v0.4.64: NFS mount diagnostics — pre-flight probe, retry, hint translation

The dominant field failure from v0.4.63 was "mount.nfs: failed to apply
fstab options" (exit 32), surfaced verbatim by the Storage tab. The
message is misleading — it has nothing to do with /etc/fstab; it comes
from nfs-utils 2.6.x's nfs_options2string() and most commonly indicates
the container is missing CAP_SYS_ADMIN, /etc/mtab is unwritable, or an
auxiliary option triggered an option-transform edge case.

Backend (crates/iso-store/src/nfs.rs):
- TCP pre-flight probe to server:port (4s timeout) before shelling out.
  Catches wrong-IP / firewall cases as "cannot reach NFS port" instead
  of letting mount.nfs spit out an unhelpful message.
- proto=tcp explicit on NFSv3 (UDP is widely deprecated, modern NAS
  appliances often don't bind UDP at all).
- Optional `port` field on NfsAddRequest (defaults to 2049), persisted
  on NfsMount.
- On "failed to apply fstab options" / "internal option parsing error"
  retry with a minimal option set (vers=N,ro/rw only) — bypasses the
  nfs-utils transformation bug; if it still fails we get a real kernel
  error to translate.
- hint_for() translates well-known stderr patterns into actionable
  guidance — CAP_SYS_ADMIN for option-transform failures, exports-table
  for access-denied, export-path hint for "no such file or directory"
  (calling out the UniFi UNAS Pro /var/nfs/shared/<name> convention),
  etc.
- normalize_server() strips http://, https://, nfs:// schemes the
  operator may have pasted by mistake, plus trailing slashes.

API (crates/http-api/src/app.rs):
- api_nfs_add now returns a structured {error, stderr, hint} JSON body
  on failure instead of plain text. UI renders the error in bold with
  the hint as a dimmer second line.

UI (crates/webui/src/app.js):
- Storage tab's "Mount failed" banner now shows the raw error + hint on
  two lines. Each persisted mount row also surfaces last_hint under
  last_error.

Terminal (crates/http-api/src/terminal.rs):
- `nfs mount` command prints "hint: ..." on a follow-up line when the
  manager returns one.

Tests:
- 8 new tests covering option string (incl. proto=tcp on v3, port=N for
  non-default), minimal-options stripping, server normalization, and
  hint translation for each well-known stderr pattern.
- All 150 tests pass; clippy -D warnings clean.

Co-Authored-By: Claude Opus 4.7 (1M context) <[email protected]>

Cargo.lock

@@ -1140,7 +1140,7 @@ checksum = "384b8ab6d37215f3c5301a95a4accb5d64aa607f1fcb26a11b5303878451b4fe"
 
 [[package]]
 name = "openpxe"
-version = "0.4.63"
+version = "0.4.64"
 dependencies = [
  "anyhow",
  "axum",
@@ -1162,7 +1162,7 @@ dependencies = [
 
 [[package]]
 name = "openpxe-core"
-version = "0.4.63"
+version = "0.4.64"
 dependencies = [
  "anyhow",
  "bcrypt",
@@ -1181,7 +1181,7 @@ dependencies = [
 
 [[package]]
 name = "openpxe-dhcp-proxy"
-version = "0.4.63"
+version = "0.4.64"
 dependencies = [
  "anyhow",
  "bytes",
@@ -1195,7 +1195,7 @@ dependencies = [
 
 [[package]]
 name = "openpxe-http-api"
-version = "0.4.63"
+version = "0.4.64"
 dependencies = [
  "anyhow",
  "axum",
@@ -1226,7 +1226,7 @@ dependencies = [
 
 [[package]]
 name = "openpxe-ipxe-assets"
-version = "0.4.63"
+version = "0.4.64"
 dependencies = [
  "openpxe-core",
  "rust-embed",
@@ -1236,7 +1236,7 @@ dependencies = [
 
 [[package]]
 name = "openpxe-iso-store"
-version = "0.4.63"
+version = "0.4.64"
 dependencies = [
  "anyhow",
  "bcrypt",
@@ -1260,7 +1260,7 @@ dependencies = [
 
 [[package]]
 name = "openpxe-tftp"
-version = "0.4.63"
+version = "0.4.64"
 dependencies = [
  "anyhow",
  "bytes",
@@ -1274,7 +1274,7 @@ dependencies = [
 
 [[package]]
 name = "openpxe-webui"
-version = "0.4.63"
+version = "0.4.64"
 
 [[package]]
 name = "parking_lot"

Cargo.toml

@@ -12,7 +12,7 @@ members = [
 ]
 
 [workspace.package]
-version = "0.4.63"
+version = "0.4.64"
 edition = "2021"
 rust-version = "1.95"
 license = "MIT OR Apache-2.0"

crates/http-api/src/app.rs

@@ -1713,11 +1713,12 @@ async fn api_nfs_list(State(state): State<AppState>) -> Json<serde_json::Value>
 async fn api_nfs_add(State(state): State<AppState>, Json(req): Json<NfsAddRequest>) -> Response {
     match state.nfs.add(req).await {
         Ok(m) => (StatusCode::CREATED, Json(m)).into_response(),
-        // Anything from the manager surfaces as a user-fixable validation
-        // error — bad host, kernel without NFS support, missing
-        // `mount.nfs`, dead server. We pass the message through verbatim
-        // so the UI can show it to the operator.
-        Err(e) => (StatusCode::BAD_REQUEST, format!("{e}")).into_response(),
+        // v0.4.64: the manager returns a structured `NfsMountError` with
+        // `error` + optional `hint` + the raw `stderr`, so the UI can
+        // show both — the raw message for completeness, the hint for
+        // "what to fix next". Previously this was a plain text body
+        // which collapsed both bits of information into one line.
+        Err(err) => (StatusCode::BAD_REQUEST, Json(err)).into_response(),
     }
 }
 

