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@ -3,11 +3,13 @@
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<title> Text-Terminal-HOWTO
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<title> Text-Terminal-HOWTO
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<author> David S. Lawyer <url url="mailto:dave@lafn.org">
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<author> David S. Lawyer <url url="mailto:dave@lafn.org">
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<date> v1.17, December 2000
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<date> v1.18, December 2000
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<!--
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<!--
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Change log:
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Change log:
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v1.17 December 2000 Don't run getty from the command line,
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v1.18 Dec. 2000 mesg command, respawning error cause, chaos when 2
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processes open same terminal, rebooting
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v1.17 Dec. 2000 Don't run getty from the command line,
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XDM-and-X-Terminal mini-HOWTO, substitutes for "local mode",
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XDM-and-X-Terminal mini-HOWTO, substitutes for "local mode",
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character mapping with "mapchan"
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character mapping with "mapchan"
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v1.16 October 2000 Thin clients+; NC Howtos; Correction of bad typo
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v1.16 October 2000 Thin clients+; NC Howtos; Correction of bad typo
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@ -151,10 +153,9 @@ sites see: <url url="http://linuxdoc.org/mirrors.html">.
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Various formats are available. If you only want to quickly check the
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Various formats are available. If you only want to quickly check the
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date of the latest version look at <url
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date of the latest version look at <url
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url="http://linuxdoc.org/HOWTO/Text-Terminal-HOWTO.html">. The
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url="http://linuxdoc.org/HOWTO/Text-Terminal-HOWTO.html">. The
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version your are currently reading is: v1.17, December 2000 . New in this version
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version your are currently reading is: v1.18, December 2000 . New in this version:
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is: Don't run getty from the command line,
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v1.18: mesg command, respawning error cause, chaos when 2 processes
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XDM-and-X-Terminal mini-HOWTO, substitutes for "local mode",
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open same terminal, rebooting.
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character mapping with "mapchan"
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|
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<sect1> Related HOWTOs, etc. <label id="related_howtos">
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<sect1> Related HOWTOs, etc. <label id="related_howtos">
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<p> Go to the websites shown above to get these.
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<p> Go to the websites shown above to get these.
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@ -1810,7 +1811,7 @@ Using the above 2 connections provide full modem control signals and
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seemingly allow one to set "stty -clocal". Then one must turn on the
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seemingly allow one to set "stty -clocal". Then one must turn on the
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terminal first (asserts DTR) before the port may be opened in a normal
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terminal first (asserts DTR) before the port may be opened in a normal
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manner by getty, etc. But there is likely to be trouble if you fail
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manner by getty, etc. But there is likely to be trouble if you fail
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to turn on the terminal first (see <ref id="fast_respawn" name="Getty
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to turn on the terminal first (see <ref id="rapid_respawn" name="Getty
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Respawning Too Rapidly">). For this reason one should use "stty
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Respawning Too Rapidly">). For this reason one should use "stty
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clocal" which is the default (ignores modem control lines) and the
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clocal" which is the default (ignores modem control lines) and the
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additional wires in these cables then serve no useful purpose.
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additional wires in these cables then serve no useful purpose.
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@ -3206,6 +3207,7 @@ which runs <tt/stty/ since on seldom need it.
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Change Log:
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Change Log:
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May 2000: <sect2> IRQs near end ttyS0 -> ttyS1 + clarity
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May 2000: <sect2> IRQs near end ttyS0 -> ttyS1 + clarity
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Nov. 2000: auto_irq may work on the 2nd try
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Nov. 2000: auto_irq may work on the 2nd try
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Dec. 2000: saving state of serial module
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-->
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-->
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<p> This part is in 3 HOWTOs: Modem, Serial, and Text-Terminal. There
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<p> This part is in 3 HOWTOs: Modem, Serial, and Text-Terminal. There
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are some minor differences, depending on which HOWTO it appears in.
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are some minor differences, depending on which HOWTO it appears in.
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@ -3239,14 +3241,15 @@ Linux.
