TTY, devpts: document pty count limiting
PATCH RESEND 1/1 TTY, devpts: document pty count limiting
Logic has been changed in kernel 3.4 by commit e9aba5158a80 ("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 <[email protected]>
--- Documentation/filesystems/devpts.txt | 9 +++++++++ Documentation/sysctl/kernel.txt | 1 + 2 files changed, 10 insertions(+)
Documentation/filesystems/devpts.txt +9 -0
@@ -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
@@ -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 ]