{"record":{"id":"55b345a61bcb651b","repo":"vitessio/vitess","slug":"fullyqualifiedhostname-failed-to-retrieve-the-hos","errorCode":null,"errorMessage":"FullyQualifiedHostname: failed to retrieve the hostname of this machine: %v","messagePattern":"FullyQualifiedHostname: failed to retrieve the hostname of this machine: (.+?)","errorType":"error_code","errorClass":null,"httpStatus":null,"severity":"critical","filePath":"go/netutil/netutil.go","lineNumber":67,"sourceCode":"}\n\n// JoinHostPort is an extension to net.JoinHostPort that also formats the\n// integer port.\nfunc JoinHostPort(host string, port int32) string {\n\treturn net.JoinHostPort(host, strconv.FormatInt(int64(port), 10))\n}\n\n// FullyQualifiedHostname returns the FQDN of the machine.\nfunc FullyQualifiedHostname() (string, error) {\n\t// The machine hostname (which is also returned by os.Hostname()) may not be\n\t// set to the FQDN, but only the first part of it e.g. \"localhost\" instead of\n\t// \"localhost.localdomain\".\n\t// To get the full FQDN, we do the following:\n\n\t// 1. Get the machine hostname. Example: localhost\n\thostname, err := os.Hostname()\n\tif err != nil {\n\t\treturn \"\", fmt.Errorf(\"FullyQualifiedHostname: failed to retrieve the hostname of this machine: %v\", err)\n\t}\n\n\t// 2. Look up the IP address for that hostname. Example: 127.0.0.1\n\tips, err := net.LookupHost(hostname)\n\tif err != nil {\n\t\treturn \"\", fmt.Errorf(\"FullyQualifiedHostname: failed to lookup the IP of this machine's hostname (%v): %v\", hostname, err)\n\t}\n\tif len(ips) == 0 {\n\t\treturn \"\", fmt.Errorf(\"FullyQualifiedHostname: lookup of the IP of this machine's hostname (%v) did not return any IP address\", hostname)\n\t}\n\t// If multiple IPs are returned, we only look at the first one.\n\tlocalIP := ips[0]\n\n\t// 3. Reverse lookup the IP. Example: localhost.localdomain\n\tresolvedHostnames, err := net.LookupAddr(localIP)\n\tif err != nil {\n\t\treturn \"\", fmt.Errorf(\"FullyQualifiedHostname: failed to reverse lookup this machine's local IP (%v): %v\", localIP, err)\n\t}","sourceCodeStart":49,"sourceCodeEnd":85,"githubUrl":"https://github.com/vitessio/vitess/blob/01a25a7d176f94613b8d59d799f438380a8760e4/go/netutil/netutil.go#L49-L85","documentation":"FullyQualifiedHostname builds the machine's FQDN and first calls os.Hostname(). This error means the OS itself failed to return the local hostname, so the FQDN cannot be derived. It almost always indicates a broken local hostname configuration (e.g. unset/invalid hostname or resource limits).","triggerScenarios":"Calling FullyQualifiedHostname / FullyQualifiedHostnameOrPanic (or anything that calls it: vtctld BuildTabletFromInput, backup ExecuteBackup/executeFullBackup, populateListeningURL) when os.Hostname() fails on the host.","commonSituations":"Containers with misconfigured/empty hostname; hosts whose hostname exceeds OS limits; systems under fd/memory pressure where the syscall fails.","solutions":["Fix the machine's hostname (e.g. `hostnamectl set-hostname myhost` or docker `--hostname`) and retry","Verify the hostname resolves locally: `hostname` should return a non-empty name","Restart the container/pod with a valid hostname setting","If panic path (FullyQualifiedHostnameOrPanic), set a valid hostname before starting the Vitess binary"],"exampleFix":"// shell, before\n$ hostname\n(empty or errors)\n// after\n$ sudo hostnamectl set-hostname tablet-1\n$ hostname\ntablet-1","handlingStrategy":"fallback","validationCode":"if h, err := os.Hostname(); err != nil || h == \"\" {\n    return fmt.Errorf(\"hostname unavailable: %v\", err)\n}","typeGuard":null,"tryCatchPattern":"fqdn, err := netutil.FullyQualifiedHostname()\nif err != nil {\n    log.Warn(\"FQDN lookup failed, falling back to os.Hostname\", slog.Any(\"error\", err))\n    fqdn, err = os.Hostname()\n}","preventionTips":["Set a valid hostname on every machine/container before starting Vitess","Ensure hostnamectl/docker --hostname is configured in your provisioning","Check `hostname` output in startup health scripts"],"tags":["network","hostname","dns"],"backgroundTag":"hostname-resolution-failed","analyzedSha":"01a25a7d176f94613b8d59d799f438380a8760e4","analyzedAt":"2026-09-01T17:28:30.605Z","contentChangedAt":null,"schemaVersion":2},"datasetVersion":"2026-09-08T10:18:20.063Z"}