install xautolock

 $ sudo apt install xautolock

[sudo] password for dhwan: 

Reading package lists... Done

Building dependency tree       

Reading state information... Done

The following NEW packages will be installed:

  xautolock

0 upgraded, 1 newly installed, 0 to remove and 24 not upgraded.

Need to get 25,1 kB of archives.

After this operation, 69,6 kB of additional disk space will be used.

Get:1 http://id.archive.ubuntu.com/ubuntu focal/universe amd64 xautolock amd64 1:2.2-6 [25,1 kB]

Fetched 25,1 kB in 32s (782 B/s)     

Selecting previously unselected package xautolock.

(Reading database ... 310974 files and directories currently installed.)

Preparing to unpack .../xautolock_1%3a2.2-6_amd64.deb ...

Unpacking xautolock (1:2.2-6) ...

Setting up xautolock (1:2.2-6) ...

Processing triggers for man-db (2.9.1-1) ...