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- Committer: Bazaar Package Importer
- Author(s): Nathaniel McCallum
- Date: 2004-09-03 15:15:33 UTC
- Revision ID: james.westby@ubuntu.com-20040903151533-px02yqlrchs4fv2t
Tags: upstream-4.0.2
Import upstream version 4.0.2
- files added:
- FAQ
- doc
- doc/install.sh
- etc
- terminfo
- utf8encodings
added
removed
doc/FAQ
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jw 21.10.93
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05.05.94
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screen: frequently asked questions -- known problems -- unimplemented bugs
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=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
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Q: Why is it impossible to download a file with Kermit/sz/rz when
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screen is running? Do I need to set some special variables?
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A: Screen always interprets control-sequences sent by the
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applications and translates/optimizes them for the current
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terminal type. Screen always parses the user input for its
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escape character (CTRL-A). Both are basic screen features and
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cannot be switched off. Even if it were possible to switch
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screen into a completely transparent mode, you could never switch
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between windows, while kermit/sz/rz is downloading a file. You
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must wait til the end as kermit/sz/rz will not transmit your
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input during a file transfer and as kermit/sz/rz would be very
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confused if screen switched away the window containing the
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other kermit/sz/rz. Simply detach your screen session for each
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file transfer and start the transfer program only from the shell
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where you started screen.
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Q: I am using screen with a YYY terminal, which supports the XXX
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graphic language. I am very happy with it, except one thing: I
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cannot render graphics into screen windows.
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A: You are out of luck there. Screen provides a fixed set of escape
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sequences in order to make it possible to switch terminal types.
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Screen has to know exactly what the escape sequences do to the
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terminal because it must hold an image in memory. Otherwise
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screen could not restore the image if you switch to another
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window. Because of this you have to change screens escape
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sequence parser (ansi.c) to pass the XXX graphics sequences to
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the terminal. Of course the graphics will be lost if you switch
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to another window. Screen will only honour graphics sequences
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that are demanded by an overwhelming majority.
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Q: For some unknown reason, the fifo in /tmp/screens/S-myname is
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gone, and i can't resume my screen session. Is there a way to
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recreate the fifo?
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A: Screen checks the fifo/socket whenever it receives a SIGCHLD
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signal. If missing, the fifo/socket is recreated then. If screen
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is running non set-uid the user can issue a 'kill -CHLD
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screenpid' directly (it is -CHILD on some systems). Screenpid is
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the process-id of the screen process found in a 'ps -x' listing.
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But usually this won't work, as screen should be installed set-
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uid root. In this case you will not be able to send it a signal,
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but the kernel will. It does so, whenever a child of screen
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changes its state. Find the process-id (shellpid below) of the
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"least important" shell running inside screen. The try 'kill
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-STOP shellpid'. If the fifo/socket does not reappear, destroy
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the shell process. You sacrify one shell to save the rest. If
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nothing works, please do not forget to remove all processes
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running in the lost screen session.
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Q: When you start "screen" a page of text comes up to start you
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off. Is there a way to get rid of this text as a command line
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argument or by using a switch of some sort.
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A: Just put the following line in your ~/.screenrc:
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startup_message off
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Many peole ask this, although it is in the man page, too :-)
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Q: Start "screen emacs" and run emacs function suspend-emacs
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(ctrl-z). The window containing emacs vanishes.
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A: This is a known bug. Unfortunatly there is no easy fix
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because this is specified in the POSIX standard. When a new
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window is created Screen opens up a new session because the
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window has to get the pty as a controlling terminal (a
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session can only have one controlling terminal). With the
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setsid() call the process also creates a new process
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group. This process group is orphaned, because there is no
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process in the session which is not in the process
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group. Now if the process group leader (i.e. your program)
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gets a TTIN/TTOU/TSTP, POSIX states that the kernel must
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send a KILL signal to the process group because there is no
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one left to continue the process. Even if screen would
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try to restart the program, that would be after it received the
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KILL signal which cannot be caught or ignored.
