pam_namespace(8) — Linux manual page


PAM_NAMESPACE(8)              Linux-PAM Manual              PAM_NAMESPACE(8)

NAME         top

       pam_namespace - PAM module for configuring namespace for a session

SYNOPSIS         top [debug] [unmnt_remnt] [unmnt_only] [require_selinux]
                        [gen_hash] [ignore_config_error]
                        [ignore_instance_parent_mode] [unmount_on_close]
                        [use_current_context] [use_default_context]

DESCRIPTION         top

       The pam_namespace PAM module sets up a private namespace for a
       session with polyinstantiated directories. A polyinstantiated
       directory provides a different instance of itself based on user name,
       or when using SELinux, user name, security context or both. If an
       executable script /etc/security/namespace.init exists, it is used to
       initialize the instance directory after it is set up and mounted on
       the polyinstantiated directory. The script receives the
       polyinstantiated directory path, the instance directory path, flag
       whether the instance directory was newly created (0 for no, 1 for
       yes), and the user name as its arguments.

       The pam_namespace module disassociates the session namespace from the
       parent namespace. Any mounts/unmounts performed in the parent
       namespace, such as mounting of devices, are not reflected in the
       session namespace. To propagate selected mount/unmount events from
       the parent namespace into the disassociated session namespace, an
       administrator may use the special shared-subtree feature. For
       additional information on shared-subtree feature, please refer to the
       mount(8) man page and the shared-subtree description at and

OPTIONS         top

           A lot of debug information is logged using syslog

           For programs such as su and newrole, the login session has
           already setup a polyinstantiated namespace. For these programs,
           polyinstantiation is performed based on new user id or security
           context, however the command first needs to undo the
           polyinstantiation performed by login. This argument instructs the
           command to first undo previous polyinstantiation before
           proceeding with new polyinstantiation based on new id/context

           For trusted programs that want to undo any existing bind mounts
           and process instance directories on their own, this argument
           allows them to unmount currently mounted instance directories

           If selinux is not enabled, return failure

           Instead of using the security context string for the instance
           name, generate and use its md5 hash.

           If a line in the configuration file corresponding to a
           polyinstantiated directory contains format error, skip that line
           process the next line. Without this option, pam will return an
           error to the calling program resulting in termination of the

           Instance parent directories by default are expected to have the
           restrictive mode of 000. Using this option, an administrator can
           choose to ignore the mode of the instance parent. This option
           should be used with caution as it will reduce security and
           isolation goals of the polyinstantiation mechanism.

           Explicitly unmount the polyinstantiated directories instead of
           relying on automatic namespace destruction after the last process
           in a namespace exits. This option should be used only in case it
           is ensured by other means that there cannot be any processes
           running in the private namespace left after the session close. It
           is also useful only in case there are multiple pam session calls
           in sequence from the same process.

           Useful for services which do not change the SELinux context with
           setexeccon call. The module will use the current SELinux context
           of the calling process for the level and context

           Useful for services which do not use pam_selinux for changing the
           SELinux context with setexeccon call. The module will use the
           default SELinux context of the user for the level and context

           This option can be used on systems where the / mount point or its
           submounts are made shared (for example with a mount
           --make-rshared / command). The module will mark the whole
           directory tree so any mount and unmount operations in the
           polyinstantiation namespace are private. Normally the
           pam_namespace will try to detect the shared / mount point and
           make the polyinstantiated directories private automatically. This
           option has to be used just when only a subtree is shared and / is

           Note that mounts and unmounts done in the private namespace will
           not affect the parent namespace if this option is used or when
           the shared / mount point is autodetected.


       Only the session module type is provided. The module must not be
       called from multithreaded processes.

RETURN VALUES         top

           Namespace setup was successful.

           Unexpected system error occurred while setting up namespace.

           Unexpected namespace configuration error occurred.

FILES         top

           Main configuration file

           Directory for additional configuration files

           Init script for instance directories

EXAMPLES         top

       For the <service>s you need polyinstantiation (login for example) put
       the following line in /etc/pam.d/<service> as the last line for
       session group:

       session required [arguments]

       To use polyinstantiation with graphical display manager gdm, insert
       the following line, before exit 0, in /etc/gdm/PostSession/Default:


       This allows gdm to restart after each session and appropriately
       adjust namespaces of display manager and the X server. If
       polyinstantiation of /tmp is desired along with the graphical
       environment, then additional configuration changes are needed to
       address the interaction of X server and font server namespaces with
       their use of /tmp to create communication sockets. Please use the
       initialization script /etc/security/namespace.init to ensure that the
       X server and its clients can appropriately access the communication
       socket X0. Please refer to the sample instructions provided in the
       comment section of the instance initialization script
       /etc/security/namespace.init. In addition, perform the following
       changes to use graphical environment with polyinstantiation of /tmp:

                 1. Disable the use of font server by commenting out "FontPath"
                    line in /etc/X11/xorg.conf. If you do want to use the font server
                    then you will have to augment the instance initialization
                    script to appropriately provide /tmp/.font-unix from the
                    polyinstantiated /tmp.
                 2. Ensure that the gdm service is setup to use pam_namespace,
                    as described above, by modifying /etc/pam.d/gdm.
                 3. Ensure that the display manager is configured to restart X server
                    with each new session. This default setup can be verified by
                    making sure that /usr/share/gdm/defaults.conf contains
                    "AlwaysRestartServer=true", and it is not overridden by

SEE ALSO         top

       namespace.conf(5), pam.d(5), mount(8), pam(8).

AUTHORS         top

       The namespace setup scheme was designed by Stephen Smalley, Janak
       Desai and Chad Sellers. The pam_namespace PAM module was developed by
       Janak Desai <>, Chad Sellers <>
       and Steve Grubb <>. Additional improvements by
       Xavier Toth <> and Tomas Mraz <>.

COLOPHON         top

       This page is part of the linux-pam (Pluggable Authentication Modules
       for Linux) project.  Information about the project can be found at 
       ⟨⟩.  If you have a bug report for this manual
       page, see ⟨//⟩.  This page was obtained from the
       tarball Linux-PAM-1.3.0.tar.bz2 fetched from
       ⟨⟩ on 2020-08-13.  If you discover
       any rendering problems in this HTML version of the page, or you
       believe there is a better or more up-to-date source for the page, or
       you have corrections or improvements to the information in this
       COLOPHON (which is not part of the original manual page), send a mail

Linux-PAM Manual                 04/01/2016                 PAM_NAMESPACE(8)

Pages that refer to this page: namespace.conf(5)namespaces(7)