yep, i know that question was asked many times, but unfortunately i didn't find the complete answer on it.
so, how to limit the number of simultaneous processes per user?
i found two solutions:
using pam_limits. in that case i need to configure /etc/security/limits.conf file. unfortunately, this solution works only for pam aware applications, that is it's not universal.
using ulimit called from $HOME/profile. unfortunately it doens't work in all cases too. i tried to set "ulimit -u 100" and then launched in the same shell "stress --vm 200 --vm--bytes 100". application was successfully launched and i got more than 200 processes under user root.
i need to build a robust system, so solutions which work only in some cases are inappropriate.