Most info on getty has been moved to Modem-HOWTO with a little info on the use of getty with directly connected terminals now found in Text-Terminal-HOWTO.
A few Linux programs will monitor various modem control lines and indicate if they are positive (1 or green) or negative (0 or red).
irqtune will give serial port interrupts higher
priority to improve performance.hdparm for hard-disk tuning may help some more.
Don't ever use setserial with Laptops (PCMCIA).
setserial is a program which allows you to tell the device driver
software the I/O address of the serial port, which interrupt (IRQ) is
set in the port's hardware, what type of UART you have, etc. It can
also show how the driver is currently set. In addition, it can probe
the hardware (if certain options are given).
If you only have one or two serial ports, they will usually get set up
correctly without using setserial. Otherwise (or if there are
problems with the serial port) you will likely need to deal with
setserial. Besides the manual for setserial, check out info in
/usr/doc/setserial.../ or the like. It should tell you how
setserial is handled in your distribution of Linux.
Setserial is often run automatically at boot-time by a start-up
shell-script. It will only work if the serial module is loaded. If
you should for some reason unload the serial module later on, the
changes previously made by setserial will be forgotten by the
kernel (but not by /etc/serial.conf). So setserial must be run
again to reestablish them. In addition to running via a start-up
script, something akin to setserial runs when the serial module
is loaded. Thus when you watch the start-up messages on the screen it
may look like it ran twice, and in fact it has.
Setserial can set the time that the port will keep operating after it's closed (in order to output any characters still in its buffer in main RAM). This is needed at slow baud rates of 1200 or lower. It's also needed at higher speeds if there are a lot of "flow control" waits.
With appropriate options, setserial can probe (at a given I/O
address) for a serial port but you must guess the I/O address. If you
ask it to probe for /dev/ttyS2 for example, it will only probe at the
address it thinks ttyS2 is at. If you tell setserial that ttyS2 is at
a different address, then it will probe at that address, etc. See
Probing
Setserial does not set either IRQ's nor I/O addresses in the serial port hardware itself. It's set in the hardware either by jumpers or by plug-and-play. You must tell setserial these identical values that have been set in the hardware. Do not just invent some values that you think would be nice to use and then tell them to setserial. However, if you know the I/O address but don't know the IRQ you may command setserial to attempt to determine the IRQ.
You can see a list of possible commands to use (but not the one-letter
options such as -v for verbose --which you should normally use when
troubleshooting) by just typing setserial with no arguments.
Note that setserial calls an I/O address a "port". If you type:
setserial-g /dev/ttyS*you'll see some info about how that device driver is configured for your ports. Add a "v" to the option "-g" to see more. But this doesn't tell you if the hardware actually has these values set in it. If fact, you can run setserial and assign a purely fictitious I/O address, any IRQ, and whatever uart type you would like to have. Then the next time you type "setserial ..." it will display these bogus values without complaint. Note that assignments made by setserial are lost when the PC is powered down so it is usually run automatically somewhere each time that Linux is booted.
In order to try to find out if you have a certain piece of serial
hardware you must first know (or guess) its I/O address (or the device driver
must have an I/O address for it, likely previously set by setserial).
To try to detect the physical hardware use the -v (verbose) and
autoconfig command to setserial. If the resulting message
shows a uart type such as 16550A, then you're OK. If instead it shows
"unknown" for the uart type, then there is supposedly no serial
port at all at that I/O address. Some cheap serial ports don't
identify themselves correctly so if you see "unknown" you still
might have a serial port there.
Besides auto-probing for uart type, setserial can auto-probe for IRQ's
but this doesn't always work right either. In versions of setserial
>= 2.15, your last probe test may be saved and put into the
configuration file /etc/serial.conf which will be used next
time you start Linux. The script that runs setserial at
boot-time does not usually probe, but you could change it so that it
does. See the next section.
Yes, but ... Your distribution may already do this on startup. But you may want to customize it. It's easy to do for setserial < 2.15. Just add some lines to the file that runs setserial on start-up. See Old configuration method: edit a script For example, for ttyS3 you would add:
/sbin/setserial /dev/ttyS3 auto_irq skip_test autoconfig
/sbin/setserial /dev/ttyS3 irq 5 uart 16550A skip_test
For versions >= 2.15 (provided your distribution implemented the change, Redhat didn't) it's much harder to do since the file that runs setserial on startup, /etc/init.d/setserial or the like was not intended to be edited by the user. There may be no helpful comments in it like there were in earlier versions.
