Hi,
I ran a program that writes continuously from 1 every line.
After some time I ran '/dev/null > temp'
Problem1: bash: /dev/null: Permission denied
(Yes, the permissions of /dev/null are correct ... crw-rw-rw-. I removed and created it again, but no change)
I used 'cat temp' to see the contents and first few lines deleted (working correctly).
Problem2: I can't open the file (with double click or with any graphical editor like gedit)

Apart from these problems, I have another question... Is there a way to trim a active log file to say 80% without affecting any logs that server might be writing.

Thank you

Adarsh

Problem 1

/dev/null is a device not a command, but is not even required for what you are doing as the remainder of the line is what is clearing the contents of temp:

Problem 2

As the file is being constantly written to, I am not suprised you are having issues opening the file with a graphical editor.

When I am looking at log files, I would tend to either cat the file or use tail -f:
To reduce the size of a file while it is still being used:

Either use > {file} this however *empties* the file completely (not reducing by 80%)
or move the current file to a new location:

Have you looked at what logrotate can do?

@Disillusionist
Even after the file is done with writing... it is not opening

@Catkin
Yes, read about it and it says with 'copytruncate' option it copies the original file and empties the file to zero. If possible I want to retain some recent data in that file.