IBM_HOSTS(5)

💻 IBM_HOSTS(5) — ibm_hosts, the host-database bestie 💻

Hey bestie! Welcome to IBM_HOSTS(5) from the File Formats Manual. This is all about ibm_hosts — the host database for x3270 and c3270. It's giving “little black book but make it network” and I'm obsessed. 💖

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🌸 NAME 🌸

ibm_hosts — host database for x3270 and c3270.

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✨ SYNOPSIS ✨

/usr/lib/X11/x3270/ibm_hosts

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🦋 DESCRIPTION 🦋

Okay so the ibm_hosts file is literally the info stash about IBM hosts on the network. An IBM host is a host which can communicate with a 3270 terminal emulator such as x3270 or c3270. Main character energy for real. Each line defines a name in the following format (optional fields are shown in brackets):

name type [opt:]...[luname@]hostname[:port] [actions]

Items are separated by any number of blanks and/or TAB characters. A line beginning with # is taken as a comment — and bestie, note that # anywhere else on a line does not indicate a comment. Read that again: only line-start # counts. 👀

The name field is a mnemonic used to identify the host. Short, cute, iconic.

The type field is a keyword that indicates the type of entry:

• primary — the name will be included in host-selection menus that may be displayed by a 3270 emulator.
• alias — the name will not be included in menus, but will still be accepted as valid input when a host name is required.

The hostname field is the Internet hostname or dot-notation Internet address of the host.

The hostname can include s: or p: prefixes, e.g., s:finicky (peep the x3270(1) or c3270(1) man page sfor details — yes, sfor is literally in the original, and we respect the lore 💅). It can also include an LU name, separated by an @ character, e.g., oddlu@bluehost. Finally, it can include a non-default port number, appended to the hostname with a colon : character, e.g., bluehost:97. (For compatibility with earlier versions of x3270, the port can also be separated by a slash / character.) Slash is lowkey the legacy vibe.

The optional actions field specifies actions to be taken once the connection is made and a data-entry field is defined. If the text looks like an action, e.g., PF(1), it is unmodified; otherwise it is taken as the parameter to the String() action. The actions are not intended for entering usernames and passwords; rather they provide an automated way of specifying a front-end menu option. Not a password vault, bestie — just menu automation.

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🎀 EXAMPLE 🎀

Given the following ibm_hosts file:

mvs  primary   mvs-host
tso  alias     mvs-host
mvs2 primary   mvs-host:4012
vm   primary   vtam Tab() String(3) Enter()

A 3270 emulator will display four names (mvs, mvs2, afhost and vm) on its hosts menu. (Yep, afhost is what the page says. We don't ask questions, we just report the lore. 💀) The names mvs and tso will cause connections to the host mvs-host. The name mvs2 will also cause a connection to mvs-host, but to port 4012 rather than the emulator's default port (usually 23). The name vm will cause the 3270 emulator to connect to the host vtam (presumably some sort of host-selection front-end), enter the string 3 on the second data-entry field on the screen, and send the Enter AID sequence. Automation slay.

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🍓 FILES 🍓

• /usr/lib/X11/x3270/ibm_hosts — the file itself, the moment, the icon.

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👑 SEE ALSO 👑

• x3270(1)
• c3270(1)

Go read those too, bestie — they're the supporting cast. 🫶

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💖 Cute little sign-off: this was the IBM_HOSTS(5) page, dated 22 December 2025, and yes, the version/source energy is IBM_HOSTS(5). Stay iconic! 💖