Error code

Please advise regarding the following error message:

Arduino: 1.8.3 (Linux), Board: "Arduino/Genuino Mega or Mega 2560, ATmega2560 (Mega 2560)"

Archiving built core (caching) in: /tmp/arduino_cache_520958/core/core_arduino_avr_mega_cpu_atmega2560_12330cb3e710267cdccf791b88a3e42c.a
Sketch uses 1462 bytes (0%) of program storage space. Maximum is 253952 bytes.
Global variables use 9 bytes (0%) of dynamic memory, leaving 8183 bytes for local variables. Maximum is 8192 bytes.
/home/brianeo/Downloads/arduino-1.8.3/hardware/tools/avr/bin/avrdude -C/home/brianeo/Downloads/arduino-1.8.3/hardware/tools/avr/etc/avrdude.conf -v -patmega2560 -cwiring -P/dev/ttyACM0 -b115200 -D -Uflash:w:/tmp/arduino_build_227785/Blink.ino.hex:i 

avrdude: Version 6.3, compiled on Jan 17 2017 at 11:00:16
         Copyright (c) 2000-2005 Brian Dean, http://www.bdmicro.com/
         Copyright (c) 2007-2014 Joerg Wunsch

         System wide configuration file is "/home/brianeo/Downloads/arduino-1.8.3/hardware/tools/avr/etc/avrdude.conf"
         User configuration file is "/home/brianeo/.avrduderc"
         User configuration file does not exist or is not a regular file, skipping

         Using Port                    : /dev/ttyACM0
         Using Programmer              : wiring
         Overriding Baud Rate          : 115200
avrdude: ser_open(): can't open device "/dev/ttyACM0": Permission denied
ioctl("TIOCMGET"): Inappropriate ioctl for device
ioctl("TIOCMGET"): Inappropriate ioctl for device
avrdude: ser_send(): write error: Bad file descriptor
avrdude: stk500_send(): failed to send command to serial port
avrdude: stk500v2_ReceiveMessage(): timeout
(cut)
avrdude: stk500v2_getsync(): timeout communicating with programmer

avrdude done.  Thank you.

the selected serial port avrdude: stk500_send(): failed to send command to serial port
 does not exist or your board is not connected

This report would have more information with
"Show verbose output during compilation"
option enabled in File -> Preferences.

https://www.arduino.cc/en/Guide/Linux#toc6

Grazie molto! I would never have found the help reference page on my own. One point that I want to clarify for the benefit of other Linux novices dealing with the Arduino port error message concerns this part of the directions:

Open Terminal and type:

ls -l /dev/ttyACM*

The letters after ls -l /dev/tty must refer to your own port. In my set-up it is USB0, instead of ACM*, as written in the help file text. Attached is a screen print of my desktop after entering the changes, and before logout.
One more thing: your password is concealed in terminal. You may think you entered it, but if not, the changes will not go into effect.