omshell
OMAPI Command Shell
see also :
dhclient
Synopsis
omshell
add an example, a script, a trick and tips
examples
no example yet ...
... Feel free to add your own example above to help other Linux-lovers !
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 provides 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.
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.
contributions
This software is free software. At various times its development
has been underwritten by various organizations, 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 project depends on you.
If you have features you want, please consider implementing them.
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(8). 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
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
available in omshell, with some syntax pointers.
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.
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 client-hostname
= "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 properties 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 follows:
> 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.
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 key generated from
dnssec-keygen or another key generation program.
connect
This starts the OMAPI connection to the server as specified by
the server statement.
refreshing objects
A local object may be refreshed with the current remote object
properties using the refresh command. This is useful for
object that change periodically, like leases, to see if they have
been updated. This isn’t particularly useful for hosts.
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 previous
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>
>
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 following
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 particular 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
hexadecimal, as are the starting and ending times of the lease.
see also
dhcpctl,
omapi, dhcpd, dhclient , dhcpd.conf,
dhclient.conf.
author
omshell
was written by Ted Lemon of Nominum, Inc. Information about
Nominum can be found at http://www.nominum.com. This
preliminary documentation was written by Wendy Verschoor of
Nominum, Inc., while she was testing omshell.