DEVFS(8) BSD System Manager's Manual DEVFS(8)NAMEdevfs — DEVFS control
SYNOPSISdevfs [-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 argu‐
ments. 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.
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 proper‐
ties, including the visibility, of certain nodes. For example, one might
want to hide all disk nodes in a jail(2)'s /dev.
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 mount-
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 match.
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
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 “operator” for all devices of type tape.
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 is
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 path that matches pattern,
which 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
ruleset match). Include commands in the referenced
ruleset are not resolved.
Set the file mode to filemode, which is interpreted as
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 mount-
point, and 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 regard‐
less of the mount-point specified with -m. The mount-point is only rele‐
vant when changing what its current ruleset is or when using one of the
/etc/defaults/devfs.rules Default devfs configuration file.
/etc/devfs.rules Local devfs configuration file. Rule‐
sets in here override those in
/etc/defaults/devfs.rules with the same
ruleset number, otherwise the two files
are effectively merged.
/etc/devfs.conf Boot-time devfs configuration file.
Example boot-time devfs configuration
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 prescribed by
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 mode 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 type disk group wheel
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 still applied.
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 it:
devfs rule apply unhide
which applies unhide to all the nodes, causing them to reappear.
devfs rule -s 10 add - < my_rules
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 rule‐
sets. 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).
SEE ALSOchmod(1), jail(2), glob(3), devfs(5), devfs.conf(5), devfs.rules(5),
chown(8), jail(8), mknod(8)AUTHORS
BSD February 21, 2010 BSD