crates/http-api/src/terminal.rs

@@ -321,10 +321,25 @@ async fn nfs_command(s: &AppState, args: &[String]) -> Result<String, String> {
                 export: export.to_string(),
                 version,
                 read_only,
+                // v0.4.64: terminal callers can't override the port yet
+                // — keep the default 2049. We could plumb a 4th arg
+                // later if anyone asks.
+                port: None,
             };
             match s.nfs.add(req).await {
                 Ok(m) => Ok(format!("mounted {} ({} isos)", m.id, m.iso_count)),
-                Err(e) => Err(format!("mount failed: {e}")),
+                // v0.4.64: `add` now returns a structured `NfsMountError`.
+                // We render the raw error plus the hint (if any) on
+                // separate lines so the terminal output mirrors what
+                // the Storage tab shows.
+                Err(e) => {
+                    let mut out = format!("mount failed: {}", e.error);
+                    if let Some(h) = e.hint {
+                        out.push_str("\nhint: ");
+                        out.push_str(&h);
+                    }
+                    Err(out)
+                }
             }
         }
         Some("unmount") => {

crates/iso-store/src/nfs.rs

@@ -9,14 +9,15 @@
 //! 1. Operator submits a mount spec via the Storage tab:
 //!    `{ server: "10.0.0.20", export: "/srv/isos", version: "v41" }`.
 //! 2. We slugify a stable id, mkdir `<work_dir>/nfs/<id>/`, then shell out
-//!    to `/bin/mount -t nfs -o vers=...,ro,nolock server:export local`.
+//!    to `mount.nfs -v -o vers=...,ro,nolock,proto=tcp server:export local`.
 //! 3. On success we walk the mount point looking for `*.iso` files and
 //!    register each one with the `IsoStore` as an external source — same
 //!    introspection pipeline as a web upload, but no sha256 (the bytes
 //!    live on a remote machine; hashing them would suck them through the
 //!    network on every restart).
-//! 4. On failure we record `last_error` on the spec and persist anyway
-//!    so the UI can show a row in red rather than silently dropping it.
+//! 4. On failure we record `last_error` + `hint` on the spec and persist
+//!    anyway so the UI can show a row in red with an actionable hint
+//!    rather than silently dropping it.
 //!
 //! ## Operational notes
 //!
@@ -28,6 +29,28 @@
 //! - Mount commands are issued sequentially under a single mutex to avoid
 //!   `mount` racing on the same target dir.
 //!
+//! ## v0.4.64 diagnostics rework
+//!
+//! Field reports showed `mount.nfs: failed to apply fstab options` (exit
+//! code 32) was the dominant failure surfaced through the UI — a deeply
+//! unhelpful message from nfs-utils 2.6.x that has nothing to do with
+//! `/etc/fstab`. It comes from `nfs_options2string()` and lights up when
+//! the kernel can't accept the assembled options, when mtab can't be
+//! written (container without `CAP_SYS_ADMIN`), or when an obscure option
+//! triggers a transformation edge case. In v0.4.64 we:
+//!
+//!   1. Probe TCP reach to `server:port` before shelling out so a wrong
+//!      IP / closed firewall surfaces as a clear "cannot reach NFS port"
+//!      instead of `failed to apply fstab options`.
+//!   2. Pass `proto=tcp` explicitly on NFSv3 (UDP is widely deprecated
+//!      and several NAS appliances don't bind it at all).
+//!   3. On `failed to apply fstab options`, retry with a stripped-down
+//!      option set (`vers=N,ro/rw`) — that frequently succeeds and at
+//!      minimum produces a real kernel error.
+//!   4. Translate well-known stderr patterns into operator-friendly hints
+//!      and persist them on the mount so the UI can show "what to fix
+//!      next" instead of the raw mount.nfs message.
+//!
 //! ## Persistence
 //!
 //! Mount specs (without runtime state) live at `<work_dir>/nfs.json`,
@@ -42,9 +65,20 @@ use serde::{Deserialize, Serialize};
 use std::collections::HashMap;
 use std::path::{Path, PathBuf};
 use std::sync::Arc;
+use std::time::Duration;
 use time::OffsetDateTime;
 use tokio::process::Command;
 
+/// Default port for NFS over TCP. We expose it as a constant so the
+/// pre-flight probe and the option string assembly use the same value.
+const DEFAULT_NFS_PORT: u16 = 2049;
+
+/// How long to wait for a TCP connection to the NFS server before
+/// declaring it unreachable. Short enough that a wrong IP doesn't make
+/// the UI hang for half a minute; long enough that a slow appliance
+/// can still answer.
+const PROBE_TIMEOUT: Duration = Duration::from_secs(4);
+
 /// Wire-protocol versions we support. Keep this enum closed — silently
 /// accepting "auto" or letting the kernel negotiate would mean operators
 /// could never confirm which version is in use.
@@ -65,6 +99,14 @@ impl NfsVersion {
             Self::V41 => "vers=4.1",
         }
     }
+
+    /// Short label for UI surfaces and log lines.
+    fn label(self) -> &'static str {
+        match self {
+            Self::V3 => "NFSv3",
+            Self::V41 => "NFSv4.1",
+        }
+    }
 }
 
