GNU Screen - ArchWiki

# GNU Screen

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- dtach
- tmux

GNU Screen is a wrapper that allows separation between the text program and the shell from which it was launched. This allows the user to, for example, start a text program in a terminal in X, kill X, and continue to interact with the program.

## Installation

GNU Screen can be installed using the screen package.

## Usage

Commands are entered pressing the "escape key" `Ctrl+a` and then the key binding.

Some users find the default escape key `Ctrl+a` inconvenient. The escape key can be changed to another key as described below.

### Common Commands

- `Ctrl+a` `?` Displays commands and its defaults (VERY important)
- `Ctrl+a` `:` Enter to the command prompt of screen
- `Ctrl+a` `"` Window list
- `Ctrl+a` `0` opens window 0
- `Ctrl+a` `A` Rename the current window
- `Ctrl+a` `a` Sends `Ctrl+a` to the current window
- `Ctrl+a` `c` Create a new window (with shell)
- `Ctrl+a` `S` Split current region into two regions
- `Ctrl+a` `tab` Switch the input focus to the next region
- `Ctrl+a` `Ctrl+a` Toggle between current and previous region
- `Ctrl+a` `Esc` Enter Copy Mode (use enter to select a range of text)
- `Ctrl+a` `]` Paste text
- `Ctrl+a` `Q` Close all regions but the current one
- `Ctrl+a` `X` Close the current region
- `Ctrl+a` `d` Detach from the current screen session, and leave it running. Use `screen -r` to resume

### Command Prompt Commands

- `Ctrl+a` `:quit` Closes all windows and closes screen session
- `Ctrl+a` `:source ~/.screenrc` Reloads screenrc configuration file (can alternatively use /etc/screenrc)

### Named sessions

To create a named session, run screen with the following command:

    $ screen -S session_name

To (re)name an existing a session, run the following command while screen is running:

`Ctrl+a` `:sessionname session_name`

To print a list of pid.tty.host strings identifying your screen sessions:

    $ screen -list

To attach to a named screen session, run this command:

    $ screen -x session_name

or

    $ screen -r session_name

### Autostart with systemd

This service autostarts screen for the specified user (e.g. `systemctl enable screen@florian`). Running this as a system unit is important, because systemd --user instance is not guaranteed to be running and will be killed when the last session for given user is closed.

    /etc/systemd/system/screen@.service

    [Unit]
    Description=screen
    After=network.target

    [Service]
    Type=simple
    User=%i
    ExecStart=/usr/bin/screen -DmS autoscreen
    ExecStop=/usr/bin/screen -S autoscreen -X quit

    [Install]
    WantedBy=multi-user.target

## Tips and tricks

### Change the escape key

It can be a good idea to change the default escape key, not only because "a" is usually typed with the left pinky, but also because `Ctrl+a` is mapped to the common command `beginning-of-line` in GNU Readline and Bash-like shells.

The escape key can be changed with the `escape` option in `~/.screenrc`, or the `-e` option to `screen`.

For example, if you find that you rarely type `Ctrl+j` in your shell or editor, you could use `escape ^Jj` to set the escape key to `Ctrl+j`. The second "j" means that a literal `Ctrl+j` can be sent to the terminal via the sequence `Ctrl+j j`. For Dvorak keyboard users, `Ctrl+t` (`escape ^Tt`) might be more convenient.

More exotic options include `escape ``` which sets the escape key to ```, or `escape ^^^` which sets it to `Ctrl+^`.

The escape key is also called the "command character" in Screen documentation.

### Start at window 1

By default, the first screen window is 0. If you'd rather never have a window 0 and start instead with 1, add the following lines on your configuration:

    ~/.screenrc

    bind c screen 1
    bind ^c screen 1
    bind 0 select 10
    screen 1

### Nested Screen Sessions

It is possible to get stuck in a nested screen session. A common scenario: you start an ssh session from within a screen session. Within the ssh session, you start screen. By default, the outer screen session that was launched first responds to `Ctrl+a` commands. To send a command to the inner screen session, use `Ctrl+a` `a`, followed by your command. For example:

- `Ctrl+a` `a` `d` Detaches the inner screen session.
- `Ctrl+a` `a` `K` Kills the inner screen session.

### Use 256 colors

This article or section is out of date.

Reason: screen 4.4 sets `$TERM` to `screen.$TERM`, although the manual says something different. There should be no need to modify it in `~/.screenrc`. (Discuss in Talk:GNU Screen#)

By default, screen uses an 8-color terminal emulator. To enable more colors, you need to be using a terminal that supports them and set the correct term value. This will use terminfo to describe how the ANSI escape codes will be interpreted. An entry in the terminfo database structure must exist, ncurses provides many common descriptions stored under `/usr/share/terminfo/`.

