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Improve error when can't acquire db lock #13340

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Merged
tomberek merged 1 commit into from
Aug 18, 2025
Merged

Improve error when can't acquire db lock #13340

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11 changes: 10 additions & 1 deletion src/libstore/local-store.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -221,7 +221,16 @@ LocalStore::LocalStore(ref<const Config> config)
schema upgrade is in progress. */
if (!config->readOnly) {
Path globalLockPath = dbDir + "/big-lock";
globalLock = openLockFile(globalLockPath.c_str(), true);
try {
globalLock = openLockFile(globalLockPath.c_str(), true);
} catch (SysError & e) {
if (e.errNo == EACCES || e.errNo == EPERM) {
e.addTrace({},
"This command may have been run as non-root in a single-user Nix installation,\n"
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@edolstra edolstra Jun 11, 2025

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I'm confused by the tense ("may have been") here. Is the current command being run as non-root, or was a previous command run as non-root?

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@mkenigs mkenigs Jun 11, 2025

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I mean the current command

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@Mic92 Mic92 Jun 11, 2025 •
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we could probably also check check "isNonRootuser()" to make a more concrete error.

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@roberth roberth Jun 20, 2025

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I think in the general case where the file isn't owned by the current uid, we can add the hint that maybe you wanted to connect to a nix daemon instead.

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@mkenigs mkenigs Jun 23, 2025 •
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I guess we could say "you may want to start a Nix daemon", but the user doesn't really connect to the Nix daemon themselves so I don't think "you may want to connect to a Nix daemon instead" would be very helpful, because it's not actionable. Did you have something in mind?

"or the Nix daemon may have crashed.");
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@edolstra edolstra Jun 11, 2025

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Why would a daemon crash cause this issue?

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@mkenigs mkenigs Jun 11, 2025

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I had gleaned that from open issues, although maybe that's no longer the case? I just tried e.g. this reproducer and didn't get the error #3435 (comment)

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@mkenigs mkenigs Jun 11, 2025

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I do see the error if I sudo rm /nix/var/nix/daemon-socket/socket

}
throw;
}
}

if (!config->readOnly && !lockFile(globalLock.get(), ltRead, false)) {
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3 changes: 2 additions & 1 deletion tests/functional/read-only-store.sh
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Expand Up @@ -42,7 +42,8 @@ chmod -R -w $TEST_ROOT/var

# Make sure we fail on add operations on the read-only store
# This is only for adding files that are not *already* in the store
expectStderr 1 nix-store --add eval.nix | grepQuiet "error: opening lock file '$(readlink -e $TEST_ROOT)/var/nix/db/big-lock'"
# Should show enhanced error message with helpful context
expectStderr 1 nix-store --add eval.nix | grepQuiet "This command may have been run as non-root in a single-user Nix installation"
expectStderr 1 nix-store --store local?read-only=true --add eval.nix | grepQuiet "Permission denied"

# Test the same operations from before should again succeed
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