 /// One configured mount. The id is generated from server+export so the
@@ -78,6 +120,12 @@ pub struct NfsMount {
     /// Read-only by default — most ISO libraries are. Operators that need
     /// write can flip this off but OpenPXE itself never writes.
     pub read_only: bool,
+    /// TCP port for the NFS service. Defaults to 2049; configurable for
+    /// the (rare) case where the appliance binds the service elsewhere.
+    /// v0.4.64: previously inferred at runtime; now persisted so the UI
+    /// can echo the value back to the operator.
+    #[serde(default = "default_port")]
+    pub port: u16,
     /// Local mount point under `<work_dir>/nfs/`.
     pub local_path: PathBuf,
     /// Whether the mount is currently active.
@@ -85,6 +133,12 @@ pub struct NfsMount {
     /// Last error encountered on a `mount` or `umount` attempt; cleared on
     /// success.
     pub last_error: Option<String>,
+    /// v0.4.64: operator-friendly translation of `last_error` — e.g. for
+    /// "failed to apply fstab options" we surface "CAP_SYS_ADMIN may be
+    /// missing on the container". `None` means we don't have a friendlier
+    /// rendition than the raw error.
+    #[serde(default)]
+    pub last_hint: Option<String>,
     #[serde(with = "time::serde::rfc3339::option")]
     pub last_attempt: Option<OffsetDateTime>,
     /// Number of `.iso` files found on the share (re-counted on each scan).
@@ -100,6 +154,9 @@ pub struct NfsAddRequest {
     pub version: NfsVersion,
     #[serde(default = "default_ro")]
     pub read_only: bool,
+    /// Optional TCP port — defaults to 2049 if omitted or zero.
+    #[serde(default)]
+    pub port: Option<u16>,
 }
 
 fn default_version() -> NfsVersion {
@@ -108,6 +165,35 @@ fn default_version() -> NfsVersion {
 fn default_ro() -> bool {
     true
 }
+fn default_port() -> u16 {
+    DEFAULT_NFS_PORT
+}
+
+/// Outcome of an `add` attempt. `Ok` carries the mount; `Err` from the
+/// API layer is converted to this richer shape so the UI can render the
+/// raw error and the actionable hint independently.
+#[derive(Debug, Clone, Serialize)]
+pub struct NfsMountError {
+    /// The first line / summary of what went wrong.
+    pub error: String,
+    /// Verbatim stderr from `mount.nfs` (trimmed). May be empty.
+    pub stderr: String,
+    /// Operator-friendly hint or `None` if we don't have one.
+    pub hint: Option<String>,
+}
+
+impl NfsMountError {
+    fn from_raw(error: impl Into<String>, stderr: impl Into<String>) -> Self {
+        let stderr = stderr.into();
+        let error = error.into();
+        let hint = hint_for(&stderr).or_else(|| hint_for(&error));
+        Self {
+            error,
+            stderr,
+            hint,
+        }
+    }
+}
 
 #[derive(Debug, Default)]
 struct Inner {
@@ -165,6 +251,7 @@ impl NfsManager {
             // when the process died. We'll try to remount each one.
             m.mounted = false;
             m.last_error = None;
+            m.last_hint = None;
             self.inner.lock().mounts.insert(m.id.clone(), m.clone());
             if let Err(e) = self.try_mount(&m.id).await {
                 tracing::warn!(
@@ -178,20 +265,42 @@ impl NfsManager {
     }
 
     /// Add a new mount. Returns the resulting `NfsMount` (with `mounted`
-    /// reflecting reality) or an error if the spec was invalid.
-    pub async fn add(&self, req: NfsAddRequest) -> Result<NfsMount> {
-        let server = req.server.trim().to_string();
+    /// reflecting reality) or a structured `NfsMountError` describing
+    /// what went wrong.
+    pub async fn add(
+        &self,
+        req: NfsAddRequest,
+    ) -> std::result::Result<NfsMount, NfsMountError> {
+        let server = normalize_server(&req.server);
         let export = req.export.trim().to_string();
         if server.is_empty() {
-            return Err(Error::Invalid("server is required".into()));
+            return Err(NfsMountError::from_raw(
+                "server is required",
+                "",
+            ));
         }
         if !export.starts_with('/') {
-            return Err(Error::Invalid("export path must start with '/'".into()));
+            return Err(NfsMountError::from_raw(
+                "export path must start with '/'",
+                "",
+            ));
         }
+        if export.contains('\0') || server.contains('\0') {
+            return Err(NfsMountError::from_raw(
+                "server / export must not contain NUL bytes",
+                "",
+            ));
+        }
+        let port = req.port.filter(|p| *p != 0).unwrap_or(DEFAULT_NFS_PORT);
 
         let id = mount_id(&server, &export);
         let local_path = self.work_root.join(&id);
-        tokio::fs::create_dir_all(&local_path).await?;
+        if let Err(e) = tokio::fs::create_dir_all(&local_path).await {
+            return Err(NfsMountError::from_raw(
+                format!("failed to create local mount point: {e}"),
+                "",
+            ));
+        }
 
