XRINGD(8)

💖 XRINGD — the Linux extended modem ring server 💖

okay bestie, sit down, hydrate, because we're about to talk about xringd, section 8 of the System Manager's Manual, and it's honestly giving iconic vintage Unix energy. It's the Linux extended Ring server and it's about to make your landline do tricks. 🎀

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✨ SYNOPSIS ✨

xringd [ options ] [ modem_device_file ]

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🌸 DESCRIPTION 🌸

So here's the tea: xringd is the Linux extended Ring server, and what it does is listen on a modem device for specific ring-delay patterns — we call those sequences — and each sequence, once it's been fully recognised, runs a command you picked out (subject to the usual unix permissions, obviously, we're not feral). And the delays? They're not single numbers, they're delay ranges. Slay.

Your sequences and your commands get read from a configuration file. And here's the best part: xringd does not disturb your other modem programs, not even your getty. It literally coexists with them, it's so well-behaved. 😌 xringd probes (asynchronously, no blocking, no drama) for the actual RING signal on the serial line.

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💅 OPTIONS 💅

• -a command_on_each_ring — run this command on every single ring. Use it to replace your boring phone ring, because your phone deserves main character energy. 🔥
• -c config_file — use an alternate configuration file. The default is /etc/xringd.conf.
• -d — run in debug mode (no daemon — logging = 100). xringd does not run as a daemon and produces log messages on standard error.
• -h | -? — see a mini usage info. short king behavior, we love it. 🫶
• -i msecs-ignored — if consecutive rings have a time (in msec) distance less than this one, they're taken as one. This exists for countries where a ring creates two sounds and modems that subsequently cause two changes on the serial RI line. Use this option to make two near RIs look as one to xringd. A value of 100-800 will most likely be the most appropriate.
• -l loglevel — logging level. Default=1. Use 10+ for more info. When running as daemon you can use -l 10 or 100 to get debug messages via syslog(LOG_DEBUG, ...). 0 means NO logging at all. (yes, zero, silence, mute, nothing, enjoy the quiet 🍓)
• -m modem_device_file — the modem device file (can also be given as the final argument).
• -e — disables ECHO on modem device upon opening. This will avoid echo races reported with some modems. 🙈
• -n — performs only a syntax check of its configuration file. It implies -d. Try this first when you write a new configuration file. xringd does not become a daemon and produces log messages on standard error.
• -t init_time — after a reset (or the first time it is run), the time (in seconds) to wait until rings are accepted. Default: 15

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🦋 CONFIGURATION FILE 🦋

The configuration file consists of lines of the following format:

R secs[-secs] [ R secs[-secs] ] ... : command

Each line is related to a sequence (pattern) that can be potentially matched. The command at the end gets executed if the sequence was fully matched. A full match is found if the delays between the rings are within the delay ranges given in the configuration line of a sequence. A full match will also reset the state machine. It will start accepting new rings as when run the first time. R means ring and it should always be the first symbol in a sequence. periodt.

Comment lines start with a # symbol at the beginning of the line. Empty lines are ignored.

👀 Note that command line options can also be included in the config file. A line should start with the - of an option. See example below. Options -c and -n are ignored in the config file. Options in the configuration file take precedence over the ones in the command line.

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🌈 EXAMPLE CONFIGURATION 🌈

# xringd configuration file -- sample
#
-a /usr/local/audio/bin/play /usr/local/lib/sounds/ring.au
-l 100
#
# 2 rings 10-16 sec apart followed by 30 secs silence
R 10-16 R 30 : /etc/ppp/ppp.start office1
# 3 rings 10-20 sec apart followed by 20 secs silence
R 10-20 R 10-20 R 20 : /etc/ppp/ppp.start office2
# 2 nearish rings then 1 ring after 20-26 secs, silence for 30 secs
R 1-5 R 20-26 R 30 : /usr/local/bin/turn-heater on

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🎀 FILES 🎀

• /etc/xringd.conf — the default configuration file.
• /dev/modem — the default modem device used.

