Difference between revisions of "GNU Screen"

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(To attach exiting process (process started outside screen), to a screen window)
(Add a GRUB entry to boot into Screen: mingetty dropped to AUR)
(3 intermediate revisions by 2 users not shown)
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=== Attatch an existing running program to screen ===
 
=== Attatch an existing running program to screen ===
If you started a program outside screen, but now you would like it to be inside, you use '''raptyr''' to reparent the process from it's current tty to one inside 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.
  
 
[[Pacman|Install]] the package {{Pkg|reptyr}} from the [[Official Repositories]].  
 
[[Pacman|Install]] the package {{Pkg|reptyr}} from the [[Official Repositories]].  
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Get the PID of the process (you can use {{ic|ps ax}} for that). Now just enter the PID as argument to reptyr inside a screen window.
 
Get the PID of the process (you can use {{ic|ps ax}} for that). Now just enter the PID as argument to reptyr inside a screen window.
 
{{bc|$ reptyr ''<pid>''}}
 
{{bc|$ reptyr ''<pid>''}}
 +
 
===Add a GRUB entry to boot into Screen===
 
===Add a GRUB entry to boot into Screen===
 
{{Out of date|[https://www.archlinux.org/news/end-of-initscripts-support/ Initscripts] is deprecated, and the use of runlevels as well. Also, this instructions are for legacy GRUB}}
 
{{Out of date|[https://www.archlinux.org/news/end-of-initscripts-support/ Initscripts] is deprecated, and the use of runlevels as well. Also, this instructions are for legacy GRUB}}
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}}
 
}}
  
The above line uses mingetty to [[automatically login some user to a virtual console on startup]]. You will need to install the {{pkg|mingetty}} package from the [[Official Repositories|official repositories]]. The inittab line segments are separated by colons. The first part (scr*) is simply an id. The second part is the runlevel: This should only happen on runlevel 4 (which is not used in any default setup - 3 is by default for a tty login and 5 is for X). 'Respawn' causes init to repeat the command (i.e. autologin) if the user logs out.  
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The above line uses {{AUR|mingetty}} to [[automatically login some user to a virtual console on startup]]. The inittab line segments are separated by colons. The first part (scr*) is simply an id. The second part is the runlevel: This should only happen on runlevel 4 (which is not used in any default setup - 3 is by default for a tty login and 5 is for X). 'Respawn' causes init to repeat the command (i.e. autologin) if the user logs out.  
 
We will need to see that nothing else happens on virtual console 1 when we use runlevel 4, so remove {{ic|4}} from the the first of the agetty lines:
 
We will need to see that nothing else happens on virtual console 1 when we use runlevel 4, so remove {{ic|4}} from the the first of the agetty lines:
  
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</nowiki>}}
 
</nowiki>}}
 
Set inittab/mingetty to automatically log in to vc/3 on runlevel 5 and you are set.
 
Set inittab/mingetty to automatically log in to vc/3 on runlevel 5 and you are set.
 +
 +
===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:
 +
{{bc|<nowiki>
 +
if [ -z $STY ]
 +
then
 +
        PS1="YOUR REGULAR PROMPT"
 +
else 
 +
        PS1="YOUR SCREEN PROMPT"
 +
fi
 +
</nowiki>}}
 +
[http://serverfault.com/questions/257975/how-to-check-if-im-in-screen-session]
  
 
== Troubleshooting ==
 
== Troubleshooting ==

Revision as of 19:49, 21 May 2013

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. Here are a couple of tips and tricks you may be interested in.

Installation

GNU Screen can be installed using the screen package found in the official repositories.

Usage

Commands are entered pressing Template:Keypress and then the key binding.

Common Commands

Tips and tricks

Change the escape key

The escape key can be changed with the escape option in ~/.screenrc. For example:

escape ``

sets the escape key to Template:Keypress.

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:

$HOME/.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 Template:Keypress commands. To send a command to the inner screen session, use Template:Keypress Template:Keypress, followed by your command. For example:

Use 256 colors

By default, screen uses an 8-color terminal emulator. Use the following line to enable more colors, which is useful if you are using a more-capable terminal emulator:

$HOME/.screenrc
term screen-256color

If this fails to render 256 colors in xterm, try the following instead:

$HOME/.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

Use 256 Colors with Rxvt-Unicode (urxvt)

If you are using rxvt-unicode from the official repositories, you may need to add this line in your ~/.screenrc to enable 256 colors while in screen.

$HOME/.screenrc
terminfo rxvt-unicode 'Co#256:AB=\E[48;5;%dm:AF=\E[38;5;%dm'

Informative statusbar

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

$HOME/.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}]'

Turn welcome message off

$HOME/.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:

$HOME/.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 Template:Keypress Template:Keypress. However, this is very inconvenient. To use the scroll bar of e.g. xterm or konsole, add the following line:

$HOME/.screenrc
termcapinfo xterm* ti@:te@

Attatch 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 package reptyr from the Official Repositories.

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>

Add a GRUB entry to boot into Screen

Tango-view-refresh-red.pngThis article or section is out of date.Tango-view-refresh-red.png

Reason: Initscripts is deprecated, and the use of runlevels as well. Also, this instructions are for legacy GRUB (Discuss in Talk:GNU Screen#)

If you mostly use X but occasionally want to run a Screen-as-window-manager session, here is one way to do it by adding a GRUB entry for Screen on a virtual console (text terminal).

GRUB allows you to designate what runlevel you want so we will use runlevel 4 for this purpose. Clone an appropriate GRUB entry and add a 4 to the kernel boot parameters list, like so:

# (0) Arch Linux
title  Arch Linux Screen
root   (hd0,2)
kernel /vmlinuz-linux root=/dev/disk/your_disk ro acpi_no_auto_ssdt irqpoll 4
initrd /initramfs-linux.img

Add some entries to /etc/inittab to indicate what should happen on runlevel 4, substituting your user name for <user>:

# GNU Screen on runlevel 4
scr2:4:respawn:/sbin/mingetty --autologin <user> tty1 linux

The above line uses mingettyAUR to automatically login some user to a virtual console on startup. The inittab line segments are separated by colons. The first part (scr*) is simply an id. The second part is the runlevel: This should only happen on runlevel 4 (which is not used in any default setup - 3 is by default for a tty login and 5 is for X). 'Respawn' causes init to repeat the command (i.e. autologin) if the user logs out. We will need to see that nothing else happens on virtual console 1 when we use runlevel 4, so remove 4 from the the first of the agetty lines:

c1:235:respawn:/sbin/agetty -8 38400 vc/1 linux

Once we are logged in, we want to ensure that screen is started. Add the following to the end of your ~/.bash_profile:

vico="$(tty | grep -oE ....$)"
case "$vico" in
   tty1) TERM=screen; exec /usr/bin/screen -R arch;;
esac

This checks for the current runlevel and will launch a screen session immediately after the automatic login if the runlevel is 4.

This can also be adapted to run screen on a virtual console next to X, simply checking for the current tty instead of the current runlevel. This checks to see if we are on virtual console 3:

vico="$(tty | grep -oE ....$)"
case "$vico" in
  vc/3) TERM=screen; exec /usr/bin/screen;;
esac

Set inittab/mingetty to automatically log in to vc/3 on runlevel 5 and you are set.

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]

Troubleshooting

Fix Midnight Commander hard hang when starting in screen

In some cases (need deeper inspection) old gpm bug gets alive. So, then you try to run mc inside screen, you get a frozen screen window. Try to kill gpm daemon before starting mc and/or disable it in /etc/rc.conf.

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:

$HOME/.screenrc
altscreen on

See Also