title: Shared, writable folders in jupyterhub
body: <p>We are currently building a jupyterhub environment in a docker container and struggling with shared folders. Our goal is to set up a shared folder which is writable for all users.</p>
  <p>In each user's home folder there is a symbolic link <code>~/shared</code> to <code>/opt/shared</code>. The target folder has the permissions <code>777</code> and is owned by the group <i>jupyter</i>. Each user is member of the group <i>jupyter</i>. However, if one user creates a file in the shared folder logged in with his account into the web app, the permissions are set to <code>644</code>. Therefore, no other user can edit the file.</p>
  <p>I've tried to set the <code>umask</code> to <code>000</code> in the <code>/etc/profiles</code> and the <code>~/.bashrc</code> files for each user. However, jupyter seems to ignore it. Is there a possibility to configure jupyter to create new files with <code>g+w</code> rights as default? I would like to avoid setting up access control lists with <code>setfacl</code> at the file system level because it requires custom flags in the <code>/etc/fstab</code>.</p>