The reason is that there is a IMO pretty non-sensical design decision in ulimit, that when setting limits without specifying -S (for the soft limit) or -H (for the hard limit) then both the soft *and* the hard limit are set. Say, -n (=number of open files) has a soft limit of 1k and a hard limit of 1M on my system. If I (think I) set the soft limit with `ulimit -n 2048` the soft limit is now 2k, but the hard limit is also 2k, and when I later try to set the soft limit higher with say `ulimit -n 4096` it won't work, because the hard limit is set to 2k already. This is stupid, but it is like it is. The only remedy is to always specify that you want to set the soft limit by using the -S switch, i.e. use either `ulimit -S -n 2048` or `ulimit -Sn 2048` instead of just `ulimit -n 2048`.