bootptab - Internet Bootstrap Protocol server database
The bootptab file is the configuration database file for bootpd, the Internet Bootstrap
Protocol server. Its format is similar to that of termcap(5) in which two-character case-
sensitive tag symbols are used to represent host parameters. These parameter declarations
are separated by colons (:), with a general format of:
where hostname is the actual name of a bootp client (or a "dummy entry"), and tg is a two-
character tag symbol. Replies are returned to clients only if an entry with the client's
Ethernet or IP address exists in the booptab file. Dummy entries have an invalid hostname
(one with a "." as the first character) and are used to provide default values used by
other entries via the tc=.dummy-entry mechanism. Most tags must be followed by an equal
sign and a value as above. Some may also appear in a boolean form with no value (i.e.
:tg:). The currently recognized tags are:
bs Bootfile size in 512-octet blocks
cs Cookie server address list
df Merit dump file
dn Domain name
ds Domain name server address list
ef Extension file
gw Gateway address list
ha Host hardware address
hd Bootfile home directory
hn Send client's hostname to client
ht Host hardware type (see Assigned Numbers RFC)
im Impress server address list
ip Host IP address
lg Log server address list
lp LPR server address list
ns IEN-116 name server address list
nt NTP (time) Server (RFC 1129)
ra Reply address override
rl Resource location protocol server address list
rp Root path to mount as root
sa TFTP server address client should use
sm Host subnet mask
sw Swap server address
tc Table continuation (points to similar "template" host entry)
td TFTP root directory used by "secure" TFTP servers
to Time offset in seconds from UTC
ts Time server address list
vm Vendor magic cookie selector
yd YP (NIS) domain name
ys YP (NIS) server address
There is also a generic tag, Tn, where n is an RFC1084 vendor field tag number. Thus it
is possible to immediately take advantage of future extensions to RFC1084 without being
forced to modify bootpd first. Generic data may be represented as either a stream of
hexadecimal numbers or as a quoted string of ASCII characters. The length of the generic
data is automatically determined and inserted into the proper field(s) of the
RFC1084-style bootp reply.
The following tags take a whitespace-separated list of IP addresses: cs, ds, gw, im, lg,
lp, ns, nt, ra, rl, and ts. The ip, sa, sw, sm, and ys tags each take a single IP
address. All IP addresses are specified in standard Internet "dot" notation and may use
decimal, octal, or hexadecimal numbers (octal numbers begin with 0, hexadecimal numbers
begin with '0x' or '0X'). Any IP addresses may alternatively be specified as a hostname,
causing bootpd to lookup the IP address for that host name using gethostbyname(3). If the
ip tag is not specified, bootpd will determine the IP address using the entry name as the
host name. (Dummy entries use an invalid host name to avoid automatic IP lookup.)
The ht tag specifies the hardware type code as either an unsigned decimal, octal, or hexa-
decimal integer or one of the following symbolic names: ethernet or ether for 10Mb Ether-
net, ethernet3 or ether3 for 3Mb experimental Ethernet, ieee802, tr, or token-ring for
IEEE 802 networks, pronet for Proteon ProNET Token Ring, or chaos, arcnet, or ax.25 for
Chaos, ARCNET, and AX.25 Amateur Radio networks, respectively. The ha tag takes a hard-
ware address which may be specified as a host name or in numeric form. Note that the
numeric form must be specified in hexadecimal; optional periods and/or a leading '0x' may
be included for readability. The ha tag must be preceded by the ht tag (either explicitly
or implicitly; see tc below). If the hardware address is not specified and the type is
specified as either "ethernet" or "ieee802", then bootpd will try to determine the hard-
ware address using ether_hostton(3).
The hostname, home directory, and bootfile are ASCII strings which may be optionally sur-
rounded by double quotes ("). The client's request and the values of the hd and bf sym-
bols determine how the server fills in the bootfile field of the bootp reply packet.
