DEVFS(8) FreeBSD System Manager's Manual DEVFS(8)
NAME
devfs - DEVFS control
SYNOPSIS
devfs [-m mount-point] keyword argument ...
DESCRIPTION
The devfs utility provides an interface to manipulate properties of
devfs(5) mounts.
The rules, by default as configured by /etc/rc.conf, are loaded at boot
via the devfs service(8). The rules can be reloaded by running the
command:
service devfs restart
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.
Rule Subsystem
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
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 conditions 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 valid rulespecs.
rule showsets Report the numbers of existing rulesets.
ruleset ruleset Set ruleset number ruleset as the current ruleset for
the mount-point.
Rule Specification
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
ignored.
The following conditions are recognized. Conditions are ANDed together
when matching a device; if OR is desired, multiple rules can be written.
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 effectively 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 node.
IMPLEMENTATION NOTES
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
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 apply commands.
FILES
/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.
EXAMPLES
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 automatically
(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 -
SEE ALSO
chmod(1), jail(2), glob(3), devfs(5), devfs.conf(5), devfs.rules(5),
chown(8), jail(8), mknod(8), service(8)
HISTORY
The devfs utility first appeared in FreeBSD 5.0.
AUTHORS
Dima Dorfman
FreeBSD 13.1-RELEASE-p6 December 1, 2020 FreeBSD 13.1-RELEASE-p6
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