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MOUNT_PORTAL(8) NetBSD System Manager's Manual MOUNT_PORTAL(8)
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mount_portal -- mount the portal daemon
mount_portal [-o options] /etc/portal.conf mount_point
The mount_portal command attaches an instance of the portal daemon to the
global filesystem namespace. The conventional mount point is /p. The
directory specified by mount_point is converted to an absolute path
before use. This command is normally executed by mount(8) at boot time.
The options are as follows:
-o Options are specified with a -o flag followed by a comma sepa-
rated string of options. See the mount(8) man page for possible
options and their meanings.
The portal daemon provides an open service. Objects opened under the
portal mount point are dynamically created by the portal daemon according
to rules specified in the named configuration file. Using this mechanism
allows descriptors such as sockets to be made available in the filesystem
The portal daemon works by being passed the full pathname of the object
being opened. The daemon creates an appropriate descriptor according to
the rules in the configuration file, and then passes the descriptor back
to the calling process as the result of the open system call.
By convention, the portal daemon divides the namespace into sub-names-
paces, each of which handles objects of a particular type.
Currently, four sub-namespaces are implemented: tcp, fs, rfilter and
wfilter. The tcp namespace takes a hostname and a port (slash separated)
and creates an open TCP/IP connection. The fs namespace opens the named
file, starting back at the root directory. This can be used to provide a
controlled escape path from a chrooted environment.
The rfilter and wfilter namespaces open a pipe to a process, typically a
data-filter such as compression or decompression programs. The rfilter
namespace opens a read-only pipe, while the wfilter namespace opens a
write-only pipe. See the EXAMPLES section below for more examples.
The configuration file contains a list of rules. Each rule takes one
line and consists of two or more whitespace separated fields. A hash
(``#'') character at beginning of the line, or after whitespace, causes
the remainder of a line to be ignored. Blank lines are ignored.
The first field is a pathname prefix to match against the requested path-
name. If a match is found, the second field tells the daemon what type
of object to create. Subsequent fields are passed to the creation func-
The rfilter and wfilter namespaces have additional meanings for the
remaining fields. The third field specifies a prefix that is to be
stripped off of the passed name before passing it on to the pipe program.
If the prefix does not match, no stripping is performed. The fourth
argument specifies the program to use for the pipe. Any remaining fields
are passed to the pipe program. If the string ``%s'' exists within these
remaining fields, it will be replaced by the path after stripping is per-
formed. If there is no field after the program name, ``%s'' will be
assumed, to maintain similarity with the tcp and fs namespaces.
A tutorial and several examples are provided in
/usr/share/examples/mount_portal. The following is an example configura-
# @(#)portal.conf 5.1 (Berkeley) 7/13/92
tcp/ tcp tcp/
fs/ file fs/
echo/ rfilter echo/ echo %s
echo_nostrip/ rfilter nostrip echo %s
echo_noslash rfilter echo_noslash echo %s
gzcat/ rfilter gzcat/ gzcat %s
gzip/ wfilter gzip/ gzip > %s
gzip9/ wfilter gzip9/ gzip -9 > %s
ftp/ rfilter ftp/ ftp -Vo - %s
ftp:// rfilter nostrip ftp -Vo - %s
http:// rfilter nostrip ftp -Vo - %s
bzcat/ rfilter bzcat/ bzcat %s
nroff/ rfilter nroff/ nroff -man %s
As is true with many other filesystems, a weird sense of humor is handy.
Notice that after the keynames, like nroff/ and bzcat/, we typically use
another slash. In reality, the mount_portal process changes directory to
/, which makes the subsequent slash unnecessary. However, the extra
slash provides a visual hint that we are not operating on an ordinary
file. An alternative would be to change the configuration file to some-
nroff% rfilter nroff% nroff -man
One might then use
mount(2), unmount(2), fstab(5), mount(8)
The mount_portal utility first appeared in 4.4BSD. The rfilter and
wfilter capabilities first appeared in NetBSD 1.5. The portal kernel
driver was removed and mount_portal was converted to use puffs(3) in
This filesystem may not be NFS-exported.
NetBSD 10.99 May 23, 2019 NetBSD 10.99