---
name: "pty"
section: "4"
platform: "freebsd"
package: "base"
version: "16.0-CURRENT-20261027-61c70dc16a79"
release: "FreeBSD 16.0-CURRENT (2026-10-27)"
platforms: ["linux", "freebsd", "openbsd", "macos"]
url: "https://new.carta.tech/pty/4"
---

# pty(4)

old-style compatibility pseudo-terminal driver

## NAME

**pty** – old-style compatibility pseudo-terminal driver

## SYNOPSIS

**device pty**

## DESCRIPTION

The **pty** driver provides support for the traditional BSD naming scheme that was used for accessing pseudo-terminals before it was replaced by [pts(4)](/pts/4.md). This traditional naming is still used in Linux. When the device */dev/ptyXX* is being opened, a new terminal shall be created with the [pts(4)](/pts/4.md) driver. A device node for this terminal shall be created, which has the name */dev/ttyXX*.

The **pty** driver also provides a cloning System V */dev/ptmx* device.

New code should not try to allocate pseudo-terminals using this interface. It is only provided for compatibility with older C libraries that tried to open such devices when [posix\_openpt(2)](/posix_openpt/2.md) was being called, and for running Linux binaries.

## FILES

The BSD-style compatibility pseudo-terminal driver uses the following device names:

- */dev/pty\[l-sL-S\]\[0-9a-v\]*

  Pseudo-terminal master devices.

- */dev/tty\[l-sL-S\]\[0-9a-v\]*

  Pseudo-terminal slave devices.

- */dev/ptmx*

  Control device, returns a file descriptor to a new master pseudo-terminal when opened.

## DIAGNOSTICS

None.

## SEE ALSO

[posix\_openpt(2)](/posix_openpt/2.md), [pts(4)](/pts/4.md), [tty(4)](/tty/4.md)

## HISTORY

A pseudo-terminal driver appeared in 4.2BSD.

## BUGS

Unlike previous implementations, the master and slave device nodes are destroyed when the PTY becomes unused. A call to [stat(2)](/stat/2.md) on a nonexistent master device will already cause a new master device node to be created. The master device can only be destroyed by opening and closing it.

The **pty** driver cannot be unloaded, because it cannot determine if it is being used.