'ping' tty ports?

[rockom]

Is their a method with code to check on the existence and availability of tty ports (ttyS0, ttyUSB0, etc...) without actually opening them?

For example, if the port is already in use how do know if it's not available or no-existent.
Something like setserial that returns a list of tty's would be great.

Thanks,
-Rocko

[GeorgeVita]

Hi rockom, some ideas and 'retrigger' of this thread:

Existence of port: ls /dev/ttyS* /dev/ttyU*
Used & locked by any program: ls /var/lock/*ttyS* /var/lock/*ttyU*

>>> /dev/ttySx exist always as they are h/w reserved

Use minicom (must be installed) to 'lock' any port and check again.

More reading at: http://tldp.org/HOWTO/Serial-HOWTO.html

Regards,
George

[rockom]

Thank you for the reply.

I downloaded the source code for setserial to see how it's being done by that solution. It looks like setserial actually opens each port momentarily to check the status and gather information.

-Rocko

[meastwood]

You could try playing around with 'lsof' - this will list open files - it uses a device cache file. The man page says it is not great on reporting all locks. The down side also is that to read some information you need root access -


$ sudo lsof /dev/tty[0-9]
Output information may be incomplete.
COMMAND PID USER FD TYPE DEVICE SIZE NODE NAME
getty 2269 root 0u CHR 4,4 652 /dev/tty4
getty 2269 root 1u CHR 4,4 652 /dev/tty4
getty 2269 root 2u CHR 4,4 652 /dev/tty4
getty 2270 root 0u CHR 4,5 655 /dev/tty5
getty 2270 root 1u CHR 4,5 655 /dev/tty5
getty 2270 root 2u CHR 4,5 655 /dev/tty5
getty 2274 root 0u CHR 4,2 646 /dev/tty2
getty 2274 root 1u CHR 4,2 646 /dev/tty2
getty 2274 root 2u CHR 4,2 646 /dev/tty2
getty 2276 root 0u CHR 4,3 649 /dev/tty3
getty 2276 root 1u CHR 4,3 649 /dev/tty3
getty 2276 root 2u CHR 4,3 649 /dev/tty3
getty 2277 root 0u CHR 4,6 658 /dev/tty6
getty 2277 root 1u CHR 4,6 658 /dev/tty6
getty 2277 root 2u CHR 4,6 658 /dev/tty6
console-k 2806 root 12r CHR 4,0 1808 /dev/tty0
Xorg 2994 root 5w CHR 4,7 2318 /dev/tty7
getty 3395 root 0u CHR 4,1 643 /dev/tty1
getty 3395 root 1u CHR 4,1 643 /dev/tty1
getty 3395 root 2u CHR 4,1 643 /dev/tty1

An extra flag can be used to make the output more friendly for scripts - such as 'awk'.