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Show which PID is causing a temp root

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Example:

  error: Cannot delete path '/nix/store/klyng5rpdkwi5kbxkncy4gjwb490dlhb-foo.drv' because it's in use by Nix process '{nix-process:3605324}'.
This commit is contained in:
Eelco Dolstra 2025-06-27 16:50:48 +02:00
parent cae732f7a1
commit 31b00218fe
6 changed files with 35 additions and 20 deletions
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26
src/libstore/gc.cc
View file

@ -208,7 +208,7 @@ void LocalStore::findTempRoots(Roots & tempRoots, bool censor)
while ((end = contents.find((char) 0, pos)) != std::string::npos) {
Path root(contents, pos, end - pos);
debug("got temporary root '%s'", root);
tempRoots[parseStorePath(root)].emplace(censor ? censored : fmt("{temp:%d}", pid));
tempRoots[parseStorePath(root)].emplace(censor ? censored : fmt("{nix-process:%d}", pid));
pos = end + 1;
}
}
@ -465,7 +465,7 @@ void LocalStore::collectGarbage(const GCOptions & options, GCResults & results)
{
// The temp roots only store the hash part to make it easier to
// ignore suffixes like '.lock', '.chroot' and '.check'.
std::unordered_set<std::string> tempRoots;
std::unordered_map<std::string, GcRootInfo> tempRoots;
// Hash part of the store path currently being deleted, if
// any.
@ -574,7 +574,8 @@ void LocalStore::collectGarbage(const GCOptions & options, GCResults & results)
debug("got new GC root '%s'", path);
auto hashPart = std::string(storePath->hashPart());
auto shared(_shared.lock());
shared->tempRoots.insert(hashPart);
// FIXME: could get the PID from the socket.
shared->tempRoots.insert_or_assign(hashPart, "{nix-process:unknown}");
/* If this path is currently being
deleted, then we have to wait until
deletion is finished to ensure that
@ -618,10 +619,14 @@ void LocalStore::collectGarbage(const GCOptions & options, GCResults & results)
/* Read the temporary roots created before we acquired the global
GC root. Any new roots will be sent to our socket. */
Roots tempRoots;
findTempRoots(tempRoots, options.censor);
for (auto & root : tempRoots)
_shared.lock()->tempRoots.insert(std::string(root.first.hashPart()));
{
Roots tempRoots;
findTempRoots(tempRoots, options.censor);
for (auto & root : tempRoots)
_shared.lock()->tempRoots.insert_or_assign(
std::string(root.first.hashPart()),
*root.second.begin());
}
/* Synchronisation point for testing, see tests/functional/gc-non-blocking.sh. */
if (auto p = getEnv("_NIX_TEST_GC_SYNC_2"))
@ -735,11 +740,12 @@ void LocalStore::collectGarbage(const GCOptions & options, GCResults & results)
{
auto hashPart = std::string(path->hashPart());
auto shared(_shared.lock());
if (shared->tempRoots.count(hashPart)) {
if (auto i = shared->tempRoots.find(hashPart); i != shared->tempRoots.end()) {
if (options.action == GCOptions::gcDeleteSpecific)
throw Error(
"Cannot delete path '%s' because it's in use by a Nix process.",
printStorePath(start));
"Cannot delete path '%s' because it's in use by '%s'.",
printStorePath(start),
i->second);
return markAlive();
}
shared->pending = hashPart;

5
src/libstore/include/nix/store/gc-store.hh
View file

@ -7,8 +7,11 @@
namespace nix {
// FIXME: should turn this into an std::variant to represent the
// several root types.
using GcRootInfo = std::string;
typedef std::unordered_map<StorePath, std::unordered_set<std::string>> Roots;
typedef std::unordered_map<StorePath, std::unordered_set<GcRootInfo>> Roots;
struct GCOptions

1
tests/functional/gc-runtime.nix
View file

@ -9,6 +9,7 @@ mkDerivation {
cat > $out/program <<EOF
#! ${shell}
echo x > \$TEST_ROOT/fifo
sleep 10000
EOF

9
tests/functional/gc-runtime.sh
View file

@ -21,11 +21,16 @@ nix-env -p "$profiles/test" -f ./gc-runtime.nix -i gc-runtime
outPath=$(nix-env -p "$profiles/test" -q --no-name --out-path gc-runtime)
echo "$outPath"
fifo="$TEST_ROOT/fifo"
mkfifo "$fifo"
echo "backgrounding program..."
"$profiles"/test/program &
sleep 2 # hack - wait for the program to get started
"$profiles"/test/program "$fifo" &
child=$!
echo PID=$child
cat "$fifo"
expectStderr 1 nix-store --delete "$outPath" | grepQuiet "Cannot delete path.*because it's referenced by the GC root '/proc/"
nix-env -p "$profiles/test" -e gc-runtime
nix-env -p "$profiles/test" --delete-generations old

4
tests/functional/gc.sh
View file

@ -23,10 +23,10 @@ if nix-store --gc --print-dead | grep -E "$outPath"$; then false; fi
nix-store --gc --print-dead
inUse=$(readLink "$outPath/reference-to-input-2")
if nix-store --delete "$inUse"; then false; fi
expectStderr 1 nix-store --delete "$inUse" | grepQuiet "Cannot delete path.*because it's referenced by the GC root "
test -e "$inUse"
if nix-store --delete "$outPath"; then false; fi
expectStderr 1 nix-store --delete "$outPath" | grepQuiet "Cannot delete path.*because it's referenced by the GC root "
test -e "$outPath"
for i in "$NIX_STORE_DIR"/*; do

10
tests/functional/local-overlay-store/delete-refs-inner.sh
View file

@ -22,14 +22,14 @@ input2=$(nix-build ../hermetic.nix --no-out-link --arg busybox "$busybox" --arg
input3=$(nix-build ../hermetic.nix --no-out-link --arg busybox "$busybox" --arg withFinalRefs true --arg seed 2 -A passthru.input3 -j0)
# Can't delete because referenced
expectStderr 1 nix-store --delete $input1 | grepQuiet "Cannot delete path"
expectStderr 1 nix-store --delete $input2 | grepQuiet "Cannot delete path"
expectStderr 1 nix-store --delete $input3 | grepQuiet "Cannot delete path"
expectStderr 1 nix-store --delete $input1 | grepQuiet "Cannot delete path.*because it's referenced by path"
expectStderr 1 nix-store --delete $input2 | grepQuiet "Cannot delete path.*because it's referenced by path"
expectStderr 1 nix-store --delete $input3 | grepQuiet "Cannot delete path.*because it's referenced by path"
# These same paths are referenced in the lower layer (by the seed 1
# build done in `initLowerStore`).
expectStderr 1 nix-store --store "$storeA" --delete $input2 | grepQuiet "Cannot delete path"
expectStderr 1 nix-store --store "$storeA" --delete $input3 | grepQuiet "Cannot delete path"
expectStderr 1 nix-store --store "$storeA" --delete $input2 | grepQuiet "Cannot delete path.*because it's referenced by path"
expectStderr 1 nix-store --store "$storeA" --delete $input3 | grepQuiet "Cannot delete path.*because it's referenced by path"
# Can delete
nix-store --delete $hermetic