Global IO Redirection (SLIME User Manual, version 2.28)

### 7.2 Globally redirecting all IO to the REPL

When connecting via `M-x slime-connect` SLIME does not change `*standard-output*` and friends outside of the REPL. If you have any other threads which call `format`, `write-string`, etc. that output will be seen only in the `*inferior-lisp*` buffer or on the terminal, more often than not this is inconvenient. So, if you want code such as this:

    (run-in-new-thread
      (lambda ()
        (write-line "In some random thread.~%" *standard-output*)))

to send its output to SLIME’s repl buffer, as opposed to `*inferior-lisp*`, set `swank:*globally-redirect-io*` to T in `~/.swank.lisp`

But when started using `M-x slime` the streams are redirected by default.