ntpdate output to text file

[vince66]

Hello guys,
I would like redirect the output of ntpdate(8) into a file.
However, the command:

ntpdate -b pool.ntp.org | tee -a filename.txt

not fills the text file with the output I see on the screen.
How can I do ?

Thanks in advance.

 

[SirDice]

Parts of the output are printed on STDERR.

Bourne shells:
ntpdate -b pool.ntp.org >> filename.txt 2>&1

C shells:
ntpdate -b pool.ntp.org >>& filename.txt