diff --git a/share/sysinstall/hooks/sortix-1.1-random-seed b/share/sysinstall/hooks/sortix-1.1-random-seed
new file mode 100644
index 00000000..e69de29b
diff --git a/sysinstall/hooks.c b/sysinstall/hooks.c
index 3af2f307..8de00b75 100644
--- a/sysinstall/hooks.c
+++ b/sysinstall/hooks.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016, 2017 Jonas 'Sortie' Termansen.
+ * Copyright (c) 2016, 2017, 2018 Jonas 'Sortie' Termansen.
  *
  * Permission to use, copy, modify, and distribute this software for any
  * purpose with or without fee is hereby granted, provided that the above
@@ -29,21 +29,41 @@
 #include "hooks.h"
 #include "release.h"
 
+// Files in the /share/sysinstall/hooks directory are added whenever an
+// incompatible operating system change is made that needs additional actions.
+// These files are part of the system manifest and their lack can be tested
+// in upgrade_prepare, but not in upgrade_finalize (as they would have been
+// installed there). If a file is lacking, then a hook should be run taking
+// the needed action. For instance, if /etc/foo becomes the different /etc/bar,
+// then /share/sysinstall/hooks/osname-x.y-bar would be made, and if it is
+// absent then upgrade_prepare converts /etc/foo to /etc/bar. The file is then
+// made when the system manifest is upgraded.
+//
+// Hooks are meant to run once. However, they must handle if the upgrade fails
+// between the hook running and the hook file being installed when the system
+// manifest is installed.
+//
+// If this system is used, follow the instructions in following-development(7)
+// and add an entry in that manual page about the change.
+__attribute__((used))
+static bool hook_needs_to_be_run(const char* target_prefix, const char* hook)
+{
+	char* path;
+	if ( asprintf(&path, "%sshare/sysinstall/hooks/%s",
+	              target_prefix, hook) < 0 )
+	{
+		warn("asprintf");
+		_exit(2);
+	}
+	bool result = access_or_die(path, F_OK) < 0;
+	free(path);
+	return result;
+}
+
 void upgrade_prepare(const struct release* old_release,
                      const struct release* new_release,
                      const char* source_prefix,
                      const char* target_prefix)
-{
-	(void) old_release;
-	(void) new_release;
-	(void) source_prefix;
-	(void) target_prefix;
-}
-
-void upgrade_finalize(const struct release* old_release,
-                      const struct release* new_release,
-                      const char* source_prefix,
-                      const char* target_prefix)
 {
 	(void) old_release;
 	(void) new_release;
@@ -51,8 +71,7 @@ void upgrade_finalize(const struct release* old_release,
 	(void) target_prefix;
 
 	// TODO: After releasing Sortix 1.1, remove this compatibility.
-	if ( version_compare(old_release->version_major, old_release->version_minor,
-	                     old_release->version_dev, 1, 1, false) < 0 ) // < 1.1
+	if ( hook_needs_to_be_run(target_prefix, "sortix-1.1-random-seed") )
 	{
 		char* random_seed_path;
 		if ( asprintf(&random_seed_path, "%sboot/random.seed", target_prefix) < 0 )
@@ -68,3 +87,14 @@ void upgrade_finalize(const struct release* old_release,
 		free(random_seed_path);
 	}
 }
+
+void upgrade_finalize(const struct release* old_release,
+                      const struct release* new_release,
+                      const char* source_prefix,
+                      const char* target_prefix)
+{
+	(void) old_release;
+	(void) new_release;
+	(void) source_prefix;
+	(void) target_prefix;
+}