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-rw-r--r--Documentation/sysctl/README1
-rw-r--r--Documentation/sysctl/user.txt66
2 files changed, 67 insertions, 0 deletions
diff --git a/Documentation/sysctl/README b/Documentation/sysctl/README
index 8c3306e01d52..91f54ffa0077 100644
--- a/Documentation/sysctl/README
+++ b/Documentation/sysctl/README
@@ -69,6 +69,7 @@ proc/ <empty>
sunrpc/ SUN Remote Procedure Call (NFS)
vm/ memory management tuning
buffer and cache management
+user/ Per user per user namespace limits
These are the subdirs I have on my system. There might be more
or other subdirs in another setup. If you see another dir, I'd
diff --git a/Documentation/sysctl/user.txt b/Documentation/sysctl/user.txt
new file mode 100644
index 000000000000..1291c498f78f
--- /dev/null
+++ b/Documentation/sysctl/user.txt
@@ -0,0 +1,66 @@
+Documentation for /proc/sys/user/* kernel version 4.9.0
+ (c) 2016 Eric Biederman <ebiederm@xmission.com>
+
+==============================================================
+
+This file contains the documetation for the sysctl files in
+/proc/sys/user.
+
+The files in this directory can be used to override the default
+limits on the number of namespaces and other objects that have
+per user per user namespace limits.
+
+The primary purpose of these limits is to stop programs that
+malfunction and attempt to create a ridiculous number of objects,
+before the malfunction becomes a system wide problem. It is the
+intention that the defaults of these limits are set high enough that
+no program in normal operation should run into these limits.
+
+The creation of per user per user namespace objects are charged to
+the user in the user namespace who created the object and
+verified to be below the per user limit in that user namespace.
+
+The creation of objects is also charged to all of the users
+who created user namespaces the creation of the object happens
+in (user namespaces can be nested) and verified to be below the per user
+limits in the user namespaces of those users.
+
+This recursive counting of created objects ensures that creating a
+user namespace does not allow a user to escape their current limits.
+
+Currently, these files are in /proc/sys/user:
+
+- max_cgroup_namespaces
+
+ The maximum number of cgroup namespaces that any user in the current
+ user namespace may create.
+
+- max_ipc_namespaces
+
+ The maximum number of ipc namespaces that any user in the current
+ user namespace may create.
+
+- max_mnt_namespaces
+
+ The maximum number of mount namespaces that any user in the current
+ user namespace may create.
+
+- max_net_namespaces
+
+ The maximum number of network namespaces that any user in the
+ current user namespace may create.
+
+- max_pid_namespaces
+
+ The maximum number of pid namespaces that any user in the current
+ user namespace may create.
+
+- max_user_namespaces
+
+ The maximum number of user namespaces that any user in the current
+ user namespace may create.
+
+- max_uts_namespaces
+
+ The maximum number of user namespaces that any user in the current
+ user namespace may create.