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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-27 10:05:51 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-27 10:05:51 +0000 |
commit | 5d1646d90e1f2cceb9f0828f4b28318cd0ec7744 (patch) | |
tree | a94efe259b9009378be6d90eb30d2b019d95c194 /Documentation/filesystems/devpts.rst | |
parent | Initial commit. (diff) | |
download | linux-upstream/5.10.209.tar.xz linux-upstream/5.10.209.zip |
Adding upstream version 5.10.209.upstream/5.10.209upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to '')
-rw-r--r-- | Documentation/filesystems/devpts.rst | 36 |
1 files changed, 36 insertions, 0 deletions
diff --git a/Documentation/filesystems/devpts.rst b/Documentation/filesystems/devpts.rst new file mode 100644 index 000000000..a03248ddf --- /dev/null +++ b/Documentation/filesystems/devpts.rst @@ -0,0 +1,36 @@ +.. 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. |