The error messages could be something like "No modem detected", "Modem not responding", or (strange) "You are already online" (from Minicom). If you have installed an internal modem (serial port is builtin) or are using an external one and don't know what serial port it's connected to then the problem is to find the serial port. See My Serial Port is Physically There but Can't be Found This section is about finding out which serial port has the modem on it.
There's a program that looks for modems on commonly used serial ports called "wvdialconf". Just type "wvdialconf <a-new-file-name>". It will create the new file as a configuration file but you don't need this file unless you are going to use "wvdial" for dialing. See What is wvdialconf ? Unfortunately, if your modem is in "online data" mode, wvdialconf will report "No modem detected" See No response to AT
Your problem could be due to a winmodem (or the like) which can't be used with Linux. See Avoid most software modems The "setserial program may be used to detect serial ports but will not detect modems on them. Thus "wvdialconf" is best to try first.
Another way try to find out if there's a modem on a port is to start "minicom" on the port (after first setting up minicon for the correct serial port --you will need to save the setup and then exit minicom and start it again). Then type "AT" and you should see OK (or 0 if it's set for "digit result codes"). The results may be:
The modem should send you "OK" in response to your "AT" which you type to the modem (using minicom or the like). If you don't see "OK" (and in most cases don't even see the "AT" you typed either) the modem is not responding (assuming there is really a modem on the port you are typing to).
One reason that a real modem doesn't respond is that it is in "online data" mode where it can't accept any AT commands. It may be in use by another process. If such a process is running on the port you may see it by typing "ps -t ttyS2" or the like. However the process that's using the serial port (where the modem is) may be running on a terminal such at /dev/tty1 and will not be found using the above command.
You may have been using the modem and then abruptly disconnected (such as killing the process with signal 9). In that case your modem did not get reset to "command mode" where it can interact to AT commands. Thus the message from minicom "You are already online. Hangup first." Well, you are sort of online but you are may not be connected to anything over the phone line. wvdial will report "modem not responding" for the same situation.
To fix this as a last resort you could reboot the computer. Another way to try to fix this is to send +++ to the modem to tell it to escape back to "command mode" from "online data mode". On both sides of the +++ sequence there must be about 1 second of delay (nothing sent during "guard time"). This may not work if another process is using the modem since the +++ sequence could wind up with other characters inserted in between them or after the +++ (during the guard time). Ironically, even if the modem line is idle, putting an unexpected +++ is likely to set off an exchange of packets (or the like) that will violate the required guard time so that the +++ doesn't do what you wanted. +++ is usually in the string that is named "hangup string" so if you command minicom (or the like) to hangup it might work. Another way to do this is to just exit minicom and then run minicom again.
There must be very low noise on the line for it to work at even close to 56k. Some phone lines are so bad that the speeds obtainable are much slower than 56k (like 28.8k or even slower). Sometimes extension phones connected to the same line can cause problems. To test this you might connect your modem directly at the point where the telephone line enters the building with the feeds for everything else on that line disconnected (if others can tolerate such a test).
Flow control (both at your PC and/or modem-to-modem) may not be enabled. For the uploading case: If you have set a high DTE speed (like 115.2k) then flow from your modem to your PC may work OK but uploading flow in the other direction will not all get thru due to the telephone line bottleneck. This will result in many errors and the resending of packets. It may thus take far too long to send a file. In some cases, files don't make it thru at all.
For the downloading case: If you're downloading long uncompressed files or web pages (and your modem uses data compression) or if you've set a low DTE speed, then downloading may also be broken due to no flow control.
Make sure you are using the correct syntax for your version of
init. The different init's that are out there use different
syntax in the /etc/inittab file. Make sure you are using the
correct syntax for your version of getty.
Id "S3" is just an example. In this case look on the line which
starts with "S3" in /etc/inittab. This is causing the problem.
Make sure the syntax for this line is correct and that the device
(ttyS3) exists and can be found.
Make sure your modem is configured correctly. Look at registers
E and Q.
This can occur when your modem is chatting with getty.
If you use uugetty, verify that your /etc/gettydefs syntax is
correct by doing the following:
linux# getty -c /etc/gettydefs
This can also happen when the uugetty initialization is failing.
See section
uugetty Still Doesn't Work.
This can happen when your modem doesn't reset when DTR is dropped.
Greg Hankins saw his RD and SD LEDs go crazy when this happened.
You need to have your modem reset. Most Hayes compatible modems
do this with &D3, but on his USR Courier, he had to set
&D2 and S13=1. Check your modem manual (if you have
one).
