There is no default group named "sudo" on FreeBSD. There is no connection between the command "sudo" and the presence of a group named "sudo".
You can see which groups you have on your system using:
$ cat /etc/group
It is common on many Linux distributions (including Ubuntu) to have a group named "sudo". On FreeBSD it is most common to use the groups "wheel" or "operators" for the same purpose.
sudo program reads a configuration file. This file determines which users and groups are allowed to do what.
If sudo was installed with the
pkg package installer then you find the sudo configuration file here:
The interesting part of the configuration file are the following lines:
## Uncomment to allow members of group wheel to execute any command
# %wheel ALL=(ALL) ALL
## Same thing without a password
# %wheel ALL=(ALL) NOPASSWD: ALL
## Uncomment to allow members of group sudo to execute any command
# %sudo ALL=(ALL) ALL
My guess is that someone set your system up to allow sudo for the group "wheel" and added your user to that group. The group "sudo" does simply not exist and you cannot add anyone to a non-existing group.
You should either add the user to the "wheel" group (or whatever defined in
/usr/local/etc/sudoers) - or you should create the group "sudo" and make sure it is not commented out in
Further reading in section 13.14. Shared Administration with Sudo in the FreeBSD Handbook. The man pages for the command sudo and the configuration file for the full monty.