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 <khlebnikov@xxxxxxxxxxxxxx>
---
Documentation/filesystems/devpts.txt | 9 +++++++++
Documentation/sysctl/kernel.txt | 1 +
2 files changed, 10 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 a93b414672a7..d05e70b7d8dd 100644
--- a/Documentation/sysctl/kernel.txt
+++ b/Documentation/sysctl/kernel.txt
@@ -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 ]
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