         let mount = NfsMount {
             id: id.clone(),
@@ -199,15 +308,28 @@ impl NfsManager {
             export,
             version: req.version,
             read_only: req.read_only,
+            port,
             local_path,
             mounted: false,
             last_error: None,
+            last_hint: None,
             last_attempt: None,
             iso_count: 0,
         };
         self.inner.lock().mounts.insert(id.clone(), mount);
         self.persist_locked();
-        self.try_mount(&id).await?;
+        self.try_mount(&id).await.map_err(|e| {
+            // try_mount has already persisted last_error/last_hint. We
+            // refetch them so the API response reflects exactly what the
+            // UI will see when it lists mounts.
+            let m = self.get(&id);
+            NfsMountError {
+                error: m.as_ref().and_then(|m| m.last_error.clone())
+                    .unwrap_or_else(|| e.to_string()),
+                stderr: String::new(),
+                hint: m.and_then(|m| m.last_hint),
+            }
+        })?;
         Ok(self.get(&id).expect("mount just inserted"))
     }
 
@@ -276,63 +398,113 @@ impl NfsManager {
         // Already mounted? Skip — `mount` would error on a busy target
         // and confuse the operator's UI status.
         if is_mountpoint(&m.local_path).await {
-            self.update_status(id, true, None, now);
+            self.update_status(id, true, None, None, now);
             // Even though already mounted, we still want a fresh ISO count.
             let count = self.scan_and_register(&m).await.unwrap_or(0);
             self.update_iso_count(id, count);
             return Ok(());
         }
 
-        let opts = mount_options(&m);
-        let target = format!("{}:{}", m.server, m.export);
-
-        let output = Command::new("mount")
-            .arg("-t")
-            .arg("nfs")
-            .arg("-o")
-            .arg(&opts)
-            .arg(&target)
-            .arg(&m.local_path)
-            .output()
-            .await;
-
-        match output {
-            Ok(out) if out.status.success() => {
-                tracing::info!(
-                    target: "openpxe::nfs",
-                    id = %id, server = %m.server, export = %m.export,
-                    version = ?m.version,
-                    "NFS mount succeeded"
-                );
-                self.update_status(id, true, None, now);
-                let count = self.scan_and_register(&m).await.unwrap_or(0);
-                self.update_iso_count(id, count);
-                Ok(())
-            }
-            Ok(out) => {
-                let err = format!(
-                    "mount exit {}: {}",
-                    out.status.code().unwrap_or(-1),
-                    String::from_utf8_lossy(&out.stderr).trim()
-                );
-                tracing::warn!(target: "openpxe::nfs", id = %id, "{err}");
-                self.update_status(id, false, Some(err.clone()), now);
-                Err(Error::Invalid(err))
-            }
-            Err(e) => {
-                let err = format!("could not exec /bin/mount: {e}");
-                tracing::error!(target: "openpxe::nfs", id = %id, "{err}");
-                self.update_status(id, false, Some(err.clone()), now);
-                Err(Error::Invalid(err))
-            }
+        // v0.4.64: pre-flight TCP probe. Catches the dominant failure
+        // mode (wrong IP / firewall) before mount.nfs gets a chance to
+        // emit its unhelpful "failed to apply fstab options" message.
+        if let Err((err, hint)) = tcp_probe(&m.server, m.port).await {
+            tracing::warn!(target: "openpxe::nfs", id = %id, "{err}");
+            self.update_status(id, false, Some(err.clone()), Some(hint), now);
+            return Err(Error::Invalid(err));
         }
+
+        // First attempt: full option set.
+        let full_opts = mount_options(&m, /*minimal*/ false);
+        let target = format!("{}:{}", m.server, m.export);
+        let attempt = run_mount_nfs(&full_opts, &target, &m.local_path).await;
+
+        let (success, stderr, exit_code) = match attempt {
+            Ok((true, stderr, _)) => (true, stderr, 0),
+            Ok((false, stderr, code)) => (false, stderr, code),
+            Err(e) => {
+                let err = format!("could not exec mount(8): {e}");
+                let hint = Some(
+                    "the runtime image is missing /bin/mount or nfs-common — \
+                     verify the container hasn't been stripped down"
+                        .to_string(),
+                );
+                tracing::error!(target: "openpxe::nfs", id = %id, "{err}");
+                self.update_status(id, false, Some(err.clone()), hint, now);
+                return Err(Error::Invalid(err));
+            }
+        };
+
+        if success {
+            tracing::info!(
+                target: "openpxe::nfs",
+                id = %id, server = %m.server, export = %m.export,
+                version = %m.version.label(), port = m.port,
+                "NFS mount succeeded"
+            );
+            self.update_status(id, true, None, None, now);
+            let count = self.scan_and_register(&m).await.unwrap_or(0);
+            self.update_iso_count(id, count);
+            return Ok(());
+        }
+
+        // Second attempt: if the first attempt failed with the
+        // "failed to apply fstab options" oddity, retry with a minimal
+        // option set. nfs-utils 2.6.x sometimes chokes on the assembled
+        // option string for reasons unrelated to the actual options
+        // being valid; the stripped form bypasses the transformation
+        // edge case.
+        let trigger_retry = looks_like_option_transform_failure(&stderr);
+        let (final_success, final_stderr, final_exit_code) = if trigger_retry {
+            tracing::info!(
+                target: "openpxe::nfs", id = %id,
+                "retrying with minimal options after option-transform failure"
+            );
+            let minimal = mount_options(&m, /*minimal*/ true);
+            match run_mount_nfs(&minimal, &target, &m.local_path).await {
+                Ok((true, s, _)) => (true, s, 0),
+                Ok((false, s, c)) => (false, s, c),
+                Err(e) => (false, format!("could not exec mount(8): {e}"), -1),
+            }
+        } else {
+            (false, stderr, exit_code)
+        };
+
+        if final_success {
+            tracing::info!(
+                target: "openpxe::nfs", id = %id,
+                "NFS mount succeeded on minimal-options retry"
+            );
+            self.update_status(id, true, None, None, now);
+            let count = self.scan_and_register(&m).await.unwrap_or(0);
+            self.update_iso_count(id, count);
+            return Ok(());
+        }
+
+        // Failure path: persist a clear error and a hint, log both.
+        // `mount(8)` passes mount.nfs's stderr through verbatim, so the
+        // user-visible text reads like "mount.nfs: ..." — we prepend the
+        // exit code so the operator can tell at a glance that the helper
+        // ran but rejected the request, vs the helper not running at all.
+        let err = if final_stderr.is_empty() {
+            format!("mount exit {final_exit_code}")
+        } else {
+            format!("mount exit {final_exit_code}: {}", final_stderr.trim())
+        };
+        let hint = hint_for(&final_stderr);
+        tracing::warn!(
+            target: "openpxe::nfs", id = %id,
+            hint = ?hint, "{err}"
+        );
+        self.update_status(id, false, Some(err.clone()), hint, now);
+        Err(Error::Invalid(err))
     }
 
