install fail postgresql in ubuntu 12.04

# aptitude install postgresql-9.1 postgresql-client-9.1

Configurando libpq5 (9.1.4-0ubuntu12.04) ...
Configurando postgresql-client-common (129) ...
Configurando postgresql-client-9.1 (9.1.4-0ubuntu12.04) ...
update-alternatives: a usar /usr/share/postgresql/9.1/man/man1/psql.1.gz para disponibilizar /usr/share/man/man1/psql.1.gz (psql.1.gz) em modo automático.
Configurando postgresql-common (129) ...
Building PostgreSQL dictionaries from installed myspell/hunspell packages...
  en_us
  pt
  pt_br
Configurando postgresql-9.1 (9.1.4-0ubuntu12.04) ...
Creating new cluster (configuration: /etc/postgresql/9.1/main, data: /var/lib/postgresql/9.1/main)...
initdb: could not change permissions of directory "/var/lib/postgresql/9.1/main": Operação não permitida
Error: initdb failed
Error: could not create default cluster. Please create it manually with

  pg_createcluster 9.1 main --start

or a similar command (see 'man pg_createcluster').
update-alternatives: a usar /usr/share/postgresql/9.1/man/man1/postmaster.1.gz para disponibilizar /usr/share/man/man1/postmaster.1.gz (postmaster.1.gz) em modo automático.
Processando gatilhos para libc-bin ...
ldconfig deferred processing now taking place

Então tento rodar o comando:
#pg_createcluster 9.1 main --start

e recebo o erro:
Creating new cluster (configuration: /etc/postgresql/9.1/main, data: /var/lib/postgresql/9.1/main)...
could not change directory to "/root"
initdb: could not change permissions of directory "/var/lib/postgresql/9.1/main": Operação não permitida
Error: initdb failed