This section is about the controlling the terminal-computer interface and/or changing the terminal set-up while using the terminal. It explains (or points to explanations of) how the user of a terminal can control and inspect the interface and how to use various commands provided by the device driver. It does not explain how to use the many application programs, shells or most Linux utilities. Two commands commonly used at the terminal are:
You should be able to turn on the power to the terminal, hit the "return" (or "enter") key and then get a login prompt. Then type your account name and your password when prompted for it. If nothing happens, make sure the host computer is OK. If the host computer is shut down (no power) what you type at the terminal keyboard may appear on the screen since the transmit and receive pins at the computer may be connected together resulting in echoing of characters by an "off" computer. If you can't log in when the host computer is running, see Trouble-Shooting.
When typing at the command line, the shell (such as the Bash shell) is reading what you type and reacting to it. What you type first passes thru the terminal driver part of your operating system. This driver may translate certain characters (such as changing the "return" character generated by the "return" key into a "new-line" character for Linux files). It also recognizes certain control codes which you may type at the keyboard such as ^C to interrupt the execution of a program. It also normally echos what you type back to the display. Stty may be used to configure how this terminal driver behaves, including disabling some (or all) of its functionality.
When the display doesn't look right or what you type doesn't display correctly, you may have a corrupted terminal interface. It could also be a bug in the program you're using, a hardware failure, or possibly an incorrect configuration. If everything was working normally but it suddenly goes bad, it may be that the interface got corrupted by something you did. Two ways to corrupt the interface are to send a binary file to the terminal or to abnormally exit an application program.
Your terminal will change its characteristics if sent certain escape sequences or control characters. It you inadvertently try to display a binary file, it might contain such sequences which may put your terminal into some strange mode of operation or even make it unusable. Always view or edit a binary file with programs designed for that purpose so that this doesn't happen. Most editors and pagers will handle binary OK so as not to corrupt the interface. Some may display a message telling you that they can't edit binary. But using "cat ...." or "cp .... /dev/tty.." where .... is a binary file, will send the binary to the terminal and likely corrupt things.
Corruption it can also happen when using a communications program where a remote computer may send binary to your screen. There are numerous other ways it can happen so be prepared for it. Even a supposed ASCII file may contain unwanted control codes.
To fix this problem reset the terminal. There may be a key which does this directly at the terminal (perhaps in setup mode) or you may try typing either "reset" or "setterm -reset" (although you may not be able to see what you're typing). This will send the reset string from the terminfo entry to the terminal.
Large application programs (such as editors) often use the stty command (or the like) in their code to temporarily change the stty configuration when you are running the program. This may put the device driver into "raw" mode so that every character you type goes directly thru to the application program. Echoing by the driver is disabled so that everything you see on the screen comes directly from the application program. Thus many control commands (such as ^C) may not work within such applications.
When you tell such an application to quit, the application program first restores the stty settings to what they were before the application program started. If you abnormally exit the program (you may guess this has happened when what you type no longer displays on the screen) then you may still be in "raw mode" on the command line.
To get out of raw mode and restore the normal stty settings type "stty sane". However, you must type this just after a "return" and end it with a "return". But hitting the "return" key doesn't do the job since the "return" code no longer gets translated to the new-lines that the shell is waiting for. So just type new-line (^J) instead of "return". The "sane" terminal interface may not be exactly the same as the normal one but it usually works. "stty sane" may also useful to get out of a corrupted interface due to other causes.
A number of control characters which you may type at the keyboard are "caught" by the terminal driver and perform various tasks. To see these control commands type: stty -a and look at lines 2-4. They are tersely explained in the stty manual pages. They may be changed to different control characters or disabled using the stty command. Thus your control characters might be different than those described below. They are used for command-line editing, interrupting, scrolling, and to pass the next character thru transparently.
While the terminal driver has a few commands for command-line editing, some shells have a built-in real editor (such as "readline" in the Bash shell). Such an editor is normally on by default so you don't need to do anything to enable it. If it's available you don't need to learn many of the following commands although they often still work along with the command-line editor. The most important to learn are ^C (interrupt), ^D, and scrolling.
If what you want to see scrolls off the bottom of the screen, you may prevent this by sending a "stop" signal (^S or Xoff) to the host (provided Xon-Xoff Flow Control is enabled). Send a "start signal to resume (^Q or Xon). Some terminals have a "No Scroll" key which will alternately send Xoff and Xon. If you have hardware flow control
If you want to both stop scrolling and quit, use ^C. If you want to stop scrolling to do something else but want to keep the program in memory so you can resume scrolling later, use ^Z suspend.
An alternative scrolling method is to pipe the output thru a pager such as more, less, or most. However, the output might not be standard output but could be error output which the pager doesn't recognize. To fix this you may need to use redirection "2>&1" to get the pager to work OK. It is often simpler to just use ^S and ^Q unless you need to scroll backwards.
At a PC console (emulating a terminal) you may scroll backwards by using Shift-PageUp. This is frequently needed since the scrolling is too fast to stop it where you want using ^S. Once you've scrolled backwards Shift-PageDown will scroll forward again.
^V sends the next character typed (usually a control character) directly thru the device driver with no action or interpretation. Echoed back are two ASCII characters such as ^C.
These utility programs will provide information about the terminal interface:
The terminal settings are normally set once when the terminal is installed using the setup procedures in the terminal manual. However, some settings may be changed when the terminal is in use. You normally would not give any "stty" of "setserial" commands when the terminal is in use as they are likely to corrupt the terminal interface. However, there are changes you may make to the appearance of the terminal screen or to its behavior without destroying the integrity of the interface. Sometimes these changes are made automatically by application programs so you may not need to deal with them.
One direct method of making such changes is to use the setup key at the terminal and then use menus or the like to make the changes. To do this you may need to be familiar with the terminal. The other 3 methods send an escape sequence from the computer to the terminal to make the changes. These 3 examples show different methods of doing this to set reverse video:
This is the easiest command to use. It uses long options (but doesn't use the -- before them) and consults the terminfo database to determine what code to send. You may change the color, brightness, linewrap, keyboard repeat, cursor appearance, etc.
The "tput" command is similar to "setterm" but instead of using ordinary words as arguments, you must use the abbreviations used by terminfo. Many of the abbreviations are quite terse and hard to remember.
In the example "echo ^[[7m" to set reverse video, the ^[ is the escape character. To type it type ^V^[ (or ^V followed by the escape key). To use this "echo" method you must find out what code to use from your terminal manual or from terminfo or termcap. It's simpler to use setterm or tput although echo will execute a little faster. So you might use echo ... in shell scripts which deal with only one type of terminal.
When you turn off the terminal the changes you made will be lost (unless you saved them in non-volatile terminal memory by pressing certain keys at the terminal). If you want to use them again without having to retype them, put the commands in a shell script or make it a shell function. Then run it when you want to make the changes. One way to make the changes semi-permanent is to put the commands in a file that runs each time you login or start up the computer.