diff options
Diffstat (limited to '')
| -rw-r--r-- | Documentation/filesystems/devpts.txt | 26 |
1 files changed, 26 insertions, 0 deletions
diff --git a/Documentation/filesystems/devpts.txt b/Documentation/filesystems/devpts.txt new file mode 100644 index 000000000..9f94fe276 --- /dev/null +++ b/Documentation/filesystems/devpts.txt @@ -0,0 +1,26 @@ +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. |