No meu caso, a razão era PERL5LIB, apontando para o diretório HOME de outro usuário:
postgres@delly:~$ echo $PERL5LIB
/home/sveta/build/mysql-sandbox/share/perl/5.22.1:
Depois de configurá-lo para uma string vazia, o psql começou a trabalhar:
postgres@delly:~$ psql
Can't locate strict.pm: /home/sveta/build/mysql-sandbox/share/perl/5.22.1/strict.pm: Permission denied at /usr/bin/psql line 19.
BEGIN failed--compilation aborted at /usr/bin/psql line 19.
postgres@delly:~$ echo $PERL5LIB
/home/sveta/build/mysql-sandbox/share/perl/5.22.1:
postgres@delly:~$ export PERL5LIB=
postgres@delly:~$ echo $PERL5LIB
postgres@delly:~$ psql
psql (9.5.10)
Type "help" for help.
postgres=#