Things I can identify in the poster:

- A wizard (which is a reference to a highly knowledgeable UNIX expert)

- the cauldron the wizard is using is in the shape of a seashell, and there are shells on the wizard's hat (on UNIX the shell is a textual interface between the user and the operating system)

- the wizard's hat has the word "su" on it ("su" is the "superuser" command used to "become" a "superuser", ie. the most powerful user on a UNIX system, where one can perform administrative tasks that ordinary users are not capable of doing)

- the wizard's robe contains: ">" and "<", which are symbols used for input and output redirection, "%" and "$" which are sometimes used in shell prompts and "$" is used in regular expressions to indicate the end of the line, "*" is another character used in regular expressions to mean "zero or more of the previous character" and used in the shell for "globbing" (as a "wildcard" for specifying a variable or "anything goes" part of a filename), "!" is used in shell history commands to reference previous commands

- there are containers at the bottom of the picture with the words: "diff" - a utility used to show difference between various texts, "tar" - a utility for creating, listing, and extracting archives, "null" - a reference to /dev/null, a "device" file that outputs the end of file when read and which discards any output sent to it, "troff" is a text formatting utility sometimes used for formatting documentation, "awk" is a language used for text manipulation, "C" is the main programming language used on UNIX, and "B" is a language that "C" descended from, "UUCP" - a once common but now obsolete file transfer utility

- there is a scroll with the words "shell script" on it, which refers to a program containing shell commands

- in the background there are pouches with the words: "spawn", which refers to creating a new process, what looks like "JFO" (not sure what this is), and "nroff" - another text formatting utility, "root" (the default name of the "superuser" account)

- there's a shelf with books bearing these titles: "Daemons" (which are background processes, usually used as "servers" on a unix system, which perform some function indefinitely, contrasting with regular applications which are more one-off processes that usually perform one function and exit), "Who am I" - a reference to the "whoami" utility that will tell you your user id, "traps" - the "trap" utility can be used to respond to signals, which are one way to perform inter-process communication on UNIX, usually used to indicate exceptional events, "Spells" - a word in keeping with the wizard theme, but I don't know if there's anything specific in UNIX that would be considerd a "spell" per se, "Curses" - a graphics library

- there is a container on the shelf with the word "pwd", which is a shell command used to tell you what the current directory is

- there is a box on the shelf with the word "mbox", which is a type of mail file on UNIX, and this box with the word "mbox" contains scrolls, which could be mail messages

- there is a black cat, which is also in keeping with the wizard theme, but I'm not sure whether it corresponds to anything specific in UNIX either (update: of course it's a reference to one of the most common and well-known commands on UNIX: "cat", which is used to output the contents of a file... don't know how I missed one of the most obvious symbols in the whole picture!)

- there is a black boot leaning against the wall. To "boot" a user off a UNIX system is to terminate or end their connection, "kicking" them off the system. "booting" a UNIX system is a term used for starting the system. "rebooting" refers to restarting the system.

- in the window a person with a scythe is reaping (or chopping down) some crops... to "reap" processes on UNIX is to kill them (or terminate/end them)

- under the ceiling are many pipes. pipes are used on UNIX for interprocess communication

- there is a bucket under a leaking pipe. The bucket may be there just for aesthetic reasons, though there is an informal "bit bucket" term which could refer to an abstraction for discarding information. The leaking pipe might be a reference to a "leaking abstraction", which is an abstraction (a high-level representation of something) which is supposed to "abstract away" or not reveal anything about how it's implemented, but when it "leaks" it inadvertently reveals something about how it's implemented anyway, causing all sorts of problems, like difficulties in switching to a different implementation.

- other probably purely aesthetic elements in the picture are a castle on a hill, mountains, and a sky seen through the window, a fireplace and a table. the "oregano" container on the table is probably also purely aethetic, as is the mortar (in the pestle with the word "tar")

- on the table lies a fork, which refers to "forking" a process (which creates a copy from an existing process and is a way UNIX has of creating new "child" processes from existing "parent" processes)

- on the "awk" container on the table is a spool of thread. "threads" on UNIX are lightweight processes. the spool of thread has the letters "usr" on it, which refers to the /usr partition on a UNIX system, which usually contains all sorts of UNIX utilities and libraries. To "spool" messages is to collect them for processing.

- the wizard is pouring glowing liquid from test tubes, with what look like circuit traces coming out of the cauldron. In the cauldron there is a ladle with an iron hook at the end. I'm not sure what any of these elements are supposed to represent.

- there is a spigot in the bottom of the cauldron, and it's emptying out in to the container labeled "null", which (as mentioned above) is a reference to the /dev/null device on UNIX, which will discard everything sent to it, so can be thought of as having infinite capacity, so even though it's a lot smaller in size than the cauldron all the liquid from the cauldron and more could be poured in to it without overflowing

- there is a log with the word "login", next to the fireplace. "login" is a process used to respond to what the user types at the "login:" prompt when first connecting to a UNIX machine. A "log" is a text file containing (usually timestamped) information about what a process is doing or to record series of events

- on the wizard's hat is a scroll which reads: "DMR", "KT", and "BWK". "KT" is probably Ken Thompson, one of the creators of UNIX. I don't recognize the others.

That's all I can spot.

Here is a direct link to the high resolution 32 MB PNG image of the poster: [1]

[1] - https://archive.org/download/unix-magic-poster-gary-overcare... Magic Poster - Gary Overcare (1).png