--- name: "devfsd" section: "8" platform: "linux" package: "devfsd" version: "1.3.25-19" release: "Debian 3.1 (Sarge)" platforms: ["linux"] url: "https://new.carta.tech/devfsd" --- # devfsd(8) optional daemon for managing devfs (the Linux Device Filesystem) ## NAME devfsd - optional daemon for managing devfs (the Linux Device Filesystem) ## SYNOPSIS **devfsd** **mntpnt** \[ **-v** \] \[ **-d** \] \[ **-t num** \] \[ **-D mask** \] \[ **-fg** \] \[ **-np** \] ## DESCRIPTION The *devfsd* programme is a daemon, run by the system boot scripts, which can provide for intelligent management of device entries in the Device Filesystem (devfs). It is desirable to start the daemon at the beginning of the boot scripts, in particular before filesystem checks. As part of its setup phase *devfsd* creates certain symbolic links which are compiled into the code. These links are required by **/usr/src/linux/Documentation/devices.txt**. This behaviour may change in future revisions. *devfsd* will read the special control file *.devfsd* in a mounted devfs, listening for the creation and removal of device entries (this is termed a change operation). For each change operation, *devfsd* can take many actions. The daemon will normally run itself in the background and send messages to syslog. The opening of the syslog service is automatically delayed until */dev/log* is created. At startup, before switching to daemon mode, *devfsd* will scan the mounted device tree and will generate synthetic **REGISTER** events for each leaf node and directory. ## OPTIONS - **mntpnt** This specifies a mount point for where devfs is mounted. This is typically "/dev". The daemon will change directory to this mount point before opening any files. - **-v** This option will print the protocol version numbers for *devfsd* and the kernel-side protocol version provided by devfs itself. The programme then exits. - **-d** Run *devfsd* in debug mode. Used for debugging the kernel-side protocol implemented by devfs. This also prints the protocol version numbers. In this mode the daemon runs in the foreground. - **-t num** Set the trace level to *num*. If the level is greater than 0 then output is sent to stderr rather than [syslog(3)](/syslog/3.md). If the level is greater than 1 then *devfsd* will run in trace mode. Higher levels yield more trace information. - **-D mask** Set the debug mask for devfs. - **-fg** Run the daemon in the foreground. - **-np** Exit after parsing the configuration file and processing synthetic **REGISTER** events. Do not poll for events. This is primarily used for creating compatibility entries without needing a daemon running in the background. ## CONFIGURATION The configuration file /etc/devfs/devfsd.conf configures the *devfsd* programme. It is a simple ASCII file with one configuration option per line. Comment lines must start with a leading '#' character. Comment lines and blank lines are ignored. Each configuration option is a keyword followed by zero or more parameters, depending on the option. The following section details the configuration options. Below are the permitted keywords: - **INCLUDE location** Include the configuration file named by *location*. Variable expansion is applied to *location* (see the section on VARIABLE EXPANSION below). If this is a directory, then all files (except those which start with '.') are read. This is recursive (i.e. files which are in fact subdirectories are also read). If the first character of *location* is "+", then the rest of *location* is the name of an NIS map to load. This operation is silently ignored if the NIS domain has not yet been set (**SIGHUP** should then be sent after the NIS domain has been set). - **OPTIONAL\_INCLUDE location** As above, except that if the file does not exist, it is silently ignored. - **CLEAR\_CONFIG** Clear the current configuration. - **RESTORE directory** This will restore entries previously saved under *directory* to devfs. Only symbolic links or entries with the sticky bit set will be restored. This action is taken as the configuration file is read. With appropriate **COPY** actions, complete persistence is acheived. The config file can also be used to specify actions that should be taken at specified events. Each line specifies an event and action. Multiple actions (of the same or different types) per event may be specified (one action per line). Events are processed in order, with the first event config line being processed first. The syntax is: - **EVENT devname ACTION \[args...\]** where *EVENT* is the event and *ACTION* is the action to take when the event occurs. The action is only taken when *devname* matches the name of the device entry affected (this does not include the mount point for the filesystem). This is processed as a regular expression. Some actions support extra arguments, passed as *args*. Variable expansion is applied to the arguments (see the section on VARIABLE EXPANSION below). After variable expansion, regular expression substitution is performed (see the section on REGULAR EXPRESSION SUBSTITUTION). Note that the following special variable names are also recognised: - **devpath** the full path name of the new device - **devname** the name of the new device inside the devfs namespace - **mode** the mode of the device entry in octal - **uid** the user ID of the process or inode - **gid** the group ID of the process or inode The following events are recognised: - **REGISTER** The device entry or directory was registered by a device driver. - **UNREGISTER** The device entry was unregistered by a device driver. - **ASYNC\_OPEN** The inode was opened (the opening process does not wait for a response). - **CLOSE** The file was closed. - **LOOKUP** An inode lookup was performed and there was no device entry. This event is not sent if the initiating process is devfsd or one of its children. - **CHANGE** Some inode attributes were changed. - **CREATE** An inode was created by a process. - **DELETE** An inode was deleted by a process. The following actions are recognised: - **PERMISSIONS owner\_and\_group access\_mode** *owner\_and\_group* specifies the owner and group that the file should be set to. This must be of the form "user.group" and either "user" or "group" component may be symbolic or numeric. To specify that the user or group be left alone, use a numeric value of "-1" for the respective component. *access\_mode* specifies the access mode the file should be set to. This must be either an octal value or a symbolic string of nine characters with the form "rwxrwxrwx". Where access is not given, a '-' character should be used in place (e.g. "rw-rw-r--" gives read and write access to the user and group and only read access to everybody else). - **MODLOAD** This action will pass "/dev/$devname" (i.e. "/dev/" prefixed to the device name) to the module loading facility. In addition, the */etc/modutils/devfs* configuration file is used. - **EXECUTE path \[arg...