From 58a85fa4621faaa89286065f5583328783085722 Mon Sep 17 00:00:00 2001
From: Bob van der Linden <bobvanderlinden@gmail.com>
Date: Wed, 8 Aug 2018 21:21:21 +0200
Subject: [PATCH] mention nix-store --query --roots when a path cannot be
 deleted

---
 src/libstore/gc.cc | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/src/libstore/gc.cc b/src/libstore/gc.cc
index b415d5421..65220a9f6 100644
--- a/src/libstore/gc.cc
+++ b/src/libstore/gc.cc
@@ -791,7 +791,11 @@ void LocalStore::collectGarbage(const GCOptions & options, GCResults & results)
             assertStorePath(i);
             tryToDelete(state, i);
             if (state.dead.find(i) == state.dead.end())
-                throw Error(format("cannot delete path '%1%' since it is still alive") % i);
+                throw Error(format(
+                    "cannot delete path '%1%' since it is still alive. "
+                    "To find out why use: "
+                    "nix-store --query --roots"
+                    ) % i);
         }
 
     } else if (options.maxFreed > 0) {