Thank you for these informations, it helps me to understand how skas works. I read on the skas website that "This also provides a noticable speedup by eliminating the signal delivery that used to happen for every UML system call." I read that UML processes (in TT mode) in user space were controlled with signals (especially to do the transition between the user mode and the kernel mode). The presentation of skas suggests that this transition and communications between UML and its processes are not executed anymore with signals. Do you know what is used instead ?