sudo apt-get install task

➜  ~ sudo apt-get install task
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following additional packages will be installed:
  taskwarrior
The following NEW packages will be installed:
  task taskwarrior
0 upgraded, 2 newly installed, 0 to remove and 3 not upgraded.
Need to get 626 kB of archives.
After this operation, 2206 kB of additional disk space will be used.
Do you want to continue? [Y/n] y
Get:1 http://lu.archive.ubuntu.com/ubuntu xenial/universe amd64 taskwarrior amd64 2.5.0+dfsg-1build1 [618 kB]
Get:2 http://lu.archive.ubuntu.com/ubuntu xenial/universe amd64 task amd64 2.5.0+dfsg-1build1 [8196 B]                                                                                       
Fetched 626 kB in 2min 0s (5195 B/s)                                                                                                                                                         

Selecting previously unselected package taskwarrior.
(Reading database ... 99545 files and directories currently installed.)
Preparing to unpack .../taskwarrior_2.5.0+dfsg-1build1_amd64.deb ...
Unpacking taskwarrior (2.5.0+dfsg-1build1) ...
Selecting previously unselected package task.
Preparing to unpack .../task_2.5.0+dfsg-1build1_amd64.deb ...
Unpacking task (2.5.0+dfsg-1build1) ...
Processing triggers for man-db (2.7.5-1) ...
Setting up taskwarrior (2.5.0+dfsg-1build1) ...
Setting up task (2.5.0+dfsg-1build1) ...