{"record":{"id":"c7e50b1bfffce17b","repo":"hashicorp/nomad","slug":"failed-to-open-current-netns-v","errorCode":null,"errorMessage":"failed to open current netns: %v","messagePattern":"failed to open current netns: (.+?)","errorType":"exception","errorClass":null,"httpStatus":null,"severity":"error","filePath":"client/lib/nsutil/ns_linux.go","lineNumber":182,"sourceCode":"\treturn ns.file.Fd()\n}\n\nfunc (ns *netNS) errorIfClosed() error {\n\tif ns.closed {\n\t\treturn fmt.Errorf(\"%q has already been closed\", ns.file.Name())\n\t}\n\treturn nil\n}\n\nfunc (ns *netNS) Do(toRun func(NetNS) error) error {\n\tif err := ns.errorIfClosed(); err != nil {\n\t\treturn err\n\t}\n\n\tcontainedCall := func(hostNS NetNS) error {\n\t\tthreadNS, err := GetCurrentNS()\n\t\tif err != nil {\n\t\t\treturn fmt.Errorf(\"failed to open current netns: %v\", err)\n\t\t}\n\t\tdefer threadNS.Close()\n\n\t\t// switch to target namespace\n\t\tif err = ns.Set(); err != nil {\n\t\t\treturn fmt.Errorf(\"error switching to ns %v: %v\", ns.file.Name(), err)\n\t\t}\n\t\tdefer func() {\n\t\t\terr := threadNS.Set() // switch back\n\t\t\tif err == nil {\n\t\t\t\t// Unlock the current thread only when we successfully switched back\n\t\t\t\t// to the original namespace; otherwise leave the thread locked which\n\t\t\t\t// will force the runtime to scrap the current thread, that is maybe\n\t\t\t\t// not as optimal but at least always safe to do.\n\t\t\t\truntime.UnlockOSThread()\n\t\t\t}\n\t\t}()\n","sourceCodeStart":164,"sourceCodeEnd":200,"githubUrl":"https://github.com/hashicorp/nomad/blob/482b49bf1aec006f089bcfc7e632d8f6ac303e5e/client/lib/nsutil/ns_linux.go#L164-L200","documentation":"Inside netNS.Do(), after switching into the target namespace, the code calls GetCurrentNS() to capture the current (contained) namespace to switch back to later. This error wraps a failure of GetCurrentNS() at that point, meaning the thread could not open a handle to its own (new) network namespace.","triggerScenarios":"GetCurrentNS() failing inside the containedCall closure of Do() — typically because /proc/self/ns/net (via the thread's ns path) cannot be opened: /proc not mounted, fd exhaustion (EMFILE), or permission problems in the contained environment.","commonSituations":"Running inside a container with no /proc mounted; the process hit its file-descriptor limit after opening the target ns; a restricted environment where /proc/self/ns/net is not accessible.","solutions":["Ensure /proc is mounted inside the environment where Do() runs","Check and raise the process fd limit (ulimit -n) — opening the ns adds descriptors","Run with sufficient privileges (CAP_SYS_ADMIN) to open namespace files","Verify /proc/self/ns/net is readable; test with os.Open in isolation","Inspect the wrapped error from GetCurrentNS for the exact errno"],"exampleFix":"// before\nthreadNS, err := GetCurrentNS()\nif err != nil {\n    return fmt.Errorf(\"failed to open current netns: %v\", err) // EMFILE\n}\n// after\nif err := raiseFdLimit(); err != nil {\n    return fmt.Errorf(\"cannot raise fd limit: %w\", err)\n}\nthreadNS, err := GetCurrentNS()\nif err != nil {\n    return fmt.Errorf(\"failed to open current netns: %w\", err)\n}","handlingStrategy":"validation","validationCode":"func precheckNetnsEnv() error {\n    if _, err := os.Stat(\"/proc/self/ns/net\"); err != nil {\n        return fmt.Errorf(\"/proc/self/ns/net unavailable: %w\", err)\n    }\n    var l syscall.Rlimit\n    if err := syscall.Getrlimit(syscall.RLIMIT_NOFILE, &l); err == nil && l.Cur < 1024 {\n        return fmt.Errorf(\"fd limit low: %d\", l.Cur)\n    }\n    return nil\n}","typeGuard":null,"tryCatchPattern":"ns.Do(func(hostNS NetNS) error {\n    // work\n    return nil\n})\n// on error:\nif err != nil && strings.Contains(err.Error(), \"failed to open current netns\") {\n    return fmt.Errorf(\"cannot open contained ns; check /proc mount and fd limit: %w\", err)\n}","preventionTips":["Mount /proc in containers running namespace switches","Raise RLIMIT_NOFILE for the client process","Grant CAP_SYS_ADMIN to the process","Validate /proc/self/ns/net readability before Do()"],"tags":["linux","network-namespace","procfs","file-descriptors"],"backgroundTag":"netns-open-failed","analyzedSha":"482b49bf1aec006f089bcfc7e632d8f6ac303e5e","analyzedAt":"2026-09-04T07:54:14.808Z","contentChangedAt":"2026-09-04T07:54:14.808Z","schemaVersion":2},"datasetVersion":"2026-09-08T10:18:20.063Z"}