Function unlockpt 

pub fn unlockpt(fd: &PtyMaster) -> Result<()>

Available on crate feature term only.

Unlock a pseudoterminal master/slave pseudoterminal pair (see unlockpt(3))

unlockpt() unlocks the slave pseudoterminal device corresponding to the master pseudoterminal referred to by fd. This must be called before trying to open the slave side of a pseudoterminal.