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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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