There is a DEBUG option that comes with getty_ps. Edit your
config file
/etc/conf.{uu}getty.ttySN and
add DEBUG=NNN. Where NNN is one of the following
combination of numbers according to what you are trying to debug:
D_OPT 001 option settings
D_DEF 002 defaults file processing
D_UTMP 004 utmp/wtmp processing
D_INIT 010 line initialization (INIT)
D_GTAB 020 gettytab file processing
D_RUN 040 other runtime diagnostics
D_RB 100 ringback debugging
D_LOCK 200 uugetty lockfile processing
D_SCH 400 schedule processing
D_ALL 777 everything
DEBUG=010 is a good place to start.
If you are running syslogd, debugging info
will appear in your log files. If you aren't running syslogd
info will appear in /tmp/getty:ttySN for debugging
getty
and /tmp/uugetty:ttySN for uugetty, and in
/var/adm/getty.log. Look at the
debugging info and see what is going on. Most likely, you will need
to tune some of the parameters in your config
file, and reconfigure your modem.
You could also try mgetty. Some people have better luck with
it.
If a device (such as a modem) give evidence of working, then the serial port that it's on has been found. If it doesn't work at all, then you need to make sure your serial port can be found.
Check the BIOS menus and BIOS messages. For the PCI bus use lspci. If it's an ISA bus PnP serial port, try "pnpdump --dumpregs" and/or see Plug-and-Play-HOWTO. Using "scanport" will scan all ISA bus ports and may discover an unknown port that could be a serial port (but it doesn't probe the port). It could hang your PC. You may try probing with setserial. See Probing. If nothing seems to get thru the port it may be accessible but have a bad interrupt. See Extremely Slow: Text appears on the screen slowly after long delays.
If two ports have the same IO address then probing it will erroneously indicate only one port. Plug-and-play detection will find both ports so this should only be a problem if at least one port is not plug-and-play. All sorts of errors may be reported/observed for devices on "sharing" a port but the fact that there are two devices on the same a port doesn't seem to get detected (except hopefully by you). If the IRQs are different then probing for IRQs with setserial might "detect" this situation by failing to detect an IRQ. See Probing.
It's likely mis-set/conflicting interrupts. Here are some of the symptoms which will happen the first time you try to use a modem, terminal, or printer. In some cases you type something but nothing appears on the screen until many seconds later. Only the last character typed may show up. It may be just an invisible <return> character so all you notice is that the cursor jumps down one line. In other cases where a lot of data should appear on the screen, only a batch of about 16 characters appear. Then there is a long wait of many seconds for the next batch of characters. You might also get "input overrun" error messages (or find them in logs).
For more details on the symptoms and why this happens see the Serial-HOWTO section: "Interrupt Problem Details".
If it involves Plug-and-Play devices, see also Plug-and-Play-HOWTO.
As a quick check to see if it really is an interrupt problem, set the IRQ to 0 with "setserial". This will tell the driver to use polling instead of interrupts. If this seems to fix the "slow" problem then you had an interrupt problem. You should still try to solve the problem since polling uses excessive computer resources and sometimes drastically decreases your thruput.
Checking to find the interrupt conflict may not be easy since Linux supposedly doesn't permit any interrupt conflicts and will send you a /dev/ttyS?: Device or resource busy error message if it thinks you are attempting to create a conflict. But a real conflict can be created if "setserial" has incorrect information. Thus using "setserial" will not reveal the conflict (nor will looking at /proc/interrupts which bases its info on "setserial"). You still need to know what "setserial" thinks so that you can pinpoint where it's wrong and change it when you determine what's really set in the hardware.
What you need to do is to check how the hardware is set by checking jumpers or using PnP software to check how the hardware is actually set. For PnP run either "pnpdump --dumpregs" (if ISA bus) or run "lspci" (if PCI bus). Compare this to how Linux (e.g. "setserial") thinks the hardware is set.
One reason may be that whatever is on the serial port (such as a modem, terminal, printer) doesn't work as fast as you thought it did. A 56k Modem seldom works at 56k and the Internet often has congestion and bottlenecks that slow things down. If the modem on the other end does not have a digital connection to the phone line (and uses a special "digital modem" not sold in most computer stores), then speeds above 33.6k are not possible.
Another possible reason is that the serial driver thinks you have an obsolete serial port (UART 8250,16450 or early 16550). See What Are UARTs?. Use "setserial -g /dev/ttyS*". If it shows anything less than a 16550A, this is likely your problem. Then if "setserial" has it wrong, change it. See What is Setserial for more info. Of course if you really do have an obsolete serial port, lying about it to setserial will only make things worse.
Linux does not do any IRQ detection on startup. When the serial module loads it only does serial device detection. Thus, disregard what it says about the IRQ, because it's just assuming the standard IRQs. This is done, because IRQ detection is unreliable, and can be fooled. But if and when setserial runs from a start-up script, it changes the IRQ's and displays the new (and hopefully correct) state on on the startup screen. If the wrong IRQ is not corrected by a later display on the screen, then you've got a problem.
