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36 lines
1.4 KiB
36 lines
1.4 KiB
.. SPDX-License-Identifier: GPL-2.0 |
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===================== |
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The Devpts Filesystem |
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===================== |
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Each mount of the devpts filesystem is now distinct such that ptys |
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and their indicies allocated in one mount are independent from ptys |
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and their indicies in all other mounts. |
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All mounts of the devpts filesystem now create a ``/dev/pts/ptmx`` node |
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with permissions ``0000``. |
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To retain backwards compatibility the a ptmx device node (aka any node |
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created with ``mknod name c 5 2``) when opened will look for an instance |
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of devpts under the name ``pts`` in the same directory as the ptmx device |
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node. |
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As an option instead of placing a ``/dev/ptmx`` device node at ``/dev/ptmx`` |
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it is possible to place a symlink to ``/dev/pts/ptmx`` at ``/dev/ptmx`` or |
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to bind mount ``/dev/ptx/ptmx`` to ``/dev/ptmx``. If you opt for using |
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the devpts filesystem in this manner devpts should be mounted with |
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the ``ptmxmode=0666``, or ``chmod 0666 /dev/pts/ptmx`` should be called. |
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Total count of pty pairs in all instances is limited by sysctls:: |
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kernel.pty.max = 4096 - global limit |
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kernel.pty.reserve = 1024 - reserved for filesystems mounted from the initial mount namespace |
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kernel.pty.nr - current count of ptys |
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Per-instance limit could be set by adding mount option ``max=<count>``. |
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This feature was added in kernel 3.4 together with |
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``sysctl kernel.pty.reserve``. |
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In kernels older than 3.4 sysctl ``kernel.pty.max`` works as per-instance limit.
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