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.

Return Value

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

Conforming to

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

See Also

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


This page is part of release 5.04 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.

Referenced By

getpt(3), grantpt(3), ioctl_tty(2), posix_openpt(3), pts(4), ptsname(3), pty(7).

2017-07-13 Linux Programmer's Manual