Added UNIX note for determining PID from X11 window using `xprop`.

diff --git a/data/notes/unix_misc.md b/data/notes/unix_misc.md
index ea2a1bd..f4af328 100644 (file)
--- a/data/notes/unix_misc.md
+++ b/data/notes/unix_misc.md
@@ -88,3 +88,55 @@ execute the following command.
 
 At this point you have a fully interative `bash` session running on the Debian
 machine, controlled from the FreeBSD machine. 
 
 At this point you have a fully interative `bash` session running on the Debian
 machine, controlled from the FreeBSD machine. 

+
+
+# Determine PID of X11 Window #
+
+This note explains how to determine the Process ID (PID) corresponding to a
+program running in an X11 window, even if the program has locked up.
+
+I occasionally find myself needing to kill an X11 program like my terminal
+emulator (`st`) after it locks up, only to be greeted by list of almost
+indistinguishable processes.
+
+    % ps aux | grep st
+    ataylor  6358    0.0  0.0   19292    6848  -  Is   18Jan21        0:00.22 st
+    ataylor 13449    0.0  0.0   18824    6752  -  Is   11Nov20        0:12.00 st
+    ataylor 15194    0.0  0.0   19208    7416  -  Is    4Aug20        6:22.17 st
+    ataylor 17303    0.0  0.0   19380    7492  -  Is   16Feb21        0:08.18 st
+    ataylor 24875    0.0  0.0   18812    8212  -  Is   24Feb21        0:05.34 st
+    ataylor 25313    0.0  0.0   19388    6928  -  Is   21Sep20        0:04.07 st
+    ataylor 26013    0.0  0.0   18348    6364  -  Is   29Jun20        0:27.78 st
+    ataylor 26677    0.0  0.0   20756    9152  -  Is   20Dec20        0:00.86 st
+    ataylor 27383    0.0  0.0   19152    8552  -  Is   Fri17          0:00.96 st
+    ataylor 28440    0.0  0.0   18916    5100  -  Is   14Mar20        0:24.59 st
+    ataylor 28491    0.0  0.0   18320    8528  -  Is   18:22          0:03.22 st
+    ataylor 31469    0.0  0.0   19280    7000  -  Is   13Feb21        0:10.73 st
+    ataylor 35707    0.0  0.0   19152    9100  -  Ss   23:45          0:00.08 st
+    ataylor 39426    0.0  0.0   20980    7900  -  Is   14Mar20        3:11.24 st
+    ataylor 42211    0.0  0.0   18980    9080  -  Is   17:33          0:02.43 st
+    ataylor 50065    0.0  0.0   19000    6800  -  Is    3Jan21        0:00.80 st
+    ataylor 50765    0.0  0.0   18764    6364  -  Is    9Jan21        0:05.97 st
+    ataylor 50780    0.0  0.0   18896    6656  -  Is   28Oct20        0:01.38 st
+    ataylor 53637    0.0  0.0   20568    8636  -  Is   26Dec20        0:16.79 st
+    ataylor 68757    0.0  0.0   19836    8912  -  Is   24Jan21        0:00.56 st
+    ataylor 69466    0.0  0.0   18980    9012  -  Is   Sun04          0:01.42 st
+    ataylor 72775    0.0  0.0   19260    7236  -  Is    7Jan21        0:01.10 st
+    ataylor 73530    0.0  0.0   18764    6912  -  Is    4Nov20        0:17.34 st
+    ataylor 73701    0.0  0.0   21040    9120  -  Is   20Nov20        0:18.44 st
+    ataylor 75901    0.0  0.0   18456    7640  -  Is    8Feb21        0:28.57 st
+    ataylor 80220    0.0  0.0   18884    6756  -  Is   25Dec20        0:04.87 st
+    ataylor 81521    0.0  0.0   18496    8652  -  Is   01:04          0:12.21 st
+    ataylor 83818    0.0  0.0   18956    5072  -  Is   10Apr20        0:09.37 st
+    ataylor 89395    0.0  0.0   18920    4984  -  Is   15Apr20        0:11.99 st
+
+Use `xprop` to obtain the PID from the window's various X11-related properties.
+First, run the command `xprop _NET_WM_PID`. It will appear to hang, but your
+mouse cursor will change to crosshairs. Place the crosshairs over the X11
+window in question and click. This tells `xprop` which window you are
+interested in and `xprop` then tells you the PID. For example, if I click on
+one of the `st` windows from the previous example, we see that it is PID 75901.
+
+    % xprop _NET_WM_PID
+    _NET_WM_PID(CARDINAL) = 75901
+