See the description of API connect() for AIX platform, http://www-01.ibm.com/support/knowledgecenter/ssw_aix_71/com.ibm.aix.commtrf2/connect.htm?lang=en The behavior is different when connect() operation got interrupted by signal. On AIX, although the connect() call can be interrupted by signal, the underlying connection will be made asynchronously, as it is described from the docs "EINTR The attempt to establish a connection was interrupted by delivery of a signal that was caught; the connection will be established asynchronously."