141 lines
5.2 KiB
Plaintext
141 lines
5.2 KiB
Plaintext
udhcp client (udhcpc)
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--------------------
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The udhcp client negotiates a lease with the DHCP server and notifies
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a set of scripts when a leases is obtained or lost.
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command line options
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-------------------
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The command line options for the udhcp client are:
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-c, --clientid=CLIENTID Client identifier
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-H, --hostname=HOSTNAME Client hostname
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-h, Alias for -H
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-f, --foreground Do not fork after getting lease
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-b, --background Fork to background if lease cannot be
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immediately negotiated.
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-i, --interface=INTERFACE Interface to use (default: eth0)
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-n, --now Exit with failure if lease cannot be
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immediately negotiated.
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-p, --pidfile=file Store process ID of daemon in file
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-q, --quit Quit after obtaining lease
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-r, --request=IP IP address to request (default: none)
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-s, --script=file Run file at dhcp events (default:
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/usr/share/udhcpc/default.script)
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-v, --version Display version
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If the requested IP address cannot be obtained, the client accepts the
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address that the server offers.
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udhcp client scripts
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-------------------
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When an event occurs, udhcpc calls the action script. udhcpc never does
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any configuration of the network interface itself, but instead relies on
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a set of scripts. The script by default is
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/usr/share/udhcpc/default.script but this can be changed via the command
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line arguments. The three possible arguments to the script are:
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deconfig: This argument is used when udhcpc starts, and
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when a leases is lost. The script must put the interface in an
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up, but deconfigured state, ie: ifconfig $interface 0.0.0.0.
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bound: This argument is used when udhcpc moves from an
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unbound, to a bound state. All of the paramaters are set in
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enviromental variables, The script should configure the interface,
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and set any other relavent parameters (default gateway, dns server,
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etc).
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renew: This argument is used when a DHCP lease is renewed. All of
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the paramaters are set in enviromental variables. This argument is
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used when the interface is already configured, so the IP address,
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will not change, however, the other DHCP paramaters, such as the
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default gateway, subnet mask, and dns server may change.
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nak: This argument is used with udhcpc receives a NAK message.
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The script with the deconfig argument will be called directly
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afterwards, so no changes to the network interface are neccessary.
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This hook is provided for purely informational purposes (the
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message option may contain a reason for the NAK).
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The paramaters for enviromental variables are as follows:
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$HOME - The set $HOME env or "/"
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$PATH - the set $PATH env or "/bin:/usr/bin:/sbin:/usr/sbin"
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$1 - What action the script should perform
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interface - The interface this was obtained on
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ip - The obtained IP
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siaddr - The bootp next server option
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sname - The bootp server name option
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boot_file - The bootp boot file option
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subnet - The assigend subnet mask
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timezone - Offset in seconds from UTC
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router - A list of routers
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timesvr - A list of time servers
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namesvr - A list of IEN 116 name servers
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dns - A list of DNS server
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logsvr - A list of MIT-LCS UDP log servers
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cookiesvr - A list of RFC 865 cookie servers
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lprsvr - A list of LPR servers
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hostname - The assigned hostname
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bootsize - The length in 512 octect blocks of the bootfile
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domain - The domain name of the network
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swapsvr - The IP address of the client's swap server
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rootpath - The path name of the client's root disk
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ipttl - The TTL to use for this network
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mtu - The MTU to use for this network
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broadcast - The broadcast address for this network
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ntpsrv - A list of NTP servers
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wins - A list of WINS servers
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lease - The lease time, in seconds
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dhcptype - DHCP message type (safely ignored)
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serverid - The IP of the server
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message - Reason for a DHCPNAK
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tftp - The TFTP server name
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bootfile - The bootfile name
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additional options are easily added in options.c.
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note on udhcpc's random seed
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---------------------------
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udhcpc will seed its random number generator (used for generating xid's)
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by reading /dev/urandom. If you have a lot of embedded systems on the same
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network, with no entropy, you can either seed /dev/urandom by a method of
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your own, or doing the following on startup:
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ifconfig eth0 > /dev/urandom
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in order to seed /dev/urandom with some data (mac address) unique to your
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system. If reading /dev/urandom fails, udhcpc will fall back to its old
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behavior of seeding with time(0).
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signals accepted by udhcpc
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-------------------------
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udhcpc also responds to SIGUSR1 and SIGUSR2. SIGUSR1 will force a renew state,
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and SIGUSR2 will force a release of the current lease, and cause udhcpc to
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go into an inactive state (until it is killed, or receives a SIGUSR1). You do
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not need to sleep between sending signals, as signals received are processed
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sequencially in the order they are received.
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compile time options
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-------------------
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options.c contains a set of dhcp options for the client:
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name[10]: The name of the option as it will appear in scripts
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flags: The type of option, as well as if it will be requested
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by the client (OPTION_REQ)
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code: The DHCP code for this option
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