---
name: "unlockpt"
section: "3p"
platform: "linux"
package: "man-pages"
version: "6.19-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/unlockpt/3p"
---

# unlockpt(3p)

unlock a pseudo-terminal master/slave pair

## PROLOG

This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

## NAME

unlockpt — unlock a pseudo-terminal master/slave pair

## SYNOPSIS

```
#include <stdlib.h>
```

int unlockpt(int *fildes*);

## DESCRIPTION

The *unlockpt*() function shall unlock the slave pseudo-terminal device associated with the master to which *fildes* refers.

Conforming applications shall ensure that they call *unlockpt*() before opening the slave side of a pseudo-terminal device.

## RETURN VALUE

Upon successful completion, *unlockpt*() shall return 0. Otherwise, it shall return -1 and set *errno* to indicate the error.

## ERRORS

The *unlockpt*() function may fail if:

- **EBADF**

  The *fildes* argument is not a file descriptor open for writing.

- **EINVAL**

  The *fildes* argument is not associated with a master pseudo-terminal device.

*The following sections are informative.*

## EXAMPLES

None.

## APPLICATION USAGE

None.

## RATIONALE

See the RATIONALE section for *posix\_openpt()*.

## FUTURE DIRECTIONS

None.

## SEE ALSO

*grantpt()*, *open()*, *posix\_openpt()*, *ptsname()*

The Base Definitions volume of POSIX.1‐2017, ***\<stdlib.h\>***

## COPYRIGHT

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting\_bugs.html .