dhcpcd.8

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.Dd August 31, 2010
.Dt DHCPCD 8 SMM
.Os
.Sh NAME
.Nm dhcpcd
.Nd an RFC 2131 compliant DHCP client
.Sh SYNOPSIS
.Nm
.Op Fl bdgknpqwABDEGHJKLTV
.Op Fl c , -script Ar script
.Op Fl e , -env Ar value
.Op Fl f , -config Ar file
.Op Fl h , -hostname Ar hostname
.Op Fl i , -vendorclassid Ar vendorclassid
.Op Fl l , -leasetime Ar seconds
.Op Fl m , -metric Ar metric
.Op Fl o , -option Ar option
.Op Fl r , -request Ar address
.Op Fl s , -inform Ar address Ns Op Ar /cidr
.Op Fl t , -timeout Ar seconds
.Op Fl u , -userclass Ar class
.Op Fl v , -vendor Ar code , Ar value
.Op Fl y , -reboot Ar seconds
.Op Fl z , -allowinterfaces Ar pattern
.Op Fl C , -nohook Ar hook
.Op Fl F , -fqdn Ar FQDN
.Op Fl I , -clientid Ar clientid
.Op Fl O , -nooption Ar option
.Op Fl Q , -require Ar option
.Op Fl S , -static Ar value
.Op Fl W , -whitelist Ar address Ns Op Ar /cidr
.Op Fl X , -blacklist Ar address Ns Op Ar /cidr
.Op Fl Z , -denyinterfaces Ar pattern
.Op interface
.Op ...
.Nm
.Fl k , -release
.Op interface
.Nm
.Fl U, -dumplease
.Ar interface
.Nm
.Fl x , -exit
.Op interface
.Nm
.Fl v , -version
.Sh DESCRIPTION
.Nm
is an implementation of the DHCP client specified in
.Li RFC 2131 .
.Nm
gets the host information
.Po
IP address, routes, etc
.Pc
from a DHCP server and configures the network
.Ar interface
of the
machine on which it is running.
.Nm
then runs the configuration script which writes DNS information to
.Xr resolvconf 8 ,
if available, otherwise directly to
.Pa /etc/resolv.conf .
If the hostname is currently blank, (null) or localhost, or
.Va force_hostname
is YES or TRUE or 1 then
.Nm
sets the hostname to the one supplied by the DHCP server.
.Nm
then daemonises and waits for the lease renewal time to lapse.
It will then attempt to renew its lease and reconfigure if the new lease
changes.
.Pp
.Nm
is also an implementation of the BOOTP client specified in
.Li RFC 951 .
.Ss Local Link configuration
If
.Nm
failed to obtain a lease, it probes for a valid IPv4LL address
.Po
aka ZeroConf, aka APIPA
.Pc .
Once obtained it restarts the process of looking for a DHCP server to get a
proper address.
.Pp
When using IPv4LL,
.Nm
nearly always succeeds and returns an exit code of 0.
In the rare case it fails, it normally means that there is a reverse ARP proxy
installed which always defeats IPv4LL probing.
To disable this behaviour, you can use the
.Fl L , -noipv4ll
option.
.Ss Multiple interfaces
If a list of interfaces are given on the command line, then
.Nm
only works with those interfaces, otherwise
.Nm
discovers available Ethernet interfaces.
If any interface reports a working carrier then
.Nm
will try and obtain a lease before forking to the background,
otherwise it will fork right away.
This behaviour can be modified with the
.Fl b , -background
and
.Fl w , -waitip
options.
.Pp
If a single interface is given then
.Nm
only works for that interface and runs as a separate instance.
The
.Fl w , -waitip
option is enabled in this instance to maintain compatibility with older
versions.
.Pp
Interfaces are preferred by carrier, DHCP lease/IPv4LL and then lowest metric.
For systems that support route metrics, each route will be tagged with the
metric, otherwise
.Nm
changes the routes to use the interface with the same route and the lowest
metric.
See options below for controlling which interfaces we allow and deny through
the use of patterns.
.Ss Hooking into DHCP events
.Nm
runs
.Pa /libexec/dhcpcd-run-hooks ,
or the script specified by the
.Fl c , -script
option.
This script runs each script found in
.Pa /libexec/dhcpcd-hooks
in a lexical order.
The default installation supplies the scripts
.Pa 01-test ,
.Pa 10-mtu ,
.Pa 20-resolv.conf
and
.Pa 30-hostname .
