omshell(3)
NAME
omshell - OMAPI Command Shell
SYNOPSIS
omshell
DESCRIPTION
The OMAPI Command Shell, omshell, provides an interactive
way to connect to, query, and possibly change, the ISC
DHCP Server's state via OMAPI, the Object Management API.
By using OMAPI and omshell, you do not have to stop, make
changes, and then restart the DHCP server, but can make
the changes while the server is running. Omshell pro
vides a way of accessing OMAPI.
OMAPI is simply a communications mechanism that allows you
to manipulate objects. In order to actually use omshell,
you must understand what objects are available and how to
use them. Documentation for OMAPI objects can be found in
the documentation for the server that provides them - for
example, in the dhcpd(1) manual page and the dhclient(1)
manual page.
CONTRIBUTIONS
This software is free software. At various times its
development has been underwritten by various organiza
tions, including the ISC and Vixie Enterprises. The
development of 3.0 has been funded almost entirely by
Nominum, Inc.
At this point development is being shepherded by Ted
Lemon, and hosted by the ISC, but the future of this pro
ject depends on you. If you have features you want,
please consider implementing them.
LOCAL AND REMOTE OBJECTS
Throughout this document, there are references to local
and remote objects. Local objects are ones created in
omshell with the new command. Remote objects are ones on
the server: leases, hosts, and groups that the DHCP server
knows about. Local and remote objects are associated
together to enable viewing and modification of object
attributes. Also, new remote objects can be created to
match local objects.
OPENING A CONNECTION
omshell is started from the command line. Once omshell is
started, there are several commands that can be issued:
- server address
- where address is the IP address of the DHCP server to
connect to. If this is not specified, the default
server is 127.0.0.1 (localhost). - port number
- where number is the port that OMAPI listens on. By
default, this is 7911. - key name secret
- This specifies the TSIG key to use to authenticate
the OMAPI transactions. name is the name of a key
defined in dhcpd.conf with the omapi-key statement. The secret is the secret generated from dnssec-keygen or another key generation program. - connect
- This starts the OMAPI connection to the server as
specified by the server statement.
CREATING LOCAL OBJECTS
Any object defined in OMAPI can be created, queried,
and/or modified. The object types available to OMAPI are
defined in dhcpd(8) and dhclient. When using omshell,
objects are first defined locally, manipulated as desired,
and then associated with an object on the server. Only
one object can be manipulated at a time. To create a
local object, use
- new object-type
- object-type is one of group, host, or lease.
- At this point, you now have an object that you can set
properties on. For example, if a new lease object was
created with new lease, any of a lease's attributes can be set as follows: - set attribute-name = value
- Attribute names are defined in dhcpd(8) and
dhclient(8). Values should be quoted if they are
strings. So, to set a lease's IP address, you would
do the following:set ip-address = 192.168.4.50
ASSOCIATING LOCAL AND REMOTE OBJECTS
At this point, you can query the server for information
about this lease, by
open
Now, the local lease object you created and set the IP
address for is associated with the corresponding lease
object on the DHCP server. All of the lease attributes
from the DHCP server are now also the attributes on the
local object, and will be shown in omshell.
VIEWING A REMOTE OBJECT
To query a lease of address 192.168.4.50, and find out its
attributes, after connecting to the server, take the fol
lowing steps:
new lease
This creates a new local lease object.
set ip-address = 192.168.4.50
This sets the local object's IP address to be 192.168.4.50
open
Now, if a lease with that IP address exists, you will see
all the information the DHCP server has about that partic
ular lease. Any data that isn't readily printable text
will show up in colon-separated hexadecimal values. In
this example, output back from the server for the entire
transaction might look like this:
> new "lease"
obj: lease
> set ip-address = 192.168.4.50
obj: lease
ip-address = c0:a8:04:32
> open
obj: lease
ip-address = c0:a8:04:32
state = 00:00:00:02
dhcp-client-identifier = 01:00:10:a4:b2:36:2c
client-hostname = "wendelina"
subnet = 00:00:00:06
pool = 00:00:00:07
hardware-address = 00:10:a4:b2:36:2c
hardware-type = 00:00:00:01
ends = dc:d9:0d:3b
starts = 5c:9f:04:3b
tstp = 00:00:00:00
tsfp = 00:00:00:00
cltt = 00:00:00:00
As you can see here, the IP address is represented in hex
adecimal, as are the starting and ending times of the
lease.
MODIFYING A REMOTE OBJECT
Attributes of remote objects are updated by using the set
command as before, and then issuing an update command.
