Why is Postgres not respecting my log file name convention dictated by "log_filename"? I’m using Postgres 9.5 on Ubuntu 14.04.  I have these settings set in my /etc/postgresql/9.5/main/postgresql.conf file

log_filename = 'postgresql-%Y-%m-%d_%H%M%S.log' # log file name pattern,
                                        # can include strftime() escapes
#log_file_mode = 0600                   # creation mode for log files,
                                        # begin with 0 to use octal notation
log_truncate_on_rotation = on           # If on, an existing log file with the
                                        # same name as the new log file will be
                                        # truncated rather than appended to.
                                        # But such truncation only occurs on
                                        # time-driven rotation, not on restarts
                                        # or size-driven rotation.  Default is
                                        # off, meaning append to existing files
                                        # in all cases.
#log_rotation_age = 1d                  # Automatic rotation of logfiles will
                                        # happen after that time.  0 disables.
log_rotation_size = 50MB                # Automatic rotation of logfiles will
                                        # happen after that much log output.
                                        # 0 disables.


Although I have restarted my server using the

sudo /etc/init.d/postgresql restart


command, when I run some transaction and check my logs, the log files are not respecting my files names …

myuser@mymachine:~$ ls -al /var/log/postgresql/
total 1912144
drwxrwxr-t  2 root     postgres       4096 Dec 31 14:27 .
drwxrwxr-x 14 root     syslog         4096 Dec 31 06:55 ..
-rw-r-----  1 postgres postgres 1957826560 Dec 31 14:30 postgresql-9.5-main.log
-rw-r-----  1 postgres postgres     194785 Dec 26 06:46 postgresql-9.5-main.log.1


Why is Postgres not respecting the filename convention I specified in the configuration file and how do I get it to?
You need to edit the values for logging_collector and log_directory so that it knows you want to manage the logs and where they should go.

https://www.postgresql.org/docs/9.5/static/runtime-config-logging.html 

Look at the section for log_filename.