UNLOCKPT(3) Linux Programmer's Manual UNLOCKPT(3)

unlockpt - unlock a pseudoterminal master/slave pair

#include <stdlib.h>
int unlockpt(int fd);

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
Since glibc 2.24:
_XOPEN_SOURCE >= 500 ||
Glibc 2.23 and earlier:

The unlockpt() function unlocks the slave pseudoterminal device corresponding to the master pseudoterminal referred to by fd.
unlockpt() should be called before opening the slave side of a pseudoterminal.

When successful, unlockpt() returns 0. Otherwise, it returns -1 and sets errno appropriately.

The fd argument is not a file descriptor open for writing.
The fd argument is not associated with a master pseudoterminal.

unlockpt() is provided in glibc since version 2.1.

For an explanation of the terms used in this section, see attributes(7).
Interface Attribute Value
unlockpt () Thread safety MT-Safe

POSIX.1-2001, POSIX.1-2008.

grantpt(3), posix_openpt(3), ptsname(3), pts(4), pty(7)