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<tt/Setserial/ is often run automatically at boot-time by a start-up
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<tt/Setserial/ is often run automatically at boot-time by a start-up
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shell-script for the purpose of assigning IRQs, etc. to the driver.
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shell-script for the purpose of assigning IRQs, etc. to the driver.
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Setserial will only work if the serial module is loaded (or if the
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Setserial will only work if the serial module is loaded (or if the
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equivalent was compiled into your kernel). If you should (for some
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equivalent was compiled into your kernel). If the serial module gets
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reason) unload the serial module later on, the changes previously made
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unloaded later on, the changes previously made by <tt/setserial/ will
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by <tt/setserial/ will be forgotten by the kernel. So <tt/setserial/
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be forgotten by the kernel. But recent (2000) distributions may
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must be run again to reestablish them. In addition to running via a
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contain scripts that save and restore this. If not, then
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start-up script, something akin to <tt/setserial/ also runs earlier
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<tt/setserial/ must be run again to reestablish them. In addition to
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when the serial module is loaded (or the like). Thus when you watch
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running via a start-up script, something akin to <tt/setserial/ also
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the start-up messages on the screen it may look like it ran twice, and
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runs earlier when the serial module is loaded (or the like). Thus
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in fact it has.
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when you watch the start-up messages on the screen it may look like it
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ran twice, and in fact it has.
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Setserial can set the time that the port will keep operating after
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Setserial can set the time that the port will keep operating after
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it's closed (in order to output any characters still in its buffer in
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it's closed (in order to output any characters still in its buffer in
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@ -3287,15 +3290,16 @@ having problems there is a good chance that "setserial" has it wrong.
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In fact, you can run "setserial" and assign a purely fictitious I/O
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In fact, you can run "setserial" and assign a purely fictitious I/O
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port address, any IRQ, and whatever uart type you would like to have.
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port address, any IRQ, and whatever uart type you would like to have.
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Then the next time you type "setserial ..." it will display these
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Then the next time you type "setserial ..." it will display these
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bogus values without complaint. Of course the serial port driver will
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bogus values without complaint. They will also be officially
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not work correctly (if at all) if you attempt to use such a port.
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registered with the kernel as seen by the "scanport" command.
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Thus when giving parameters to "setserial" anything goes. Well
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Of course the serial port driver will not work correctly (if at all)
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almost. If you assign one port a base address that is already assigned
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if you attempt to use such a port. Thus when giving parameters to
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(such as 3e8) it will not accept it. But if you use 3e9 it will
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"setserial" anything goes. Well almost. If you assign one port a
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accept it. Unfortunately 3e9 is already assigned since it is within
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base address that is already assigned (such as 3e8) it will not accept
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the range starting at base address 3e8. Thus the moral of the story
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it. But if you use 3e9 it will accept it. Unfortunately 3e9 is
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is to make sure of your data before assigning resources with
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already assigned since it is within the range starting at base address
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setserial.
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3e8. Thus the moral of the story is to make sure of your data before
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assigning resources with setserial.
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While assignments made by setserial are lost when the PC is powered
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While assignments made by setserial are lost when the PC is powered
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off, a configuration file may restore them (or a previous
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off, a configuration file may restore them (or a previous
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@ -3338,7 +3342,7 @@ probe for UARTs is made automatically and reported on the screen. But
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the IRQs shown may be wrong. The second report of the same is the
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the IRQs shown may be wrong. The second report of the same is the
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result of a script which usually does no probing and thus provides no
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result of a script which usually does no probing and thus provides no
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reliable information as to how the hardware is actually set. It only
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reliable information as to how the hardware is actually set. It only
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shows configuration date someone wrote into the script or data that
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shows configuration data someone wrote into the script or data that
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got saved in /etc/serial.conf.
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got saved in /etc/serial.conf.
