1 udhcp server/client package readme
2 -------------------------
4 The udhcp server/client package is primarily geared towards embedded
5 systems. It does however, strive to be fully functional, and RFC
11 The only command line argument to udhcpd is an optional specifed
12 config file. If no config file is specified, udhcpd uses the default
13 config file, /etc/udhcpd.conf. Ex:
15 udhcpd /etc/udhcpd.eth1.conf
17 The udhcp server employs a number of simple config files:
22 The udhcpd.leases behavior is designed for an embedded system. The
23 file is written either every auto_time seconds, or when a SIGUSR1
24 is received (the auto_time timer restarts if a SIGUSR1 is received).
25 If you send a SIGTERM to udhcpd directly after a SIGUSR1, udhcpd will
26 finish writing the leases file and wait for the aftermentioned script
27 to be executed and finish before quiting, so you do not need to sleep
28 between sending signals. When the file is written, a script can be
29 optionally called to commit the file to flash. Lease times are stored
30 in the file by time remaining in lease (for systems without clock
31 that works when there is no power), or by the absolute time that it
32 expires in seconds from epoch. In the remainig format, expired leases
33 are stored as zero. The file is of the format:
44 example: hexdump udhcpd.leases
46 0000000 1000 c95a 27d9 0000 0000 0000 0000 0000
47 0000010 a8c0 150a 0d00 2d29 5000 23fc 8566 0000
48 0000020 0000 0000 0000 0000 a8c0 140a 0d00 4e29
55 The format is fairly simple, there is a sample file with all the
56 available options and comments describing them in samples/udhcpd.conf
62 The udhcp client negotiates a lease with the DHCP server and notifies
63 a set of scripts when a leases is obtained or lost. The command line
64 options for the udhcp client are:
66 -c, --clientid=CLIENTID Client identifier
67 -H, --hostname=HOSTNAME Client hostname
69 -f, --foreground Do not fork after getting lease
70 -b, --background Fork to background if lease cannot be
71 immediately negotiated.
72 -i, --interface=INTERFACE Interface to use (default: eth0)
73 -n, --now Exit with failure if lease cannot be
74 immediately negotiated.
75 -p, --pidfile=file Store process ID of daemon in file
76 -q, --quit Quit after obtaining lease
77 -r, --request=IP IP address to request (default: none)
78 -s, --script=file Run file at dhcp events (default:
79 /usr/share/udhcpc/default.script)
80 -v, --version Display version
82 If the requested IP address cannot be obtained, the client accepts the
83 address that the server offers.
85 When an event occurs, udhcpc calls the action script. The script by
86 default is /usr/share/udhcpc/default.script but this can be changed via
87 the command line arguments. The three possible arguments to the script
90 deconfig: This argument is used when udhcpc starts, and
91 when a leases is lost. The script should put the interface in an
92 up, but deconfigured state, ie: ifconfig $interface 0.0.0.0.
94 bound: This argument is used when udhcpc moves from an
95 unbound, to a bound state. All of the paramaters are set in
96 enviromental variables, The script should configure the interface,
97 and set any other relavent parameters (default gateway, dns server,
100 renew: This argument is used when a DHCP lease is renewed. All of
101 the paramaters are set in enviromental variables. This argument is
102 used when the interface is already configured, so the IP address,
103 will not change, however, the other DHCP paramaters, such as the
104 default gateway, subnet mask, and dns server may change.
106 nak: This argument is used with udhcpc receives a NAK message.
107 The script with the deconfig argument will be called directly
108 afterwards, so no changes to the network interface are neccessary.
109 This hook is provided for purely informational purposes (the
110 message option may contain a reason for the NAK).
112 The paramaters for enviromental variables are as follows:
114 $HOME - The set $HOME env or "/"
115 $PATH - the set $PATH env or "/bin:/usr/bin:/sbin:/usr/sbin"
116 $1 - What action the script should perform
117 interface - The interface this was obtained on
119 siaddr - The bootp next server option
120 sname - The bootp server name option
121 boot_file - The bootp boot file option
122 subnet - The assigend subnet mask
123 timezone - Offset in seconds from UTC
124 router - A list of routers
125 timesvr - A list of time servers
126 namesvr - A list of IEN 116 name servers
127 dns - A list of DNS server
128 logsvr - A list of MIT-LCS UDP log servers
129 cookiesvr - A list of RFC 865 cookie servers
130 lprsvr - A list of LPR servers
131 hostname - The assigned hostname
132 bootsize - The length in 512 octect blocks of the bootfile
133 domain - The domain name of the network
134 swapsvr - The IP address of the client's swap server
135 rootpath - The path name of the client's root disk
136 ipttl - The TTL to use for this network
137 mtu - The MTU to use for this network
138 broadcast - The broadcast address for this network
139 ntpsrv - A list of NTP servers
140 wins - A list of WINS servers
141 lease - The lease time, in seconds
142 dhcptype - DHCP message type (safely ignored)
143 serverid - The IP of the server
144 message - Reason for a DHCPNAK
145 tftp - The TFTP server name
146 bootfile - The bootfile name
148 additional options are easily added in options.c.
150 udhcpc also responds to SIGUSR1 and SIGUSR2. SIGUSR1 will force a renew state,
151 and SIGUSR2 will force a release of the current lease, and cause udhcpc to
152 go into an inactive state (until it is killed, or receives a SIGUSR1). You do
153 not need to sleep between sending signals, as signals received are processed
154 sequencially in the order they are received.
161 The Makefile contains three of the compile time options:
163 DEBUG: If DEBUG is defined, udhcpd will output extra debugging
164 output, compile with -g, and not fork to the background when run.
165 SYSLOG: If SYSLOG is defined, udhcpd will log all its messages
166 syslog, otherwise, it will attempt to log them to stdout.
168 COMBINED_BINARY: If COMBINED_BINARY is define, one binary, udhcpd,
169 is created. If called as udhcpd, the dhcp server will be started.
170 If called as udhcpc, the dhcp client will be started.
172 dhcpd.h contains the other two compile time options:
174 LEASE_TIME: The default lease time if not specified in the config
177 DHCPD_CONFIG_FILE: The defualt config file to use.
179 options.c contains a set of dhcp options for the client:
181 name[10]: The name of the option as it will appear in scripts
183 flags: The type of option, as well as if it will be requested
184 by the client (OPTION_REQ)
186 code: The DHCP code for this option
190 udhcp is now a drop-in component for busybox (http://busybox.net).
191 To update busybox to the latest revision, simply do a:
193 cp *.[ch] README AUTHORS COPYING ChangeLog TODO \
194 <busybox_source>/networking/udhcp
196 The only two files udhcp does not provide are config.in and
197 Makefile.in, so these may need to be updated from time to time.