     async fn umount_one(&self, id: &str) -> Result<()> {
         let _g = self.mount_lock.lock().await;
         let Some(m) = self.get(id) else { return Ok(()) };
         if !is_mountpoint(&m.local_path).await {
-            self.update_status(id, false, None, OffsetDateTime::now_utc());
+            self.update_status(id, false, None, None, OffsetDateTime::now_utc());
             return Ok(());
         }
         // -l = lazy: detach immediately, finish when no process has a
@@ -344,7 +516,7 @@ impl NfsManager {
             .await;
         match out {
             Ok(o) if o.status.success() => {
-                self.update_status(id, false, None, OffsetDateTime::now_utc());
+                self.update_status(id, false, None, None, OffsetDateTime::now_utc());
                 Ok(())
             }
             Ok(o) => {
@@ -353,12 +525,24 @@ impl NfsManager {
                     o.status.code().unwrap_or(-1),
                     String::from_utf8_lossy(&o.stderr).trim()
                 );
-                self.update_status(id, false, Some(e.clone()), OffsetDateTime::now_utc());
+                self.update_status(
+                    id,
+                    false,
+                    Some(e.clone()),
+                    None,
+                    OffsetDateTime::now_utc(),
+                );
                 Err(Error::Invalid(e))
             }
             Err(e) => {
                 let e = format!("could not exec /bin/umount: {e}");
-                self.update_status(id, false, Some(e.clone()), OffsetDateTime::now_utc());
+                self.update_status(
+                    id,
+                    false,
+                    Some(e.clone()),
+                    None,
+                    OffsetDateTime::now_utc(),
+                );
                 Err(Error::Invalid(e))
             }
         }
@@ -410,10 +594,18 @@ impl NfsManager {
         Ok(count)
     }
 
-    fn update_status(&self, id: &str, mounted: bool, err: Option<String>, ts: OffsetDateTime) {
+    fn update_status(
+        &self,
+        id: &str,
+        mounted: bool,
+        err: Option<String>,
+        hint: Option<String>,
+        ts: OffsetDateTime,
+    ) {
         if let Some(m) = self.inner.lock().mounts.get_mut(id) {
             m.mounted = mounted;
             m.last_error = err;
+            m.last_hint = hint;
             m.last_attempt = Some(ts);
         }
         self.persist_locked();
@@ -453,18 +645,34 @@ impl NfsManager {
     }
 }
 
-fn mount_options(m: &NfsMount) -> String {
+/// Build the `-o` option list. With `minimal=true` we strip everything
+/// except the protocol version and ro/rw — used on the retry path when
+/// the first attempt failed at option transformation, which historically
+/// indicates one of the auxiliary options confused `nfs_options2string()`.
+fn mount_options(m: &NfsMount, minimal: bool) -> String {
     let mut opts = vec![m.version.vers_arg().to_string()];
     if m.read_only {
         opts.push("ro".into());
     } else {
         opts.push("rw".into());
     }
+    if minimal {
+        return opts.join(",");
+    }
+    // Explicit TCP. NFSv4.x is TCP-only by spec, but stating it
+    // doesn't hurt and on NFSv3 it's necessary on appliances that
+    // don't bind UDP (which is most modern ones).
+    opts.push("proto=tcp".into());
     // `nolock` for v3 — many storage appliances disable lockd; we don't
-    // need locking for read-only ISO access anyway.
+    // need locking for read-only ISO access anyway. nfs-utils still
+    // tries to contact rpc.statd without it which is a no-op overhead.
     if matches!(m.version, NfsVersion::V3) {
         opts.push("nolock".into());
     }
+    // Non-standard port hint to the kernel.
+    if m.port != DEFAULT_NFS_PORT {
+        opts.push(format!("port={}", m.port));
+    }
     // Soft mount with a generous timeout — better to surface a hung share
     // as a user-visible error than to wedge the iPXE client forever on a
     // dead NFS server.
@@ -474,6 +682,158 @@ fn mount_options(m: &NfsMount) -> String {
     opts.join(",")
 }
 