So, even though I have my ttyS2 set at IRQ 5, I still see
ttyS02 at 0x03e8 (irq = 4) is a 16550A
setserial to tell Linux the IRQ you are using.
Check the file permissions on this port with "ls -l /dev/ttyS?"_ If you own the ttyS? then you need read and write permissions: crw with the c (Character device) in col. 1. It you don't own it then it should show rw- in cols. 8 & 9 which means that everyone has read and write permission on it. Use "chmod" to change permissions. There are more complicated ways to get access like belonging to a "group" that has group permission.
This means that an operation requested by setserial, stty, etc. couldn't be done because the kernel doesn't support doing it. Formerly this was often due to the "serial" module not being loaded. But with the advent of PnP, it may likely mean that there is no modem (or other serial device) at the address where the driver (and setserial) thinks it is. If there is no modem there, commands (for operations) sent to that address obviously don't get done. See What is set in my serial port hardware?
If the "serial" module wasn't loaded but "lsmod" shows you it's now loaded it might be the case that it's loaded now but wasn't loaded when you got the error message. In many cases the module will automatically loaded when needed (if it can be found). To force loading of the "serial" module it may be listed in the file: /etc/modules.conf or /etc/modules. The actual module should reside in: /lib/modules/.../misc/serial.o.
When a port is "opened" by a program a lockfile is created in /var/lock/. Wrong permissions for the lock directory will not allow a lockfile to be created there. Use "ls -ld /var/lock" to see if the permissions are OK: usually rwx for everyone (repeated 3 times). If it's wrong, use "chmod" to fix it. Of course, if there is no "lock" directory no lockfile can be created there. For more info on lockfiles see the Serial-HOWTO subsection: "What Are Lock Files".
This means that someone else (or some other process) is supposedly using the serial port. There are various ways to try to find out what process is "using" it. One way is to look at the contents of the lockfile (/var/lock/LCK...). It should be the process id. If the process id is say 261 type "ps 261" to find out what it is. Then if the process is no longer needed, it may be gracefully killed by "kill 261". If it refuses to be killed use "kill -9 261" to force it to be killed, but then the lockfile will not be removed and you'll need to delete it manually. Of course if there is no such process as 161 then you may just remove the lockfile but in most cases the lockfile should have been automatically removed if it contained a stale process id (such as 261).
This means that the device you are trying to access (or use) is supposedly busy (in use) or that a resource it needs (such as an IRQ) is supposedly being used by another device. Sometimes it actually is "busy" but in other cases it erroneously appears to be "busy".
The ``resource busy'' part often means (example for ttyS2) ``You
can't use ttyS2 since another device is using ttyS2's
interrupt.'' The potential interrupt conflict is inferred from what
"setserial" thinks. A more accurate error message would be ``Can't
use ttyS2 since the setserial data (and kernel data) indicates
that another device is using ttyS2's interrupt''. If two devices
use the same IRQ and you start up only one of the devices, everything
is OK because there is no conflict yet. But when you next try to
start the second device (without quitting the first device) you get a
"... resource busy" error message. This is because the kernel only
keeps track of what IRQs are actually in use and conflicts don't
happen unless the devices are in use (open).
There are two cases. There may be a real interrupt conflict that is
being avoided. But if setserial has it wrong, there may be no reason
why ttyS2 can't be used, except that setserial erroneously predicts a
conflict. What you need to do is to find the interrupt setserial
thinks ttyS2 is using. This is easier said than done since you can't
use the "setserial" command for ttyS2 since the IRQ for ttyS2 is
supposedly "busy" and you will get the same "... busy" error message.
To fix this either reboot or: exit or gracefully kill all likely
conflicting processes. If you reboot: 1. Watch the boot-time
messages for the serial ports. 2. Hope that the file that runs
"setserial" at boot-time doesn't (by itself) create the same conflict
again.
If you think you know what IRQ ttyS2 is using then you may look
at /proc/interrupts to find what else is currently using this IRQ.
You might also want to double check that any suspicious IRQs shown
here (and by "setserial") are correct (the same as set in the
hardware). A way to test whether or not it is a potential interrupt
conflict is to set the IRQ to 0 (polling) using "setserial". Then if
the busy message goes away, it was likely a potential interrupt
conflcit. It's not a good idea to leave it permanently set at 0 since
more CPU resources will be used.
This paragraph is mainly for the case when a modem is used for both
dial-in and dial-out. If the DCD signal is sent to a port, that port
will think it's busy. This problem can arise when you are trying to
dial out with a modem when DCD or DTR are not implemented correctly.
DCD should only be on (asserted) when there is an actual connection
(ie someone has dialed in), not when getty is watching the port.
Check to make sure that your modem is configured to only assert DCD
when there is a connection. DTR should be on (asserted) whenever
something is using, or watching the line, like getty,
kermit, or some other comm program.
These are some of the programs you might want to use in troubleshooting: