This study considers the decentralised periodic event-triggered consensus problem for continuous-time linear multi-agent systems (MASs) under general directed graphs. The authors discretise the continuous-time MASs based on zero-order hold, and propose an event-triggered consensus control (ETCC) algorithm rendering the states of agents reach consensus. They prove that under the proposed ETCC implemented in multiple steps, there is no Zeno-like behaviour exhibited in the sense of sampling. To relax the requirement of the periodic monitoring in the ETCC, it is further proposed a self-triggered consensus control algorithm, where the next triggering instant is predetermined by each agent at the previous triggering instant. For the case where the states of MASs are unavailable, the authors further propose an observer-based ETCC algorithm. Simulation results are given to illustrate the theoretical results.