Expanding on the discussion here, why does starting commands via parallel into an schroot cause all the problems described?
I can for example, stagger start a number of commands through schroot as long as they don't start at the same time with no problem.
Example (each has been started one-at-a-time:
% schroot -p -- nice -19 makepkg -s
% schroot -p -- htop
schroot -p -- mprime
The solution is not to use schroot at all but to simply call chroot directly via parallel which works fine.
Example worker code for parallel. See the complete build script for more.
% sudo linux32 chroot --userspec=1000:100 /opt/arch32 /bin/bash -c 'cd $here ; nice -19 makepkg -scd --skipinteg --config $HOME/bin/repo/makepkg.i686'