\]** This action allows you to run a programme. *path* is the pathname of the programme to run and *arg* is a set of optional arguments passed to the programme (maximum 6). *path* is the first argument (i.e. argv\[0\]) passed to the programme. - **MFUNCTION path function \[arg...\]** This action allows you to run a "main"-style function within a shared object. *path* is the pathname of the shared object, with the special path of "GLOBAL" signifying all global symbols (e.g. from libc). The default directory is **/lib/devfsd**. *function* is the name of the function symbol to run and *arg* is a set of optional arguments passed to the function (maximum 5). *path* is the first argument (i.e. argv\[0\]) passed to the function. The prototype for this function is similar to the *main* function of C programmes. The prototype is: int func (int argc, char \*\*argv); - **CFUNCTION path function \[arg...\]** This action is similar to the **MFUNCTION** action, except for the calling convention. The prototype for this function is: int func (void \*arg1, void \*arg2, void \*arg3, void \*arg4, void \*arg5); Up to 5 arguments may be passed, each being of type *void \**. The following special arguments are recognised: - **EVENT** a *struct devfsd\_notify\_struct \** is passed - **COPY source destination** This action will copy the device type and permissions of *source* to *destination*. The sticky bit is set on the destination inode if the source inode was create manually (i.e. not by a driver or *devfsd*). - **IGNORE** This action causes all subsequent processing for the event to be ignored. - **MKOLDCOMPAT** This action creates an "old" compatibility entry for the device. - **MKNEWCOMPAT** This action creates a "new" compatibility entry for the device. - **RMOLDCOMPAT** This action removes an "old" compatibility entry for the device. - **RMNEWCOMPAT** This action removes a "new" compatibility entry for the device. ## VARIABLE EXPANSION A subset of normal Bourne shell variable expansion is applied to various expressions. The currently supported subset is: *$variable*, *${variable}* and *${variable:-word}*. Variables are taken from the environment. The following variable names are also defined : - **hostname** The hostname of the machine - **mntpnt** The mount point for devfs ## REGULAR EXPRESSION SUBSTITUTION Sections of the matched regular expression can be included in an action. Use *\\0* to refer to the entire regular expression matched, *\\1* to refer to the first parenthesized subexpression, *\\2* to refer to the second, and so on. (Use *\\\\* to include an actual backslash.) See [**devfsd.conf**(5)](/devfsd.conf/5.md) for examples of regular expression substitution. ## SIGNALS *devfsd* responds to signals in a variety of ways: - **SIGINT** *devfsd* will exit cleanly. - **SIGTERM** *devfsd* will exit cleanly. - **SIGHUP** The configuration file is re-read and any shared objects are reloaded. Then the mounted device tree is scanned and synthetic **REGISTER** events are generated for each leaf node. - **SIGUSR1** The configuration file is re-read and any shared objects are reloaded. No synthetic **REGISTER** events are generated. ## EXAMPLES **Create and destroy old compatibility entries:** ``` REGISTER .* MKOLDCOMPAT UNREGISTER .* RMOLDCOMPAT ``` **Create and destroy new compatibility entries:** ``` REGISTER .* MKNEWCOMPAT UNREGISTER .* RMNEWCOMPAT ``` **Load modules:** ``` LOOKUP .* MODLOAD ``` **Make and remove a symbolic link:** ``` REGISTER mydir/mydev CFUNCTION GLOBAL mksymlink $devname mydev UNREGISTER mydir/mydev CFUNCTION GLOBAL unlink mydev ``` **Give sndusers group access to sound drivers** ``` REGISTER sound/.* PERMISSIONS root.sndusers rw-rw---- ``` ## FILES - **/etc/devfs/devfsd.conf** the configuration file. If this file is missing or has zero size, *devfsd* will exit after its setup phase. - **/etc/modutils/devfs** the generic module configuration file (required for the **MODLOAD** action), which is installed with *devfsd*. This in turn includes */etc/modules.conf* ## CAVEATS Make sure you understand the implications of regular expression matching. For example, if you had a configuration line such as: **LOOKUP cdrom CFUNCTION GLOBAL mksymlink ${mntpnt}/cdroms/cdrom0 $devpath** then referencing "/dev/cdrom1" will create the symbolic link "/dev/cdrom1". Further, referencing "/dev/cdroms/1" would also create the "/dev/cdroms/1" symbolic link. This is probably not what you want. If there was not already a "/dev/cdroms" directory, then you would get a "/dev/cdrom" symbolic link. Definately not what you want! The correct configuration line would be: **LOOKUP ^cdrom$ CFUNCTION GLOBAL mksymlink ${mntpnt}/cdroms/cdrom0 $devpath** ## SEE ALSO [**init**(8)](/init/8.md), [**devfsd.conf**(5)](/devfsd.conf/5.md), [**modprobe**(8)](/modprobe/8.md) ## AUTHOR Richard Gooch (rgooch@atnf.csiro.au) ## AVAILABILITY The Device Filesystem daemon is available from: http://www.atnf.csiro.au/~rgooch/linux/ ## FURTHER READING It is strongly recommended to read the devfs FAQ, which contains configuration tips. It is available at: http://www.atnf.csiro.au/~rgooch/linux/docs/devfs.html ## MAILING LIST A mailing list exists for devfs kernel patch and devfsd release announcements. This list also has a small amount of discussion traffic (a few messages per week). You may subscribe by sending a message to **majordomo@oss.sgi.com** with **subscribe devfs** in the message *body*.