replace switch_root shell script with binary

The switch_root shell script did not work with bash-4.0-2, because "exec" gets the real path of the executable which is then "/sysroot/lib/ld-linux.so.2" instread of "./lib/ld-linux.so.2".

Also the required chroot binary might live in /usr/bin, which can be mounted later.

Here is the switch_root code from nash, which can be stripped down further, but which works.

From f1b1e4f8694104f007e4483c36b0bf40a5760167 Mon Sep 17 00:00:00 2001
From: Harald Hoyer <[email protected]>
Date: Wed, 4 Mar 2009 13:41:07 +0100
Subject: [PATCH] replace switch_root shell script with binary

The switch_root shell script did not work with bash-4.0-2, because "exec" gets the real path of the executable which is then "/sysroot/lib/ld-linux.so.2" instead of "./lib/ld-linux.so.2". Also the required chroot binary might live in /usr/bin, which can be mounted later.

Here is the switch_root code from nash, which can be stripped down further, but which works.

---
 Makefile      |   11 +-
 init          |    3 +
 switch_root   |  111 ------------
 switch_root.c |  556 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 566 insertions(+), 115 deletions(-)
 delete mode 100755 switch_root
 create mode 100644 switch_root.c

index dbc2a7d..9441bbe 100644
@@ -1,7 +1,9 @@
-all:
-	@echo "Nothing to do"
+switch_root: switch_root.c
+	gcc -o switch_root switch_root.c	
 
-install:
+all: switch_root
+
+install: all
 	mkdir -p $(DESTDIR)/usr/libexec/dracut
 	mkdir -p $(DESTDIR)/sbin
 	mkdir -p $(DESTDIR)/usr/libexec/dracut/hooks

@@ -16,6 +18,7 @@ install:
 	for module in modules/*.sh; do install -m 0755 $$module $(DESTDIR)/usr/libexec/dracut ; done
 clean:
 	rm -f *~
+	rm -f switch_root
 
-archive:
+archive: 
 	git archive --format=tar HEAD --prefix=dracut/ |bzip2 > dracut-$(shell git rev-list  --abbrev-commit  -n 1 HEAD  |cut -b 1-8).tar.bz2

index 9605141..a0e83a7 100755
@@ -103,6 +103,9 @@ INIT=$(getarg init); INIT=${INIT#init=}
 }
 	    
 source_all pre-pivot
+
+kill $(pidof udevd)
+
 echo "Switching to real root filesystem $root"
 exec switch_root "$NEWROOT" "$INIT"  $CMDLINE || {
     # davej doesn't like initrd bugs

1.6.0.6

That is a little odd -- dash does not exhibit that behaviour.

The only command that tries to use ./lib/ld-linux.so.2 is the final chroot, and at that point /sysroot does not mean anything anymore because of the move mount we did. Is this a bug in bash we can work around by setting $PWD?

yeah, but /usr/sbin and /usr/bin are stupid places to have chroot, it is a core utility anyways. :)

[ patch snipped ]

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