diff --git a/.bashrc.d/20_emulate_pstree.sh b/.bashrc.d/20_emulate_pstree.sh
index a8a1337..e2f231c 100644
--- a/.bashrc.d/20_emulate_pstree.sh
+++ b/.bashrc.d/20_emulate_pstree.sh
@@ -7,8 +7,64 @@ case "$SRC_ENABLED" in
 esac
 # ---------------------------------
 
+#
+# pstree_compat.sh
+#
+# Meant to be sourced (e.g. from .bashrc). Defines functions only —
+# sourcing this file must never print anything or execute pstree.
+#
+# Compatibility target: bash 3.2+ (RHEL 5) and bash 4.1 (Debian Squeeze).
+#
+# CAVEAT: this guard only protects against an old/wrong *bash*. If this
+# file is sourced by a non-bash POSIX shell (e.g. dash as /bin/sh on
+# Debian), the bashisms below (arrays, [[ ]], local -a) will cause a
+# parse error at function-definition time, before any runtime check
+# can run. Only source this from bash (.bashrc, not .profile/.sh).
+#
+# After sourcing, call:
+#   pstree_compat          # root pid 1
+#   pstree_compat 1234     # specific pid
+#
+
+#
+# Returns 0 if running under bash >= 3.0, else prints an error to
+# stderr and returns 1. Called at the top of every public entry point,
+# never at source time.
+#
+bash_pstree_check_bash()
+{
+    if [[ -z "$BASH_VERSION" ]]; then
+        printf 'pstree_compat: requires bash, current shell is not bash\n' >&2
+        return 1
+    fi
+    if [[ -z "${BASH_VERSINFO[0]}" ]] || (( BASH_VERSINFO[0] < 3 )); then
+        printf 'pstree_compat: requires bash >= 3.0 (found %s)\n' "$BASH_VERSION" >&2
+        return 1
+    fi
+    return 0
+}
+
+pstree_compat()
+{
+    bash_pstree_check_bash || return 1
+
+    local root_pid="${1:-1}"
+    if command -v pstree >/dev/null 2>&1; then
+        pstree -p "$root_pid"
+    else
+        bash_pstree "$root_pid"
+    fi
+}
+
+#
+# Iterative (non-recursive) process tree walker.
+# Avoids deep bash function recursion, which can blow the stack
+# and crash the shell on large/deep process trees.
+#
 bash_pstree()
 {
+    bash_pstree_check_bash || return 1
+
     local root_pid="${1:-1}"
     local procdir pid key value name ppid idx
 
@@ -17,9 +73,6 @@ bash_pstree()
     NAMES=()
     idx=0
 
-    #
-    # Build process table from /proc/*/status.
-    #
     for procdir in /proc/[0-9]*; do
         [[ -d "$procdir" ]] || continue
         [[ -r "$procdir/status" ]] || continue
@@ -41,33 +94,28 @@ bash_pstree()
     done
 
     bash_pstree_set_chars
-    bash_pstree_root "$root_pid"
+
+    if ! bash_pstree_find_name "$root_pid" >/dev/null; then
+        return 1
+    fi
+
+    bash_pstree_walk "$root_pid"
 }
 
-#
-# Pick UTF-8 box-drawing chars if the locale supports them, else
-# fall back to plain ASCII (works on any RHEL5 console/terminal).
-#
 bash_pstree_set_chars()
 {
     local charmap
     charmap=$(locale charmap 2>/dev/null)
-
     if [[ "$charmap" == "UTF-8" ]]; then
-        BPT_VERT="│   "
-        BPT_TEE="├── "
-        BPT_LAST="└── "
+        BPT_VERT="│   "; BPT_TEE="├── "; BPT_LAST="└── "
     else
-        BPT_VERT="|   "
-        BPT_TEE="|-- "
-        BPT_LAST="\`-- "
+        BPT_VERT="|   "; BPT_TEE="|-- "; BPT_LAST="\`-- "
     fi
 }
 
 bash_pstree_find_name()
 {
-    local target="$1"
-    local i
+    local target="$1" i
     for ((i = 0; i < ${#PIDS[@]}; i++)); do
         if [[ "${PIDS[$i]}" == "$target" ]]; then
             printf '%s' "${NAMES[$i]}"
@@ -78,13 +126,12 @@ bash_pstree_find_name()
 }
 
 #
-# Print numerically-sorted child PIDs of $1, one per line.
+# Prints numerically-sorted children of $1, one per line.
+# Called once per node during the iterative walk (not recursively).
 #
 bash_pstree_children()
 {
-    local parent="$1"
-    local i list
-    list=""
+    local parent="$1" i list=""
     for ((i = 0; i < ${#PIDS[@]}; i++)); do
         if [[ "${PPIDS[$i]}" == "$parent" ]]; then
             list="$list${PIDS[$i]}
@@ -94,56 +141,78 @@ bash_pstree_children()
     [[ -n "$list" ]] && printf '%s' "$list" | sort -n
 }
 
