userbindmount.md

user bind mount

what

libuserbindmount is a library providing support for bind mount in user namespaces. userbindmount is a utility command based on libuserbindmount.

why

A common usage of libuserbindmount is to support user configuration of files whose path is hard-coded in libraries (e.g. to allow the choice of the domain name server for name resolution: /etc/resolv.conf is hardcoded in glibc).

how

In your code add:

userbindmount_string("nameserver 9.9.9.9\n", "/etc/resolv.conf", 0600);

The library supports the substitution of file contents using strings (as in the example here above), other files or data.

The project supplies also a command named userbindount. Here is an example:

$ echo "nameserver 9.9.9.9" > /tmp/resolv.conf
$ userbindmount /tmp/resolv.conf /etc/resolv.conf --
$ cat /etc/resolv.conf
nameserver 9.9.9.9
$ exit

where

userbindmount is useful to test user level networking stacks (in many cases the name resolver configured in /etc/resolv.conf is meaningless in the virtual networks).

references:

• userbindmount