|Each mount of the devpts filesystem is now distinct such that ptys
|and their indicies allocated in one mount are independent from ptys
|and their indicies in all other mounts.
|All mounts of the devpts filesystem now create a /dev/pts/ptmx node
|with permissions 0000.
|To retain backwards compatibility the a ptmx device node (aka any node
|created with "mknod name c 5 2") when opened will look for an instance
|of devpts under the name "pts" in the same directory as the ptmx device
|As an option instead of placing a /dev/ptmx device node at /dev/ptmx
|it is possible to place a symlink to /dev/pts/ptmx at /dev/ptmx or
|to bind mount /dev/ptx/ptmx to /dev/ptmx. If you opt for using
|the devpts filesystem in this manner devpts should be mounted with
|the ptmxmode=0666, or chmod 0666 /dev/pts/ptmx should be called.
|Total count of pty pairs in all instances is limited by sysctls:
|kernel.pty.max = 4096 - global limit
|kernel.pty.reserve = 1024 - reserved for filesystems mounted from the initial mount namespace
|kernel.pty.nr - current count of ptys
|Per-instance limit could be set by adding mount option "max=<count>".
|This feature was added in kernel 3.4 together with sysctl kernel.pty.reserve.
|In kernels older than 3.4 sysctl kernel.pty.max works as per-instance limit.