umview(1) User Mode implementation of View-OS


umview [ options ] prog


The main goal of the View-OS project is to give each process its own view of the system resources. For example, each process can mount filesystems or hide some file or directories. It is also possible to assign virtual network interfaces, IP addresses or define virtual devices for each process (or for hierarchies of processes).
umview is the user mode implementation of View-OS concepts. It is a modular partial virtual machine. umview before loading any module is completely transparent, a process behaves inside umview as it would have behaved outside. Each module can customize specific entities: there are modules to mount filesystems at user-level (umfuse) , to define virtual network interfaces (lwipv6) , to define virtual devices (umdev) , to provide interpreters for executables, e.g. to support executables for foreign architectures (umbinfmt) , to hide, move, overlay parts of the file system (viewfs).
These are some examples of modules provided by the View-OS team. umview aims to provide a general interface to customize the system call semantics of process under specified conditions. So more modules will be added both by the View-OS team and by third parties.


-V name
--viewname name
set the name of the view. The view can be read and set using vuname or viewname commands.
-p module [ , module_options ]
--preload module [ , module_options ]
preload modules. Modules will be loaded as shared libraries thus all the rules to load libraries apply. Modules must be loaded from a directory within the search path or should be specified by their pathnames. If necessary configure the LD_LIBRARY_PATH environment variable appropriately. module_options are module specific configuration options, thus the reader should refer to each service module manual for a complete description. Modules can be loaded at run time using the um_add_service command.
set kmview in human mode, i.e. force the check of capabilities and permissions. uid is 0 at startup, in this way it is possible to load modules and mount services. When a process sets its uid as an unprivileged user (via setuid(2) or viewsu(1)), capability and permissions are enforced.
-f rcfile
--rc rcfile
Use rcfile as the initialization file for kmview. kmview always executes /etc/viewosrc if exists, then kmview executes the initialization file set by this option or ~/.viewosrc.
umview is able to provide module nesting, i.e. a module can provide services on the basis of virtual services provided by another module or even by the module itself. For example it is possible to mount a file system image which is stored in an already virtually mounted filesystem. This feature requires the pure_libc library. The -x or --nonesting option disables the nesting feature.
umview is able to use some specific kernel extensions (when present) to increase its performance. The source distribution of umview include the kernel patches for the latest kernels. The kernel extensions are enabled by default when available. This option disables the kernel extensions.
This option disables the PTRACE_MULTI kernel extension.
This option disables the PTRACE_SYSVM kernel extension.
This option disables the PTRACE_SYSVIEWOS kernel extension (already experimental, not yet released).
-o file
--output file
This option diverts the debugging output to the file specified, it is useful when umview has been compiled with debugging extensions.
Print the version and exit.
Print a short help message and exit.


View-OS is a project of the Computer Science Department, University of Bologna. Project Leader: Renzo Davoli. Development Team: P. Angelelli, A. Bacchelli, M. Belletti, P. Beverini, D. Billi, A. Forni, L. Gardenghi, A. Gasparini, D. Lacamera, C. Martellini, A. Seraghiti <>

Howto's and further information can be found on the project wiki <>.