liveinit: start ash bash-compatible and save init debug output to file

When the value of 'debug' parameter is equal to or greater than '2',
the init script enables 'set -x' which results in verbose output of
init script execution. When the 'ash' shell is started as '/bin/sh' instead
of '/bin/ash', it enables bash-compatible mode. Then the script can use
'BASH_XTRACEFD' to log the verbose script output to a file '/debug_init.log'.

This is extremely useful for init debugging. Logging to file is enabled when
the value of 'debug' is '4' or higher.
When you boot with 'debug=4, you will end up in the rescue shell of the initrd.
You can then inspect '/debug_init.log' to diagnose issues with the boot-up,
and you can copy that logfile for instance to /mnt/overlay/root/ if you want
to preserve it. After typing 'exit', the live init will hand-over to
the Slackware OS initialization and after logging in you can copy the logfile
to a network location if you want.

1 files changed, 12 insertions, 2 deletions

diff --git a/liveinit.tpl b/liveinit.tpl
index a5a7e9c..d00650d 100644
--- a/liveinit.tpl
+++ b/liveinit.tpl
@@ -1,4 +1,4 @@
-#!/bin/ash
+#!/bin/sh
 #
 # Copyright 2004  Slackware Linux, Inc., Concord, CA, USA
 # Copyright 2007, 2008, 2009, 2010, 2012  Patrick J. Volkerding, Sebeka, MN, USA
@@ -305,7 +305,17 @@ for ARG in $(cat /proc/cmdline); do
 done
 
 # Verbose boot script execution:
-[ $DEBUG -ge 2 ] && set -x
+if [ $DEBUG -ge 2 ]; then
+  if [ $DEBUG -ge 4 ]; then
+    # We save (verbose) shell output to local file;
+    # These busybox compile options make it possible:
+    # CONFIG_SH_IS_ASH=y
+    # CONFIG_ASH_BASH_COMPAT=y
+    exec 5> debug_init.log
+    export BASH_XTRACEFD="5"
+  fi
+  set -x
+fi
 
 debugit () {
   if [ $DEBUG -eq 0 -o $DEBUG -gt 3 ]; then