1 .. SPDX-License-Identifier: GPL-2.0 2 3 ===================== 4 The Devpts Filesystem 5 ===================== 6 7 Each mount of the devpts filesystem is now distinct such that ptys 8 and their indices allocated in one mount are independent from ptys 9 and their indices in all other mounts. 10 11 All mounts of the devpts filesystem now create a ``/dev/pts/ptmx`` node 12 with permissions ``0000``. 13 14 To retain backwards compatibility the a ptmx device node (aka any node 15 created with ``mknod name c 5 2``) when opened will look for an instance 16 of devpts under the name ``pts`` in the same directory as the ptmx device 17 node. 18 19 As an option instead of placing a ``/dev/ptmx`` device node at ``/dev/ptmx`` 20 it is possible to place a symlink to ``/dev/pts/ptmx`` at ``/dev/ptmx`` or 21 to bind mount ``/dev/ptx/ptmx`` to ``/dev/ptmx``. If you opt for using 22 the devpts filesystem in this manner devpts should be mounted with 23 the ``ptmxmode=0666``, or ``chmod 0666 /dev/pts/ptmx`` should be called. 24 25 Total count of pty pairs in all instances is limited by sysctls:: 26 27 kernel.pty.max = 4096 - global limit 28 kernel.pty.reserve = 1024 - reserved for filesystems mounted from the initial mount namespace 29 kernel.pty.nr - current count of ptys 30 31 Per-instance limit could be set by adding mount option ``max=<count>``. 32 33 This feature was added in kernel 3.4 together with 34 ``sysctl kernel.pty.reserve``. 35 36 In kernels older than 3.4 sysctl ``kernel.pty.max`` works as per-instance limit.
Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.