-bash_pstree_root()
-{
-    local pid="$1" name
-    name=$(bash_pstree_find_name "$pid") || return
-    printf '%s(%s)\n' "$name" "$pid"
-    bash_pstree_show_children "$pid" ""
-}
-
 #
-# $1 = parent pid, $2 = prefix accumulated so far
+# Iterative preorder walk using an explicit stack (three parallel
+# arrays) instead of function recursion.
 #
-bash_pstree_show_children()
+bash_pstree_walk()
 {
-    local parent="$1" prefix="$2"
-    local child name last_line
-
-    local children
-    children=$(bash_pstree_children "$parent")
-    [[ -n "$children" ]] || return
-
-    last_line=$(printf '%s\n' "$children" | tail -n 1)
-
-    while IFS= read -r child; do
-        [[ -n "$child" ]] || continue
-        name=$(bash_pstree_find_name "$child") || continue
-        if [[ "$child" == "$last_line" ]]; then
-            printf '%s%s%s(%s)\n' "$prefix" "$BPT_LAST" "$name" "$child"
-            bash_pstree_show_children "$child" "${prefix}    "
-        else
-            printf '%s%s%s(%s)\n' "$prefix" "$BPT_TEE" "$name" "$child"
-            bash_pstree_show_children "$child" "${prefix}${BPT_VERT}"
+    local root_pid="$1"
+    local -a S_PID S_PRINT_PREFIX S_CHILD_PREFIX
+    local top pid print_prefix child_prefix name
+    local children child last_child new_prefix branch cont
+    local -a rev_children
+    local i n visited_guard=0
+    local max_iterations=200000   # safety valve against any /proc PPid cycle
+
+    S_PID=("$root_pid")
+    S_PRINT_PREFIX=("")
+    S_CHILD_PREFIX=("")
+
+    while [[ ${#S_PID[@]} -gt 0 ]]; do
+        visited_guard=$((visited_guard + 1))
+        if [[ $visited_guard -gt $max_iterations ]]; then
+            printf 'bash_pstree: aborting, too many nodes (possible /proc cycle)\n' >&2
+            return 1
         fi
-    done <<< "$children"
-}
 
-#
-# Wrapper:
-#
-#   pstree_compat
-#   pstree_compat 1234
-#
-pstree_compat()
-{
-    local root_pid="${1:-1}"
-    if command -v pstree >/dev/null 2>&1; then
-        pstree -p "$root_pid"
-    else
-        bash_pstree "$root_pid"
-    fi
+        top=$((${#S_PID[@]} - 1))
+        pid="${S_PID[$top]}"
+        print_prefix="${S_PRINT_PREFIX[$top]}"
+        child_prefix="${S_CHILD_PREFIX[$top]}"
+
+        # pop
+        unset 'S_PID[top]' 'S_PRINT_PREFIX[top]' 'S_CHILD_PREFIX[top]'
+        S_PID=("${S_PID[@]}")
+        S_PRINT_PREFIX=("${S_PRINT_PREFIX[@]}")
+        S_CHILD_PREFIX=("${S_CHILD_PREFIX[@]}")
+
+        name=$(bash_pstree_find_name "$pid") || continue
+        printf '%s%s(%s)\n' "$print_prefix" "$name" "$pid"
+
+        children=$(bash_pstree_children "$pid")
+        [[ -n "$children" ]] || continue
+
+        last_child=$(printf '%s\n' "$children" | tail -n 1)
+
+        rev_children=()
+        n=0
+        while IFS= read -r child; do
+            [[ -n "$child" ]] || continue
+            rev_children[$n]="$child"
+            n=$((n + 1))
+        done <<< "$children"
+
+        for ((i = n - 1; i >= 0; i--)); do
+            child="${rev_children[$i]}"
+            if [[ "$child" == "$last_child" ]]; then
+                branch="$BPT_LAST"
+                cont="${child_prefix}    "
+            else
+                branch="$BPT_TEE"
+                cont="${child_prefix}${BPT_VERT}"
+            fi
+            new_prefix="${child_prefix}${branch}"
+
+            S_PID+=("$child")
+            S_PRINT_PREFIX+=("$new_prefix")
+            S_CHILD_PREFIX+=("$cont")
+        done
+    done
 }
 
-alias pstree='pstree_compat'
+# NOTE: intentionally no code runs here. Sourcing this file must be a no-op
+# other than defining the functions above.
+
+alias pstree="pstree_compat"