Patch-Source: https://src.fedoraproject.org/rpms/at/blob/f36/f/at-3.2.5-aborted-jobs.patch (updated)
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From 65700164d93a096fc1dc0aeb295e70c8b2225e07 Mon Sep 17 00:00:00 2001
From: Marcela Mašláňová <mmaslano@redhat.com>
Date: Dec 02 2013 15:34:37 +0000
Subject: There are two bugs:

1. It looks like the at command does not validate that it has succeeded
to write all data before it makes the file executable (i.e on a disk
full an empty file might get created).
2. After 60 minutes (run_time + CHECK_INTERVAL <= now), atd (approx line
750) starts to unlink the lockfile and retries the execution of the job,
leaving us with this unfortunate loop.

Reproducer:
ATD_PID=$(ps -C atd -o pid=)
QUEUE=a
JOBNO=$(printf '%05x' 123)
BAD_TIME=$(expr $(date +%s) / 60 - 61)
CTM=$(printf '%08x' $BAD_TIME )
FILENAME=/var/spool/at/${QUEUE}${JOBNO}${CTM}
touch $FILENAME
chmod 0700 $FILENAME
kill -HUP ${ATD_PID}
sleep 0.5
ls -l $FILENAME
rm -f $FILENAME

Thanks to: Anders Blomdell

diff --git a/atd.c b/atd.c
--- a/atd.c
+++ b/atd.c
@@ -696,12 +696,18 @@ run_loop()
 	/* Is the file already locked?
 	 */
 	if (buf.st_nlink > 1) {
+	    if (run_time < buf.st_mtime)
+		run_time = buf.st_mtime;
 	    if (run_time + CHECK_INTERVAL <= now) {
 
 		/* Something went wrong the last time this was executed.
 		 * Let's remove the lockfile and reschedule.
+		 * We also change the timestamp to avoid rerunning the job more
+		 * than once every CHECK_INTERVAL.
 		 */
 		strncpy(lock_name, dirent->d_name, sizeof(lock_name));
+		if (utime(lock_name, 0) < 0)
+			syslog(LOG_ERR, "utime couldn't be set for lock file %s\n", lock_name);
 		lock_name[0] = '=';
 		unlink(lock_name);
 		next_job = now;