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It may be that two serial ports both have the same IO address set in
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It may be that two serial ports both have the same IO address set in
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@ -3855,7 +3859,7 @@ characters which are sent to the screen (output). This is nice for
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remapping the keyboard for foreign language alphabets. Most
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remapping the keyboard for foreign language alphabets. Most
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distributions don't seem to supply it (let me know if any do). Source
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distributions don't seem to supply it (let me know if any do). Source
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code by Yura Kalinichenko (Ukraine) is at <url
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code by Yura Kalinichenko (Ukraine) is at <url
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url="http://www.kron.vinnica.ua/free">
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url="http://www.kron.vinnica.ua/free/download/">
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<sect>Terminfo and Termcap (detailed) <label id="termcap2">
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<sect>Terminfo and Termcap (detailed) <label id="termcap2">
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@ -4185,7 +4189,7 @@ by default. Check <tt>/etc/profile</tt>, etc. for <tt/ls/ aliases.
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See <ref id="ls_color" name="Example for ls Function"> for how to
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See <ref id="ls_color" name="Example for ls Function"> for how to
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have <tt/ls/ do color for the console and do monochrome for terminals.
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have <tt/ls/ do color for the console and do monochrome for terminals.
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<sect1> Display Freezes (hung terminal)
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<sect1> Display Freezes (hung terminal) <label id="display_freezes">
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<p> The symptom of a hung terminal is where what you type doesn't display
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<p> The symptom of a hung terminal is where what you type doesn't display
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on the terminal (or in some cases displays but doesn't do anything).
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on the terminal (or in some cases displays but doesn't do anything).
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If what you type is invisible (or does nothing) type ^Q to restart flow
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If what you type is invisible (or does nothing) type ^Q to restart flow
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@ -4198,11 +4202,14 @@ you interaction with it fatally illegal.
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If you want to quit the program you were running and you can't do it
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If you want to quit the program you were running and you can't do it
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by the usual methods (some programs have special keys you must hit to
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by the usual methods (some programs have special keys you must hit to
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exit) then try killing it from another terminal using "top" or "kill".
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exit) then try killing it from another terminal using "top" or "kill".
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If the process refuses to die, you may try sending it signal 9 from
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If the process refuses to die, then kill it with signal 9 from top (or
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top which should force it to exit. The "9" type of forced exit may
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use "kill" on the command line). The "9" type of forced exit may leave
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leave some temporary files lying around as well as a corrupted
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some temporary files lying around as well as a corrupted interface.
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interface. Killing the login shell should result in a startup of
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If this doesn't work, killing the login shell should result in a
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getty with a new login prompt.
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startup of getty with a new login prompt. If all else fails, you may
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need to reboot the computer or even power it down. Just rebooting may
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not alter the possibly corrupted content of the serial port hardware
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registers.
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<label id="ctrl_s">
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<label id="ctrl_s">
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People new to Linux may unintentionally press Ctrl-S (^S) (or the "No
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People new to Linux may unintentionally press Ctrl-S (^S) (or the "No
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@ -4565,7 +4572,7 @@ the host computer and not inside the terminal as they are with
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<sect1> Logging Out
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<sect1> Logging Out
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<p> To log out type either "logout" or "exit". Under some
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<p> To log out type either "logout" or "exit". Under some
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circumstances your request will be refused, but you should be told why.
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circumstances your request will be refused, but you should be told why.
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One reason for refusal is if you are not in the same shell into which
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One reason for refusal is if you are not in the same shell that
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you logged into. Another way to log out is to press ^D. Since ^D is
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you logged into. Another way to log out is to press ^D. Since ^D is
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also used for other purposes, you may not want it to log you out. If
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also used for other purposes, you may not want it to log you out. If
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you set IGNOREEOF in the Bash shell then ^D will no longer log you
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you set IGNOREEOF in the Bash shell then ^D will no longer log you
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@ -4574,8 +4581,9 @@ out.
