16.04 - How do I unlock apt?

Ubuntu 16.04 with Cinnamon desktop.

I cannot update. Attempting gives

$ sudo apt-get update
Reading package lists... Done
E: Could not get lock /var/lib/apt/lists/lock - open (11: Resource temporarily unavailable)

E: Unable to lock directory /var/lib/apt/lists/

I can check to see what file has this locked:

$ sudo lsof /var/lib/apt/lists/lock
lsof: WARNING: can't stat() fuse.gvfsd-fuse file system /run/user/1000/gvfs
  Output information may be incomplete.
COMMAND   PID USER   FD   TYPE DEVICE SIZE/OFF   NODE NAME
aptd    11127 root    9u   REG   0,24        0 181089 /var/lib/apt/lists/lock

aptd    11127 root   57u   REG   0,24        0 181089 /var/lib/apt/lists/lock
aptd    11127 root   58u   REG   0,24        0 181089 /var/lib/apt/lists/lock
$ ps aux | egrep "11127|PID" | egrep -v grep
USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
root     11127  0.5  1.4 296068 103516 ?       SNl  08:59   0:06 /usr/bin/python3 /usr/sbin/aptd

I don't know what /usr/sbin/aptd is or if it's safe to kill. man /usr/sbin/aptd exists, but it didn't tell me much. I can't find anything about this in particular online, either.

Is /usr/sbin/aptd related to the small orange square with the white star in my system tray that keeps trying to remind me to update? Is it safe to kill?

Edit: After waiting a while, whatever had the lock released it on its own. No need to kill anything.