[PATCH] TTY, devpts: document pty count limiting
From: Konstantin Khlebnikov <hidden>
Date: 2015-10-21 10:09:04
Also in:
lkml
Subsystem:
documentation, the rest · Maintainers:
Jonathan Corbet, Linus Torvalds
Logic was changed in kernel 3.4 by commit e9aba5158a80 ("tty: rework pty
count limiting") but still isn't documented. Better late than never.
Signed-off-by: Konstantin Khlebnikov <redacted>
---
Documentation/filesystems/devpts.txt | 9 +++++++++
Documentation/sysctl/kernel.txt | 7 +++++++
2 files changed, 16 insertions(+)
diff --git a/Documentation/filesystems/devpts.txt b/Documentation/filesystems/devpts.txt
index 68dffd87f9b7..30d2fcb32f72 100644
--- a/Documentation/filesystems/devpts.txt
+++ b/Documentation/filesystems/devpts.txt@@ -51,6 +51,15 @@ where 'ns_exec -cm /bin/bash' calls clone() with CLONE_NEWNS flag and execs /bin/bash in the child process. A pty created by the sshd is not visible in the original mount of /dev/pts. +Total count of pty pairs in all instances is limited by sysctls: +kernel.pty.max = 4096 - global limit +kernel.pty.reserve = 1024 - reserve for initial instance +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. + User-space changes ------------------
diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt
index 6fccb69c03e7..01a42021c2e5 100644
--- a/Documentation/sysctl/kernel.txt
+++ b/Documentation/sysctl/kernel.txt@@ -63,6 +63,7 @@ show up in /proc/sys/kernel: - printk_delay - printk_ratelimit - printk_ratelimit_burst +- pty/ - randomize_va_space - real-root-dev ==> Documentation/initrd.txt - reboot-cmd [ SPARC only ]
@@ -683,6 +684,12 @@ send before ratelimiting kicks in. ============================================================== +pty/: + +See Documentation/filesystems/devpts.txt. + +============================================================== + randomize_va_space: This option can be used to select the type of process address