If the bf option is specified, its value is copied into the reply packet. Otherwise, the
name supplied in the client request is used. If the hd option is specified, its value is
prepended to the boot file in the reply packet, otherwise the path supplied in the client
request is used. The existence of the boot file is NOT verified by bootpd because the
boot file may be on some other machine.
The bs option specified the size of the boot file. It can be written as bs=auto which
causes bootpd to determine the boot file size automatically.
Some newer versions of tftpd provide a security feature to change their root directory
using the chroot(2) system call. The td tag may be used to inform bootpd of this special
root directory used by tftpd. (One may alternatively use the bootpd "-c chdir" option.)
The hd tag is actually relative to the root directory specified by the td tag. For exam-
ple, if the real absolute path to your BOOTP client bootfile is /tftpboot/boot-
files/bootimage, and tftpd uses /tftpboot as its "secure" directory, then specify the fol-
lowing in bootptab:
If your bootfiles are located directly in /tftpboot, use:
The sa tag may be used to specify the IP address of the particular TFTP server you wish
the client to use. In the absence of this tag, bootpd will tell the client to perform
TFTP to the same machine bootpd is running on.
The time offset to may be either a signed decimal integer specifying the client's time
zone offset in seconds from UTC, or the keyword auto which uses the server's time zone
offset. Specifying the to symbol as a boolean has the same effect as specifying auto as
The bootfile size bs may be either a decimal, octal, or hexadecimal integer specifying the
size of the bootfile in 512-octet blocks, or the keyword auto which causes the server to
automatically calculate the bootfile size at each request. As with the time offset, spec-
ifying the bs symbol as a boolean has the same effect as specifying auto as its value.
The vendor magic cookie selector (the vm tag) may take one of the following keywords: auto
(indicating that vendor information is determined by the client's request), rfc1048 or
rfc1084 (which always forces an RFC1084-style reply), or cmu (which always forces a CMU-
The hn tag is strictly a boolean tag; it does not take the usual equals-sign and value.
It's presence indicates that the hostname should be sent to RFC1084 clients. Bootpd
attempts to send the entire hostname as it is specified in the configuration file; if this
will not fit into the reply packet, the name is shortened to just the host field (up to
the first period, if present) and then tried. In no case is an arbitrarily-truncated
hostname sent (if nothing reasonable will fit, nothing is sent).
Often, many host entries share common values for certain tags (such as name servers,
etc.). Rather than repeatedly specifying these tags, a full specification can be listed
for one host entry and shared by others via the tc (table continuation) mechanism. Often,
the template entry is a dummy host which doesn't actually exist and never sends bootp
requests. This feature is similar to the tc feature of termcap(5) for similar terminals.
Note that bootpd allows the tc tag symbol to appear anywhere in the host entry, unlike
termcap which requires it to be the last tag. Information explicitly specified for a host
always overrides information implied by a tc tag symbol, regardless of its location within
the entry. The value of the tc tag may be the hostname or IP address of any host entry
previously listed in the configuration file.
Sometimes it is necessary to delete a specific tag after it has been inferred via tc.
This can be done using the construction tag@ which removes the effect of tag as in term-
cap(5). For example, to completely undo an IEN-116 name server specification, use ":ns@:"
at an appropriate place in the configuration entry. After removal with @, a tag is eligi-
ble to be set again through the tc mechanism.
Blank lines and lines beginning with "#" are ignored in the configuration file. Host
entries are separated from one another by newlines; a single host entry may be extended
over multiple lines if the lines end with a backslash (\). It is also acceptable for
lines to be longer than 80 characters. Tags may appear in any order, with the following
exceptions: the hostname must be the very first field in an entry, and the hardware type
must precede the hardware address.
An example /etc/bootptab file follows:
# Sample bootptab file (domain=andrew.cmu.edu)
# Special domain name server and option tags for next host
:T99="Special ASCII string":\
DARPA Internet Request For Comments RFC951, RFC1048, RFC1084, Assigned Numbers
4.3 Berkeley Distribution October 31, 1991 BOOTPTAB(5)