---
name: "TIOCPKT"
section: "2const"
platform: "linux"
package: "man-pages"
version: "6.19-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/TIOCPKT"
---

# TIOCPKT(2const)

pseudoterminal ioctls

## NAME

TIOCPKT, TIOCGPKT, TIOCSPTLCK, TIOCGPTLCK, TIOCGPTPEER - pseudoterminal ioctls

## LIBRARY

Standard C library (*libc*, *-lc*)

## SYNOPSIS

```
#include <asm/termbits.h>  /* Definition of TIOC* constants */
#include <sys/ioctl.h>
```

**int ioctl(int** *fd***, TIOCPKT, const int \****mode***);** **int ioctl(int** *fd***, TIOCPKT, int \****mode***);**

**int ioctl(int** *fd***, TIOCSPTLCK, const int \****lock***);** **int ioctl(int** *fd***, TIOCGPTLCK, int \****lock***);**

**int ioctl(int** *fd***, TIOCGPTPEER, int** *flags***);**

## DESCRIPTION

- **TIOCPKT**

  Enable (when \**mode* is nonzero) or disable packet mode. Can be applied to the master side of a pseudoterminal only (and will return **ENOTTY** otherwise). In packet mode, each subsequent [**read**(2)](/read/2.md) will return a packet that either contains a single nonzero control byte, or has a single byte containing zero ('\\0') followed by data written on the slave side of the pseudoterminal. If the first byte is not **TIOCPKT\_DATA** (0), it is an OR of one or more of the following bits:

-

  | | |
  | --- | --- |
  | **TIOCPKT\_FLUSHREAD** | The read queue for the terminal is flushed. |
  | **TIOCPKT\_FLUSHWRITE** | The write queue for the terminal is flushed. |
  | **TIOCPKT\_STOP** | Output to the terminal is stopped. |
  | **TIOCPKT\_START** | Output to the terminal is restarted. |
  | **TIOCPKT\_DOSTOP** | The start and stop characters are **^S**/**^Q**. |
  | **TIOCPKT\_NOSTOP** | The start and stop characters are not **^S**/**^Q**. |

-

  While packet mode is in use, the presence of control status information to be read from the master side may be detected by a [**select**(2)](/select/2.md) for exceptional conditions or a [**poll**(2)](/poll/2.md) for the **POLLPRI** event.

-

  This mode is used by [**rlogin**(1)](/rlogin/1.md) and [**rlogind**(8)](/rlogind/8.md) to implement a remote-echoed, locally **^S**/**^Q** flow-controlled remote login.

- **TIOCGPKT**

  Return the current packet mode setting in the integer pointed to by *mode*.

- **TIOCSPTLCK**

  Set (if *\*lock* is nonzero) or remove (if *\*lock* is zero) the lock on the pseudoterminal slave device. (See also [**unlockpt**(3)](/unlockpt/3.md).)

- **TIOCGPTLCK**

  Place the current lock state of the pseudoterminal slave device in the location pointed to by *lock*.

- **TIOCGPTPEER**

  Given a file descriptor in *fd* that refers to a pseudoterminal master, open (with the given [**open**(2)](/open/2.md)-style *flags*) and return a new file descriptor that refers to the peer pseudoterminal slave device. This operation can be performed regardless of whether the pathname of the slave device is accessible through the calling process's mount namespace.

-

  Security-conscious programs interacting with namespaces may wish to use this operation rather than [**open**(2)](/open/2.md) with the pathname returned by [**ptsname**(3)](/ptsname/3.md), and similar library functions that have insecure APIs. (For example, confusion can occur in some cases using [**ptsname**(3)](/ptsname/3.md) with a pathname where a devpts filesystem has been mounted in a different mount namespace.)

## RETURN VALUE

On success, 0 is returned. On error, -1 is returned, and *errno* is set to indicate the error.

## ERRORS

- **ENOTTY**

  ## HISTORY

- **TIOCGPKT**

  Linux 3.8.

- **TIOCGPTLCK**

  Linux 3.8.

- **TIOCGPTPEER**

  Linux 4.13.

The BSD ioctls **TIOCSTOP**, **TIOCSTART**, **TIOCUCNTL**, and **TIOCREMOTE** have not been implemented under Linux.

## SEE ALSO

[**ioctl**(2)](/ioctl/2.md), [**ioctl\_tty**(2)](/ioctl_tty/2.md)