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⭐ SIGNALS ⭐

The following signals have the specified effect when sent to the xringd process.

• SIGINT, SIGTERM — clean exit the server. bye bestie 👋
• SIGUSR1 — "simulates" a RING as if it came from the modem.
• SIGHUP — restart the internal machine ignoring any current state. Reread the config file. Close and reopen the modem device. If a syntax error is found in a line all the following lines are ignored. So when you restart, make sure you look at the log for any reported errors. A better way is to always "parse" your config file with xringd -n to check its syntax first.

💀 fr fr, always xringd -n first. Trust.

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🧚 NOTES 🧚

At the moment, xringd is device dependent on Linux kernel 1.3.48+ and serial devices that support the TIOCMIWAIT, TIOCGICOUNT ioctl(2) calls. These were added by the same author to the Linux kernel so that a process can wait on a modem DCD, RI, DSR, CTS change on a serial port and can also read a kernel count of the interrupts on each one of these 4 lines. RI was used for this program. (Other possibilities exist in using this ioctl for instrumentation projects.) Note that these ioctls are only implemented for 16xx0 uarts now (Jan96).

You have to use a proper serial cable for this to work. A cable with all pins properly connected to your modem (especially the RI line for this program!) and serial port will save you any trouble. Internal modems should normally work.

If you activate a program which uses the modem after ringd it should normally flush the input buffer. In many cases you will have a few RING strings in your serial tty buffer that will most likely confuse a dialup script (eg. chat).

The richness of the ring-delay pattern "language" is not great. However, you certainly have many possibilities. Beware of overlaps though, and always have something that will "unlock" any current sequence (eq. 4 consecutive rings that safely exit from any current state).

If someone calls in while you are on the delay phase of your "pattern" then you are obviously out of luck. 😭

Only tone dialing phones allow quick dial that can meet short timing restrictions possibly imposed by your configuration file. Make sure you use the redial button on the calling phone if there is one — you will be able to "dial" in about a second. Pulse dialers may introduce unexpected delays. If they are your only choice, use longer delays and wider delay ranges.

It was reported by a user that the "rings" you hear on the calling handset do not directly correspond to the ones actually heard on the receiving end. In the tests done with xringd in a few countries, the number of rings remained the same on calling and called set. Just leave each one of the rings you hear on the calling end to "settle" (do not break them before they finish). A delay between a ring heard on the caller set and the equivalent one on the called one was noticed but causes no problem for xringd. Feel free to send me your comments on this.

Many getty-like programs may be configured to pick up the phone on the first ring. Obviously, this will make xringd minimally useful. Make your getty to reply after 2-4 rings so that you have many possibilities open for xringd.

pppd (and probably some other programs) like to hold a tty in exclusive mode. Make sure you start xringd before such programs, otherwise it won't be allowed to open the modem device. Also, when such a program closes it may leave the line hung up. You need to restart (kill -HUP) xringd in such a case. It does not make sense to run xringd on a line which is permanently used for PPP/SLIP — such a line never "rings"!

Spurious interrupts (and thus pseudo-RINGs) may occur during modem switch on/off; run xringd after your modem is switched on.

⚠️ SECURITY VIBE CHECK ⚠️ It is highly recommended — for security reasons — to make the configuration file inaccessible (even for read) to anything but xringd. Treat it as a shadow-password-like file. It is very easy for anyone to call your number and activate a command, if they know a RING-delay sequence "password". So try not to disarm your home-alarm via it. You have been warned!

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👑 AUTHOR 👑

Angelo Haritsis (ah@doc.ic.ac.uk).

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and that's the whole page, bestie 💖 no cap, every flag, every signal, every warning, all of it. this one lives in section 8 of the System Manager's Manual — XRINGD(8), in case you need to cite it in the group chat. go forth and make your modem ring in patterns. 🌸✨🦋