Install memtest86+ into your grub menu by the following command:

# memtest-setup

It will install 20_memtest86+ GRUB 2 template into /etc/grub.d and you will also
need to regenerate GRUB 2 config by running:

# grub2-mkconfig -o /boot/grub2/grub.cfg

This is not done automatically because it could overwrite any custom changes
in /boot/grub2/grub.cfg.

By default ELF version of memtest86+ is installed, which should work on most of
the systems. In case it doesn't work for you, you can try to install the non-ELF
version by running:

# memtest-setup -b

Or you can switch between ELF and non-ELF versions of memtest86+ by using
INSTALL_ELF variable from /etc/memtest86+.conf. Setting it to '1' will instruct
GRUB 2 to install ELF version of memtest86+ and setting it to '0' will instruct
GRUB 2 to install non-ELF version. If the variable is empty or unset, the ELF
version is installed (it's due to backward compatibility). For the change
to take effect you need to regenerate your GRUB 2 config by running:

# grub2-mkconfig -o /boot/grub2/grub.cfg

The non-ELF version is known to cause various problems and it may not work on
several systems. That's why the ELF version is installed by default.

In case of problems you can also try to install the non-ELF version of
memtest86+ on floppy disk or USB flash disk and boot the memtest86+ from it.
The following command installs the memtest86+ on floppy disk
(WARNING: all data previosly stored on the disk will be lost):

# dd if=/boot/memtest86+-VERSION of=/dev/fd0

For USB flash disk the command is the same, just change the 'of' device
appropriately (usually USB flash disk is /dev/sdb, but double check that
the device string matches your USB flash disk before you run the command,
wrong device string may cause significat harm, e.g. it can destroy content
of your system or data disks).

The memtest86+ now supports some command line parameters:
  console= - serial console can be used for memtest86+ control/display,
             example of usage:
             Only ttyS0 and ttyS1 are supported.

  btrace   - enable boot trace.

  maxcpus= - limit number of CPUs to use.

  onepass  - run one pass and exit if there are no errors.

  tstlist= - setup a list of tests to run.

  cpumask= - set a CPU (hexadecimal) mask to select CPU's to use for testing.

You can add memtest86+ command line parameters into grub like you are
used with kernel command line parameters, e.g.:
 linux16 /memtest86+-VERSION console=ttyS0

Unfortunately this is currently supported only with non-ELF memtest86+ image.
You cannot use the command line parameters with the ELF image, because the
command line handling is currently not supported by grub for ELF images.

If you need to use serial console with ELF image, you need to recompile
memtest86+ and explicitly enable/configure serial line. In such case
edit the config.h in memtest86+ sources the following way:

#define SERIAL_TTY 0
#define SERIAL_BAUD_RATE 9600

and recompile memtest86+. This will explicitly enable serial console and
set it to use ttyS0,9600.

NOTE: explicitly enabled serial console may significantly slow down the memory