When the kernel loads the serial module (or if the "module" is
built into the kernel) then only ttyS{0-3} are auto-detected and
the driver is set to IRQs 4 and 3 (regardless of what the hardware is
actually set at). You see this as a boot-time message just like as if
setserial had been run.. If you use 3 or more ports, this may
result in IRQ conflicts.
To fix such conflicts by telling setserial the true IRQs (or for other
reasons) there may be a file somewhere that runs setserial again.
This happens early at boot-time before any process uses the serial
port. In fact, your distribution may have set things up so that the
setserial program runs automatically from a start-up script at
boot-time. More info about how to handle this situation should be
found in /usr/doc/setserial.../ or the like.
Prior to setserial version 2.15, the way to configure setserial
was to manually edit the shell-script that ran setserial at boot-time.
Starting with version 2.15 (1999) of setserial this shell-script
is not edited but instead gets its data from a configuration file:
/etc/serial.conf. Furthermore not even serial.conf is intended to be
edited. Instead just use setserial on the command line.
Normally, what you changed with the setserial command is saved to the
configuration file (serial.conf) when you shutdown (normally) or
reboot. This only works if "###AUTOSAVE### or the like is on the
first line of serial.conf. If you should use setserial
experimentally and it doesn't work out right, then don't forget to
redo it so that the experimental settings don't get saved by mistake.
The file most commonly used to run setserial at boot-time (in
conformance with the configuration file) is now /etc/init.d/setserial
(Debian) or /etc/init.d/serial (Redhat), or etc., but it also should
not normally be edited.
To disable a port, use setserial to set it to
"uart none". The format of /etc/serial.conf appears to be just like
that of the parameters placed after "setserial" on the command line
with one line for each port. If you don't use autosave, you may edit
/etc/serial.conf manually. For 2.15, the Debian distribution installs
the system with autosave enabled, but Redhat 6.0 just had a file
/usr/doc/setserial-2.15/rc.serial which you have to move to
/etc/init.d/.
BUG: As of July 1999 there is a bug/problem since with ###AUTOSAVE### only the setserial parameters displayed by "setserial -G /dev/ttyS?" (where ? = 0, 1, 2, ...) get saved but the other parameters don't get saved. This will only affect a small minority of users since the parameters not saved are seldom used anyway. It's been reported as a bug and may be fixed by now.
In order to force the current settings set by setserial to be saved to
the configuration file (serial.conf) without shutting down, do what
normally happens when you shutdown: Run the shell-script
/etc/init.d/{set}serial stop. The "stop" command will save
the current configuration but the serial ports still keep working OK.
I some cases you may wind up with both the old and new configuration methods installed but hopefully only one of them runs at boot-time. Debian labeled obsolete files with "...pre-2.15".
Prior to 2.15 (1999) there was no /etc/serial.conf file to configure setserial. Thus you need to find the file that runs "setserial" at boot time and edit it. If it doesn't exist, you need to create one (or place the commands in a file that runs early at boot-time). If such a file is currently being used it's likely somewhere in the /etc directory-tree. But Redhat <6.0 has supplied it in /usr/doc/setserial/ although you need to move it to the /etc tree before using it. You might use "locate" to try to find such a file. For example, you could type: locate "*serial*".
What you are looking for could be named rc.serial, or 0setserial
(Debian). If such a file is supplied, it should contain a number of
commented-out examples. By uncommenting some of these and/or
modifying them, you should be able to set things up correctly. Make
sure that you are using a valid path for setserial, and a valid
device name. You could do a test by executing this file manually
(just type its name as the super-user) to see if it works right.
Testing like this is a lot faster than doing repeated reboots to get
it right. Of course you can also test a single setserial command
by just typing it on the command line.
The script /etc/rc.d/rc.serial was commonly used in the past.
The Debian distribution used /etc/rc.boot/0setserial.
Another file once used is /etc/rc.d/rc.local but it's
not a good idea to use this since it may not be run early enough.