+/// Invoke `mount -t nfs`. Returns `(success, stderr_trimmed,
+/// exit_code)`. `stderr` is captured separately from `stdout`;
+/// `mount(8)` passes mount.nfs's stderr through verbatim, so we get the
+/// same diagnostics ("mount.nfs: ...") whether we invoke `mount.nfs`
+/// directly or go through the generic wrapper.
+///
+/// We deliberately stay on `mount` rather than `mount.nfs` directly
+/// because `/bin/mount` is in every user's PATH; `mount.nfs` lives in
+/// `/sbin` (or `/usr/sbin`) and is *not* in the default PATH for the
+/// non-root `openpxe` user. The generic `mount` binary knows where its
+/// NFS helper lives and dispatches accordingly.
+async fn run_mount_nfs(
+    opts: &str,
+    target: &str,
+    local: &Path,
+) -> std::io::Result<(bool, String, i32)> {
+    let output = Command::new("mount")
+        .arg("-t")
+        .arg("nfs")
+        .arg("-o")
+        .arg(opts)
+        .arg(target)
+        .arg(local)
+        .output()
+        .await?;
+    let stderr = String::from_utf8_lossy(&output.stderr).trim().to_string();
+    let code = output.status.code().unwrap_or(-1);
+    Ok((output.status.success(), stderr, code))
+}
+
+/// Try to open a TCP connection to `server:port` within `PROBE_TIMEOUT`.
+/// On failure returns `(error_text, hint_text)` — pre-formatted so the
+/// caller can persist both.
+async fn tcp_probe(server: &str, port: u16) -> std::result::Result<(), (String, String)> {
+    use tokio::net::TcpStream;
+    let addr = format!("{server}:{port}");
+    let connect = TcpStream::connect(&addr);
+    match tokio::time::timeout(PROBE_TIMEOUT, connect).await {
+        Ok(Ok(_stream)) => Ok(()),
+        Ok(Err(e)) => Err((
+            format!("cannot reach NFS port: {addr}: {e}"),
+            format!(
+                "verify the NFS service is running on {server} and that port {port} is open"
+            ),
+        )),
+        Err(_) => Err((
+            format!("cannot reach NFS port: {addr}: timed out after {}s", PROBE_TIMEOUT.as_secs()),
+            format!(
+                "no TCP answer from {server}:{port} within {}s — check the IP and any firewall in between",
+                PROBE_TIMEOUT.as_secs()
+            ),
+        )),
+    }
+}
+
+/// Detect mount.nfs's "failed to apply fstab options" / "internal option
+/// parsing error" path. These messages come from
+/// `nfs_options2string()` / `nfs_validate_options()` in nfs-utils and
+/// are emitted *before* the mount(2) syscall, so retrying with a
+/// stripped option set often succeeds.
+fn looks_like_option_transform_failure(stderr: &str) -> bool {
+    let s = stderr.to_ascii_lowercase();
+    s.contains("failed to apply fstab options")
+        || s.contains("internal option parsing error")
+}
+
+/// Translate a mount.nfs stderr blob into an operator-friendly hint.
+/// Returns `None` if we don't have a translation — the caller will fall
+/// back to surfacing the raw stderr.
+#[allow(clippy::if_same_then_else)] // ordering matters; keep the patterns explicit
+fn hint_for(stderr: &str) -> Option<String> {
+    let s = stderr.to_ascii_lowercase();
+    if s.contains("failed to apply fstab options") || s.contains("internal option parsing error") {
+        // The dominant report from the field: mount.nfs failed at the
+        // option-transform layer. Most common root cause is missing
+        // CAP_SYS_ADMIN in the container.
+        Some(
+            "mount.nfs couldn't finalize the mount. Most common cause: the container is \
+             missing CAP_SYS_ADMIN (run with --cap-add=SYS_ADMIN, or use a privileged SCC on \
+             OpenShift). Also check that /etc/mtab exists and the host kernel has NFS client \
+             support."
+                .into(),
+        )
+    } else if s.contains("operation not permitted") || s.contains("permission denied") {
+        Some(
+            "the container is missing CAP_SYS_ADMIN — mount(2) returns EPERM without it. Re-run \
+             with --cap-add=SYS_ADMIN, or grant the OpenShift pod a privileged SCC."
+                .into(),
+        )
+    } else if s.contains("access denied by server") {
+        Some(
+            "the server rejected this client. Check the export's allowed-hosts list includes \
+             this OpenPXE host's IP (or 0.0.0.0/0 for testing)."
+                .into(),
+        )
+    } else if s.contains("no route to host") || s.contains("network is unreachable") {
+        Some("the server is not reachable on this network. Check the IP, subnet, and routes.".into())
+    } else if s.contains("connection refused") {
+        Some(
+            "the NFS service isn't listening on this address/port. Verify NFS is running and \
+             that the export path is correct (e.g. UniFi UNAS Pro exports under \
+             /var/nfs/shared/<name>, not the share name on its own)."
+                .into(),
+        )
+    } else if s.contains("connection timed out") {
+        Some(
+            "no answer from the server within the connect timeout. Most likely a firewall is \
+             dropping the connection, or the server isn't running NFS on this port."
+                .into(),
+        )
+    } else if s.contains("no such file or directory")
+        || s.contains("mount: bad option")
+        || s.contains("does not exist")
+    {
+        Some(
+            "the export path doesn't exist on the server, or a mount option isn't recognized. \
+             Double-check the export — many NAS appliances bury it under a service root like \
+             /var/nfs/shared/<share>."
+                .into(),
+        )
+    } else if s.contains("rpc: program not registered") || s.contains("mount system call failed") {
+        Some(
+            "the server didn't respond on the expected RPC programs. NFSv4.1 needs nfsd on TCP \
+             2049; NFSv3 also needs portmap (111) and mountd. If the server only speaks one \
+             version, switch the dropdown to match."
+                .into(),
+        )
+    } else if s.contains("protocol not supported") || s.contains("invalid argument") {
+        Some(
+            "the server doesn't speak the requested NFS version. Try the other entry in the \
+             Version dropdown."
+                .into(),
+        )
+    } else {
+        None
+    }
+}
+
+/// Normalize a server input: trim, strip a `http(s)://` prefix that the
+/// operator may have pasted by mistake, and drop a trailing slash. Port
+/// suffixes (`host:1234`) are preserved so the kernel sees them; the
+/// explicit `port=` option still wins if the operator set one.
+fn normalize_server(raw: &str) -> String {
+    let s = raw.trim();
+    let s = s
+        .strip_prefix("http://")
+        .or_else(|| s.strip_prefix("https://"))
+        .or_else(|| s.strip_prefix("nfs://"))
+        .unwrap_or(s);
+    s.trim_end_matches('/').to_string()
+}
+
 fn mount_id(server: &str, export: &str) -> String {
     let raw = format!("{server}{export}");
     slugify_str(&raw)
@@ -500,6 +860,23 @@ async fn is_mountpoint(path: &Path) -> bool {
 mod tests {
     use super::*;
 
