Ftp users are unable to upload, create and modify
files and folder on VSFTPD.
(they could login and see files and folders,
but they couldn't modify)

My VPS is running ubuntu 14.04 LTS.

I installed VSFTPD to manage the folder
of websites in /var/www/html/(userfolder).
Then i installed XINETD to run VSFTPD.

About permissions:
I tried to give to the main folder 766 755 and (just for test) also 777.
I tried a lot of other configuration... ...but, no one result...

I create user whit this:
sudo useradd -c "example comment" -g ftp -m -k /dev/null -s /bin/false -d /var/www/html/(user-folder) user

After the creation of a user i run with root these 2 line:

chown (user):ftp /var/www/html/(folder)

chmod a-w /var/www/html/(folder)

What i failed???

# _________________________________
#                        My vsftpd.conf is this:
# _________________________________
#         File di configurazione Server FTP
#
# Acc
anonymous_enable=NO
anon_upload_enable=NO
anon_mkdir_write_enable=NO
# DIR SETTINGS
local_enable=YES
write_enable=YES
dirmessage_enable=YES
# LOG SETTINGS
xferlog_enable=YESiii
xferlog_file=/var/www/vsftpd.log
xferlog_std_format=YES
# CONNECTION SETTINGS
connect_from_port_20=NO
# listen=NO must be started from inetd whit: etc
listen=NO
listen_port=21
ftpd_banner=Welcome!
chroot_local_user=YES
check_shell=NO
# USERS SETTINGS
userlist_deny=NO
userlist_enable=YES
# WRITE ALLOWED USER IN IT
userlist_file=/etc/vsftpd.user_list
# PAM
# pam_service_name=/bin/false
# pam_service_name=vsftpd
pam_service_name=ftp
# Sand
seccomp_sandbox=NO


___________________________________

My XINETD.CONF is this:
___________________________________

# Simple configuration file for xinetd
#
# Some defaults, and include /etc/xinetd.d/

#defaults
#{
#
# Please note that you need a log_type line to be able to use log_on_success
# and log_on_failure. The default is the following :
# log_type = SYSLOG daemon info
#
#}

service ftp
{
    socket_type = stream
    wait = no
    user = root
    server = /usr/sbin/vsftpd
    log_on_success += DURATION
    nice = 10
    disable = no
}

includedir /etc/xinetd.d

The last error in the vsftpd's log is this:
Mon Jun 23 08:05:23 2014
1 7... 0 /sda.txt a _ i r (user) ftp 0 * i

The port 21 is open.