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<sect1> Chatting between Terminals, Spying
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<sect1> Chatting between Terminals, Spying
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<p> If two persons logged into terminals on the same host computer
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<p> If two persons logged into terminals on the same host computer
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want to chat with each other they may use the "write" or the "talk"
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want to chat with each other they may use the "write" or the "talk"
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program. On the Internet, chatting may be done using the "lynx"
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(better) program. One may prevent anyone (except the superuser) from
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browser.
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writing (sending messages) to their terminal by using the "mesg"
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command.
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For spying on what someone else is doing at their terminal use the
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For spying on what someone else is doing at their terminal use the
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"ttysnoop" program. In "ttysnoop" the two terminals have the same
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"ttysnoop" program. In "ttysnoop" the two terminals have the same
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@ -4657,19 +4665,25 @@ involves the serial port itself see the Serial-HOWTO.
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|
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Here is a list of possible problems:
|
Here is a list of possible problems:
|
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<itemize>
|
<itemize>
|
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<item> <ref id="term_OK" name="Is the Terminal OK ?">
|
<item><ref id="term_OK" name="Is the Terminal OK ?">
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Suspect the terminal is defective.
|
Suspect the terminal is defective.
|
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<item> <ref id="flow_ctrl_ng" name="Missing Text"> Either skips
|
<item><ref id="display_freezes" name="Display Freezes (hung
|
||||||
over some text or displays some text OK and hangs.
|
terminal)">
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<item> <ref id="stopped_" name="Programs get Stopped"> with
|
<ref id="keys_erratic" name="All Keys Work Erratically; Must Hit a Key
|
||||||
|
a Few Times">
|
||||||
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<item><ref id="flow_ctrl_ng" name="Missing Text"> Either skips
|
||||||
|
over some text or displays some text OK and hangs.
|
||||||
|
<item><ref id="keys_erratic" name="All Keys Work Erratically; Must Hit
|
||||||
|
a Key a Few Times">
|
||||||
|
<item><ref id="stopped_" name="Programs get Stopped"> with
|
||||||
message "Stopped"
|
message "Stopped"
|
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<item> <ref id="fast_respawn" name="Getty Respawning Too Rapidly">
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<item><ref id="rapid_respawn" name="Getty Respawning Too Rapidly">
|
||||||
(console error message)
|
(console error message)
|
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<item> <ref id="after_login" name="Fails Just After Login">
|
<item><ref id="after_login" name="Fails Just After Login">
|
||||||
<item> <ref id="cant_login" name="Can't Login"> but login prompt is
|
<item><ref id="cant_login" name="Can't Login"> but login prompt is
|
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OK.
|
OK.
|
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<item> <ref id="garbled" name="Garbled Login Prompt">
|
<item><ref id="garbled" name="Garbled Login Prompt">
|
||||||
<item> <ref id="blank_" name="No Sign of any Login Prompt">
|
<item><ref id="blank_" name="No Login Prompt">
|
||||||
</itemize>
|
</itemize>
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|
|
||||||
There are two cases where the terminal goes bad. One is when it's
|
There are two cases where the terminal goes bad. One is when it's
|
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@ -4749,28 +4763,62 @@ for this is to turn it on with the keyboard unplugged and see if it
|
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displays an error message.
|
displays an error message.
|
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|
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<sect1> Missing Text <label id="flow_ctrl_ng">
|
<sect1> Missing Text <label id="flow_ctrl_ng">
|
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<p> If some text displays on the terminal OK and then it stops
|
<p> If several lines or text displays on the terminal OK and then it
|
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without finishing (in the middle of a word, etc.) or if chunks of text
|
stops without finishing (in the middle of a word, etc.) or if big
|
||||||
are missing, you likely have a problem with flow control. If you
|
chunks of text are missing, you likely have a problem with flow
|
||||||
can't figure out right away what's causing it, decrease the speed. If
|
control. If you can't figure out right away what's causing it,
|
||||||
that fixes it, it's likely a flow control problem. It may be that
|
decrease the speed. If that fixes it, it's likely a flow control
|
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flow control is not working at all due to failure to configure it
|
problem. It may be that flow control is not working at all due to
|
||||||
correctly, or due to incorrect cable wiring (for hardware flow
|
failure to configure it correctly, or due to incorrect cable wiring
|
||||||
control). See <ref id="flow_control" name="Flow Control">
|
(for hardware flow control). See <ref id="flow_control" name="Flow
|
||||||
|
Control">
|
||||||
|
|
||||||
|
If you can type OK at the terminal but when text is sent to the
|
||||||
|
terminal only about 1 in every 16 characters sent gets thru, then you
|
||||||
|
may have given the wrong UART to setserial. This will happen if the
|
||||||
|
port is an obsolete 16550 (or lower) but you've told setserial it's a
|
||||||
|
16550A or higher.
