procfs has a number of mounting restrictions that are not documented anywhere. Signed-off-by: Alexey Gladkov --- Documentation/filesystems/proc.rst | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst index 8256e857e2d7..c8864fcbdec7 100644 --- a/Documentation/filesystems/proc.rst +++ b/Documentation/filesystems/proc.rst @@ -52,6 +52,7 @@ fixes/update part 1.1 Stefani Seibold June 9 2009 4 Configuring procfs 4.1 Mount options + 4.2 Mount restrictions 5 Filesystem behavior @@ -2410,6 +2411,19 @@ will use the calling process's active pid namespace. Note that the pid namespace of an existing procfs instance cannot be modified (attempting to do so will give an `-EBUSY` error). +4.2 Mount restrictions +-------------------------- + +If user namespaces are in use, the kernel additionally checks the instances of +procfs available to the mounter and will not allow procfs to be mounted if: + + 1. This mount is not fully visible. + + a. It's root directory is not the root directory of the filesystem. + b. If any file or non-empty procfs directory is hidden by another mount. + + 2. A new mount overrides the readonly option or any option from atime familty. + Chapter 5: Filesystem behavior ============================== -- 2.53.0