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I have "rtc" in /etc/modules but

modinfo rtc

outputs:

ERROR: modinfo: could not find module rtc

and lsmod doesn't show rtc

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What version of Ubuntu and kernel are you running. Architecture? I only have lp listed in /etc/modules on my 10.04 through 12.04 systems. – John S Gruber May 27 '12 at 5:06
What other lines are in /etc/modules? – John S Gruber May 27 '12 at 5:12

3 Answers

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The legacy real-time-clock driver rtc certainly exists:

./linux-3.2.0/drivers/char/rtc.c

but I believe it's only used in the module context as an include while building modules for specific RTC devices. For example, here's the rtc drivers available for Ubuntu's Linux kernel 3.2:

izx@i5:~/src-kernel$ ls /lib/modules/3.2.0-24-generic/kernel/drivers/rtc/
rtc-88pm860x.ko  rtc-ds1742.ko    rtc-max6900.ko   rtc-rs5c372.ko
rtc-ab3100.ko    rtc-ds3232.ko    rtc-max6902.ko   rtc-rv3029c2.ko
rtc-ab8500.ko    rtc-ds3234.ko    rtc-max8925.ko   rtc-rx8025.ko
rtc-bq32k.ko     rtc-em3027.ko    rtc-max8998.ko   rtc-rx8581.ko
rtc-bq4802.ko    rtc-fm3130.ko    rtc-mc13xxx.ko   rtc-s35390a.ko
rtc-ds1286.ko    rtc-isl12022.ko  rtc-msm6242.ko   rtc-stk17ta8.ko
rtc-ds1305.ko    rtc-isl1208.ko   rtc-pcf2123.ko   rtc-v3020.ko
rtc-ds1307.ko    rtc-m41t80.ko    rtc-pcf50633.ko  rtc-wm831x.ko
rtc-ds1374.ko    rtc-m41t93.ko    rtc-pcf8563.ko   rtc-wm8350.ko
rtc-ds1390.ko    rtc-m41t94.ko    rtc-pcf8583.ko   rtc-x1205.ko
rtc-ds1511.ko    rtc-m48t35.ko    rtc-r9701.ko
rtc-ds1553.ko    rtc-m48t59.ko    rtc-rp5c01.ko
rtc-ds1672.ko    rtc-m48t86.ko    rtc-rs5c348.ko

As Florian asked, why do you need this module? What is your platform? Are you using a specific RTC device?

/etc/modules is used to load external modules at startup -- the modules (.ko files) must first be present under /lib/modules/your-kernel-version/....; just having them in /etc/modules means nothing.

You can safely remove rtc from /etc/modules.

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I don't know why it is in /etc/modules and I don't know why if it is there it doesn't appear as loaded. Just that. – Robert May 27 '12 at 3:07
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There is no kernel module named rtc so it can't be loaded and lsmod and modinfo can't find it.

Why do you think there should be such a module? What do you want to do?

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what does the line rtc in /etc/modules mean then? – Robert May 27 '12 at 3:09
It indeed means "load the module 'rct' at startup". But if that module doesn't exist it just does nothing. Maybe that line is a leftover from an older installation where that module did exist. – Florian Diesch May 27 '12 at 3:36
I want to know if I can remove that line or to understand what it is doing there. An older installation? There hasn't been an older installation, only a few previous kernels. If it does not exist, what is /lib/modules/2.6.38-15-generic/kernel/drivers/rtc, then? – Robert May 27 '12 at 3:42
That's a folder that contains some kernel modules. – Florian Diesch May 27 '12 at 4:14
up vote 0 down vote

There are a couple of rtc drivers built statically into the Ubuntu kernel. Namely rtc_cmos and rtc_m41t80. (I have /dev/rtc and /dev/rtc0 on my 12.04 system, by the way.) rtc_cmos supports the legacy PC cmos real time clock. The other certain i2c real time clocks.

The config file for each built Ubuntu kernel is placed into /boot along with the headers and the kernel image itself so you can see how it was set up.

Built in drivers don't show up in lsmod, for example.

At one time there was a driver simply named rtc, but not now. I'd suggest that some package places that name in /etc/modules.

The Ubuntu kernel source is here.

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