123456789101112131415161718192021222324252627282930313233343536 |
- .. SPDX-License-Identifier: GPL-2.0
- =====================
- The Devpts Filesystem
- =====================
- 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
- node.
- 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.
|