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Commit 8b253b07 authored Feb 21, 2016 by Konstantin Khlebnikov Committed by Greg Kroah-Hartman Mar 07, 2016

TTY, devpts: document pty count limiting



Logic has been changed in kernel 3.4 by commit e9aba515
("tty: rework pty count limiting") but still not documented.

Sysctl kernel.pty.max works as global limit, kernel.pty.reserve ptys
are reserved for initial devpts instance (mounted without "newinstance").
Per-instance limit also could be set by mount option "max=%d".

Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent 465893e1

Documentation/filesystems/devpts.txt

+9 −0

Original line number	Diff line number	Diff line
		@@ -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
		------------------

Documentation/sysctl/kernel.txt

+1 −0

Original line number	Diff line number	Diff line
		@@ -64,6 +64,7 @@ show up in /proc/sys/kernel:
		- printk_delay
		- printk_ratelimit
		- printk_ratelimit_burst
		- pty ==> Documentation/filesystems/devpts.txt
		- randomize_va_space
		- real-root-dev ==> Documentation/initrd.txt
		- reboot-cmd [ SPARC only ]