+    fn make_mount(version: NfsVersion, ro: bool, port: u16) -> NfsMount {
+        NfsMount {
+            id: "x".into(),
+            server: "s".into(),
+            export: "/e".into(),
+            version,
+            read_only: ro,
+            port,
+            local_path: PathBuf::from("/tmp/x"),
+            mounted: false,
+            last_error: None,
+            last_hint: None,
+            last_attempt: None,
+            iso_count: 0,
+        }
+    }
+
     #[test]
     fn version_arg() {
         assert_eq!(NfsVersion::V3.vers_arg(), "vers=3");
@@ -507,44 +884,39 @@ mod tests {
     }
 
     #[test]
-    fn mount_options_v3_includes_nolock() {
-        let m = NfsMount {
-            id: "x".into(),
-            server: "s".into(),
-            export: "/e".into(),
-            version: NfsVersion::V3,
-            read_only: true,
-            local_path: PathBuf::from("/tmp/x"),
-            mounted: false,
-            last_error: None,
-            last_attempt: None,
-            iso_count: 0,
-        };
-        let opts = mount_options(&m);
-        assert!(opts.contains("vers=3"));
-        assert!(opts.contains("ro"));
-        assert!(opts.contains("nolock"));
-        assert!(opts.contains("soft"));
+    fn mount_options_v3_includes_nolock_and_tcp() {
+        let m = make_mount(NfsVersion::V3, true, DEFAULT_NFS_PORT);
+        let opts = mount_options(&m, false);
+        assert!(opts.contains("vers=3"), "got: {opts}");
+        assert!(opts.contains("ro"), "got: {opts}");
+        assert!(opts.contains("nolock"), "got: {opts}");
+        assert!(opts.contains("proto=tcp"), "got: {opts}");
+        assert!(opts.contains("soft"), "got: {opts}");
+        assert!(!opts.contains("port="), "default port shouldn't appear: {opts}");
     }
 
     #[test]
-    fn mount_options_v41_no_nolock() {
-        let m = NfsMount {
-            id: "x".into(),
-            server: "s".into(),
-            export: "/e".into(),
-            version: NfsVersion::V41,
-            read_only: false,
-            local_path: PathBuf::from("/tmp/x"),
-            mounted: false,
-            last_error: None,
-            last_attempt: None,
-            iso_count: 0,
-        };
-        let opts = mount_options(&m);
-        assert!(opts.contains("vers=4.1"));
-        assert!(opts.contains("rw"));
-        assert!(!opts.contains("nolock"));
+    fn mount_options_v41_has_tcp_no_nolock() {
+        let m = make_mount(NfsVersion::V41, false, DEFAULT_NFS_PORT);
+        let opts = mount_options(&m, false);
+        assert!(opts.contains("vers=4.1"), "got: {opts}");
+        assert!(opts.contains("rw"), "got: {opts}");
+        assert!(opts.contains("proto=tcp"), "got: {opts}");
+        assert!(!opts.contains("nolock"), "got: {opts}");
+    }
+
+    #[test]
+    fn mount_options_minimal_drops_everything_except_vers_and_mode() {
+        let m = make_mount(NfsVersion::V3, true, DEFAULT_NFS_PORT);
+        let opts = mount_options(&m, true);
+        assert_eq!(opts, "vers=3,ro");
+    }
+
+    #[test]
+    fn mount_options_non_default_port_appears() {
+        let m = make_mount(NfsVersion::V41, true, 2050);
+        let opts = mount_options(&m, false);
+        assert!(opts.contains("port=2050"), "got: {opts}");
     }
 
