RTCWake does not respect Epoch time: The Ultimate Guide to Overcoming this Annoying Issue

Are you tired of dealing with RTCWake’s disregard for Epoch time? You’re not alone! Many developers and system administrators have struggled with this frustrating issue, only to find themselves scratching their heads in confusion. But fear not, dear reader, for we’re about to embark on a journey to solve this problem once and for all.

What is RTCWake and Epoch time?

Before we dive into the nitty-gritty, let’s take a step back and understand what we’re dealing with. RTCWake is a Linux kernel module that allows systems to wake up from sleep or hibernation at a specific time.Epoch time, on the other hand, is a way of representing time as a single number, measured in seconds since January 1, 1970, 00:00:00 (UTC).

The Problem: RTCWake Ignores Epoch time

So, why does RTCWake refuse to respect Epoch time? The issue lies in how RTCWake interprets the time argument passed to it. Instead of using the Epoch time format, RTCWake expects the time to be in seconds since the system’s BIOS clock, which can lead to inconsistencies and unexpected behavior.

This might not seem like a big deal, but trust us, it can cause a world of pain when trying to schedule tasks or automate system wake-ups. But don’t worry, we’ve got a solution for you!

Solution 1: Using the `date` Command to Convert Epoch time

One way to overcome this limitation is to use the `date` command to convert the Epoch time to a format that RTCWake can understand. Here’s an example:

sudo rtcwake -m no -s $(date -d "@$(echo $EPOCH_TIME)" +%s) -t $(date -d "@$(echo $EPOCH_TIME)" +%s)

In this command:

• `$EPOCH_TIME` is the Epoch time you want to wake the system up at.
• `date -d “@$(echo $EPOCH_TIME)” +%s` converts the Epoch time to seconds since the system’s BIOS clock.
• `rtcwake -m no -s` sets the wake-up time to the converted value.
• `-t` specifies the time in seconds since the system’s BIOS clock.

Solution 2: Using a Script to Handle the Conversion

If you need to perform this conversion frequently or as part of a larger automation script, you can create a dedicated script to handle the Epoch time conversion.

#!/bin/bash

EPOCH_TIME=$1

BIOS_TIME=$(date -d "@$EPOCH_TIME" +%s)

sudo rtcwake -m no -s $BIOS_TIME -t $BIOS_TIME

Save this script to a file (e.g., `rtcwake_epoch.sh`), make it executable with `chmod +x rtcwake_epoch.sh`, and then run it with the Epoch time as an argument:

./rtcwake_epoch.sh 1643723400

Solution 3: Patching the RTCWake Source Code

If you’re feeling adventurous and want to tackle the problem at its roots, you can patch the RTCWake source code to support Epoch time directly.

First, you’ll need to download the RTCWake source code and apply the following patch:

diff -Naur rtcwake.c.orig rtcwake.c
--- rtcwake.c.orig  2019-03-27 11:35:24.000000000 +0200
+++ rtcwake.c   2023-02-15 14:30:29.000000000 +0200
@@ -143,7 +143,7 @@
     if (strcmp(argv[argc-1], "-t") == 0) {
         time_t t = atol(argv[argc-2]);
-        time_t now = time(NULL);
+        time_t now = (time_t)epoch_time;
         if (t < now)
             t += 24*60*60; /* add 24 hours if time is in the past */
         rtcwake_set_time(t);

Then, recompile the patched source code and install the updated RTCWake module.

Conclusion

RTCWake’s disregard for Epoch time might seem like a minor issue, but it can cause significant problems when scheduling tasks or automating system wake-ups. By using one of the solutions outlined in this article, you’ll be able to overcome this limitation and achieve the precision and reliability you need.

Remember, when working with RTCWake and Epoch time, it’s essential to understand the underlying mechanics and take the necessary steps to ensure accurate conversions. With the right tools and know-how, you’ll be able to tame the beast and make RTCWake respect Epoch time once and for all!

Solution	Description	Complexity
Using the `date` Command	Converts Epoch time to seconds since the system’s BIOS clock using the `date` command.	Low
Using a Script	Creates a dedicated script to handle the Epoch time conversion and execute the `rtcwake` command.	Medium
Patching the RTCWake Source Code	Modifies the RTCWake source code to support Epoch time directly.	High

Which solution will you choose? Remember, the key to success lies in understanding the underlying mechanics and taking the necessary steps to ensure accurate conversions.

Frequently Asked Questions

Q: What is the purpose of RTCWake?

A: RTCWake is a Linux kernel module that allows systems to wake up from sleep or hibernation at a specific time.

Q: What is Epoch time?

A: Epoch time is a way of representing time as a single number, measured in seconds since January 1, 1970, 00:00:00 (UTC).

Q: Why does RTCWake not respect Epoch time?

A: RTCWake expects the time argument to be in seconds since the system’s BIOS clock, not in Epoch time format.

Q: Can I use RTCWake with Epoch time without converting it?

A: No, you cannot use RTCWake with Epoch time without converting it to seconds since the system’s BIOS clock.

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