached, all the active terminals remain active and so do commands that didn't finish yet. To list existing sessions:
To resume this session:
initiate screen with a human readable session name.
all other clients to view (and act on) the active live terminal can join via
then its like conference call style terminal.
Session within Session Recursion
You can use a Screen within a Screen session. This occurs when you connect to a another host's Screen session from within your Screen session.
To signal the secondary (remote) Screen session with the Meta key, you issue the key twice to signal the second (remote) Session.
|Ctrl+a||Your normal meta key usage on your local screen|
|Ctrl+aa||Signals the second (remote) Session|
|Ctrl+aaa||Signals the third (remote) Session|
|Ctrl+aaaa||Signals the fourth (remote) Session, and so on|
Some tend to remap the Meta key on the other terminals so they don't have to count. However, if you use the console/terminal often, there tends to be a shortage of keys on the keyboard.
Customizing the status line, or hardstatus line in GNU Screen terminology is quite common. The following will get you started.
Screenshot of what my hardstatus line looks like using the above hardstatus incantation, along with nine additional terminal titles (ie. screen -t bash 7 bash --noprofile") defined within the .screenrc file. Each terminal gives me Calendar (calcurse), HTop (htop), startx (manual startx/DWM WM), Root (su), WWW (elinks), EMail (mutt) and a multitude of additional (bash) shells for working in. (This screenshot unfortunately omits color.)
Solutions to Common Problems
After quitting an editor like Vim, contents of the edited file remain in the screen window
Add the following line to screen preferences file
Programs with too much output make older window contents scrolled away
You can increase the scrollback buffer size with following line in your preferences file
TTY Autologin with a GNU Screen Session
The following will allow your system to auto login as your user, and automatically initiate a GNU Screen session on tty2. A good scenario for this; You're off the network, secluded from society, and you find entering a password is a bit redundant. The following demonstrates using the BASH Shell.
MinGetty will give you autologin capability along without having to use a password.
Comment-out the second TTY (ie. c2, or terminal number of your choosing) and add mingetty with autologin capability.
Replace the above "USER_NAME" with your login name!
Add a line within your boot loader's configuration file to specify loading the init #4 level. (Referencing the "scr2:4" level specified within the above inittab file.) Also, utilize the "nox" option as well. (As I can recall, the line ending with "4" specifies runlevel four in correspondence to the above inittab entry. And the nox avoids XDM starting(?) If something needs further documenting here for clarification, please do so!)
The following configuration states, use framebuffer at the specified screen size using nox and start init level 4.
At this point, your system can now auto login on TTY2 with your default shell. Assuming you're using the BASH shell, you can start GNU Screen automatically by adding the "screen" command to your $HOME/.bash_profile file. This file is executed automatically when you first login. (Make sure you start any subsequent BASH shells using the "bash --no-profile" switch, including shells started within the $HOME/.screenrc files!)
With a little further scripting within $HOME/.bash_profile and a second entry within /etc/inittab, you could specify runlevel 5 for auto logging in and starting your favorite graphical desktop. (ie. XFCE4, GNOME, KDE, ...) And, while still spawning a GNU Screen session onto the desktop. But this is getting a little off topic of this GNU Screen Wiki.
Enable 256 Colors
In order for GNU Screen to allow applications or the terminal to use 256 colors, two requisites must be met:
1) The "term screen-256color" line must be specified prior to any 'screen' definitions. (ie. "screen -t Mail") The resulting side effect of specifying after 'screen' definitions, the $TERM variable will be defined as 'screen' instead of the required 'screen-256color', and applications will not be able to see the terminal supports 256 colors.
2) Requires both the application and terminal to be compiled with 256 color support.