ssh key authenticated user unable to use apt-get update - authentication

Question

Ubuntu Linux 16.04.5
I have configured a server for SSH Keys Authentication With PuTTY.
Key authentication works fine for the user account accessing the server, the problem is that when attempting to utilize "apt-get update" the system returns:
tornado#freeradius:~$ apt-get update
Reading package lists... Done
W: chmod 0700 of directory /var/lib/apt/lists/partial failed - SetupAPTPartialDirectory (1: Operation not permitted)
E: Could not open lock file /var/lib/apt/lists/lock - open (13: Permission denied)
E: Unable to lock directory /var/lib/apt/lists/
W: Problem unlinking the file /var/cache/apt/pkgcache.bin - RemoveCaches (13: Permission denied)
W: Problem unlinking the file /var/cache/apt/srcpkgcache.bin - RemoveCaches (13: Permission denied)
I have seen on multiple posts to similar topics that the solution is the use "sudo apt-get update" - the issue with this is the user "tornado" has no password.
Additionally, I have configured "sshd_config":
ChallengeResponseAuthentication no
PasswordAuthentication no
The user "tornado" was created using "adduser tornado --disabled-password" option, so when attempting to "sudo apt-get update" I am prompted for the user "tornado's" non-existent password.
The permission of "home/tornado" was changed to 755 which made no change with the issue at hand, so I reverted the CHMOD.
"stat /home/tornado" output
File: '/home/tornado'
Size: 4096 Blocks: 8 IO Block: 4096 directory
Device: fc00h/64512d Inode: 19267592 Links: 4
Access: (2700/drwx--S---) Uid: ( 1000/ tornado) Gid: ( 1000/ tornado)
Access: 2018-09-14 11:28:01.035536814 -0700
Modify: 2018-09-14 10:50:00.864863347 -0700
Change: 2018-09-14 11:33:13.685020607 -0700
Birth: -
"stat /home/tornado/.ssh" output
File: '/home/tornado/.ssh'
Size: 4096 Blocks: 8 IO Block: 4096 directory
Device: fc00h/64512d Inode: 19267599 Links: 2
Access: (2700/drwx--S---) Uid: ( 1000/ tornado) Gid: ( 1000/ tornado)
Access: 2018-09-14 11:28:01.035536814 -0700
Modify: 2018-09-14 10:44:34.251451611 -0700
Change: 2018-09-14 11:28:01.035536814 -0700
Birth: -
"stat /home/tornado/authorized_keys" output
File: '/home/tornado/.ssh/authorized_keys'
Size: 209 Blocks: 8 IO Block: 4096 regular file
Device: fc00h/64512d Inode: 19267590 Links: 1
Access: (0600/-rw-------) Uid: ( 1000/ tornado) Gid: ( 1000/ tornado)
Access: 2018-09-14 11:33:41.053150514 -0700
Modify: 2018-09-14 10:44:34.127451092 -0700
Change: 2018-09-14 11:28:01.035536814 -0700
Birth: -
Root privileges to the user "tornado" were granted as well ...
visudo
added:
# User privilege specification
tornado ALL=(ALL:ALL) ALL
I also attempted: "chown tornado:root /home/tornado"
which made no change to the situation.
Solved
A password was added to the user "tornado" which allows me to sudo into the root user which provides functionality.