DEVFS(8) BSD System Manager's Manual DEVFS(8)
devfs -- DEVFS control
devfs [-m mount-point] keyword argument ...
The devfs utility provides an interface to manipulate properties of devfs(5) mounts.
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 all keywords:
-m mount-point 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 asso-
ciated 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 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-point.
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 con-
ditions checked against all nodes in the mount-point and the actions taken if they match.
rule applyset 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.
rule delset 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
rule showsets Report the numbers of existing rulesets.
ruleset ruleset Set ruleset number ruleset as the current ruleset for the mount-point.
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 specifi-
cation is ignored.
The following conditions are recognized. Conditions are ANDed together when matching a device; if OR is desired, multiple rules can be writ-
path pattern Matches any node with a path that matches pattern, which is interpreted as a glob(3)-style pattern.
type devtype 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. Hiding a directory node effec-
tively hides all of its child nodes.
include ruleset 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.
mode filemode Set the file mode to filemode, which is interpreted as in chmod(1).
user uid Set the UID to uid, which may be a user name (looked up in /etc/passwd) or number.
unhide Unhide the node. If the node resides in a subdirectory, all parent directory nodes must be visible to be able to access the
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 relevant when changing what its current ruleset is or when using one of
the apply commands.
/etc/defaults/devfs.rules Default devfs configuration file.
/etc/devfs.rules Local devfs configuration file. Rulesets 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.
/usr/share/examples/etc/devfs.conf Example boot-time devfs configuration file.
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).
Specify that ruleset 10 should be the current ruleset for /dev (if it does not already exist, it is created):
devfs ruleset 10
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 add path speaker mode 666
Apply all the rules in the current ruleset to all the existing nodes. E.g., if the below rule was added after /dev/speaker was created, this
command will cause its file mode to be changed to 666 as prescribed by the rule:
devfs rule applyset
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 (quoting the argument to path is often necessary to disable the shell's globbing features):
devfs rule add path snp* mode 660 group snoopers
Add a rule to ruleset number 20. Since this ruleset is not the current ruleset for any mount-points, this rule is never applied automati-
cally (unless ruleset 20 becomes a current ruleset for some mount-point at a later time):
devfs rule -s 20 add type disk group wheel
Explicitly 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 -m /my/jail/dev rule -s 20 applyset
Since the following rule has no conditions, the action (hide) will be applied to all nodes:
devfs rule apply hide
Since hiding all nodes is not very useful, we can undo it. The following applies unhide to all the nodes, causing them to reappear:
devfs rule apply unhide
Add all the rules from the file my_rules to ruleset 10:
devfs rule -s 10 add - < my_rules
The below 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). Since show outputs valid rules, this feature can be used to copy rulesets:
devfs rule -s 20 show | devfs rule -s 10 add -
chmod(1), jail(2), glob(3), devfs(5), devfs.conf(5), devfs.rules(5), chown(8), jail(8), mknod(8)
July 12, 2013 BSD