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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 check this you might try connecting your modem directly to the point where the telephone line enters the building with the feed for everything else on that line disconnected (if others can tolerate that).
Flow control (both at your PC and/or modem) may not be enabled. If you have set a high DTE speed (like 115.2K) then flow from your modem to your PC may work OK but a lot of 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. If you're downloading long uncompressed files or web pages (and your modem uses data compression) or 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 you know about the existing serial ports before you installed an internal modem, then the problem is to find the new serial port. This is covered in the next section. 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 ?
Your problem could be due to a winmodem (or the like) which can't be used with Linux. See Avoid: winmodems. 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 to see if there's a modem on a port is to start "minicom" on the port (go to the setup menus with ^AO). Then type "AT" and you should see OK (or 0 if it's set for "digit result codes"). If it takes many seconds to get a response (including only the cursor moving down one line) then see Extremely Slow: Text appears on the screen slowly after long delays
Check the BIOS menus and BIOS messages. If it's an ISA bus PnP serial port, try "pnpdump --dumpregs" and/or see Plug-and-Play-HOWTO. For the PCI bus look at /proc/pci. You may try probing with setserial. See Probing If nothing seems to get thru the port it may be there but have a bad interrupt. See Extremely Slow: Text appears on the screen slowly after long delays
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 zero 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 but should still try to fix it since polling uses excessive computer resources.
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/ttySN: Device or resource busy error message if you attempt to create a conflict. But Linux can be tricked. For example if IRQ 5 is set in the hardware (by a jumper or Plug-and-Play) and "setserial" has told the driver it's IRQ 3, then the driver will not know that IRQ 5 is taken and will let some other device also use IRQ 5 with disastrous results. Thus when you get this error it means that Linux is wrong about how the IRQs are really set in the hardware. Checking for conflicts by looking at the settings using "setserial" or looking at /proc/interrupts will only tell you what Linux thinks and will not show any conflicts at all. Yet a conflict exists.
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" or run "lspci". Compare this to how Linux 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.
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 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.
A common cause of ``device busy'' errors, is that you set up your serial port with an interrupt already taken by something else. The serial driver knows what interrupts have been assigned by setserial (or the like) and assumes they have been set this way in the hardware. If they are not set this way in the hardware, the driver will not know about possible conflicts and ``device busy'' errors may never be seen. Instead, performance may be Extremely Slow with no error messages.
Linux doesn't complain when you assign two devices the same IRQ provided that neither device is in use. As each device starts up (initializes), it asks Linux for permission to use its hardware interrupt. Linux keeps track of which interrupt is assigned to whom, and if your interrupt is already in use, you'll see this "... busy" error message. Thus if two devices use the same IRQ and you start up only one of the devices, everything is OK. But when you next try to start the second device (without quitting the first device) you get "... busy". Of course if the driver doesn't know about the conflict because it has incorrect info about the acutal IRQ set in the hardware, then you will not see the "... busy" message. Both interrupts will be used simultaneously with extremely slow performance.
Now there's a problem when you try to use "setserial" and get this "... busy" message. Worst of all, "setserial" will neither tell you what IRQ the port is trying to use nor change it. This happens because using "setserial" to deal with a device is something like trying to start up that device. You can't use "setserial" on the device because its IRQ (what the driver thinks is the IRQ) is in use by another device. It shouldn't be this way but it is.
If this happens, how do you determine what the conflict is? You could try to figure out what the IRQ is by finding where setserial last set it (look at boot-time messages). Another way to deal with this is to look at /proc/interrupts and try to guess what the conflict is. Then exit or kill gracefully all possible conflicting processes and then try "setserial" again. Instead of this, you may just want to reboot, making sure that the file the runs "setserial" at boot-time doesn't create the same conflict again.
modemstat and statserial show the current state of
various modem signal lines (such as DTR, CTS, etc.)irqtune will give serial port interrupts higher
priority to improve performance.hdparm for hard-disk tuning may help some more.