|
||||||
|
|
||||||
If single characters are missing, perhaps the serial port is being
|
If single characters are missing, perhaps the serial port is being
|
||||||
overrun by too fast a speed. Try a slower baud rate.
|
overrun by too fast a speed. Try a slower baud rate.
|
||||||
|
|
||||||
If you are using a baud rate under 1200 (very slow, mostly used for
|
If your device is under 1200 baud (probably a very slow old hard-copy
|
||||||
old hard-copy terminals and printers) and the text gets truncated,
|
terminal or printer) and the text gets truncated, then the problem may
|
||||||
then the problem may be in the serial device driver. See
|
be in the serial device driver. See Printing-HOWTO under "Serial
|
||||||
Printing-HOWTO under "Serial devices" on how to fix this.
|
devices" on how to fix this.
|
||||||
|
|
||||||
<sect1> Getty Respawning Too Rapidly <label id="fast_respawn">
|
<sect1> All Keys Work Erratically; Must Hit a Key a Few Times
|
||||||
<sect2> Serial Module Not Loaded
|
<label id="keys_erratic">
|
||||||
<p> Use the "lsmod" command to see if the serial module is loaded.
|
<p> This is where you need to hit a key a few times before it works
|
||||||
|
(and see the letter you typed on the screen). If you type a word,
|
||||||
|
some (or even all) of the letters may be missing on the screen. If
|
||||||
|
letters are missing from a command it doesn't work and even if all
|
||||||
|
letters are present you may need to hit the return-key several times
|
||||||
|
to get the command to execute.
|
||||||
|
|
||||||
<sect2> No Modem Control Signal
|
This may be due to two different processes opening the serial port. Both
|
||||||
|
try to read what you type. Sometimes one process (the right one
|
||||||
|
--perhaps the shell) reads what you type and at other times the other
|
||||||
|
process reads what you type. An example is where the other process is
|
||||||
|
for a serial mouse (such as gpm) which doesn't echo what you type.
|
||||||
|
So another process running on the same ttySx is eating some of what
|
||||||
|
you type. To fix this, use "ps -alx" to see what else is running on
|
||||||
|
your ttySx and kill that process.
|
||||||
|
|
||||||
|
You might think that lockfiles would prevent this. But neither the
|
||||||
|
terminal nor the gpm mouse program uses lockfiles. Since others may
|
||||||
|
need to write to your terminal, it's reasonable not to use lockfiles.
|
||||||
|
See Lock-Files in the Serial-HOWTO.
|
||||||
|
|
||||||
|
<sect1> Getty Respawning Too Rapidly <label id="rapid_respawn">
|
||||||
|
<sect2> No serial support
|
||||||
|
<p> Linux provides serial support either by selecting it when
|
||||||
|
compiling the kernel or by loading the serial module. This
|
||||||
|
"respawning" error happens if serial support has neither been built
|
||||||
|
into the kernel nor provided by a serial module. You many use the
|
||||||
|
"lsmod" command to see if the serial module is loaded.
|
||||||
|
|
||||||
|
<sect2> No modem control signal
|
||||||
<p> If getty can't open and/or use a port because of the lack of a
|
<p> If getty can't open and/or use a port because of the lack of a
|
||||||
positive modem control voltage on one of the pins, then getty might
|
positive modem control voltage on one of the pins, then getty might
|
||||||
be killed. Then, per the instructions in inittab, getty respawns and
|
be killed. Then, per the instructions in inittab, getty respawns and
|
||||||
|
@ -4843,15 +4891,26 @@ If you are using agetty (often just named getty), the agetty program
|
||||||
will detect and set parity and/or bits/character if you type something.
|
will detect and set parity and/or bits/character if you type something.
|
||||||
Try it with a return to see if it fixes it.
|
Try it with a return to see if it fixes it.
|
||||||
|
|
||||||
<sect1> No Sign of any Login Prompt <label id="blank_">
|
<sect1> No Login Prompt <label id="blank_">
|
||||||
<p> This is when nothing at all happens at the terminal, but the
|
<p> This is when nothing at all happens at the terminal, but the
|
||||||
terminal seems to be working OK. One of the first things to do is to
|
terminal seems to be working OK. One of the first things to do is to
|
||||||
make sure that all cable connections are tight and connected
|
make sure that all cable connections are tight and connected
|
||||||
to the correct connector on both the computer and terminal. Other
|
to the correct connector on both the computer and terminal. Other
|
||||||
causes include defective hardware or cables (must be null-modem),
|
causes include defective hardware or cables (must be null-modem),
|
||||||
getty not running, terminal setup at wrong baud-rate, terminal in
|
getty not running, terminal setup at wrong baud-rate, terminal in
|
||||||
local mode, etc.. At this point two different avenues of
|
local mode, etc.
|
||||||
approach are (you may pursue more than one at a time).
|
|
||||||
|
At the console (or another working terminal), use "top" or "ps -al" to
|
||||||
|
see if getty is running on the port. Don't confuse it with getty
|
||||||
|
programs running on other ports or on the virtual consoles. You will
|
||||||
|
not get a login prompt unless getty runs. If getty isn't running,
|
||||||
|
carefully check the format for calling getty in /etc/inittab. Make
|
||||||
|
sure that it includes the current runlevel (shown by typing the
|
||||||
|
command "runlevel") and that it is valid for your flavor of getty.
|
||||||
|
Sometimes killing getty (it will restart automatically) helps.
|
||||||
|
|
||||||
|
At this point two different avenues of approach are (you may pursue
|
||||||
|
more than one at a time).
|
||||||
|
|
||||||
<itemize>
|
<itemize>
|
||||||
<item> <ref id="consoleD" name="Diagnose Problem from the Console">
|
<item> <ref id="consoleD" name="Diagnose Problem from the Console">
|
||||||
|
@ -4860,23 +4919,16 @@ approach are (you may pursue more than one at a time).
|
||||||
</itemize>
|
</itemize>
|
||||||
|
|
||||||
<sect2> Diagnose Problem from the Console <label id="consoleD">
|
<sect2> Diagnose Problem from the Console <label id="consoleD">
|
||||||
<p> At the console (or another working terminal), use "top" or "ps
|
<p> One test is to try to copy a something to the terminal (It might
|
||||||
-al" to see if getty is running on the port. Don't confuse it with
|
be a good idea to try this near the start of the installation process
|
||||||
getty programs running on other ports or on the virtual consoles. You
|
before setting up getty). You may use the Linux copy command such as:"cp
|
||||||
will not get a login prompt unless getty runs. If getty isn't
|
file_name /dev/ttyS1". Or your could use: "echo any_word >
|
||||||
running, carefully check the format for calling getty in /etc/inittab.
|
/dev/ttySx". If it doesn't work, use stty to make the interface as
|
||||||
Make sure that it includes the current runlevel (shown by typing the
|
simple as possible with everything disabled (such as hardware flow
|
||||||
command "runlevel") and that it is valid for your flavor of getty.
|
control: -crtscts; parity, and modem control signals: clocal). Be
|
||||||
|
sure the baud rates and the bits/byte are the same. If nothing
|
||||||
One test is to try to copy a short file to the terminal (It might be a
|
happens verify that the port is alive with a voltmeter per the next
|
||||||
good idea to try this near the start of the installation process
|
section.
