jwz: 14-Mar-2022 (Mon)

crontab(5):

Instead of the first five fields, one of eight special strings may appear:

string meaning
@reboot Run once, at startup.

Me: Hmm, I wonder if that actually works:

% crontab -l @reboot echo REBOOT

crond:

Cron Daemon Cron <root> echo REBOOT 8:46:54 AM Cron Daemon Cron <root> echo REBOOT 8:47:24 AM Cron Daemon Cron <root> echo REBOOT 8:48:35 AM Cron Daemon Cron <root> echo REBOOT 8:48:37 AM Cron Daemon Cron <root> echo REBOOT 8:48:48 AM Cron Daemon Cron <root> echo REBOOT 8:48:58 AM Cron Daemon Cron <root> echo REBOOT 8:49:59 AM Cron Daemon Cron <root> echo REBOOT 8:49:59 AM Cron Daemon Cron <root> echo REBOOT 8:49:59 AM Cron Daemon Cron <root> echo REBOOT 8:50:20 AM Cron Daemon Cron <root> echo REBOOT 8:50:31 AM Cron Daemon Cron <root> echo REBOOT 8:54:06 AM Cron Daemon Cron <root> echo REBOOT 8:54:06 AM Cron Daemon Cron <root> echo REBOOT 8:54:06 AM Cron Daemon Cron <root> echo REBOOT 8:54:06 AM Cron Daemon Cron <root> echo REBOOT 8:54:26 AM Cron Daemon Cron <root> echo REBOOT 8:54:39 AM Cron Daemon Cron <root> echo REBOOT 8:55:22 AM Cron Daemon Cron <root> echo REBOOT 8:56:11 AM Cron Daemon Cron <root> echo REBOOT 8:56:50 AM Cron Daemon Cron <root> echo REBOOT 8:57:46 AM Cron Daemon Cron <root> echo REBOOT 8:58:32 AM Cron Daemon Cron <root> echo REBOOT 8:59:16 AM Cron Daemon Cron <root> echo REBOOT 9:00:03 AM Cron Daemon Cron <root> echo REBOOT 9:00:55 AM Cron Daemon Cron <root> echo REBOOT 9:02:03 AM Cron Daemon Cron <root> echo REBOOT 9:02:42 AM Cron Daemon Cron <root> echo REBOOT 9:03:35 AM Cron Daemon Cron <root> echo REBOOT 9:04:27 AM Cron Daemon Cron <root> echo REBOOT 9:05:13 AM Cron Daemon Cron <root> echo REBOOT 9:06:05 AM Cron Daemon Cron <root> echo REBOOT 9:06:48 AM Cron Daemon Cron <root> echo REBOOT 9:07:35 AM Cron Daemon Cron <root> echo REBOOT 9:08:23 AM Cron Daemon Cron <root> echo REBOOT 9:09:07 AM Cron Daemon Cron <root> echo REBOOT 9:09:52 AM Cron Daemon Cron <root> echo REBOOT 9:10:35 AM Cron Daemon Cron <root> echo REBOOT 9:11:28 AM Cron Daemon Cron <root> echo REBOOT 9:12:20 AM Cron Daemon Cron <root> echo REBOOT 9:13:17 AM Cron Daemon Cron <root> echo REBOOT 9:14:00 AM Cron Daemon Cron <root> echo REBOOT 9:15:00 AM Cron Daemon Cron <root> echo REBOOT 9:15:49 AM Cron Daemon Cron <root> echo REBOOT 9:16:40 AM Cron Daemon Cron <root> echo REBOOT 9:17:28 AM Cron Daemon Cron <root> echo REBOOT 9:18:21 AM Cron Daemon Cron <root> echo REBOOT 9:19:08 AM Cron Daemon Cron <root> echo REBOOT 9:19:54 AM Cron Daemon Cron <root> echo REBOOT 9:20:37 AM Cron Daemon Cron <root> echo REBOOT 9:21:36 AM Cron Daemon Cron <root> echo REBOOT 9:22:32 AM Cron Daemon Cron <root> echo REBOOT 9:23:01 AM Cron Daemon Cron <root> echo REBOOT 9:23:54 AM Cron Daemon Cron <root> echo REBOOT 9:24:38 AM Cron Daemon Cron <root> echo REBOOT 9:25:18 AM Cron Daemon Cron <root> echo REBOOT 9:26:11 AM Cron Daemon Cron <root> echo REBOOT 9:27:00 AM Cron Daemon Cron <root> echo REBOOT 9:27:52 AM Cron Daemon Cron <root> echo REBOOT 9:28:43 AM Cron Daemon Cron <root> echo REBOOT 9:29:32 AM Cron Daemon Cron <root> echo REBOOT 9:30:29 AM Cron Daemon Cron <root> echo REBOOT 9:31:18 AM Cron Daemon Cron <root> echo REBOOT 9:32:18 AM Cron Daemon Cron <root> echo REBOOT 9:33:13 AM Cron Daemon Cron <root> echo REBOOT 9:33:34 AM % uptime 10:43 up 1:09, 6 users, load averages: 5.57 5.49 5.42

Update: It happened again to one of my other machines! Check this shit out! I have no idea why this machine rebooted. It was not a power failure, and system.log provides no clues. This time the cron job was "date; uptime". Several hours after this happened, it reported:

% date; uptime Wed Mar 16 09:39:03 PDT 2022 9:39 up 6:25, 3 users, load averages: 2.41 2.35 2.33

...which means it booted up at 3:14 AM. And this is the firehose of email that was generated:

Wed Mar 16 02:58:09 PDT 2022 2:58 up 28 days, 1:33, 2 users, load averages: 19.27 6.28 3.99 Wed Mar 16 02:58:09 PDT 2022 2:58 up 28 days, 1:33, 2 users, load averages: 19.27 6.28 3.99 Wed Mar 16 02:59:43 PDT 2022 2:59 up 28 days, 1:34, 2 users, load averages: 129.46 54.89 23.51 Wed Mar 16 03:01:53 PDT 2022 3:01 up 28 days, 1:36, 2 users, load averages: 153.98 98.37 45.77 Wed Mar 16 03:02:58 PDT 2022 3:02 up 28 days, 1:37, 2 users, load averages: 98.98 93.57 47.87 Wed Mar 16 03:03:50 PDT 2022 3:03 up 28 days, 1:38, 2 users, load averages: 154.26 108.06 56.02 Wed Mar 16 03:04:02 PDT 2022 3:04 up 28 days, 1:38, 2 users, load averages: 189.32 118.11 60.52 Wed Mar 16 03:04:15 PDT 2022 3:04 up 28 days, 1:39, 2 users, load averages: 204.15 123.68 63.17 Wed Mar 16 03:04:20 PDT 2022 3:04 up 28 days, 1:39, 2 users, load averages: 202.53 124.68 63.88 Wed Mar 16 03:04:32 PDT 2022 3:04 up 28 days, 1:39, 2 users, load averages: 195.38 125.66 64.93 Wed Mar 16 03:04:40 PDT 2022 3:04 up 28 days, 1:39, 2 users, load averages: 186.21 126.01 65.76 Wed Mar 16 03:04:52 PDT 2022 3:04 up 28 days, 1:39, 2 users, load averages: 158.03 121.96 65.03 Wed Mar 16 03:05:02 PDT 2022 3:05 up 28 days, 1:39, 2 users, load averages: 138.29 118.89 64.60 Wed Mar 16 03:05:12 PDT 2022 3:05 up 28 days, 1:40, 2 users, load averages: 117.26 115.02 63.87 Wed Mar 16 03:05:56 PDT 2022 3:05 up 28 days, 1:40, 2 users, load averages: 137.33 120.70 68.60 Wed Mar 16 03:06:05 PDT 2022 3:06 up 28 days, 1:41, 2 users, load averages: 152.45 124.53 70.57 Wed Mar 16 03:06:20 PDT 2022 3:06 up 28 days, 1:41, 2 users, load averages: 165.60 128.75 73.02 Wed Mar 16 03:06:27 PDT 2022 3:06 up 28 days, 1:41, 2 users, load averages: 163.87 129.00 73.43 Wed Mar 16 03:06:36 PDT 2022 3:06 up 28 days, 1:41, 2 users, load averages: 149.93 127.09 73.40 Wed Mar 16 03:06:36 PDT 2022 3:06 up 28 days, 1:41, 2 users, load averages: 149.93 127.09 73.40 Wed Mar 16 03:06:56 PDT 2022 3:06 up 28 days, 1:41, 2 users, load averages: 129.17 123.51 73.34 Wed Mar 16 03:07:56 PDT 2022 3:07 up 28 days, 1:42, 2 users, load averages: 137.78 125.27 77.33 Wed Mar 16 03:08:24 PDT 2022 3:08 up 28 days, 1:43, 2 users, load averages: 165.72 133.16 81.59 Wed Mar 16 03:08:44 PDT 2022 3:08 up 28 days, 1:43, 2 users, load averages: 153.51 132.50 82.82 Wed Mar 16 03:10:08 PDT 2022 3:10 up 28 days, 1:45, 2 users, load averages: 134.03 132.19 87.21 Wed Mar 16 03:10:08 PDT 2022 3:10 up 28 days, 1:45, 2 users, load averages: 134.03 132.19 87.21 Wed Mar 16 03:10:08 PDT 2022 3:10 up 28 days, 1:45, 2 users, load averages: 134.03 132.19 87.21 Wed Mar 16 03:10:38 PDT 2022 3:10 up 28 days, 1:45, 2 users, load averages: 103.43 125.11 86.21 Wed Mar 16 03:10:48 PDT 2022 3:10 up 28 days, 1:45, 1 user, load averages: 87.91 121.07 85.23 Wed Mar 16 03:11:16 PDT 2022 3:11 up 28 days, 1:46, 1 user, load averages: 64.13 112.71 83.25 Wed Mar 16 03:11:37 PDT 2022 3:11 up 28 days, 1:46, 1 user, load averages: 51.50 105.89 81.64 Wed Mar 16 03:11:49 PDT 2022 3:11 up 10 secs, 0 users, load averages: 2.62 0.56 0.20 Wed Mar 16 03:12:19 PDT 2022 3:12 up 28 days, 1:47, 1 user, load averages: 29.12 93.42 78.19 Wed Mar 16 03:12:19 PDT 2022 3:12 up 28 days, 1:47, 1 user, load averages: 29.12 93.42 78.19 Wed Mar 16 03:12:41 PDT 2022 3:12 up 28 days, 1:47, 1 user, load averages: 23.51 87.95 76.58 Wed Mar 16 03:13:13 PDT 2022 3:13 up 28 days, 1:48, 1 user, load averages: 23.12 80.66 74.38 Wed Mar 16 03:13:35 PDT 2022 3:13 up 28 days, 1:48, 1 user, load averages: 17.13 75.56 72.70

So my "@reboot" job ran 37 times over the course of 8½ minutes BEFORE the machine rebooted, and then zero times after.

That's... super helpful. really just super helpful.

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