You can disable each script by using the
.Fl C , -nohook
option.
See
.Xr dhcpcd-run-hooks 8
for details on how these scripts work.
.Nm
currently ignores the exit code of the script.
.Ss Fine tuning
You can fine-tune the behaviour of
.Nm
with the following options:
.Bl -tag -width indent
.It Fl b , -background
Background immediately.
This is useful for startup scripts which don't disable link messages for
carrier status.
.It Fl c , -script Ar script
Use this
.Ar script
instead of the default
.Pa /libexec/dhcpcd-run-hooks .
.It Fl d , -debug
Echo debug messages to the stderr and syslog.
.It Fl e , -env Ar value
Push
.Ar value
to the environment for use in
.Xr dhcpcd-run-hooks 8 .
For example, you can force the hostname hook to always set the hostname with
.Fl e
.Va force_hostname=YES .
.It Fl g , -reconfigure
.Nm
will re-apply IP address, routing and run
.Xr dhcpcd-run-hooks 8
for each interface.
This is useful so that a 3rd party such as PPP or VPN can change the routing
table and / or DNS, etc and then instruct
.Nm
to put things back afterwards.
.Nm
does not read a new configuration when this happens - you should rebind if you
need that functionality.
.It Fl f , -config Ar file
Specify a config to load instead of
.Pa /etc/dhcpcd.conf .
.Nm
always processes the config file before any command line options.
.It Fl h , -hostname Ar hostname
Sends
.Ar hostname
to the DHCP server so it can be registered in DNS.
If
.Ar hostname
is an empty string then the current system hostname is sent.
If
.Ar hostname
is a FQDN (ie, contains a .) then it will be encoded as such.
.It Fl i , -vendorclassid Ar vendorclassid
Override the
.Ar vendorclassid
field sent. The default is
dhcpcd <version>.
If not set then none is sent.
.It Fl k , -release
This causes an existing
.Nm
process running on the
.Ar interface
to release its lease, de-configure the
.Ar interface
and then exit.
.Nm
then waits until this process has exited.
.It Fl l , -leasetime Ar seconds
Request a specific lease time in
.Ar seconds .
By default
.Nm
does not request any lease time and leaves it in the hands of the
DHCP server.
.It Fl m , -metric Ar metric
Metrics are used to prefer an interface over another one, lowest wins.
.Nm
will supply a default metic of 200 +
.Xr if_nametoindex 3 .
An extra 100 will be added for wireless interfaces.
.It Fl o , -option Ar option
Request the DHCP
.Ar option
variable for use in
.Pa /libexec/dhcpcd-run-hooks .
.It Fl n , -rebind
Notifies
.Nm
to reload its configuration and rebind its interfaces.
If
.Nm
is not running, then it starts up as normal.
.It Fl p , -persistent
.Nm
normally de-configures the
.Ar interface
and configuration when it exits.
Sometimes, this isn't desirable if, for example, you have root mounted over
NFS.
You can use this option to stop this from happening.
.It Fl r , -request Op Ar address
.Nm
normally sends a DHCP DISCOVER to find servers to offer an address.
.Nm
then requests the address used.
You can use this option to skip the DISCOVER phase and just request the
.Ar address .
The downside is if you request an
.Ar address
the DHCP server does not know about or the DHCP server is not
authoritative, it will remain silent.
In this situation, we go back to the init state and DISCOVER again.
If no
.Ar address
is given then the first address currently assigned to the
.Ar interface
is used.
.It Fl s , -inform Op Ar address Ns Op Ar /cidr
Behaves like
.Fl r , -request
as above, but sends a DHCP INFORM instead of a REQUEST.
This does not get a lease as such, just notifies the DHCP server of the
.Ar address
in use.
You should also include the optional
.Ar cidr
network number in case the address is not already configured on the interface.
.Nm
remains running and pretends it has an infinite lease.
.Nm
will not de-configure the interface when it exits.
If
.Nm
fails to contact a DHCP server then it returns a failure instead of falling
back on IPv4LL.
.It Fl t , -timeout Ar seconds
Timeout after
.Ar seconds ,
instead of the default 30.
A setting of 0
.Ar seconds
causes
.Nm
to wait forever to get a lease.
.It Fl u , -userclass Ar class
Tags the DHCP message with the userclass
.Ar class .
DHCP servers use this to give members of the class DHCP options other than the
default, without having to know things like hardware address or hostname.
.It Fl v , -vendor Ar code , Ns Ar value
Add an encapsulated vendor option.
