---
title: iOS Tailscale Clients Report HostName="localhost" — Breaks /etc/hosts Generators
domain: troubleshooting
category: networking
tags:
  - tailscale
  - ios
  - postfix
  - etc-hosts
  - jq
status: published
created: 2026-04-29
updated: 2026-04-29
---

# iOS Tailscale Clients Report HostName="localhost" — Breaks /etc/hosts Generators

## Problem

A homegrown script that builds an `/etc/hosts` block from `tailscale status --json` silently corrupted the file the moment any iOS device joined the tailnet. After the next run, services bound to `localhost` started failing.

On the affected host (`majordiscord`), Postfix refused to start with:

```
postfix: fatal: parameter inet_interfaces: no local interface found for 100.127.114.10
```

`/etc/hosts` looked fine at the top — `127.0.0.1 localhost` was still present — but inside the Tailscale-managed block:

```
# TAILSCALE_START
100.84.42.102 tttpod
100.110.197.17 majortoot
100.95.55.40 localhost          <-- WRONG (this is an iPhone)
100.84.165.52 majormail
...
100.127.114.10 localhost         <-- WRONG (this is an iPad)
# TAILSCALE_END
```

When Postfix resolved `localhost` (because `inet_interfaces = localhost` in `main.cf`), the **last matching entry** in `/etc/hosts` won — a Tailscale IP that doesn't exist on this host — and the daemon died on bind.

## Root Cause

The script used `.HostName` from the Tailscale JSON:

```bash
tailscale status --json \
  | jq -r '.Peer[] | "\(.TailscaleIPs[0]) \(.HostName)"' \
  >> "$TEMP_HOSTS"
```

iOS Tailscale clients (iPhone, iPad) **always report `HostName: "localhost"`** in the JSON. iOS doesn't expose the real device name to apps the way macOS/Linux/Windows do, so the Tailscale client falls back to the literal string `localhost`.

Inspect it directly:

```bash
$ tailscale status --json | jq '.Peer[] | select(.OS == "iOS") | {DNSName, HostName, OS}'
{
  "DNSName": "iphone171.tail7f2d9.ts.net.",
  "HostName": "localhost",
  "OS": "iOS"
}
{
  "DNSName": "ipad166.tail7f2d9.ts.net.",
  "HostName": "localhost",
  "OS": "iOS"
}
```

Every iOS device contributes a line `<tailscale-ip> localhost` to `/etc/hosts`, hijacking the `localhost` lookup.

## Fix

Use `.DNSName` (the unique tailnet DNS name) and take the first dotted component instead of `.HostName`:

```bash
tailscale status --json \
  | jq -r '.Peer[] | "\(.TailscaleIPs[0]) \(.DNSName | rtrimstr(".") | split(".")[0])"' \
  >> "$TEMP_HOSTS"
```

`DNSName` is always set, always unique, and produces clean labels like `iphone171`, `ipad166`, `majorlab`, etc.

After patching the script and re-running it:

```bash
$ bash /root/update_tailscale_hosts.sh
$ systemctl restart postfix
$ systemctl is-active postfix
active
```

## Why It's Hard to Spot

- The corruption only triggers when an iOS device is in the tailnet — so the script "worked" for months.
- `/etc/hosts` files are commonly skimmed top-down. The bogus `localhost` line is buried in the Tailscale block, well below the legitimate `127.0.0.1 localhost` line, and looks superficially like a normal Tailscale entry.
- Postfix's error message names the IP, not `localhost`, so the connection to `/etc/hosts` isn't obvious.
- `getent hosts localhost` shows the *first* match (`127.0.0.1`), not the one Postfix's resolver actually picks for `inet_interfaces` lookup.

## Verification Checklist

If you suspect this on any host using a similar generator script:

```bash
# Any non-loopback "localhost" entries are bugs
grep -nE '^[0-9]+\..* localhost\s*$' /etc/hosts

# Look at iOS peers' HostName field
tailscale status --json | jq '.Peer[] | select(.OS == "iOS") | .HostName'
```

## Related

- [[majordiscord]] — affected host (incident logged 2026-04-29)
- [[Network Overview]] — Tailscale fleet topology