| rjw | 1f88458 | 2022-01-06 17:20:42 +0800 | [diff] [blame^] | 1 | Each mount of the devpts filesystem is now distinct such that ptys |
| 2 | and their indicies allocated in one mount are independent from ptys |
| 3 | and their indicies in all other mounts. |
| 4 | |
| 5 | All mounts of the devpts filesystem now create a /dev/pts/ptmx node |
| 6 | with permissions 0000. |
| 7 | |
| 8 | To retain backwards compatibility the a ptmx device node (aka any node |
| 9 | created with "mknod name c 5 2") when opened will look for an instance |
| 10 | of devpts under the name "pts" in the same directory as the ptmx device |
| 11 | node. |
| 12 | |
| 13 | As an option instead of placing a /dev/ptmx device node at /dev/ptmx |
| 14 | it is possible to place a symlink to /dev/pts/ptmx at /dev/ptmx or |
| 15 | to bind mount /dev/ptx/ptmx to /dev/ptmx. If you opt for using |
| 16 | the devpts filesystem in this manner devpts should be mounted with |
| 17 | the ptmxmode=0666, or chmod 0666 /dev/pts/ptmx should be called. |
| 18 | |
| 19 | Total count of pty pairs in all instances is limited by sysctls: |
| 20 | kernel.pty.max = 4096 - global limit |
| 21 | kernel.pty.reserve = 1024 - reserved for filesystems mounted from the initial mount namespace |
| 22 | kernel.pty.nr - current count of ptys |
| 23 | |
| 24 | Per-instance limit could be set by adding mount option "max=<count>". |
| 25 | This feature was added in kernel 3.4 together with sysctl kernel.pty.reserve. |
| 26 | In kernels older than 3.4 sysctl kernel.pty.max works as per-instance limit. |