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tromey@klab.caltech.edu (Tom Tromey): I've noticed this exact
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same problem. I put this in my .emacs file. It seems to work:
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;; If running under screen, disable C-z.
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(if (and (getenv "STY") (not window-system))
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(global-unset-key "\C-z"))
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Q: Screen gets the terminal size wrong and messes up.
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A: Before you start screen: Check with 'stty -a' what the terminal
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driver thinks about rows and columns. Check the environment
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variables LINES and COLUMNS. Then from within screen check with
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the info command (CTRL-A i) what size screen thinks your terminal
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is. If correcting tty driver setting and environment variables
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does not help, look up the terminal capability definition. First
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the TERMCAP environment variable. If this is not set, look up the
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terminals name as defined in the environment variable TERM in
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/etc/termcap or in the terminfo database with untic or infocmp.
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There may be :li=...: and :co=...: or even :ll=...: entries
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(cols#... and lines#... when it's terminfo) defined incorrectly.
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Either construct your own TERMCAP environment variables with
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correct settings, use screens terminfo/termcap command in your
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.screenrc file or have the database corrected by the system
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administrator.
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Q: Screen messes up the terminal output when I use my favourite ap-
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plication. Setting the terminal size does not help.
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A: Probably you got the termcap/terminfo entries wrong. Fixing this
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is a three stage procedure. First, find out if terminfo or
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termcap is used. If your system only has /etc/termcap,
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but not /usr/lib/terminfo/... then you are using termcap.
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Easy. But if your system has both, then it depends how the appli-
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cation and how screen were linked. Beware, if your applica-
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tion runs on another host via rlogin, telnet or the like, you
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should check the terminfo/termcap databases there. If you cannot
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tell if terminfo or termcap is used (or you just want to be
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save), the do all steps in stage 3 in parallel for both
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systems (on all envolved hosts). Second: Understand the basic
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rules how screen does its terminal emulation. When screen is
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started or reattached, it relies on the TERM environment variable
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to correctly reflect the terminal type you have physically
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in front of you. And the entry should either exist in the system
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terminfo/termcap database or be specified via the TERMCAP en-
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vironment variable (if screen is using the termcap system). On
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the other end, screen understands one set of control codes. It
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relies on the application using these codes. This means applica-
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tions that run under screen must be able to adapt their con-
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trol codes to screen. The application should use the TERM vari-
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able and termcap or terminfo library to find out how to drive
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its terminal. When running under screen, the terminal is virtual
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and is only defined by the set of control codes that screen
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understands. The TERM variable is automatically set to
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"screen" and the "screen"-entries should exist in the data-
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bases. If your application uses hardcoded control codes rather
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than a database, you are on your own. Hint: The codes under-
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stood by screen are a superset of the very common definition
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named "vt100". Look at the documentation of screen. The
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codes are listed there. Third: Have the entry "screen" in-
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stalled on all hosts or make sure you can live with "vt100".
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Check the codes sent by your application, when the TERM variable
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is set to "screen". Do not try to set the TERM variable inside
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screen to anything other than "screen" or "vt100" or compati-
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ble. Thus your application can drive screen correctly. Also take
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care that a good entry is installed for your physical terminal
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that screen has to drive. Even if the entry was good enough
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for your application to drive the terminal directly, screen may
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find flaws, as it tries to use other capabilities while op-
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timizing the screen output. The screenrc commands
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"termcap" and/or "terminfo" may help to fine-tune capabilities
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without calling the supervisor to change the database.
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Q: I cannot configure screen. Sed does not work.
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A: The regular expressions used in our configure scrip are too
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complicated for GNU sed version 2.03. In this regard it is bug
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compatible with Ultrix 3.1 "sed": GNU sed version 2.03 dumps
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core with our configure script. Try an older release. E.g. from
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ftp.uni-erlangen.de:/pub/utilities/screen/sed-2.02b.tar.gz
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Q: When reattaching a session from a different Workstation, the
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DISPLAY environment variable should be updated. Even ``CTLR-A
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: setenv DISPLAY newhost:0'' does not work as expected.
