# `Linx.Mount.Error`
[🔗](https://github.com/oshlabs/linx/blob/v0.2.0/lib/linx/mount/error.ex#L1)

An error returned by a `Linx.Mount` operation.

Built from a failed `mount(2)` / `umount2(2)` / `pivot_root(2)`
call against the kernel. The shape:

  * `:path` — the absolute filesystem path the operation targeted
    (the `target` argument of `mount/4`, the `target` of `umount/2`,
    etc.).
  * `:operation` — what we were trying to do, as an atom:
    * `:mount`, `:umount`, `:pivot_root` — the target syscall
      itself failed.
    * `:open_ns` — couldn't open the target namespace file
      (target process is gone, BEAM lacks read access).
    * `:unshare` — couldn't detach the worker thread's
      `fs_struct` from the BEAM's. Prerequisite for `setns` on
      a mount namespace; extremely unlikely to fail.
    * `:setns` — couldn't enter the target namespace (lacks
      `CAP_SYS_ADMIN` in the right user namespace).
    * `:chdir` — couldn't `chdir` into `new_root` before
      `pivot_root`. Typically the path doesn't exist or isn't
      a directory.
    * `:thread` — couldn't create the worker thread that does
      the cross-namespace dance. Rare; typically `EAGAIN` from
      thread-creation pressure.
    The last three only appear when a cross-namespace `:in`
    option was used.
  * `:errno` — the POSIX errno as an atom (`:enoent`, `:eacces`,
    `:ebusy`, `:einval`, `:eperm`, …).
  * `:code` — the matching positive errno integer, or `nil` if we
    don't have a mapping for this atom. Included for symmetry with
    `Linx.Cgroup.Error` / `Linx.Netlink.Error` and for callers
    unfamiliar with POSIX mnemonics.

Pattern-match on `:errno` and `:operation` to handle specific
failures:

    case Linx.Mount.mount("tmpfs", "/mnt/x", "tmpfs") do
      :ok -> :ok
      {:error, %Linx.Mount.Error{errno: :eacces}} ->
        # not enough privilege
        :no_perm
    end

Implements `Exception`, so an error can be `raise`d or rendered
with `Exception.message/1`.

# `operation`

```elixir
@type operation() ::
  :mount
  | :umount
  | :pivot_root
  | :open_ns
  | :unshare
  | :setns
  | :chdir
  | :thread
```

# `t`

```elixir
@type t() :: %Linx.Mount.Error{
  __exception__: true,
  code: pos_integer() | nil,
  errno: atom(),
  operation: operation(),
  path: Path.t()
}
```

# `from_posix`

```elixir
@spec from_posix(atom(), Path.t(), operation()) :: t()
```

Builds a `%Linx.Mount.Error{}` from a posix-atom errno, the
filesystem path that failed, and the operation we attempted.

---

*Consult [api-reference.md](api-reference.md) for complete listing*