how to detect USB be forcely unplug

minge.zu · 10-24-2008, 12:41 AM

Hi,everyone.I am newbie in Linux programming.
Now i have a problem.in my program,i have to know the flash disk whether is being unplugged.but i don't know how to do.is there any system message can be captured? or any API to check system conditions?
any advices are appreciated!

David the H. · 10-24-2008, 02:08 AM

dmesg (or /var/log/dmesg) will show output when devices are added or removed, but the output can be hard to process for specific changes.

I don't know if this is the best way, but the hal daemon monitors and reports all system hardware changes. "lshal --monitor" will show you what changes are made to the hal listings in real time as a device is added or removed, or even mounted and unmounted.

You can then use lshal with grep or something to test the state of the device in a script. Or alternately, you can use ivman, a daemon that lets you run commands on hal events. For example, you could have ivman create a text file when a device is added, and delete it when the device is removed. Then you can test for existence of that file.

I only know a little about scripting, so this is the extent of what I know, and there are probably better ways to do this in other programming languages. But hopefully this will give you some ideas.

jschiwal · 10-24-2008, 02:43 AM

HAL communicates with userland programs like KDE or Gnome via DBUS. You might want to study the python scripts that many systems have for examples on how to register with DBUS/HAL to receive event messages.

minge.zu · 10-28-2008, 05:14 AM

Quote:

Originally Posted by David the H.

dmesg (or /var/log/dmesg) will show output when devices are added or removed, but the output can be hard to process for specific changes.

I don't know if this is the best way, but the hal daemon monitors and reports all system hardware changes. "lshal --monitor" will show you what changes are made to the hal listings in real time as a device is added or removed, or even mounted and unmounted.

You can then use lshal with grep or something to test the state of the device in a script. Or alternately, you can use ivman, a daemon that lets you run commands on hal events. For example, you could have ivman create a text file when a device is added, and delete it when the device is removed. Then you can test for existence of that file.

I only know a little about scripting, so this is the extent of what I know, and there are probably better ways to do this in other programming languages. But hopefully this will give you some ideas.

thank you very much!I have taken a try as your advice.some informations can be captured with the commands `dmesg`,`lshal` and so on when unplug event takes place.but the difficult is that i can't determine which device is what i need...

minge.zu · 10-28-2008, 05:21 AM

Quote:

Originally Posted by jschiwal

HAL communicates with userland programs like KDE or Gnome via DBUS. You might want to study the python scripts that many systems have for examples on how to register with DBUS/HAL to receive event messages.

thank you! I am studying the python scripts related with DBUS/HAL.
i used:

Code:

bus.add_signal_receiver(device_removed, 'DeviceRemoved',
                                     'org.freedesktop.Hal.Manager',
                                     'org.freedesktop.Hal',
                                     '/org/freedesktop/Hal/Manager')

that will inform me when device removed.but the same problem is that i can't determine whether the device is what i need.maybe 'GetProperty(...) is useful.but i have no idea how to use it

do you have any clue?