{"id":"8894ea1a3c11a33a","repo":"BurntSushi/ripgrep","slug":"host-name-max-limit-overflowed-usize","errorCode":null,"errorMessage":"host name max limit ({}) overflowed usize","messagePattern":"host name max limit \\((.+?)\\) overflowed usize","errorType":"console","errorClass":null,"httpStatus":null,"severity":"error","filePath":"crates/cli/src/hostname.rs","lineNumber":52,"sourceCode":"\n#[cfg(unix)]\nfn gethostname() -> io::Result<OsString> {\n    use std::os::unix::ffi::OsStringExt;\n\n    // SAFETY: There don't appear to be any safety requirements for calling\n    // sysconf.\n    let limit = unsafe { libc::sysconf(libc::_SC_HOST_NAME_MAX) };\n    if limit == -1 {\n        // It is in theory possible for sysconf to return -1 for a limit but\n        // *not* set errno, in which case, io::Error::last_os_error is\n        // indeterminate. But untangling that is super annoying because std\n        // doesn't expose any unix-specific APIs for inspecting the errno. (We\n        // could do it ourselves, but it just doesn't seem worth doing?)\n        return Err(io::Error::last_os_error());\n    }\n    let Ok(maxlen) = usize::try_from(limit) else {\n        let msg = format!(\"host name max limit ({}) overflowed usize\", limit);\n        return Err(io::Error::new(io::ErrorKind::Other, msg));\n    };\n    // maxlen here includes the NUL terminator.\n    let mut buf = vec![0; maxlen];\n    // SAFETY: The pointer we give is valid as it is derived directly from a\n    // Vec. Similarly, `maxlen` is the length of our Vec, and is thus valid\n    // to write to.\n    let rc = unsafe {\n        libc::gethostname(buf.as_mut_ptr().cast::<libc::c_char>(), maxlen)\n    };\n    if rc == -1 {\n        return Err(io::Error::last_os_error());\n    }\n    // POSIX says that if the hostname is bigger than `maxlen`, then it may\n    // write a truncate name back that is not necessarily NUL terminated (wtf,\n    // lol). So if we can't find a NUL terminator, then just give up.\n    let Some(zeropos) = buf.iter().position(|&b| b == 0) else {\n        let msg = \"could not find NUL terminator in hostname\";\n        return Err(io::Error::new(io::ErrorKind::Other, msg));","sourceCodeStart":34,"sourceCodeEnd":70,"githubUrl":"https://github.com/BurntSushi/ripgrep/blob/3fce3b5bb0236da2df6d99672afb8a719642eca7/crates/cli/src/hostname.rs#L34-L70","documentation":"On Unix, hostname() calls libc::sysconf(_SC_HOST_NAME_MAX) to size the hostname buffer. If sysconf returns a non-negative value that nonetheless cannot be converted into usize (usize::try_from fails), this error is produced. It is a defensive guard against a pathological sysconf result on a broken or emulated libc.","triggerScenarios":"sysconf(_SC_HOST_NAME_MAX) returns a positive c_long that exceeds usize::MAX (only possible on targets where c_long is wider than, or a different signedness than, the pointer-sized usize) and usize::try_from(limit) returns Err.","commonSituations":"Running under a buggy syscall emulation layer, a container/VM with a misconfigured sysconf, or an unusual ABI where long is 8 bytes but usize is 4 bytes (rare 32-bit Unix variants). Practically never seen on mainstream Linux/macOS.","solutions":["Treat this as a system/libc defect: report or patch the environment returning a bogus _SC_HOST_NAME_MAX.","Avoid the hostname() call and read the hostname from an OS file (e.g. /etc/hostname) or an env var as a workaround.","Upgrade/restart the affected host so sysconf returns a sane value."],"exampleFix":"// before\nlet name = grep_cli::hostname()?;\n\n// after (fallback for broken sysconf)\nlet name = match grep_cli::hostname() {\n    Ok(n) => n,\n    Err(_) => std::fs::read_to_string(\"/etc/hostname\")\n        .unwrap_or_default().trim_end().into(),\n};","handlingStrategy":"fallback","validationCode":null,"typeGuard":null,"tryCatchPattern":"let host = match grep_cli::hostname() {\n    Ok(n) => n,\n    Err(_) => std::fs::read_to_string(\"/etc/hostname\")\n        .unwrap_or_default().trim_end().into(),\n};","preventionTips":["Treat hostname() as fallible even on Unix and always provide a fallback.","In tests/CI, prefer setting hostname via env to avoid depending on sysconf quirks.","Report recurring sysconf failures to the platform/libc maintainer."],"tags":["hostname","unix","sysconf","libc"],"analyzedSha":"3fce3b5bb0236da2df6d99672afb8a719642eca7","analyzedAt":"2026-08-06T01:39:05.073Z","schemaVersion":2}