iucvtty(1)

💅 iucvtty — like, the whole manual, but make it make sense

okay so real talk: this is the manual page for iucvtty(1), one of the IUCV terminal applications (that's the whole section name up top, iykyk). it's giving "remote login but make it z/VM" and honestly? iconic. let's get into it 🎀

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✨ NAME ✨

iucvtty — bestie, this thing lets people log in remotely over z/VM IUCV 🦋

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🌸 SYNOPSIS 🌸

iucvtty [-h|--help]
iucvtty [-v|--version]
iucvtty [-a|--allow-from regex] terminal_id [-- login_program
[login_options]]

like, that's the whole vibe right there. copy it exactly, don't @ me 💅

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💖 DESCRIPTION 💖

so the iucvtty application gives you full-screen terminal access to a Linux instance that's running as a z/VM guest operating system. and the way you actually get in? the iucvconn application — that's your bestie on the other end, connecting to a running iucvtty instance 💫

the terminal connection is based on the z/VM Inter-User Communication Vehicle (IUCV). and z/VM IUCV establishes a communication path between two z/VM guest virtual machines on the same z/VM instance. the absolute slay here: because z/VM IUCV is independent from TCP/IP, Linux instances with no external network can still be accessed. no network? no problem, periodt 🔥

terminal_id identifies the z/VM IUCV connection and it's basically the cousin of a port number in TCP/IP communications. it's case-sensitive and consists of up to 8 alphanumeric characters. it must be specified as a parameter in connection requests against an iucvtty instance — no terminal_id, no entry 🚪

when a connection is established, iucvtty starts a login program. and when the login program ends, iucvtty also exits — they leave together, ride or die 😭 so consider an inittab(5) entry to make sure iucvtty gets restarted and is ready for the next terminal session. that's your respawn era 🧚

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✨ OPTIONS ✨

• -h, --help — displays a short help text and then exits. tiny helpful queen 🎀
• -v, --version — displays the version number of iucvtty, then exits. quick flex, then bye 💅
• -a, --allow-from regex — limits permissions for incoming connections to z/VM user IDs that match the regular expression regex. if the ID does not match, the connection is refused — gatekept, as she should be 🚫 if this parameter is omitted, connections are permitted from any z/VM user ID (so, open door policy, be aware 👀).
• login_program — specifies the absolute path to the login program to be started when a connection is established. the default is /bin/login(1). and important: the login_program must be separated by two dashes (--) — do not forget the --, bestie, the parser is not gonna read your mind 🙈
• login_options — depending on the particular login program used, login_options specifies additional options. it's giving "the vibes depend on which program you brought" ✨

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🦋 EXAMPLES 🦋

to allow remote logins using the terminal identifier "lnxterm":

iucvtty lnxterm

to only allow users from LNXSYS01 to connect to terminal "lnxterm":

iucvtty -a LNXSYS01 lnxterm

to only allow users from LNXSYS10 through LNXSYS19 to connect to terminal "lnxterm":

iucvtty -a "LNXSYS1[0-9]" lnxterm

to use /sbin/sulogin instead of /bin/login for terminal "suterm":

iucvtty suterm -- /sbin/sulogin

an entry in /etc/inittab to facilitate user logins on terminal "lnxterm" with /bin/login could be:

t1:2345:respawn:/usr/bin/iucvtty lnxterm

an entry in /etc/inittab to facilitate user logins on terminal "suterm" with /sbin/sulogin in single user mode could be:

s1:S:respawn:/usr/bin/iucvtty suterm -- /sbin/sulogin

see how the -- shows up again? told you. main character energy for a couple of hyphens, honestly 💀

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🩺 DIAGNOSTICS 🩺

if the Linux kernel does not include kernel support for the AF_IUCV network addressing family, iucvtty exits and displays this message, and you're gonna want to read it exactly:

AF_IUCV address family is not available: Address family not supported by protocol

that's the "your kernel said no ❤️" arc. 😭

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🔐 SECURITY 🔐

🐧 Linux

the iucvtty program can be used by regular users. but — and this is a big but — depending on the particular login program, iucvtty must be started with superuser privileges for user authentication and authorization. for instance, /bin/login requires superuser privileges and, thus, regular users must use a different login program. so know what you're launching, bestie 👑

each connection attempt is logged to the authpriv syslog facility. every single one. the receipts are kept 📝

iucvtty uses pseudo-terminal (pts) devices to communicate with the login program. and for security reasons, some login programs — like /bin/login — do not permit root logins on pseudo-terminal devices (see also /etc/securetty(5)). so no, you can't just root your way through a pts, that's not the move 🙅

to permit root logins, consider using HVC terminal devices that are provided by the z/VM IUCV hypervisor console (HVC) device driver. that's the workaround, and yes, it's legendary ✨

🖥️ z/VM guest virtual machine

see the af_iucv(7) manual page for details about IUCV authorizations. go read it, it's the lore drop you need 📚

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👀 SEE ALSO 👀

iucvconn(1), login(1), pts(4), regex(7), securetty(5), af_iucv(7), hvc_iucv(9)

the whole friend group, all linked, all iconic 🌈

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okay that's the page!! 🫶 this came to you from s390-tools, dated March 2009 — yes, she's been around, she's a legacy icon, and she still slays. now go start that iucvtty and remember the -- 💜✨