It's been reported that other processes may try to open the serial
port before rc.local runs resulting in serial communication failure.
By default, both ttyS0 and ttyS2 share IRQ 4, while ttyS0 and ttyS3 share IRQ 3. But sharing serial interrupts is not permitted unless you: 1. have kernel 2.2 or better, and 2. you've complied in support for this, and 3. your serial hardware supports it. See
Interrupt sharing and Kernels 2.2+
If you only have two serial ports, ttyS0 and ttyS1, you're still OK since IRQ sharing conflicts don't exist for non-existent devices.
If you add an internal modem and retain ttyS0 and ttyS1, then you should attempt to find an unused IRQ and set it both on your serial port (or modem card) and then use setserial to assign it to your device driver. If IRQ 5 is not being used for a sound card, this may be one you can use for a modem. To set the IRQ in hardware you may need to use isapnp, a PnP BIOS, or patch Linux to make it PnP. To help you determine which spare IRQ's you might have, type "man setserial" and search for say: "IRQ 11".
stty does much of the configuration of the serial port but
since application programs (and the getty program) often handle it,
you may not need to use it much. It's handy if your having problems
or want to see how the port is set up. Try typing ``stty -a'' at your
terminal/console to see how it's now set. Also try typing it without
the -a (all) for a short listing which shows how it's set different
than normal. Don't try to learn all the setting unless you want to
become a serial guru. Most of the defaults should work OK and some of
the settings are needed only for certain obsolete dumb terminals made
in the 1970's (but not much after that)
Whereas setserial only deals with actual serial ports, stty is
used both for serial ports and for virtual terminals such as the standard
Linux text interface at a PC monitor. For the PC monitor, many of the
stty settings are meaningless. Changing the baud rate, etc. doesn't
appear to actually do anything.
Here are some of the items stty configures: speed (bits/sec), parity,
bits/byte, # of stop bits, strip 8th bit?, modem control signals, flow
control, break signal, end-of-line markers, change case, padding, beep
if buffer overrun?, echo, allow background tasks to write to
terminal?, define special (control) characters (such as what key to
press for interrupt). See the stty man or info page for more
details. Also see the man page: termios which covers the same
options set by stty but (as of mid 1999) covers features which the
stty man page fails to mention.
With some implementations of getty (getty_ps package), the commands that one would normally give to stty are typed into a getty configuration file: /etc/gettydefs. Even without this configuration file, the getty command line may be sufficient to set things up so that you don't need stty."')
One may write C programs which change the stty configuration, etc. Looking at some of the documentation for this may help one better understand the use of the stty command (and its many possible arguments). Serial-Programming-HOWTO is useful. The manual page: termios contains a description of the C-language structure (of type termios) which stores the stty configuration in computer memory. Many of the flag names in this C-structure are almost the same (and do the same thing) as the arguments to the stty command.
Using stty to inspect or configure the terminal that you are
currently using is easy. Doing it for a different (foreign) terminal
or serial port is tricky. For example, let's say you are at the PC
monitor (tty1) and want to use stty for the serial port ttyS2.
You need to use the redirection operator <. First, be warned that
if there is a terminal on ttyS2 and a shell running on that terminal,
then what you see will likely be deceptive and trying to set it will
not work. See
Two Interfaces at a Terminal to understand it.
Type ``stty -a < /dev/ttyS2'' to look at the settings of ttyS2. Use the same redirection operator < to set ttyS2. This makes ttyS2 the standard input to stty. This gives the stty program a link to the "file" ttyS2 so that it may "read" it. But instead of reading the bytes sent to ttyS2 as one might expect, it uses the link to find the configuration settings of the port so that it may read or change them. Some people try to use ``stty ... > /dev/ttyS2'' to set the terminal. This will not do it. Instead, it takes the message normal displayed by the stty command for the terminal you are on (say tty1) and sends this message to ttyS2. But it doesn't change any settings for ttyS2.
