WAL files are not copied

I'm using postgres 9.3 on Ubuntu 14.04 and I'm currently setting up a WAL backup. These are my changes to the postgresql.conf: [as described here: http://ift.tt/1keROsw ]

- Settings -

wal_level = archive # minimal, archive, or hot_standby # (change requires restart)

- Archiving -

archive_mode = on # allows archiving to be done

archive_command = 'cp %p /home/userName/Documents/WALS'

I did a 'sudo service postgresql restart' after changing the config and there are wal files generated:

root@control:/var/lib/postgresql/9.3/main/pg_xlog# ls -hlrt
total 49M
-rw------- 1 postgres postgres  16M Dez  2 14:24 000000010000000000000002
-rw------- 1 postgres postgres  16M Dez  2 14:24 000000010000000000000003
drwx------ 2 postgres postgres 4,0K Dez  2 14:24 archive_status
-rw------- 1 postgres postgres  16M Dez  2 14:25 000000010000000000000004



root@control:/var/lib/postgresql/9.3/main/pg_xlog# ls archive_status/
000000010000000000000002.ready  000000010000000000000003.ready

I assume that the archive_status means that WAL segments 2 and 3 are ready to be archived. But I don't find anything in the Documents/WALS (which exists).

Could someone give me a hint?