docs: filesystems: convert devpts.txt to ReST (01478b83) · Commits · 戴 / test

Documentation/admin-guide/sysctl/kernel.rst

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		pty
		===

		See Documentation/filesystems/devpts.txt.
		See Documentation/filesystems/devpts.rst.


		randomize_va_space

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		.. 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.

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		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.

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