Here's another problem with the redirection operator. Sometimes when trying to use stty, the command hangs and nothing happens (you don't get a prompt for a next command even after hitting <return>). This is likely due to the port being stuck because it's waiting for one of the modem control lines to be asserted. For example, unless you've set "clocal" to ignore modem control lines, then if no CD signal is asserted the port will not open and stty will not work for it. A similar situation seems to exist for hardware flow control. If the cable for the port doesn't even have a conductor for the pin that needs to be asserted then there is no easy way to stop the hang.
One way to try to get out of the above hang is to use a program on the port that will force it to operate even if the control lines say not to. Then hopefully this program might set the port so it doesn't need the control signal in the future in order to open: clocal or -crtscts. To use "minicom" to do this you have to reconfigure minicom for another ttyS, etc, and then exit it and restart it. Since you then have to reconfigure minicom again, it may be simpler to just reboot the PC.
Versions starting with 1.17 (still not released as of mid 1999) will no longer need to use redirection (<) but instead will use ``stty ... -F /dev/ttyS2'' (or --file instead of F) etc. This should force the port to open and avoid the 2nd problem with redirection.
When using a shell (such as bash) with command-line-editing enabled there are two different terminal interfaces (what you see when you type stty -a). When you type at the command line you have a temporary "raw" interface (or raw mode) where each character is read by the command-line-editor as you type it. Once you hit the <return> key, the command-line-editor is exited and the terminal interface is changed to the nominal "cooked" interface (cooked mode) for the terminal. This cooked mode lasts until the next prompt is sent to the terminal. Note that one never types anything to this cooked mode but what was typed in raw mode becomes cooked mode as soon as one hits the <return> key.
When a prompt is sent to the terminal the terminal goes from "cooked" to "raw" mode (just like it does when you start an editor since you are starting the command-line editor). The settings for the "raw" mode are based only on the basic settings taken from the "cooked" mode. Raw mode keeps these setting but changes several other settings in order to change the mode to "raw". It is not at all based on the settings used in the previous "raw" mode. Thus if one uses stty to change settings for the raw mode, such settings will be lost as soon as one hits the <return> key at the terminal that has supposedly been "set".
Now when one types stty to look at the terminal interface, one may either get a view of the cooked mode or the raw mode. You need to figure out which one you're looking at. It you use stty from another terminal to deal with a terminal that is displaying a command line, then the view is that of the raw mode. Any changes made will only be made to the raw mode and will be lost when someone presses <return> at the terminal you tried to "set". But if you type a stty command at your terminal (without using < for redirection) and then hit <return> it's a different story. The <return> puts the terminal in cooked mode. Your changes are saved and will still be there when the terminal goes back into raw mode (unless of course it's a setting not allowed in raw mode).
This situation can create problems. For example, suppose you corrupt your terminal interface and to restore it you go to another terminal and "stty sane <dev/ttyS1" to restore it. It will not work! Of course you can try to type "stty sane ..." at the terminal that is corrupted but you can't see what you typed. All the above not only applies to dumb terminals but to virtual terminals used on a PC Monitor as well as to the terminal windows in X. In other words, it applies to almost everyone who uses Linux. Luckily, a file that runs stty at boot-time will likely deal with a terminal (or serial port with no terminal) that has no shell running on it so there's no problem.
Should you need to have stty set up the serial interface each
time the computer starts up then you need to put the stty command
in a file that will be executed each time the computer is started up
(Linux boots). It should be run before the serial port is used
(including running getty on the port). There are many possible places
to put it. If it gets put in more than one place and you only know
about (or remember) one of those places, then a conflict is likely.
So make sure to document what you do.
One place to put it would be in the same file that runs setserial when the system is booted. The location is distribution and version dependent. It would seem best to put it after the setserial command so that the low level stuff is done first. If you have directories in the /etc tree where every file in them is executed at boot-time (System V Init) then you could create a file named "stty" for this purpose.
isapnp is a program to configure Plug-and-Play (PnP) devices
on the ISA bus including internal modems. It comes in a package
called "isapnptools" and includes another program, "pnpdump" which
finds all your ISA PnP devices and shows you options for configuring
them in a format which may be added to the PnP configuration file:
/etc/isapnp.conf. The isapnp command may be put into a startup file
so that it runs each time you start the computer and thus will
configure ISA PnP devices. It is able to do this even if your BIOS
doesn't support PnP. See Plug-and-Play-HOWTO.