fix(rhel): use /mnt/sysroot to locate target root in %post --nochroot

Parsing /proc/mounts for "rl-root" broke on RHEL 10 / Rocky 10 because
Anaconda's mount layout changed again. Use Anaconda's canonical
/mnt/sysroot mount point instead (with a fallback to the legacy
/mnt/sysimage). Works on RHEL 8, 9, 10 and their Rocky counterparts.

Author: markuslf

CHANGELOG.md

@@ -8,7 +8,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
-tbd
+### Fixed
+
+* `lf-rhel.cfg`: Fix `cp` error during the post-install phase on RHEL 10 / Rocky 10 cloud installs. The script no longer parses `/proc/mounts` to locate the installed system's root; it uses Anaconda's canonical `/mnt/sysroot` mount point (with a fallback to the legacy `/mnt/sysimage`), so the same kickstart works on RHEL/Rocky 8, 9 and 10
 
 
 ## [1.2.0] - 2026-04-15

lf-rhel.cfg

@@ -491,7 +491,18 @@ $PYTHON /tmp/pre-script.py
 
 
 %post --nochroot --erroronfail
-root_mount=$(awk '/rl-root/{m=$2} END{print m}' /proc/mounts)
+# Locate the target system's root mount. Anaconda exposes two mount points:
+# /mnt/sysroot (recommended since Fedora 31 / RHEL 8, see Anaconda's
+# docs/developer/mount-points.rst) and the legacy /mnt/sysimage. We prefer
+# sysroot and fall back to sysimage so the same kickstart works on RHEL/Rocky
+# 8, 9 and 10. Previously we parsed /proc/mounts, which broke on RHEL 10
+# because Anaconda's mount layout changed (see Issue #10 and its recurrence).
+for candidate in /mnt/sysroot /mnt/sysimage; do
+    if [ -d "$candidate/root" ]; then
+        root_mount="$candidate"
+        break
+    fi
+done
 echo "Copying /tmp/dynamic.ks to $root_mount/root/"
 cp /tmp/dynamic.ks $root_mount/root/
 [ -f /usr/share/anaconda/post-scripts/70-install-ssh-keys.ks ] && cp /usr/share/anaconda/post-scripts/70-install-ssh-keys.ks $root_mount/root/