A disclosed method may include (1) identifying an old version of software that is running on a network device, (2) receiving a new version of the software that is to replace the old version of the software during an in-service software upgrade, and then (3) performing the in-service software upgrade on the network device by making a system call that (A) loads the new version of the software onto the network device as the old version of the software continues to run and (B) transfers control of the network device from the old version of the software to the new version of the software by booting the new version of the software without shutting down the network device. Various other systems and methods are also disclosed.