     #[test]
@@ -555,4 +927,58 @@ mod tests {
         assert!(!a.contains('/'));
         assert!(!a.contains('.'));
     }
+
+    #[test]
+    fn normalize_server_strips_url_schemes_and_slashes() {
+        assert_eq!(normalize_server("  10.0.0.5  "), "10.0.0.5");
+        assert_eq!(normalize_server("http://10.0.0.5/"), "10.0.0.5");
+        assert_eq!(normalize_server("https://nas.lan//"), "nas.lan");
+        assert_eq!(normalize_server("nfs://192.168.1.51"), "192.168.1.51");
+        assert_eq!(normalize_server("nas.lan:2049"), "nas.lan:2049");
+    }
+
+    #[test]
+    fn hint_for_fstab_options_calls_out_cap_sys_admin() {
+        let h = hint_for("mount.nfs: failed to apply fstab options").unwrap();
+        assert!(
+            h.contains("CAP_SYS_ADMIN"),
+            "expected CAP_SYS_ADMIN guidance, got: {h}"
+        );
+    }
+
+    #[test]
+    fn hint_for_access_denied_points_at_exports_table() {
+        let h = hint_for("mount.nfs: access denied by server while mounting").unwrap();
+        assert!(
+            h.to_lowercase().contains("allowed-hosts") || h.to_lowercase().contains("export"),
+            "expected exports hint, got: {h}"
+        );
+    }
+
+    #[test]
+    fn hint_for_connection_refused_mentions_export_path() {
+        let h = hint_for("mount.nfs: Connection refused").unwrap();
+        assert!(
+            h.to_lowercase().contains("export"),
+            "expected export-path hint, got: {h}"
+        );
+    }
+
+    #[test]
+    fn hint_for_unknown_message_is_none() {
+        assert!(hint_for("some completely unrelated text").is_none());
+    }
+
+    #[test]
+    fn looks_like_option_transform_failure_detects_both_variants() {
+        assert!(looks_like_option_transform_failure(
+            "mount.nfs: failed to apply fstab options"
+        ));
+        assert!(looks_like_option_transform_failure(
+            "mount.nfs: internal option parsing error"
+        ));
+        assert!(!looks_like_option_transform_failure(
+            "mount.nfs: access denied"
+        ));
+    }
 }

crates/webui/src/app.js

@@ -623,19 +623,41 @@
       const nfsRo = el('input', {type:'checkbox'}); nfsRo.checked = true;
       const addNfs = el('button', {onclick: async () => {
         if (!nfsServer.value || !nfsExport.value) {
-          nfsMsg.textContent = 'Server and export are required.'; nfsMsg.className='msg err'; return;
+          nfsMsg.replaceChildren(document.createTextNode('Server and export are required.'));
+          nfsMsg.className='msg err'; return;
         }
-        nfsMsg.textContent = 'Mounting…'; nfsMsg.className = 'msg';
+        nfsMsg.replaceChildren(document.createTextNode('Mounting…'));
+        nfsMsg.className = 'msg';
         const r = await postJSON('/api/nfs', {
           server: nfsServer.value, export: nfsExport.value,
           version: nfsVer.value, read_only: nfsRo.checked,
         });
         if (r.ok) {
-          nfsMsg.textContent = 'Mounted.'; nfsMsg.className = 'msg ok';
+          nfsMsg.replaceChildren(document.createTextNode('Mounted.'));
+          nfsMsg.className = 'msg ok';
           render('storage');
         } else {
-          const t = await r.text();
-          nfsMsg.textContent = 'Mount failed: ' + t; nfsMsg.className = 'msg err';
+          // v0.4.64: the API now returns a structured
+          // {error, stderr, hint} JSON body so we can render the
+          // mount failure and an actionable hint as two distinct lines
+          // instead of one long unreadable string. The dominant field
+          // failure mode — "mount.nfs: failed to apply fstab options" —
+          // becomes useful when paired with its CAP_SYS_ADMIN hint.
+          let body = null;
+          let raw = null;
+          try { body = await r.clone().json(); }
+          catch (_) { raw = await r.text().catch(()=> 'mount failed'); }
+          const msg = body && body.error ? body.error : (raw || 'mount failed');
+          const hint = body && body.hint;
+          const parts = [el('div', {}, [
+            el('strong', {}, 'Mount failed: '),
+            document.createTextNode(msg),
+          ])];
+          if (hint) {
+            parts.push(el('div', {style:'margin-top:6px;opacity:.78;font-size:12px'}, hint));
+          }
+          nfsMsg.replaceChildren(...parts);
+          nfsMsg.className = 'msg err';
         }
       }}, 'Mount share');
 
@@ -648,6 +670,8 @@
             (m.read_only ? 'read-only' : 'read-write') + ' · ' +
             (m.mounted ? m.iso_count + ' isos' : 'not mounted')),
           m.last_error ? el('div', {class:'err'}, '⚠ ' + m.last_error) : null,
+          // v0.4.64: actionable hint paired with the raw error.
+          m.last_hint ? el('div', {style:'margin-top:4px;opacity:.78;font-size:12px'}, m.last_hint) : null,
         ]),
         el('button', {class:'ghost', onclick: async () => {
           const r = await postJSON('/api/nfs/' + encodeURIComponent(m.id) + '/scan', {});