NoMachine on Linux relies on FUSE technology to connect disks from locale to remote and vice-versa. It requires that the FUSE kernel is installed on the system and the user is allowed to mount devices by FUSE.

On CentOS v. 5  not all the required FUSE packages are installed by default and it's necessary to install them manually (1).

On Debian versions prior to v. 8, users have to manually added to group fuse to let them mount disks (2). On Debian 4, codename Etch, users have to manually add the fuse module to kernel and install required packages and add fuse group to user (3): 

"Users are allowed to use fuse if they could read and write to /dev/fuse ie they are in group fuse on debian system. Starting with Debian 8 (Jessie) this group is not required anymore." (See: https://wiki.debian.org/SystemGroups).

1) How to confgure CentOS 5 to allow connecting disks by NoMachine

1.1) If you are running Centos 5.4 (kernel 2.6.18-164) or newer, the FUSE kernel module is included in the kernel itself (see: https://wiki.centos.org/TipsAndTricks/NTFS). It's therefore necessary to install only FUSE utilities. Execute from a console: 

sudo yum install fuse

After these utilities have been installed, connecting disks by NoMachine should work-out-of-the-box without the need to restart NoMachine server.

1.1) For older CentOS versions (5.3 or earlier) besides the fuse package also the dkms and dkms-fuse packages are required. To install them:

sudo yum install fuse dkms dkms-fuse

2) How to configure Debian 7 or earlier to allow connecting disks by NoMachine

In order to add the user to group fuse, execute from a console:

sudo usermod -a -G fuse <user>

It's then necessary to restart NoMachine server:

sudo /usr/NX/bin/nxserver --restart
 

3) How to configure Debian 4 to allow connecting disks by NoMachine

You need firstly to add the fuse module to kernel. To do that run that, run the following command with administrator rights :

 sudo /sbin/modprobe fuse

Then download fuse utilites from the offical repository:

 sudo apt-get install fuse-utils

Finally add the user to the Fuse group:

sudo usermod -a -G fuse <user>