Yesterday one of my systems had a catched up a rebuild of qtwebegine. Since this one particular systems has hardware that is 8 years old, and a rebuild of qtwebengine takes a lot of time on a dualcore system, I did not have that patience to wait all the evening since I needed the CPU for other tasks. If the half of a ebuild is already build, one does not want to throw all it away. There are 2 ways to preserve already compiled and unfinished ebuilds. The precedence to do so is the building host can not be rebooted. The first way to preserve the half build package and to pick the ebuild later is to hibernate the host

host # hibernate

The sencond solution without hibernating the host is to send a CTRL+Z in the shell where the ebuild has been executed. Following command will then appear after pressing CTRL+Z

[1]  + 1151 suspended  sudo emerge -vauDN world

To resume that ebuild just type in following command:

host # %1

Or

host # fg %1

To get an overview of suspended ebuilds or jobs just type in:

host # jobs
[1]  + suspended  sudo emerge -vauDN world

Now it is specifically not a special gentoo command but a bash command to pause running jobs and then to pick them up later.