.Ar code
should be between 1 and 254 inclusive.
To add a raw vendor string, omit
.Ar code
but keep the comma.
Examples.
.Pp
Set the vendor option 01 with an IP address.
.D1 dhcpcd \-v 01,192.168.0.2 eth0
Set the vendor option 02 with a hex code.
.D1 dhcpcd \-v 02,01:02:03:04:05 eth0
Set the vendor option 03 with an IP address as a string.
.D1 dhcpcd \-v 03,\e"192.168.0.2\e" eth0
Set un-encapsulated vendor option to hello world.
.D1 dhcpcd \-v ,"hello world" eth0
.It Fl v , -version
Display both program version and copyright information.
.Nm
then exits before doing any configuration.
.It Fl w , -waitip
Wait for an address to be assigned before forking to the background.
.It Fl x , -exit
This will signal an existing
.Nm
process running on the
.Ar interface
to de-configure the
.Ar interface
and exit.
.Nm
then waits until this process has exited.
.It Fl y , -reboot Ar seconds
Allow
.Ar reboot
seconds before moving to the discover phase if we have an old lease to use.
The default is 10 seconds.
A setting of 0 seconds causes
.Nm
to skip the reboot phase and go straight into discover.
.It Fl D , -duid
Generate an
.Li RFC 4361
compliant clientid.
This requires persistent storage and not all DHCP servers work with it so it
is not enabled by default.
.Nm
generates the DUID and stores it in
.Pa /etc/dhcpcd.duid .
This file should not be copied to other hosts.
.It Fl E , -lastlease
If
.Nm
cannot obtain a lease, then try to use the last lease acquired for the
interface.
If the
.Fl p, -persistent
option is not given then the lease is used if it hasn't expired.
.It Fl F , -fqdn Ar fqdn
Requests that the DHCP server updates DNS using FQDN instead of just a
hostname.
Valid values for
.Ar fqdn
are disable, none, ptr and both.
.Nm
itself never does any DNS updates.
.Nm
encodes the FQDN hostname as specified in
.Li RFC1035 .
.It Fl I , -clientid Ar clientid
Send the
.Ar clientid .
If the string is of the format 01:02:03 then it is encoded as hex.
For interfaces whose hardware address is longer than 8 bytes, or if the
.Ar clientid
is an empty string then
.Nm
sends a default
.Ar clientid
of the hardware family and the hardware address.
.El
.Ss Restricting behaviour
.Nm
will try to do as much as it can by default.
However, there are sometimes situations where you don't want the things to be
configured exactly how the the DHCP server wants.
Here are some options that deal with turning these bits off.
.Bl -tag -width indent
.It Fl q , -quiet
Quiet
.Nm
on the command line, only warnings and errors will be displayed.
The messages are still logged though.
.It Fl z , -allowinterfaces Ar pattern
When discovering interfaces, the interface name must match
.Ar pattern
which is a space or comma separated list of patterns passed to
.Xr fnmatch 3 .
If the same interface is matched in
.Fl Z , -denyinterfaces
then it is still denied.
.It Fl A , -noarp
Don't request or claim the address by ARP.
This also disables IPv4LL.
.It Fl B , -nobackground
Don't run in the background when we acquire a lease.
This is mainly useful for running under the control of another process, such
as a debugger or a network manager.
.It Fl C , -nohook Ar script
Don't run this hook script.
Matches full name, or prefixed with 2 numbers optionally ending with
.Pa .sh .
.Pp
So to stop
.Nm
from touching your DNS or MTU settings you would do:-
.D1 dhcpcd -C resolv.conf -C mtu eth0
.It Fl G , -nogateway
Don't set any default routes.
.It Fl H , -xidhwaddr
Use the last four bytes of the hardware address as the DHCP xid instead
of a randomly generated number.
.It Fl J , -broadcast
Instructs the DHCP server to broadcast replies back to the client.
Normally this is only set for non Ethernet interfaces,
such as FireWire and InfiniBand.
In most instances,
.Nm
will set this automatically.
.It Fl K , -nolink
Don't receive link messages for carrier status.
You should only have to use this with buggy device drivers or running
.Nm
through a network manager.
.It Fl L , -noipv4ll
Don't use IPv4LL (aka APIPA, aka Bonjour, aka ZeroConf).
.It Fl O , -nooption Ar option
Don't request the specified option.
If no option given, then don't request any options other than those to
configure the interface and routing.
