gnu: Add tmon.

* gnu/packages/linux.scm (tmon): New public variable.

gnu/packages/linux.scm

@@ -5364,6 +5364,52 @@ (define-public tpacpi-bat
 supported.")
     (license license:gpl3+)))
 
+(define-public tmon
+  (package
+    (name "tmon")
+    ;; Tmon's ‘VERSION = 1.0’ hasn't been touched since 2013; the code has.
+    (version (package-version linux-libre))
+    (source (package-source linux-libre))
+    (build-system gnu-build-system)
+    (arguments
+     `(#:tests? #f                      ; no test suite
+       #:make-flags
+       (list (string-append "CC=" ,(cc-for-target))
+             (string-append "INSTALL_ROOT=" (assoc-ref %outputs "out"))
+             "BINDIR=bin")
+       #:phases
+       (modify-phases %standard-phases
+         (add-after 'unpack 'enter-subdirectory
+           (lambda _
+             (chdir "tools/thermal/tmon")
+             #t))
+         (add-after 'install 'install-man-page
+           (lambda* (#:key outputs #:allow-other-keys)
+             (let* ((out (assoc-ref outputs "out"))
+                    (man8 (string-append out "/share/man/man8")))
+               (install-file "tmon.8" man8)
+               #t)))
+         (delete 'configure))))         ; no configure script
+    (inputs
+     `(("ncurses" ,ncurses)))
+    (home-page (package-home-page linux-libre))
+    (synopsis "Monitor and test the Linux thermal subsystem in real time")
+    (description
+     "Tmon is a tool to interact with the complex thermal subsystem of the
+kernel Linux.  It helps visualize thermal relationships and real-time thermal
+data, tune and test cooling devices and sensors, and collect thermal data for
+further analysis.
+
+As computers become smaller and more thermally constrained, more sensors are
+added and new cooling capabilities introduced.  Thermal relationships can change
+dynamically.  Their complexity grows exponentially among cooling devices, zones,
+sensors, and trip points.
+
+Linux exposes this relationship through @file{/sys/class/thermal} with a matrix
+of symbolic links, trip point bindings, and device instances.  To traverse it
+by hand is no trivial task: @command{tmon} aims to make it understandable.")
+    (license license:gpl2)))
+
 (define-public turbostat
   (package
     (name "turbostat")