安装ROS2报错: Your system needs to have a fully qualified domain name (fqdn) inorder to install the var-

thomas@ubuntu:/userdata/dev_ws/src$ sudo apt install python3-colcon-ros
Reading package lists... Done
Building dependency tree       
Reading state information... Done
python3-colcon-ros is already the newest version (0.4.1-1).
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
2 not fully installed or removed.
After this operation, 0 B of additional disk space will be used.
Do you want to continue? [Y/n] y
Setting up qmail (1.06-6.2~deb10u1build0.20.04.1) ...

The hostname -f command returned: ubuntu

Your system needs to have a fully qualified domain name (fqdn) in
order to install the var-qmail packages.

Installation aborted.

dpkg: error processing package qmail (--configure):
 installed qmail package post-installation script subprocess returned error exit status 1
dpkg: dependency problems prevent configuration of qmail-run:
 qmail-run depends on qmail (>= 1.06-2.1); however:
  Package qmail is not configured yet.

dpkg: error processing package qmail-run (--configure):
 dependency problems - leaving unconfigured
No apport report written because the error message indicates its a followup error from a previous failure.
                                                                                                          Errors were encountered 
while processing:
 qmail
 qmail-run
E: Sub-process /usr/bin/dpkg returned an error code (1)
 

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解决方案:
thomas@ubuntu:/userdata/dev_ws/src$ sudo hostname thomas-ubuntu-20.04-foxy-desktop-03-04