devfs -- DEVFS control
devfs [-m mount-point] keyword argument ...
The devfs utility provides an interface to manipulate properties of
The keyword argument determines the context for the rest of the arguments.
For example, most of the commands related to the rule subsystem
must be preceded by the rule keyword. The following flags are common to
Operate on mount-point, which is expected to be a
devfs(5) mount. If this option is not specified, devfs
operates on /dev.
Rule Subsystem [Toc] [Back]
The devfs(5) rule subsystem provides a way for the administrator of a
system to control the attributes of DEVFS nodes. Each DEVFS mount-point
has a ``ruleset'', or a list of rules, associated with it. When a device
driver creates a new node, all the rules in the ruleset associated with
each mount-point are applied (see below) before the node becomes visible
to the userland. This permits the administrator to change the properties,
including the visibility, of certain nodes. For example, one might
want to hide all disk nodes in a jail(2)'s /dev.
Rule Manipulation [Toc] [Back]
Rule manipulation commands follow the rule keyword. The following flags
are common to all of the rule manipulation commands:
-s ruleset Operate on the ruleset with the number ruleset. If
this is not specified, the commands operate on the
ruleset currently associated with the specified mountpoint.
The following commands are recognized:
rule add [rulenum] rulespec
Add the rule described by rulespec (defined below) to
the ruleset. The rule has the number rulenum if it is
explicitly specified; otherwise, the rule number is
automatically determined by the kernel.
rule apply rulenum | rulespec
Apply rule number rulenum or the rule described by
rulespec to the mount-point. Rules that are
``applied'' have their conditions checked against all
nodes in the mount-point, and the actions taken if they
Apply all the rules in the ruleset to the mount-point
(see above for the definition of ``apply'').
rule del rulenum
Delete rule number rulenum from the ruleset.
Delete all rules from the ruleset.
rule show [rulenum]
Display the rule number rulenum, or all the rules in
the ruleset. The output lines (one line per rule) are
expected to be valid rulespecs.
Report the numbers of existing rulesets.
Set ruleset number ruleset as the current ruleset for
Rule Specification [Toc] [Back]
Rules have two parts: the conditions and the actions. The conditions
determine which DEVFS nodes the rule matches, and the actions determine
what should be done when a rule matches a node. For example, a rule can
be written that sets the GID to ``games'' for all devices with major number
53. If the first token of a rule specification is a single dash
(`-'), rules are read from the standard input and the rest of the specification
The following conditions are recognized. Conditions are ANDed together
when matching a device; if OR is desired, multiple rules can be written.
Matches any node with a major number equal to majdev.
Matches any node with a path that matches pattern. The
latter is interpreted as a glob(3)-style pattern.
Matches any node that is of type devtype. Valid types
are disk, mem, tape and tty.
The following actions are recognized. Although there is no explicit
delimiter between conditions and actions, they may not be intermixed.
group gid Set the GID of the node to gid, which may be a group
name (looked up in /etc/group) or number.
hide Hide the node. Nodes may later be revived manually
with mknod(8), or with the unhide action.
Apply all the rules in ruleset number ruleset to the
node. This does not necessarily result in any changes
to the node (e.g., if none of the rules in the included
Set the file mode to filemode, which is interpreted in
user uid Set the UID to uid, which may be a user name (looked up
in /etc/passwd) or number.
unhide Unhide the node.
Rulesets are created by the kernel at the first reference, and destroyed
when the last reference disappears. E.g., a ruleset is created when a
rule is added to it or when it is set as the current ruleset for a mountpoint;
a ruleset is destroyed when the last rule in it is deleted, and no
other references to it exist (i.e., it is not included by any rules, and
it is not the current ruleset for any mount-point).
Ruleset number 0 is the default ruleset for all new mount-points. It is
always empty, cannot be modified or deleted, and does not show up in the
output of showsets.
Rules and rulesets are unique to the entire system, not a particular
mount-point. I.e., a showsets will return the same information regardless
of the mount-point specified with -m. The mount-point is only relevant
when changing what its current ruleset is, or when using one of the
When the system boots, the only ruleset that exists is ruleset number 0;
since the latter may not be modified, we have to create another ruleset
before adding rules. Note that since most of the following examples do
not specify -m, the operations are performed on /dev (this only matters
for things that might change the properties of nodes).
devfs ruleset 10
Specify that ruleset 10 should be the current ruleset for /dev (if it
does not already exist, it is created).
devfs rule add path speaker mode 666
Add a rule that causes all nodes that have a path that matches
``speaker'' (this is only /dev/speaker) to have the file mode 666 (read
and write for all). Note that if any such nodes already exist, their
mode will not be changed unless this rule (or ruleset) is explicitly
applied (see below). The mode will be changed if the node is created
after the rule is added (e.g., the atspeaker module is loaded after the
above rule is added).
devfs rule applyset
Apply all the rules in the current ruleset to all the existing nodes.
E.g., if the above rule was added after /dev/speaker was created, this
command will cause its file mode to be changed to 666, as rule prescribes.
devfs rule add path snp* mode 660 group snoopers
(Quoting the argument to path is often necessary to disable the shell's
globbing features.) For all devices with a path that matches ``snp*'',
set the file more to 660, and the GID to ``snoopers''. This permits
users in the ``snoopers'' group to use the snp(4) devices.
devfs rule -s 20 add major 53 group games
Add a rule to ruleset number 20. Since this ruleset is not the current
ruleset for any mount-points, this rule is never applied automatically
(unless ruleset 20 becomes a current ruleset for some mount-point at a
later time). However, it can be applied explicitly, as such:
devfs -m /my/jail/dev rule -s 20 applyset
This will apply all rules in ruleset number 20 to the DEVFS mount on
/my/jail/dev. It does not matter that ruleset 20 is not the current
ruleset for that mount-point; the rules are applied regardless.
devfs rule apply hide
Since this rule has no conditions, the action (hide) will be applied to
all nodes. Since hiding all nodes is not very useful, we can undo like
devfs rule apply unhide
which applies unhide to all the nodes, causing them to reappear.
cat my_rules | devfs rule -s 10 add -
Add all the rules from the file my_rules to ruleset 10.
devfs rule -s 20 show | devfs rule -s 10 add -
Since show outputs valid rules, this feature can be used to copy rulesets.
The above copies all the rules from ruleset 20 into ruleset 10.
The rule numbers are preserved, but ruleset 10 may already have rules
with non-conflicting numbers (these will be preserved).
chmod(1), jail(2), glob(3), devfs(5), chown(8), jail(8), mknod(8)
FreeBSD 5.2.1 July 1, 2002 FreeBSD 5.2.1 [ Back ]