.It Fl Q , -require Ar option
Requires the
.Ar option
to be present in all DHCP messages, otherwise the message is ignored.
To enforce that
.Nm
only responds to DHCP servers and not BOOTP servers, you can
.Fl Q
.Ar dhcp_message_type .
.It Fl S, -static Ar value
Configures a static
.Ar value .
If you set
.Ic ip_address
then
.Nm
will not attempt to obtain a lease and just use the value for the address with
an infinite lease time.
.Pp
Here is an example which configures a static address, routes and dns.
.D1 dhcpcd -S ip_address=192.168.0.10/24 \e
.D1 -S routers=192.168.0.1 \e
.D1 -S domain_name_servers=192.168.0.1 \e
.D1 eth0
.It Fl T, -test
On receipt of DHCP messages just call
.Pa /libexec/dhcpcd-run-hooks
with the reason of TEST which echos the DHCP variables found in the message
to the console.
The interface configuration isn't touched and neither are any configuration
files.
To test INFORM the interface needs to be configured with the desired address
before starting
.Nm .
.It Fl U, -dumplease Ar interface
Dumps the last lease for the
.Ar interface
to stdout.
.Ar interface
could also be a path to a DHCP wire formatted file.
.It Fl V, -variables
Display a list of option codes and the associated variable for use in
.Xr dhcpcd-run-hooks 8 .
Variables are prefixed with new_ and old_ unless the option number is -.
Variables without an option are part of the DHCP message and cannot be
directly requested.
.It Fl W, -whitelist Ar address Ns Op /cidr
Only accept packets from
.Ar address Ns Op /cidr .
.Fl X, -blacklist
is ignored if
.Fl W, -whitelist
is set.
.It Fl X, -blacklist Ar address Ns Op Ar /cidr
Ignore all packets from
.Ar address Ns Op Ar /cidr .
.It Fl Z , -denyinterfaces Ar pattern
When discovering interfaces, the interface name must not match
.Ar pattern
which is a space or comma separated list of patterns passed to
.Xr fnmatch 3 .
.El
.Sh 3RDPARTY LINK MANAGEMENT
Some interfaces require configuration by 3rd parties, such as PPP or VPN.
When an interface configuration in
.Nm
is marked as STATIC or INFORM without an address then
.Nm
will monitor the interface until an address is added or removed from it and
act accordingly.
For point to point interfaces (like PPP), a default route to its
destination is automatically added to the configuration.
If the point to point interface if configured for INFORM, then
.Nm
unicasts INFORM to the destination, otherwise it defaults to STATIC.
.Sh NOTES
.Nm
requires a Berkley Packet Filter, or BPF device on BSD based systems and a
Linux Socket Filter, or LPF device on Linux based systems.
.Sh FILES
.Bl -ohang
.It Pa /etc/dhcpcd.conf
Configuration file for dhcpcd.
If you always use the same options, put them here.
.It Pa /etc/dhcpcd.duid
Text file that holds the DUID used to identify the host.
.It Pa /libexec/dhcpcd-run-hooks
Bourne shell script that is run to configure or de-configure an interface.
.It Pa /libexec/dhcpcd-hooks
A directory containing bourne shell scripts that are run by the above script.
Each script can be disabled by using the
.Fl C , -nohook
option described above.
.It Pa /var/db/dhcpcd\- Ns Ar interface Ns .lease
The actual DHCP message send by the server. We use this when reading the last
lease and use the files mtime as when it was issued.
.It Pa /var/run/dhcpcd.pid
Stores the PID of
.Nm
running on all interfaces.
.It Pa /var/run/dhcpcd\- Ns Ar interface Ns .pid
Stores the PID of
.Nm
running on the
.Ar interface .
.El
.Sh SEE ALSO
.Xr dhcpcd.conf 5 ,
.Xr dhcpcd-run-hooks 8 ,
.Xr resolv.conf 5 ,
.Xr resolvconf 8 ,
.Xr if_nametoindex 3 ,
.Xr fnmatch 3
.Sh STANDARDS
RFC 951, RFC 1534, RFC 2131, RFC 2132, RFC 2855, RFC 3004, RFC 3361, RFC 3396,
RFC 3397, RFC 3442, RFC 3927, RFC 4361, RFC 4390, RFC 4702.
.Sh AUTHORS
.An Roy Marples Aq roy@marples.name
.Sh BUGS
Please report them to http://roy.marples.name/projects/dhcpcd