PostgreSQL doesn't log

I'm using ArchLinux and PostgreSQL 9.4.4 and have enabled the logging in the config file:

$ sudo egrep -v "^[[:blank:]]*($|#|//|/\*| \*|\*/)" /var/lib/postgres/data/postgresql.conf

max_connections = 1024          # (change requires restart)
shared_buffers = 128MB          # min 128kB
dynamic_shared_memory_type = posix  # the default is the first option
logging_collector = on      # Enable capturing of stderr and csvlog
log_directory = '/tmp'      # directory where log files are written,
log_filename = 'postgresql-%Y-%m-%d_%H%M%S.log' # log file name pattern,
log_file_mode = 0644            # creation mode for log files,
log_error_verbosity = verbose       # terse, default, or verbose messages
log_statement = 'all'           # none, ddl, mod, all
log_timezone = 'Asia/Jakarta'
datestyle = 'iso, dmy'
timezone = 'Asia/Jakarta'
lc_messages = 'en_CA.UTF-8'         # locale for system error message
lc_monetary = 'en_CA.UTF-8'         # locale for monetary formatting
lc_numeric = 'en_CA.UTF-8'          # locale for number formatting
lc_time = 'en_CA.UTF-8'             # locale for time formatting
default_text_search_config = 'pg_catalog.english'

then restart or reload the service:

sudo systemctl restart postgresql
sudo systemctl reload postgresql

the /tmp permission:

$ ll /tmp/ 
total 11656
drwxrwxrwt 22 root root       580 Jun 29 10:05 ./
drwxr-xr-x 17 root root      4096 Jun 10 08:04 ../
...

the /tmp usage:

$ df | grep /tmp
tmpfs            8159996    31204   8128792   1% /tmp

doing some query on psql, but the /tmp/postgresql-* still doesn't show up. What can I do to find which part that prevent log from being created?