There is a slackbuild, which maybe fixes all this stuff, but itself has some odd dependencies. The site has an installer for the cl version.

Truecrypt binary root privileges

The Truecrypt binary needs to have root privileges. I installed Truecrypt 6.0a on Slackware 12.1 and it gives me the same message. The fix is to create a group with the privilege of running the truecrypt binary and add your unprivileged (non-root) users to the truecrypt group so they can run Truecrypt. Do the following (as root):

# groupadd truecrypt

Now you edit the sudoers file (must be done with vi!)

# visudo

Add the following 2 lines to the bottom of the sudoers file:

# Allow users of truecrypt group to run truecrypt as root.
%truecrypt ALL=(root) NOPASSWD:/usr/bin/truecrypt

Save it and exit visudo Now add your regular users to the truecrypt group

# gpasswd -a regularuser truecrypt

or for many users

# gpasswd -M first_user,second_user,etc truecrypt

Affected users need to log out and back in again.

The Truecrypt file containers default mount on:

/media/truecryptX

where X is the slot number you choose from the graphical interface when you mount the file container.

Mount and unmount with

truecrypt /path/to/encrypted/file /path/to/mount/point
truecrypt -d /path/to/mount/point
truecrypt -d # unmounts all

although mounting in non-default locations seems to cause some serious difficulties (device busy) with unmounting, so I suggest sticking with the default (in /media) unless there's a compelling reason not to.

https://wiki.archlinux.org/index.php/TrueCrypt#Mount_volumes_as_a_normal_user