My postgres is not logging anymore

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Hello.
I have a postgres cluster made by two nodes with OS Ubuntu 14.04.
About two weeks ago I did a minor update of postgres to the version
9.4.1-1.pgdg70+1. After I had to shutdown the machines and I could
start them just last week.
Since then postgresql has been stopping logging on both nodes. If I
destroy the log file and I do a restart, a new file is created but it
remains empty. I have tried to change some configuration parameters
with no success. I have tried to restart postgres on both nodes and
relocate the service as well - nothing. Apart from this everything is
working fine and my applications don't show any errors during the
connection to the database. Any ideas about how to have back the log?

Here my configuration file postgresql.conf:

- ---------------------------------------------------------
listen_addresses = '*'

work_mem = 32MB
wal_level = 'hot_standby'
synchronous_commit = on

checkpoint_segments = 128
checkpoint_completion_target = 0.9

archive_mode = on
archive_command = 'rsync -e ssh -a %p
postgres(at)172(dot)31(dot)7(dot)1:/var/lib/postgresql/pg_archive/%f'

max_wal_senders = 5
wal_keep_segments = 32

hot_standby = on
max_standby_streaming_delay = 30s
wal_receiver_status_interval = 2s
hot_standby_feedback = on

log_min_messages = error
log_min_error_statement = error
log_min_duration_statement = 10000

log_connections = on
log_disconnections = on
log_duration = on
log_error_verbosity = terse
log_statement = 'all'
log_timezone = 'localtime'

datestyle = 'iso, mdy'
timezone = 'localtime'
default_text_search_config = 'pg_catalog.english'
restart_after_crash = off
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