SysAdminGear

When you log int your server you get some error like this:
/tmp/Rs6V6BOv: Disk quota exceeded

Probably cpanel is not running and users cant send files using FTP.

Probabaly you ran out of inodes.

Run this command:
# df -i

And check if any partition is 100%.

Inodes are related to number of files you have under a directory and not to the disk space used, you should be having a large number of tmp files or a huge mail queue.

You can check the tmp files on this file: /var/tmp and mail queue on this /var/spool/exim/input/

How to change default vsftpd port (TCP port 21)?

vsftpd (Very Secute FTP Daemon) is used by Fedora, Ubuntu, RHEL and other Linux based distros.

Changing default can be a good ideia for security reasons.

Login to your server as root

Open vsftpd.conf file (by default /etc/vsftp/vsftpd.conf or /etc/vsftpd.conf)
# nano vsftpd.conf

Find line that read as follows
listen_port=21

Then, replace port 21 with new port (example 23)
listen_port=231

Save and Exite. Make sure that no other service is usign that port.

Restart vsftpd
# /etc/init.d/vsftpd restart