The set command sets the attributes on the current local
object, and the update command pushes those changes out to
the server.
Continuing with the previous example, if a set clienthostname = "something-else" was issued, followed by an
update command, the output would look about like this:
> set client-hostname = "something-else"
obj: lease
ip-address = c0:a8:04:32
state = 00:00:00:02
dhcp-client-identifier = 01:00:10:a4:b2:36:2c
client-hostname = "something-else"
subnet = 00:00:00:06
pool = 00:00:00:07
hardware-address = 00:10:a4:b2:36:2c
hardware-type = 00:00:00:01
ends = dc:d9:0d:3b
starts = 5c:9f:04:3b
tstp = 00:00:00:00
tsfp = 00:00:00:00
cltt = 00:00:00:00
> update
obj: lease
ip-address = c0:a8:04:32
state = 00:00:00:02
dhcp-client-identifier = 01:00:10:a4:b2:36:2c
client-hostname = "something-else"
subnet = 00:00:00:06
pool = 00:00:00:07
hardware-address = 00:10:a4:b2:36:2c
hardware-type = 00:00:00:01
ends = dc:d9:0d:3b
starts = 5c:9f:04:3b
tstp = 00:00:00:00
tsfp = 00:00:00:00
cltt = 00:00:00:00
NEW REMOTE OBJECTS
New remote objects are created much in the same way that
existing server objects are modified. Create a local
object using new, set the attributes as you'd wish them to
be, and then create the remote object with the same prop
erties by using
create
Now a new object exists on the DHCP server which matches
the properties that you gave your local object. Objects
created via OMAPI are saved into the dhcpd.leases file.
For example, if a new host with the IP address of
192.168.4.40 needs to be created it would be done as fol
lows:
> new host
obj: host
> set name = "some-host"
obj: host
name = "some-host"
> set hardware-address = 00:80:c7:84:b1:94
obj: host
name = "some-host"
hardware-address = 00:80:c7:84:b1:94
> set hardware-type = 1
obj: host
name = "some-host"
hardware-address = 00:80:c7:84:b1:94
hardware-type = 1
> set ip-address = 192.168.4.40
obj: host
name = "some-host"
hardware-address = 00:80:c7:84:b1:94
hardware-type = 1
ip-address = c0:a8:04:28
> create
obj: host
name = "some-host"
hardware-address = 00:80:c7:84:b1:94
hardware-type = 00:00:00:01
ip-address = c0:a8:04:28
>
Your dhcpd.leases file would then have an entry like this
in it:
- host some-host {
- dynamic;
hardware ethernet 00:80:c7:84:b1:94;
fixed-address 192.168.4.40; - }
- The dynamic; line is to denote that this host entry did
not come from dhcpd.conf, but was created dynamically via
OMAPI.
RESETTING ATTRIBUTES
If you want to remove an attribute from an object, you can
do this with the unset command. Once you have unset an
attribute, you must use the update command to update the
remote object. So, if the host "some-host" from the pre
vious example will not have a static IP address anymore,
the commands in omshell would look like this:
obj: host
name = "some-host"
hardware-address = 00:80:c7:84:b1:94
hardware-type = 00:00:00:01
ip-address = c0:a8:04:28
> unset ip-address
obj: host
name = "some-host"
hardware-address = 00:80:c7:84:b1:94
hardware-type = 00:00:00:01
ip-address = <null>
>
REFRESHING OBJECTS
A local object may be refreshed with the current remote
object properties using the refresh command. This is use
ful for object that change periodically, like leases, to
see if they have been updated. This isn't particularly
useful for hosts.
DELETING OBJECTS
Any remote object that can be created can also be
destroyed. This is done by creating a new local object,
setting attributes, associating the local and remote
object using open, and then using the remove command. If
the host "some-host" from before was created in error,
this could be corrected as follows:
obj: host
name = "some-host"
hardware-address = 00:80:c7:84:b1:94
hardware-type = 00:00:00:01
ip-address = c0:a8:04:28
> remove
obj: <null>
>
HELP
The help command will print out all of the commands avail
able in omshell, with some syntax pointers.
SEE ALSO
dhcpctl(3), omapi(3), dhcpd(8), dhclient(8),
dhcpd.conf(5), dhclient.conf(5).
AUTHOR
- omshell was written by Ted Lemon of Nominum, Inc. Infor
mation about Nominum and support contracts for DHCP and
BIND can be found at http://www.nominum.com. This prelimi nary documentation was written by Wendy Verschoor of Nominum, Inc., while she was testing omshell.