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A: Under unix every process has its own environment. The environ-
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ment of the SCREEN process can be changed with the `setenv' com-
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mand. This however cannot affect the environment of the
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shells or applications already running under screen. Subsequently
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spawned processes will reflect the changes. One should be aware
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of this problem when running applications from very old shells.
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Screen is a means for keeping processes alive.
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Q: About once every 5 times I ran the program, rather than getting
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a "screen," I got someone elses IRC output/input.
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A: What probably happened is that an IRC process was left running on
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a pseudo tty in such a way that the kernel thought the tty was
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available for reallocation. You can fix this behaviour by
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applying the SunOS 4.1.x tty jumbo patch (100513-04).
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Q: Screen compiled on SunOS 5.3 cannot reattach a detached session.
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A: You are using /usr/ucb/cc, this compiler is wrong. Actually it
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links with a C-library that mis-interprets dirent. Try again
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with /opt/SUNWspro/bin/cc!
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Q: The "talk" command does not work when Screen is active.
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A: Talk and several other programs rely on entries in the Utmp-
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Database (/etc/utmp). On some systems this Database is world
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writable, on others it is not. If it is not, screen must be
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installed with the appropriate permissions (user or group s-bit)
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just like any program that uses PTYs (rlogin, xterm, ...). When
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screen cannot write to utmp, you will see messages on you display
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which do not belong to any screen window.
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When screen can update utmp, it is not guaranteed that it does as
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you expect. First this depends on the config.h file defining
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UTMPOK, LOGINDEFAULT, and perhaps CAREFULUTMP. Second it depends
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on the screenrc files (system wide and per user), if utmp entries
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are done. Third, you can control whether windows are logged in
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with screens ``login'' command.
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Q: Seteuid() does not work as expected in AIX. Attempting a multi-
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user-attach results in a screen-panic: "seteuid: not owner".
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A: This is not a screen problem. According to Kay Nettle
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(pkn@cs.utexas.edu) you need the AIX patch PTF 423674.
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Q: When I type cd directory (any directory or just blank) from
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within one of the windows in screen, the whole thing just freezes
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up.
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A: You display the current working directory in xterm's title bar,
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This may be caused by hardcoded ESC-sequences in the shell prompt
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or in an cd alias. In Xterm the coding is
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ESC ] n ; string_to_display ^G
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where n = 1, 2, 3 selects the location of the displayed string.
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Screen misinterprets this as the ansi operating system comment
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sequence:
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ESC ] osc_string
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and waits (according to ansi) for the string terminator
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ESC \
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Screen versions after 3.5.12 may provide a workaround.
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Q: Mesg or biff cannot be turned on or off while running screen.
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A: Screen failed to change the owner of the pty it uses. You need to
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install screen setuid-root. See the file INSTALL for details.
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Q: The cursor left key deletes the characters instead of just moving the
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cursor. A redisplay (^Al) brings everything back.
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A: Your terminal emulator treats the backspace as "destructive". You
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can probably change this somewhere in the setup. We can't think
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of a reason why anybody would want a destructive backspace, but
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if you really must have it, add the lines
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termcap <TERM> 'bc@:bs@'
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terminfo <TERM> 'bc@:bs@'
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to your ~/.screenrc (replace <TERM> with the terminal type your
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emulator uses).
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Q: I have an old SysV OS (like Motorola SysV68) and sometimes screen
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doesn't reset the attributes correctly. A redisplay (^Al) doesn't
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make things better.
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A: The libcurses library has a bug if attributes are cleared with
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the special ue/se capabilities. As a workaround (other than upgrading
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your system) modify 'rmul' (and 'rmso'?) in screen's terminfo entry:
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rmul=\E[m, rmso=\E[m
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