diff --git a/.gitignore b/.gitignore
index 3097c28d..61b51d6d 100644
--- a/.gitignore
+++ b/.gitignore
@@ -29,7 +29,7 @@ parser.tab.h
 parser.tab.o
 test_parser.o
 test_parser
-
+ppidcache.o
 
 mxqsub
 /mxqsub.1
diff --git a/Makefile b/Makefile
index 065844af..ae84325c 100644
--- a/Makefile
+++ b/Makefile
@@ -520,6 +520,13 @@ keywordset.o: xmalloc.h
 
 clean: CLEAN += keywordset.o
 
+### ppidcache.o -------------------------------------------------------
+
+ppidcache.o: $(mx_util.h)
+ppidcache.o: $(mx_proc.h)
+
+clean: CLEAN += ppidcache.o
+
 ########################################################################
 
 ### mxqd ---------------------------------------------------------------
diff --git a/ppidcache.c b/ppidcache.c
new file mode 100644
index 00000000..9d07de43
--- /dev/null
+++ b/ppidcache.c
@@ -0,0 +1,119 @@
+#include <sys/types.h>
+#include <errno.h>
+#include "mx_util.h"
+#include "ppidcache.h"
+#include "mx_proc.h"
+
+struct entry {
+    pid_t pid;
+    pid_t parent;
+};
+
+struct ppidcache {
+    int count;
+    int alloc;
+    struct entry *entries;
+};
+
+struct ppidcache *ppidcache_new() {
+    struct ppidcache *ppidcache = mx_malloc_forever(sizeof(struct ppidcache));
+    ppidcache->count = 0;
+    ppidcache->alloc = 500;
+    ppidcache->entries = mx_malloc_forever(ppidcache->alloc*sizeof(struct entry));
+    return ppidcache;
+}
+
+void ppidcache_free(struct ppidcache *ppidcache) {
+    free(ppidcache->entries);
+    free(ppidcache);
+}
+
+static int _ppidcache_find(struct ppidcache *ppidcache, pid_t pid) {
+    int i;
+    for (i=0 ; i<ppidcache->count ; i++) {
+        if (ppidcache->entries[i].pid == pid)
+            return i;
+    }
+    return -1;
+}
+
+pid_t ppidcache_get_ppid(struct ppidcache *ppidcache, pid_t pid) {
+    int i = _ppidcache_find(ppidcache, pid);
+    if (i != -1)
+        return ppidcache->entries[i].parent;
+    if (ppidcache->count == ppidcache->alloc) {
+        ppidcache->alloc += 100;
+        struct entry *new = mx_malloc_forever(ppidcache->alloc * sizeof(struct entry));
+        memcpy(new, ppidcache->entries, ppidcache->count*sizeof(struct entry));
+        free(ppidcache->entries);
+        ppidcache->entries = new;
+    }
+    pid_t parent = mx_proc_get_parent(pid);
+    ppidcache->entries[ppidcache->count].pid = pid;
+    ppidcache->entries[ppidcache->count++].parent = parent;
+    return parent;
+}
+
+int ppidcache_is_descendant(struct ppidcache *ppidcache, pid_t ancestor, pid_t candidate) {
+    int fuse=100;
+    pid_t pid = candidate;
+    do {
+        pid = ppidcache_get_ppid(ppidcache, pid);
+        if (pid == 0 || pid == -1)
+            return 0;
+        if (pid == ancestor)
+            return 1;
+    } while (--fuse > 0);
+    return 0;
+}
+
+/*
+ * Load the cache with all pids from the system.
+ * Previous cached content, if any, is removed.
+ */
+void ppidcache_scan(struct ppidcache *ppidcache) {
+    _mx_cleanup_closedir_ DIR *dir = NULL;
+    pid_t pid;
+    struct dirent *dirent;
+
+    ppidcache->count = 0;
+    dir = opendir("/proc");
+    if (dir == NULL) {
+        perror("/proc");
+        return;
+    }
+    while (1) {
+        errno = 0;
+        dirent = readdir(dir);
+        if (dirent == NULL) {
+            if (errno)
+                perror("/proc");
+            return;
+        }
+        if (strspn(dirent->d_name, "0123456789") != strlen(dirent->d_name))
+            continue;
+        pid = atoi(dirent->d_name);
+        ppidcache_get_ppid(ppidcache, pid);
+    }
+}
+
+/*
+ * call cb(data, pid) for all cached(!) descendants.
+ * stop when no more descendants or when callback returns 0
+ */
+void ppidcache_do_descendants(
+    struct ppidcache *ppidcache,
+    pid_t pid,
+    int cb(void *data, pid_t pid),
+    void *data)
+{
+    int next;
+    pid_t candidate;
+
+    for (next=0 ; next<ppidcache->count; next++) {
+        candidate = ppidcache->entries[next].pid;
+        if (ppidcache_is_descendant(ppidcache, pid, candidate))
+            if ((*cb)(data, candidate) == 0)
+                return;
+    }
+}
diff --git a/ppidcache.h b/ppidcache.h
new file mode 100644
index 00000000..ca4a7e37
--- /dev/null
+++ b/ppidcache.h
@@ -0,0 +1,12 @@
+#ifndef _PPIDCACHE_H
+#define _PPIDCACHE_H
+
+#include <sys/types.h>
+
+struct ppidcache *ppidcache_new();
+void ppidcache_free (struct ppidcache *ppidcache);
+pid_t ppidcache_get_ppid(struct ppidcache *ppidcache, pid_t pid);
+int ppidcache_is_descendant(struct ppidcache *ppidcache, pid_t ancestor, pid_t candidate);
+void ppidcache_scan(struct ppidcache *ppidcache);
+void ppidcache_do_descendants(struct ppidcache *ppidcache, pid_t pid, int cb(void *data, pid_t pid), void *data);
+#endif