4 The udhcp client negotiates a lease with the DHCP server and notifies
5 a set of scripts when a leases is obtained or lost.
11 The command line options for the udhcp client are:
13 -c, --clientid=CLIENTID Client identifier
14 -H, --hostname=HOSTNAME Client hostname
16 -f, --foreground Do not fork after getting lease
17 -b, --background Fork to background if lease cannot be
18 immediately negotiated.
19 -i, --interface=INTERFACE Interface to use (default: eth0)
20 -n, --now Exit with failure if lease cannot be
21 immediately negotiated.
22 -p, --pidfile=file Store process ID of daemon in file
23 -q, --quit Quit after obtaining lease
24 -r, --request=IP IP address to request (default: none)
25 -s, --script=file Run file at dhcp events (default:
26 /usr/share/udhcpc/default.script)
27 -v, --version Display version
30 If the requested IP address cannot be obtained, the client accepts the
31 address that the server offers.
37 When an event occurs, udhcpc calls the action script. udhcpc never does
38 any configuration of the network interface itself, but instead relies on
39 a set of scripts. The script by default is
40 /usr/share/udhcpc/default.script but this can be changed via the command
41 line arguments. The three possible arguments to the script are:
43 deconfig: This argument is used when udhcpc starts, and
44 when a leases is lost. The script must put the interface in an
45 up, but deconfigured state, ie: ifconfig $interface 0.0.0.0.
47 bound: This argument is used when udhcpc moves from an
48 unbound, to a bound state. All of the paramaters are set in
49 enviromental variables, The script should configure the interface,
50 and set any other relavent parameters (default gateway, dns server,
53 renew: This argument is used when a DHCP lease is renewed. All of
54 the paramaters are set in enviromental variables. This argument is
55 used when the interface is already configured, so the IP address,
56 will not change, however, the other DHCP paramaters, such as the
57 default gateway, subnet mask, and dns server may change.
59 nak: This argument is used with udhcpc receives a NAK message.
60 The script with the deconfig argument will be called directly
61 afterwards, so no changes to the network interface are neccessary.
62 This hook is provided for purely informational purposes (the
63 message option may contain a reason for the NAK).
65 The paramaters for enviromental variables are as follows:
67 $HOME - The set $HOME env or "/"
68 $PATH - the set $PATH env or "/bin:/usr/bin:/sbin:/usr/sbin"
69 $1 - What action the script should perform
70 interface - The interface this was obtained on
72 siaddr - The bootp next server option
73 sname - The bootp server name option
74 boot_file - The bootp boot file option
75 subnet - The assigend subnet mask
76 timezone - Offset in seconds from UTC
77 router - A list of routers
78 timesvr - A list of time servers
79 namesvr - A list of IEN 116 name servers
80 dns - A list of DNS server
81 logsvr - A list of MIT-LCS UDP log servers
82 cookiesvr - A list of RFC 865 cookie servers
83 lprsvr - A list of LPR servers
84 hostname - The assigned hostname
85 bootsize - The length in 512 octect blocks of the bootfile
86 domain - The domain name of the network
87 swapsvr - The IP address of the client's swap server
88 rootpath - The path name of the client's root disk
89 ipttl - The TTL to use for this network
90 mtu - The MTU to use for this network
91 broadcast - The broadcast address for this network
92 ntpsrv - A list of NTP servers
93 wins - A list of WINS servers
94 lease - The lease time, in seconds
95 dhcptype - DHCP message type (safely ignored)
96 serverid - The IP of the server
97 message - Reason for a DHCPNAK
98 tftp - The TFTP server name
99 bootfile - The bootfile name
101 additional options are easily added in options.c.
104 note on udhcpc's random seed
105 ---------------------------
107 udhcpc will seed its random number generator (used for generating xid's)
108 by reading /dev/urandom. If you have a lot of embedded systems on the same
109 network, with no entropy, you can either seed /dev/urandom by a method of
110 your own, or doing the following on startup:
112 ifconfig eth0 > /dev/urandom
114 in order to seed /dev/urandom with some data (mac address) unique to your
115 system. If reading /dev/urandom fails, udhcpc will fall back to its old
116 behavior of seeding with time(0).
119 signals accepted by udhcpc
120 -------------------------
122 udhcpc also responds to SIGUSR1 and SIGUSR2. SIGUSR1 will force a renew state,
123 and SIGUSR2 will force a release of the current lease, and cause udhcpc to
124 go into an inactive state (until it is killed, or receives a SIGUSR1). You do
125 not need to sleep between sending signals, as signals received are processed
126 sequencially in the order they are received.
132 options.c contains a set of dhcp options for the client:
134 name[10]: The name of the option as it will appear in scripts
136 flags: The type of option, as well as if it will be requested
137 by the client (OPTION_REQ)
139 code: The DHCP code for this option