Otdfbt

I am creating automated tests for an rsync-like utility and I need to be able to set the clock back 24 hours for one of the tests. However, when I use timedatectl to set the time and date they revert back to the current time after 15 seconds.

Checking timedatectl status I see that it is not running NTP:

# timedatectl status
 Local time: Wed 2019-05-15 23:24:17 EDT
 Universal time: Thu 2019-05-16 03:24:17 UTC
 RTC time: Wed 2019-01-16 02:13:40
 Time zone: America/New_York (EDT, -0400)
 NTP enabled: no
NTP synchronized: no
 RTC in local TZ: no
 DST active: yes
 Last DST change: DST began at
 Sun 2019-03-10 01:59:59 EST
 Sun 2019-03-10 03:00:00 EDT
 Next DST change: DST ends (the clock jumps one hour backwards) at
 Sun 2019-11-03 01:59:59 EDT
 Sun 2019-11-03 01:00:00 EST

I also checked and NTPD is not running and nothing is bound to port 123.

Does timedatectl have another method of syncing time? The CentOS 7 test machine is running in a Docker container under a VirtualBox image so Internet connectivity is somewhat limited. I am also testing on CentOS directly on VirtualBox so I will need to solve for the non-Docker case as well.

VBox Guest Additions includes and enables time syncronisation with the host by default.

You can disable this with the following command:

vboxmanage setextradata <vmname> "VBoxInternal/Devices/VMMDev/0/Config/GetHostTimeDisabled" "1"

Or add the following line to your yourVM.vbox file

<ExtraDataItem name="VBoxInternal/Devices/VMMDev/0/Config/GetHostTimeDisabled" value="1"/>

timedatectl is called by systemd after specific frequency it checks /etc/adjtime, /usr/share/zoneinfo/, /etc/localtime and many other files to check if any info is available, it having it's own logic to adjust the clock without using ntp.

static int context_write_data_timezone(Context *c) 
 _cleanup_free_ char *p = NULL;
 int r = 0;

 assert(c);

 if (isempty(c->zone)) 
 if (unlink("/etc/localtime") < 0 && errno != ENOENT)
 r = -errno;

 return r;
 

 p = strappend("../usr/share/zoneinfo/", c->zone);
 if (!p)
 return log_oom();

 r = symlink_atomic(p, "/etc/localtime");
 if (r < 0)
 return r;

 return 0;