{"record":{"id":"a72153de3d1abd8b","repo":"rust-lang/cargo","slug":"failed-to-connect-to-jobserver-from-environment-va","errorCode":null,"errorMessage":"failed to connect to jobserver from environment variable `{name}={value:?}`: {e}","messagePattern":"failed to connect to jobserver from environment variable `(.+?)=(.+?)`: (.+?)","errorType":"exception","errorClass":"anyhow::Error","httpStatus":null,"severity":"error","filePath":"src/context/mod.rs","lineNumber":339,"sourceCode":"                let jobserver::FromEnv { client, var } =\n                    unsafe { jobserver::Client::from_env_ext(true) };\n\n                match client {\n                    Ok(client) => return Ok(Some(client)),\n                    Err(e)\n                        if matches!(\n                            e.kind(),\n                            FromEnvErrorKind::NoEnvVar\n                                | FromEnvErrorKind::NoJobserver\n                                | FromEnvErrorKind::NegativeFd\n                                | FromEnvErrorKind::Unsupported\n                        ) =>\n                    {\n                        Ok(None)\n                    }\n                    Err(e) => {\n                        let (name, value) = var.unwrap();\n                        Err(anyhow::anyhow!(\n                            \"failed to connect to jobserver from environment variable `{name}={value:?}`: {e}\"\n                        ))\n                    }\n                }\n            },\n        );\n        let jobserver = match &*GLOBAL_JOBSERVER {\n            Ok(jobserver) => jobserver.as_ref(),\n            Err(e) => {\n                let _ = shell.warn(e);\n                None\n            }\n        };\n\n        let env = Env::new();\n\n        let cache_key = \"CARGO_CACHE_RUSTC_INFO\";\n        let cache_rustc_info = match env.get_env_os(cache_key) {","sourceCodeStart":321,"sourceCodeEnd":357,"githubUrl":"https://github.com/rust-lang/cargo/blob/98a09e7e7d62850f14e5b6132101fc1edd19a16f/src/context/mod.rs#L321-L357","documentation":"Cargo tried to attach to an existing GNU make jobserver (semaphore-based parallelism via the `MAKEFLAGS`/`CARGO_MAKEFLAGS` env var) advertised in the environment, and the jobserver crate returned an error other than the benign `NoEnvVar`/`NoJobserver`/`NegativeFd`/`Unsupported`. The failing variable name, its raw value, and the underlying error are surfaced.","triggerScenarios":"Parent process exports a `MAKEFLAGS` containing a jobserver spec (`--jobserver-auth=<fds>`) but the file descriptors are invalid/closed; running under `make -jN` where the FDs were not inherited (e.g. cargo was exec'd after closing FDs); a stale `CARGO_MAKEFLAGS` from a previous make session.","commonSituations":"CI that wraps cargo in `make` and accidentally re-execs; containers that strip inherited FDs; custom build orchestrators that set `MAKEFLAGS` without providing live FDs; `make` older than 4.4 with incompatible auth syntax.","solutions":["Unset the offending variable before invoking cargo: `unset MAKEFLAGS; cargo build`.","Pass `--jobs N` to cargo explicitly to bypass the inherited jobserver.","Ensure the parent `make` invocation actually creates the jobserver (`make -j4`, not `make`).","Update the jobserver-providing tool (make 4.x, ninja) so the auth FDs are inheritable."],"exampleFix":"// before\nmake -j4   # Makefile rule: cargo build\n# inherits a jobserver FD that is closed -> error\n\n// after\n# Makefile\nbuild:\n\t+unset MAKEFLAGS; cargo build --jobs 4\n# or\nbuild:\n\t+cargo build --jobs 4","handlingStrategy":"validation","validationCode":"fn jobserver_env_valid() -> bool {\n    if let Ok(mf) = std::env::var(\"MAKEFLAGS\") {\n        if mf.contains(\"--jobserver-auth=\") {\n            // FDs must be open and inheritable; conservative check\n            return std::env::current_exe().is_ok();\n        }\n    }\n    true\n}","typeGuard":"null","tryCatchPattern":"match GlobalContext::load_jobserver() {\n    Err(e) if e.to_string().contains(\"failed to connect to jobserver\") => { std::env::remove_var(\"MAKEFLAGS\"); retry_without_jobserver()? }\n    r => r?,\n}","preventionTips":["In Makefiles, prefix cargo recipes with `+` and unset `MAKEFLAGS` if unsure.","Pass `--jobs N` explicitly when wrapping cargo.","Don't forward `MAKEFLAGS` across process boundaries that close FDs."],"tags":["cargo","jobserver","make","environment","parallelism"],"backgroundTag":null,"analyzedSha":"98a09e7e7d62850f14e5b6132101fc1edd19a16f","analyzedAt":"2026-08-11T17:42:36.556Z","contentChangedAt":"2026-08-11T17:42:36.556Z","schemaVersion":2},"datasetVersion":"2026-09-23T08:17:48.524Z"}