First try the generic value:

    ~/.screenrc

    term screen-256color

If that does not work, try setting it based on the used terminal. When using xterm-based terminal:

    ~/.screenrc

    term xterm-256color

When using rxvt-unicode:

    ~/.screenrc

    term rxvt-unicode-256color

Note: `/usr/share/terminfo/r/rxvt-unicode-256color` is provided by rxvt-unicode-terminfo, which is installed as a dependency of rxvt-unicode. However, if you log into a server via SSH and run screen there, this terminfo file might not be available on the server. In this case it is recommended to copy `/usr/share/terminfo/r/rxvt-unicode-256color` on the server, it can be saved in `~/.terminfo`.

As a last resort, try setting termcapinfo instead:

    ~/.screenrc

    attrcolor b ".I"    # allow bold colors - necessary for some reason
    termcapinfo xterm 'Co#256:AB=\E[48;5;%dm:AF=\E[38;5;%dm'   # tell screen how to set colors. AB = background, AF=foreground
    defbce on    # use current bg color for erased chars

### Informative statusbar

The default statusbar may be a little lacking. You may find this one more helpful:

    ~/.screenrc

    hardstatus off
    hardstatus alwayslastline
    hardstatus string '%{= kG}[ %{G}%H %{g}][%= %{= kw}%?%-Lw%?%{r}(%{W}%n*%f%t%?(%u)%?%{r})%{w}%?%+Lw%?%?%= %{g}][%{B} %m-%d %{W} %c %{g}]'

Another possibility, taken from frodfrog's blog is:

    ~/.screenrc

    hardstatus alwayslastline '%{= G}[ %{G}%H %{g}][%= %{= w}%?%-Lw%?%{= R}%n*%f %t%?%{= R}(%u)%?%{= w}%+Lw%?%= %{= g}][ %{y}Load: %l %{g}][%{B}%Y-%m-%d %{W}%c:%s %{g}]'

### Turn welcome message off

    ~/.screenrc

    startup_message off

### Turn your hardstatus line into a dynamic urxvt|xterm|aterm window title

This one is pretty simple; just switch your current `hardstatus` line into a `caption` line with notification, and edit accordingly:

    ~/.screenrc

    backtick 1 5 5 true
    termcapinfo rxvt* 'hs:ts=\E]2;:fs=\007:ds=\E]2;\007'
    hardstatus string "screen (%n: %t)"
    caption string "%{= kw}%Y-%m-%d;%c %{= kw}%-Lw%{= kG}%{+b}[%n %t]%{-b}%{= kw}%+Lw%1`"
    caption always

This will give you something like `screen (0 bash)` in the title of your terminal emulator. The caption supplies the date, current time, and colorizes your screen window collection.

### Use X scrolling mechanism

The scroll buffer of GNU Screen can be accessed with `Ctrl+a` `[`. However, this is very inconvenient. To use the scroll bar of e.g. xterm or konsole, add the following line:

    ~/.screenrc

    termcapinfo xterm* ti@:te@

### Attach an existing running program to screen

If you started a program outside screen, but now you would like it to be inside, you can use reptyr to reparent the process from it's current tty to one inside screen.

Install the reptyr package.

Get the PID of the process (you can use `ps ax` for that). Now just enter the PID as argument to reptyr inside a screen window.

    $ reptyr <pid>

### Setting a different bash prompt while in screen

If you want a different bash prompt when in a screen session, add the following to your .bashrc:

    if [ -z $STY ]
    then
            PS1="YOUR REGULAR PROMPT"
    else
            PS1="YOUR SCREEN PROMPT"
    fi

[1]

### Turn off visual bell

With this setting, screen will not make an ugly screen flash instead of a bell sound.

    ~/.screenrc

    vbell off

## Troubleshooting

### Fix for residual editor text

When you open a text editor like nano in screen and then close it, the text may stay visible in your terminal. To fix this, put the following:

    ~/.screenrc

    altscreen on

### Fix for Name column in windowlist only show "bash"

add following to ~/.screenrc

    ~/.screenrc

    windowlist string "%4n %h%=%f"

## See also

- MacOSX Hints - Automatically using screen in your shell
- Gentoo Wiki - Tutorial for screen
- Arch Forums - Regarding 256 color issue with urxvt
- Arch Forums - .screenrc configs with screenshots
- Ratpoison - A window manager based on gnu screen
- Xpra - An utility to detach/reattach X programs, in a way similar as screen does for command line based programs

Category:

- Terminal emulators

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