|
||||||
before setting up getty). Use the Linux copy command such as: cp
|
|
||||||
file_name /dev/ttyS1. If it doesn't work, use stty to make the
|
|
||||||
interface as simple as possible with everything disabled (such as
|
|
||||||
hardware flow control: -crtscts; parity, and modem control signals:
|
|
||||||
clocal). Be sure the baud rates and the bits/byte are the same. If
|
|
||||||
nothing happens verify that the port is alive with a voltmeter per the
|
|
||||||
next section.
|
|
||||||
|
|
||||||
<sect2> Measure Voltages <label id="measure_volts">
|
<sect2> Measure Voltages <label id="measure_volts">
|
||||||
<p> If you have a voltmeter handy check for a negative voltage (-4v to
|
<p> If you have a voltmeter handy check for a negative voltage (-4v to
|
||||||
|
@ -4887,21 +4939,24 @@ grounded). If there is no such negative voltage then check for it at
|
||||||
the transmit pin (TxD) on the computer (see <ref id="DB_pin-out"
|
the transmit pin (TxD) on the computer (see <ref id="DB_pin-out"
|
||||||
name="DB9-DB25"> for the pin-out). If it's present there but not at
|
name="DB9-DB25"> for the pin-out). If it's present there but not at
|
||||||
the receive pin (RxD) at the terminal, then the cable is bad (loose
|
the receive pin (RxD) at the terminal, then the cable is bad (loose
|
||||||
connection, broken wire, or not a null-modem). If voltage is absent,
|
connection, broken wire, or not a null-modem). If voltage is absent
|
||||||
then the serial port on the computer is dead. Test it with a software
|
at the computer, then its serial port is dead. Test it with a
|
||||||
diagnostic test or replace it.
|
software diagnostic test or replace it.
|
||||||
|
|
||||||
If the serial port is alive, you may want to send a file to it (with
|
If the serial port is alive, you may want to send a file to it (with
|
||||||
modem controls disabled) and see if anything gets to it. To check for
|
modem controls disabled) and see if anything gets to it. To check for
|
||||||
a transmitted signal with an analog voltmeter, look at the needle at
|
a transmitted signal with a voltmeter, check for a steady negative
|
||||||
-12 V when the line is idle. Then start sending a file (or start
|
voltage when the line is idle. Then start sending a file (or start
|
||||||
getty). You should see the needle dropping to 0 and fluttering about
|
getty). On an analog meter you should see the needle dropping to
|
||||||
0 as it measures short-run averages of the bit stream. You can see
|
almost 0 and fluttering about 0 as it measures short-run averages of
|
||||||
this also on the AC scale provided that your meter has a capacitor to
|
the bit stream. On a digital meter you will not see the fluctuations
|
||||||
block out DC voltages when on the AC scale. If it doesn't, then the
|
as well but you can switch to the AC scale to see the AC voltage
|
||||||
idle DC of -12 V will cause a high false AC reading. Without a meter,
|
created by the flow of bits. If your meter fails to block out DC on
|
||||||
you could connect a known good device (such as another terminal or an
|
the AC scale (the default of most analog meters), then you could get a
|
||||||
external modem) to the serial port and see if it works OK.
|
false high AC reading when looking at the idle DC of -12 V on the AC
|
||||||
|
scale. Without a meter, you could connect a known good device (such
|
||||||
|
as another terminal or an external modem) to the serial port and see
|
||||||
|
if it works OK.
|
||||||
|
|
||||||
<sect1> Slow: pauses of several seconds between bursts of characters
|
<sect1> Slow: pauses of several seconds between bursts of characters
|
||||||
<p> You likely have mis-set interrupts> See the Serial-HOWTO section
|
<p> You likely have mis-set interrupts> See the Serial-HOWTO section
|
||||||
|
|
Loading…
Reference in New Issue