I 'have already installed oracle-xe-universal_10.2.0.1-1.1_i386 in ubuntu.
The problem is that greek characters from the db appear like ??????.
How can i set the right nls_lang character set to solve the problem in ubuntu linux?
Character code point translation is in the realm of the client, try setting NLS_LANG environment variable.
If your client programs handle UTF8, as do many linux utilities, that is the best choice, set your <language>_<locale>.<characterset>, i.e.
Or french_france, or german_germany ... depends on the locale you want to use. Try a `putty` session to the host, the terminal can be set for many different character sets, i.e. ISO8859-<n> a.k.a. the WE8<n> or Western European, UTF, etc. under Window/Translation.
Try a few select ... from dual; statements in sqlplus with a literal, and different unicode values- the unistr() and dump() functions can come in quite handy.
select unistr('\ac20 euro' ) from dual;
... € euro ...
select dump( unistr('\ac20 euro' ) ) from dual;
... <ascii codes for the character values> ...
select dump( unistr('\ac20 euro' ),16 ) from dual; -- this one for hex dump