fsconfig – configuring a file server


service name

config device

nvram device

filsys name device

ip ipaddr

ipgw ipaddr

ipmask ipaddr

ipauth ipaddr

ipsntp ipaddr

ream name

recover name






copydev from-dev to-dev




When an fs(4) file server’s configuration has not been set, or by explicit request early in the server’s initialization (see fs(8)), the server enters ‘config mode’. The commands described here apply only in that mode. They establish configuration constants that are typically valid for the life of the server, and therefore need be run only once. If the non-volatile RAM on the server gets erased, it will be necessary to recreate the configuration.


In these commands, ipaddr is an IP address in the form and name is a text string without white space. The syntax of a device is more complicated:


Defines a SCSI disk on target (unit) id n2, controller (host adapter) n1, and LUN (logical unit number) n3. A single number specifies a target, while two numbers specify target.lun, with the missing numbers defaulting to zero. Any one of the numbers may be replaced by <m-n> to represent the values m through n inclusive. M may be greater than n. For example, (w<1-4>) is the concatenation of SCSI targets 1 through 4.  


H is similar to w, but for IDE or ATA disks, and the controllers must be specified in plan9.ini. Lun is ignored. Target 0 is an IDE master and 1 is a slave. Instead of specifying controller and target separately, one may omit the controller and specify a target of controller-number*2 + target-number, thus h2 is equivalent to h1.0.0 (second IDE controller, master drive).  


M is similar to h, but for SATA drives connected to Marvell 88SX[56]0[48][01] controllers. There is no need to specify the controllers in plan9.ini as they are autodiscovered. Hot-swapping drives is not currently supported. Similar target naming rules apply as for IDE controllers. However the controller-number is multiplied by the number of drives the controller supports rather than 2. Thus m9 is equivalent to m1.1.0 (second controller, second drive), if the first controller supports 8 drives.  




The same as w, but leaving a single block at the beginning for a label (l), or not. Only n2 is really of interest, and refers to a side of a WORM disc. These are only really relevant when used as device3 in the j device (see below).  


A pseudo-device formed from the concatenation of the devices in the list. The devices are not blank- or comma-separated.  


A pseudo-device formed from the block-wise interleaving of the devices in the list. The size of the result is the number of devices times the size of the smallest device.  


A pseudo-device formed from the mirroring of the first device in the list onto all the others. The size of the result is the size of the smallest device. One might think of this as RAID 1, and [ ] as RAID 0, though neither includes any fancy recovery mechanisms. Each block is written to all the devices, starting with the rightmost in the list and working leftward. A block is read from the first device that provides it without error, starting with the leftmost in the list and working rightward.  


A partition starting at n1% from the beginning of device with a length n2% of the size of the device. Parenthesize device if it contains periods.  


A pseudo-device that contains the byte-swapped contents of device. Since the file server writes integers to disk in its native byte order, it can be necessary to use this device to read file systems written by processors of the other byte order.  

j(device1 device2...)device3

Device1 is the SCSI juke box interface. The device2s are the SCSI drives in the jukebox and device3 represents the demountable platters in the juke box.  


A pseudo-WORM disk: blocks on device can be written only once and may not be read unless written.  


A cached WORM. The first device is the cache, the second the WORM.  


(Letter o) The read-only (dump) file system of the most-recently defined cached WORM file system.  


The service command sets the textual name of the server as known in the network databases.

The configuration information is stored in block zero on a device whose device string is written in non-volatile RAM. The config and nvram commands identify the device on which the information is recorded. The config command also erases any previous configuration.

The filsys command configures a file system on device and calls it name. Name is used as the specifier in attach messages to connect to that file system. (The file system main is the one attached to if the specifier is null; see attach(5)).

The rest of the configuration commands record IP addresses: the file server’s address (ip), the local gateway’s (ipgw), the local authentication server’s (ipauth), the local subnet mask (ipmask), and the address of a system running an SNTP server (ipsntp). Ipauth is no longer used. If the server has more than one network interface, a digit may be appended to the keywords ip, ipgw and ipmask to indicate the interface number; zero is the default.

One-time actions

The ream command initializes the named file system. It overwrites any previous file system on the same device and creates an empty root directory on the device. If name is main, the file server, until the next reboot, will accept wstat messages (see stat(5)) that change the owner and group of files, to enable initializing a fresh file system from a mkfs(8) archive.

For the recover command, the named file system must be a cached WORM. Recover clears the associated magnetic cache and initializes the file system, effectively resetting its contents to the last dump.

Allow turns off all permission checking; use with caution.

Readonly disables all writing to all devices. This is useful for trying dangerous experiments.

Noauth disables authentication.

Noattach prevents attachs.

Copyworm will copy a file system named main to one named output, block by block, and loop. It knows how to read a fake worm file system.

Copydev will copy the device from-dev to the device to-dev. block by block, and panic.

Halt will cause the server to immediately exit and reboot.

The various configuration commands only record what to do; they write no data to disk. The command end exits config mode and begins running the file server proper. The server will then perform whatever I/O is required to establish the configuration.


Initialize a file server kgbsun with a single file system interleaved between SCSI targets 3 and 4.


service kgbsun
config w3
filsys main [w<3-4>]
ream main

Initialize a file server kremvax with a single disk on target 0 partitioned as a cached pseudo-WORM file system with the cache on the third quarter of the drive and the pseudo-WORM on the interleave of the first, second, and fourth quarters.


service kremvax
config p(w0)50.1
filsys main cp(w0)50.25f[p(w0)0.25p(w0)25.25p(w0)75.25]
filsys dump o
ream main

A complete and complex example: initialize a file server fsb with a single SCSI disk on target 0 for a scratch file system, a cached WORM file system with cache disk on target 2 and an optical-disc jukebox on targets 4 (robotics) and 5 (one optical drive), and another cached WORM file system with cache disk on target 3 and another optical-disc jukebox on a second SCSI bus at targets 3 and 4. Both jukeboxes contain 16 slots of optical discs. It has two Ethernet interfaces and can reach an SNTP server on the first one.


service fsb
config w0
filsys main cw2j(w4w5)(l<0-31>)
filsys dump o
filsys hp40fx cw3j(w1.<3-4>.0)(l<0-31>)
filsys hp40fxdump o
filsys other w0
ream main
ream hp40fx
ream other




Ken Thompson, “The Plan 9 File Server”.