How to perform a mysqldump without a password prompt?

Since you are using Ubuntu, all you need to do is just to add a file in your home directory and it will disable the mysqldump password prompting. This is done by creating the file ~/.my.cnf (permissions need to be 600).

Add this to the .my.cnf file

[mysqldump]
user=mysqluser
password=secret

This lets you connect as a MySQL user who requires a password without having to actually enter the password. You don't even need the -p or --password.

Very handy for scripting mysql & mysqldump commands.

The steps to achieve this can be found in this link.

Alternatively, you could use the following command:

mysqldump -u [user name] -p[password] [database name] > [dump file]

but be aware that it is inherently insecure, as the entire command (including password) can be viewed by any other user on the system while the dump is running, with a simple ps ax command.

Adding to @Frankline's answer:

The -p option must be excluded from the command in order to use the password in the config file.

Correct:
mysqldump –u my_username my_db > my_db.sql

Wrong:
mysqldump –u my_username -p my_db > my_db.sql

.my.cnf can omit the username.

[mysqldump]
password=my_password

If your .my.cnf file is not in a default location and mysqldump doesn't see it, specify it using --defaults-file.

mysqldump --defaults-file=/path-to-file/.my.cnf –u my_username my_db > my_db.sql

A few answers mention putting the password in a configuration file.

Alternatively, from your script you can export MYSQL_PWD=yourverysecretpassword.

The upside of this method over using a configuration file is that you do not need a separate configuration file to keep in sync with your script. You only have the script to maintain.

There is no downside to this method.

The password is not visible to other users on the system (it would be visible if it is on the command line). The environment variables are only visible to the user running the mysql command, and root.

The password will also be visible to anyone who can read the script itself, so make sure the script itself is protected. This is in no way different than protecting a configuration file. You can still source the password from a separate file if you want to have the script publicly readable (export MYSQL_PWD=$(cat /root/mysql_password) for example). It is still easier to export a variable than to build a configuration file.

E.g.,

$ export MYSQL_PWD=$(>&2 read -s -p "Input password (will not echo): "; echo "$REPLY")
$ mysqldump -u root mysql | head
-- MySQL dump 10.13  Distrib 5.6.23, for Linux (x86_64)
--
-- Host: localhost    Database: mysql
-- ------------------------------------------------------
-- Server version   5.6.23
/*!40101 SET @OLD_CHARACTER_SET_CLIENT=@@CHARACTER_SET_CLIENT */;
/*!40101 SET @OLD_CHARACTER_SET_RESULTS=@@CHARACTER_SET_RESULTS */;
/*!40101 SET @OLD_COLLATION_CONNECTION=@@COLLATION_CONNECTION */;
/*!40101 SET NAMES utf8 */;

MariaDB

MariaDB documents the use of MYSQL_PWD as:

Default password when connecting to mysqld. It is strongly recommended to use a more secure method of sending the password to the server.

The page has no mentions of what a "more secure" method may be.

MySQL

This method is still supported in the latest documented version of MySQL: https://dev.mysql.com/doc/refman/8.0/en/environment-variables.html though it comes with the following warning:

Use of MYSQL_PWD to specify a MySQL password must be considered extremely insecure and should not be used. Some versions of ps include an option to display the environment of running processes. On some systems, if you set MYSQL_PWD, your password is exposed to any other user who runs ps. Even on systems without such a version of ps, it is unwise to assume that there are no other methods by which users can examine process environments.

The security of environment variables is covered in much details at https://security.stackexchange.com/a/14009/10002 and this answer also addresses the concerns mentioned in the comments. TL;DR Irrelevant for over a decade.

Having said that, the MySQL documentation also warns:

MYSQL_PWD is deprecated as of MySQL 8.0; expect it to be removed in a future version of MySQL.

To which I'll leave you with maxschlepzig's comment from below:

funny though how Oracle doesn't deprecate passing the password on the command line which in fact is extremely insecure

To use a file that is anywhere inside of OS, use --defaults-extra-file eg:

mysqldump --defaults-extra-file=/path/.sqlpwd [database] > [desiredoutput].sql

Note: .sqlpwd is just an example filename. You can use whatever you desire.

Note: MySQL will automatically check for ~/.my.cnf which can be used instead of --defaults-extra-file

If your using CRON like me, try this!

mysqldump --defaults-extra-file=/path/.sqlpwd [database] > "$(date '+%F').sql"

Required Permission and Recommended Ownership

sudo chmod 600 /path/.sqlpwd && sudo chown $USER:nogroup /path/.sqlpwd

.sqlpwd contents:

[mysqldump]
user=username
password=password

Other examples to pass in .cnf or .sqlpwd

[mysql]
user=username
password=password

[mysqldiff]
user=username
password=password

[client]
user=username
password=password

If you wanted to log into a database automatically, you would need the [mysql] entry for instance.

You could now make an alias that auto connects you to DB

alias whateveryouwant="mysql --defaults-extra-file=/path/.sqlpwd [database]"

You can also only put the password inside .sqlpwd and pass the username via the script/cli. I'm not sure if this would improve security or not, that would be a different question all-together.

For completeness sake I will state you can do the following, but is extremely insecure and should never be used in a production environment:

mysqldump -u [user_name] -p[password] [database] > [desiredoutput].sql

Note: There is NO SPACE between -p and the password.

Eg -pPassWord is correct while -p Password is incorrect.