Ubuntu 16.04 Couchdb 1.6.1 fresj install

[max]

Hi,

I just installed Couchdb 1.6.1 from apt on Ubuntu 16.04 but I'm stucksince
I changed the port to make CouchDB listen on port 80.
I already faced this problem on Ubuntu 12.04 with an install from source
and I just replaced the user in /usr/local/etc/default/couchdb :
COUCHDB_USER=root
But with this apt install I tough just editing /etc/init/couchdb.conf and
change exec su couchdb -c /usr/bin/couchdb  TO exec su root -c
/usr/bin/couchdb  will make it but it did not.
The error I got when I run "sudo couchdb" is

Apache CouchDB 1.6.1 (LogLevel=info) is starting.
Apache CouchDB has started. Time to relax.
[info] [<0.33.0>] Apache CouchDB has started on http://0.0.0.0:80/
[error] [<0.33.0>] Failed to write to URI file /run/couchdb/couch.uri: no
such file or directory
[error] [<0.32.0>] {error_report,<0.32.0>,
                    {<0.32.0>,crash_report,
                     [[{initial_call,
                        {application_master,init,
                         ['Argument__1','Argument__2','Argument__3',
                          'Argument__4']}},
                       {pid,<0.32.0>},
                       {registered_name,[]},
                       {error_info,
                        {exit,
                         {enoent,
                          {couch_app,start,
                           [normal,
                            ["/etc/couchdb/default.ini",
                             "/etc/couchdb/local.ini"]]}},
                         [{application_master,init,4,
                           [{file,"application_master.erl"},{line,134}]},
                          {proc_lib,init_p_do_apply,3,
                           [{file,"proc_lib.erl"},{line,240}]}]}},
                       {ancestors,[<0.31.0>]},
                       {messages,[{'EXIT',<0.33.0>,normal}]},
                       {links,[<0.31.0>,<0.7.0>]},
                       {dictionary,[]},
                       {trap_exit,true},
                       {status,running},
                       {heap_size,987},
                       {stack_size,27},
                       {reductions,153}],
                      []]}}
{"init terminating in
do_boot",{{badmatch,{error,{enoent,{couch_app,start,[normal,["/etc/couchdb/default.ini","/etc/couchdb/local.ini"]]}}}},[{couch,start,0,[{file,"couch.erl"},{line,18}]},{init,start_it,1,[]},{init,start_em,1,[]}]}}

So I tried to create the couch.uri file and then I could start couchdb on
port 80 but only with the command "sudo couchdb". The service "sudo
systemctl restart couchdb" is not able to start couchdb and when I try it
the couch.uri is deleted and so one... How to fix this properly ? I know I
could rewrite port 80 to 5984 using apache2 or nginx but I want to figure
out what is going on and I'd like to make it work.

Thanks for any hints.

Max.