The author is using the lifecycle of various processes in a multi-user unix environment as an allegory for life and death in general. Normally when a user connects to a unix server, any processes they start are tied to the lifecycle of their session. Therefore, if one is disconnected abruptly from the server any processes they started in that session are killed once it times out. Because of this, many users invoke their processes via the screen command. Screen is a popular unix utility that allows most any process to live outside of the normal lifecycle of a user session. A user may make use of commands to connect and disconnect to any number of screen sessions that are running in the background.
In this comic strip, one particular user named “sam” is running the IRC client irssi using the screen command and his default shell - zsh (z shell). The author picked this particular shell in order to make the humorous pun, “the ghost in z shell”. Which is a reference to the popular hentai movie Ghost in the Shell.
