[ubuntu-in] Command Line Problems

[ramnarayan.k at gmail.com]

Hi

Am having some CL problems

First sometimes when i used a command (say like dmesg -c)  am not able 
to view the entire output - when i scroll right to the top - where the 
command and the output i am not able to get to the top.

Why ? is there some setting i need to change to make the number of lines 
visible unlimited !!

Specific Problems with dmesg

*1 Am unable to pipe dmesg to a txt file output
tried using this command
dmesg -c > filename

tried it with sudo as well but got a file with 0 bytes
tried to add a dot txt extension same result file size 0 bytes


*2 Does dmesg have to be under su mode only
this is the message i get when i try is as normal used
> ram at ram-laptop:~$ dmesg -c
> klogctl: Operation not permitted

This does not occur everytime nd i cannot figure a pattern to it.

*3 After using dmesg -c i am unable on repeating the command i get no 
output. which means i either have to copy the dmesg to a file and read 
it / or worse reboot to see the whole thing again (after having an 
incomplete dmesg in the first place)

Further if i have a specific device i am searching checking for if i 
unplug and replug it the dmesg gives me only the last output (for the 
unplugged and replugged device)

I have tried removing the -c to clear buffer ring but i am still stuck 
with the latest unplugged and retarted lines and not the whole dmesg

So whats going on

I tried the -n (levels) and -s (bufsize) but i either get an error or 
nothing happens.

see sample below:
> ram at ram-laptop:~$ dmesg -s 32784
> [ 1143.048000] usb 1-1: USB disconnect, address 3
> [ 1143.048000] pl2303 ttyUSB0: pl2303 converter now disconnected from ttyUSB0
> [ 1143.052000] pl2303 1-1:1.0: device disconnected
> [ 1145.276000] usb 1-2: new full speed USB device using uhci_hcd and address 4
> [ 1145.428000] usb 1-2: configuration #1 chosen from 1 choice
> [ 1145.432000] pl2303 1-2:1.0: pl2303 converter detected
> [ 1145.432000] usb 1-2: pl2303 converter now attached to ttyUSB0
> ram at ram-laptop:~$ dmesg
> [ 1143.048000] usb 1-1: USB disconnect, address 3
> [ 1143.048000] pl2303 ttyUSB0: pl2303 converter now disconnected from ttyUSB0
> [ 1143.052000] pl2303 1-1:1.0: device disconnected
> [ 1145.276000] usb 1-2: new full speed USB device using uhci_hcd and address 4
> [ 1145.428000] usb 1-2: configuration #1 chosen from 1 choice
> [ 1145.432000] pl2303 1-2:1.0: pl2303 converter detected
> [ 1145.432000] usb 1-2: pl2303 converter now attached to ttyUSB0
> ram at ram-laptop:~$ 

***
hoping to know whats happening and how to rectify it.

thanks
ram