**Describe the bug**

kdump initramfs with squashfs fails to boot with `Failed to execute /init (error -2)`. The squash loader's `init-squash.sh` (installed as `/init`) uses `#!/bin/sh` shebang, but `/usr/bin/sh` does not exist in the outer cpio layer — only `/usr/sbin/sh` is present.

```
...
2026-05-25 11:58:48 [    0.521438] Run  as init process
2026-05-25 11:58:48 [    0.521613] Failed to execute /init (error -2)
2026-05-25 11:58:48 [    0.521768] Run /sbin/init as init process
2026-05-25 11:58:48 can't run '/etc/init.d/rcS': No such file or directory
2026-05-25 11:58:48 can't open /dev/tty4: No such file or directory
2026-05-25 11:58:48 can't open /dev/tty2: No such file or directory
2026-05-25 11:58:48 can't open /dev/tty3: No such file or directory
2026-05-25 11:58:48 Please press Enter to activate this console.
```


The busybox module creates applet symlinks based on `find_binary()` results. Since `DRACUT_PATH` defaults to `/usr/sbin /sbin /usr/bin /bin`, and the Fedora busybox package places applet symlinks under `/usr/sbin/`, `find_binary("sh")` returns `/usr/sbin/sh`. The module only creates that symlink, leaving `/usr/bin/sh` (i.e. `/bin/sh` on merged-usr) absent.

**Distribution used**

Fedora 43 (also affects Fedora 42)

**Dracut version**

dracut-107-8.fc43

**Init system**

systemd

**To Reproduce**

1. Install Fedora 43 with `busybox` (1.37.0-3.fc43) and `kexec-tools`
2. Enable kdump with squashfs (kdump-utils adds `--add 'squash-squashfs' --squash-compressor 'zstd'`)
3. `kdumpctl rebuild`
4. `echo c > /proc/sysrq-trigger`
5. Crash kernel fails with `Failed to execute /init (error -2)`

**Expected behavior**

`/usr/bin/sh` should always exist when busybox module is installed (POSIX mandates `/bin/sh`). kdump should successfully capture vmcore.

**Additional context**

Triggered by Fedora 42's [Unify /usr/bin and /usr/sbin](https://discussion.fedoraproject.org/t/f42-change-proposal-unify-usr-bin-and-usr-sbin-system-wide/99853) transition — `/usr/sbin` still exists as a separate directory and busybox places applet symlinks there.

Diagnosis:
```
$ lsinitrd /boot/initramfs-$(uname -r)kdump.img | grep -E "usr/bin/sh|usr/sbin/sh"
lrwxrwxrwx   1 root     root           14 ... usr/sbin/sh -> ../bin/busybox
# /usr/bin/sh is ABSENT
```

Workaround:
```
echo 'DRACUT_PATH="/usr/bin /bin /usr/sbin /sbin"' > /etc/dracut.conf.d/fix-path-order.conf
kdumpctl rebuild
```

My Patch:
```
diff --git a/modules.d/81busybox/module-setup.sh b/modules.d/81busybox/module-setup.sh
index abcdef1..1234567 100755
--- a/modules.d/81busybox/module-setup.sh
+++ b/modules.d/81busybox/module-setup.sh
@@ -36,4 +36,11 @@ install() {
 
         ln_r /usr/bin/busybox "$_path"
     done
+
+    # Ensure /usr/bin/sh is always available.
+    # POSIX mandates /bin/sh and most scripts use #!/bin/sh (-> /usr/bin/sh
+    # on merged-usr). find_binary may locate 'sh' at a non-standard path
+    # (e.g. /usr/sbin/sh) depending on $DRACUT_PATH ordering, so create
+    # the symlink explicitly if absent.
+    [[ -e "${_dstdir}/usr/bin/sh" ]] || ln_r /usr/bin/busybox /usr/bin/sh
 }
```

Reproducible: Always

Steps to Reproduce:
1.install busybox, kdump
2.echo c > /proc/sysrq-trigger
Actual Results:
the kdump initrd system hung

Expected Results:
create a crash kdump core