BOOTPTAB(5)

📦
version 2.4.3 · 2 versions
, in debian bookworm, debian trixie, ubuntu jammy, ubuntu noble, ubuntu questing, ubuntu resolute, ubuntu stonking

💖 bootptab(5) — the tea on your BOOTP server's little black book 💖

okay so bestie, pull up a chair — this is the manual page for bootptab, and it comes to you straight from Carnegie Mellon University 🎓✨. It's giving ✨ancient internet lore✨ but fr fr it still slaps.

🌸 NAME 🌸

bootptab — the Internet Bootstrap Protocol server database. Basically the config file where bootpd keeps everyone's info. 🫶

🦋 DESCRIPTION 🦋

So the bootptab file is the configuration database file for bootpd, the Internet Bootstrap Protocol server. Its format is similar to that of termcap(5), where you use two-character, case-sensitive tag symbols to represent host parameters. No cap, case matters. 👑

These parameter declarations get separated by colons (:), and the general format goes like this:

hostname:tg=value... :tg=value... :tg=value. ...

where hostname is the actual name of a bootp client (or a "dummy entry"), and tg is a two-character tag symbol. 💅

Dummy entries have an invalid hostname — specifically one with a . as the first character — and they exist to provide default values that other entries can borrow via the tc=.dummy-entry mechanism. Cute, right? It's giving ✨template energy✨.

Most tags must be followed by an equals-sign and a value, like above. Some may also show up in a boolean form with no value at all, i.e. :tg:. 🍓

Here are the currently recognized tags, and yes, we're doing all of them, no skipping:

  • bf — Bootfile
  • bs — Bootfile size in 512-octet blocks
  • cs — Cookie server address list
  • df — Merit dump file
  • dl — DHCP lease time in seconds
  • dn — Domain name
  • ds — Domain name server address list
  • ef — Extension file
  • ex — York ex option (huh?)
  • 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
  • ms — Message size
  • 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's also a generic tag, Tn, where n is an RFC1084 vendor field tag number. Which means — and this is the slay part — you can 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. She's automatic, she's efficient, she's iconic. 👑

🌈 IP address tags, bestie 🌈

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, which causes 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.) 🙈

🎀 ht and ha, the hardware besties 🎀

The ht tag specifies the hardware type code as either an unsigned decimal, octal, or hexadecimal integer, or one of these symbolic names:

  • ethernet or ether — for 10Mb Ethernet
  • ethernet3 or ether3 — for 3Mb experimental Ethernet
  • ieee802, tr, or token-ring — for IEEE 802 networks
  • pronet — for Proteon ProNET Token Ring
  • chaos, arcnet, or ax.25 — for Chaos, ARCNET, and AX.25 Amateur Radio networks, respectively

The ha tag takes a hardware address which may be specified as a host name or in numeric form. Heads up: the numeric form must be specified in hexadecimal; optional periods and/or a leading 0x may be included for readability. 🌸

Important, bestie: the ha tag must be preceded by the ht tag (either explicitly or implicitly; see tc below). No ht, no ha, periodt.

If the hardware address is not specified and the type is specified as either "ethernet" or "ieee802", then bootpd will try to determine the hardware address using ether_hton(3). She'll figure it out herself, ngl. 💅

🦋 Bootfile logic (the way that it works) 🦋

The hostname, home directory, and bootfile are ASCII strings which may be optionally surrounded by double quotes ("). The client's request and the values of the hd and bf symbols determine how the server fills in the bootfile field of the bootp reply packet.

  • If the client provides a file name, it is left as is. 🫶
  • Otherwise, if the bf option is specified, its value is copied into the reply packet.
  • If the hd option is specified as well, its value is prepended to the boot file copied into the reply packet.

The existence of the boot file is checked only if the bs=auto option is used (to determine the boot file size). A reply may be sent whether or not the boot file exists. Live your truth, server. ✨

💜 td, tftpd, and the chroot situation 💜

Some newer versions of tftpd(8) 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 example, if the real absolute path to your BOOTP client bootfile is /tftpboot/bootfiles/bootimage, and tftpd uses /tftpboot as its "secure" directory, then specify the following in bootptab:

:td=/tftpboot:hd=/bootfiles:bf=bootimage:

If your bootfiles are located directly in /tftpboot, use:

:td=/tftpboot:hd=/:bf=bootimage:

✨ sa, to, bs, vm, and hn ✨

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. Default behaviour, she's self-sufficient. 💅

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 its value. 🕐

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, specifying 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
  • cmu — which always forces a CMU-style reply

The hn tag is strictly a boolean tag; it does not take the usual equals-sign and value. Its presence indicates that the hostname should be sent to RFC1084 clients. bootpd attempts to send the entire hostname (including domain) 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). She'd rather send nothing than send something ugly. Periodt. 👑

🌸 tc — the table continuation icon 🌸

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. But note: bootpd allows the tc tag symbol to appear anywhere in the host entry, unlike termcap which requires it to be the last tag. Main character behaviour, honestly.

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. 💅

💀 the @ delete trick 💀

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 termcap(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 eligible to be set again through the tc mechanism. Not me deleting my own lore just to re-add it later 😭

🧚 File format rules, bestie 🧚

  • 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. No line-length gatekeeping here. 🌈
  • Tags may appear in any order, with the following exceptions:
    • the hostname must be the very first field in an entry
    • the hardware type must precede the hardware address
Those two exceptions are non-negotiable, bestie. Hostname first, hardware type before hardware address. That's the vibe check. 💅

⭐ the example, and yes it's a whole moment ⭐

An example /etc/bootptab file follows:

# Sample bootptab file (domain=andrew.cmu.edu)

.default:\
     :hd=/usr/boot:bf=null:\
     :ds=netserver, lancaster:\
     :ns=pcs2, pcs1:\
     :ts=pcs2, pcs1:\
     :sm=255.255.255.0:\
     :gw=gw.cs.cmu.edu:\
     :hn:to=-18000:

carnegie:ht=6:ha=7FF8100000AF:tc=.default:
baldwin:ht=1:ha=0800200159C3:tc=.default:
wylie:ht=1:ha=00DD00CADF00:tc=.default:
arnold:ht=1:ha=0800200102AD:tc=.default:
bairdford:ht=1:ha=08002B02A2F9:tc=.default:
bakerstown:ht=1:ha=08002B0287C8:tc=.default:

# Special domain name server and option tags for next host
butlerjct:ha=08002001560D:ds=128.2.13.42:\
     :T37=0x12345927AD3BCF:\
     :T99="Special ASCII string":\
     :tc=.default:

gastonville:ht=6:ha=7FFF81000A47:tc=.default:
hahntown:ht=6:ha=7FFF81000434:tc=.default:
hickman:ht=6:ha=7FFF810001BA:tc=.default:
lowber:ht=1:ha=00DD00CAF000:tc=.default:
mtoliver:ht=1:ha=00DD00FE1600:tc=.default:

Look at .default doing all the heavy lifting and every other host just saying tc=.default — that's ✨delegation✨ and it ate. 🔥

🎀 FILES 🎀

  • /etc/bootptab — The definition file

💜 SEE ALSO 💜

okay that's the whole page bestie, you're basically a BOOTP server admin now 🫶✨

This lil icon of a manual page comes from the 4.3 Berkeley Distribution, dated 12 November 1995 — vintage, nostalgic, and still serving looks. 💅🌸 No cap.

📦 where this page comes from