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

Portable applications must call unlockpt() before opening the slave side of a pseudo-terminal device.

Upon successful completion, unlockpt() returns 0. Otherwise, it returns -1 and sets errno to indicate the error.

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.

See attributes(5) for descriptions of the following attributes:

open(2), grantpt(3C), ptsname(3C), attributes(5)

STREAMS Programming Guide