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+# General Information
+
+* [[/hurd/neighborhurd]]
+* [[/hurd/subhurd]]
+
+---
+
+# Debugging the Hurd Startup Process
+
+_one.full_ is the subhurd's root file system image and has been installed as
+follows: [TODO]
+
+_Wx_ translates to terminal window _x_.
+
+W1
+
+    $ fsysopts one.full/ --readonly
+    $ sudo boot -I -d -s -D one.full/ one.full/boot/script.boot one.full.ext2
+    Pausing. . .
+
+(In theory it shouldn't be neccessary to run the subhurd as user _root_, but in
+practice [that doesn't work at the
+moment](http://savannah.gnu.org/bugs/?17341).)
+
+W2
+
+    $ ps -Af
+    [...]
+        root   851   385  p4  0:00.01 boot -I -d -s -D one.full/ one.full/boot/script.boot one.full.ext2
+           -   853     1   ?  0:00.00 ?
+           -   854     1   ?  0:00.00 ?
+    [...]
+    $ sudo gdb /var/tmp/one.full/hurd/ext2fs.static
+    [...]
+    (gdb) attach 853
+    Attaching to program `/var/tmp/one.full/hurd/ext2fs.static', pid 853
+    warning: Can't modify tracing state for pid 853: No signal thread
+    Can't fetch registers from thread 1: No such thread
+
+(The _boot_ program [could be modified to print out the
+pids](http://savannah.gnu.org/bugs/?19254), so that one wouldn't have to fumble
+with _ps_.)
+
+W3
+
+    $ sudo gdb /var/tmp/one.full/lib/ld.so.1
+    [...]
+    (gdb) set solib-absolute-prefix /var/tmp/one.full
+    (gdb) attach 854
+    Attaching to program `/var/tmp/one.full/lib/ld.so.1', pid 854
+    warning: Can't modify tracing state for pid 854: No signal thread
+    Can't fetch registers from thread 1: No such thread
+
+W1
+
+    [<Enter>.]
+    /hurd/ext2fs.static --bootflags=-dsf --host-priv-port=38 --device-master-port=43 --exec-server-task=47 -Tdevice pseudo-root
+    /lib/ld.so.1 /hurd/exec
+
+Now that this step has been accomplished, you can set break points in GDB, etc.
+
+W2
+
+    (gdb) continue
+    Continuing.
+    warning: Can't wait for pid 853: No child processes
+
+W1
+
+    Hurd server bootstrap: ext2fs.static[pseudo-root] exec
+
+W3
+
+    (gdb) continue
+    Continuing.
+    warning: Can't wait for pid 854: No child processes
+
+    Program received signal EXC_BAD_ACCESS, Could not access memory.
+    __mach_port_mod_refs (task=1, name=139802, right=1, delta=-1)
+        at /var/tmp/glibc-2_5-branch/build_--without-tls_--without-__thread/mach/RPC_mach_port_mod_refs.c:132
+    132             InP->Head.msgh_reply_port = __mig_get_reply_port();
+    (gdb) x/i $pc
+    0x168f2 <__mach_port_mod_refs+82>:      call   0x151b0 <__mig_get_reply_port>
+
+---
+
+Sources:
+
+* <http://www.gnu.org/software/hurd/howto/subhurd.html>
+* <http://lists.gnu.org/archive/html/bug-hurd/2007-02/msg00030.html>
+* [[Thomas_Schwinge|tschwinge]]'s mind