| PTM(4) | Device Drivers Manual | PTM(4) | 
ptm —
pseudo-device pty
ptm driver is the backend for the
  /dev/ptm device. It supports three
  ioctl(2)s. The first is
  TIOCPTMGET, which allocates a free pseudo-terminal
  device, sets its user ID to the calling user,
  revoke(2)s it, and returns the
  opened file descriptors for both the master and the slave pseudo-terminal
  device to the caller in a struct ptmget. This struct has
  the following content:
struct ptmget {
        int     cfd;
        int     sfd;
        char    cn[PATH_MAX];
        char    sn[PATH_MAX];
};
where cfd and sfd contain the master resp. slave device's file descriptor and cn and sn the corresponding paths in the file system.
The /dev/ptmx device supports two more
    ioctl(2)s,
    TIOCGRANTPT, which is used by
    grantpt(3),
    TIOCPTSNAME, which is used by
    ptsname(3).
The ptm device is included with the
    pseudo-device pty(4). It can be
    disabled by adding “options
    NO_DEV_PTM” to the kernel configuration.
ptm access deviceptm cloning device, used to implement Unix98
    ptys| November 30, 2013 | NetBSD 10.0 |