The Linux terminal has an incredibly helpful feature: it records almost every command you type into a hidden file called .bash_history. This allows you to press the “Up” arrow key to quickly recall long, complex commands you executed yesterday. You can also type history to view a massive list of your past actions.
However, this is also a massive security liability. If you need to quickly pass a plaintext password to an API via a curl command, or if you need to use a MySQL command that includes your database credentials directly in the string (e.g., mysql -u root -pMySecretPassword), those highly sensitive credentials are permanently saved in the history file. Anyone who gains access to your user account can simply type history and instantly read your passwords.
While you could manually open the .bash_history file and delete the line later, it is much safer to prevent the command from ever being recorded in the first place. You can do this by using a simple “Leading Space.”
The Leading Space Trick
By default, most modern Linux distributions (like Ubuntu, Debian, and Mint) configure Bash to completely ignore any command that begins with a blank space.
To use it, simply hit the Spacebar once before you start typing.
- Standard (Will be recorded):
curl -u admin:SuperSecret123 https://api.example.com - Hidden (Will NOT be recorded):
curl -u admin:SuperSecret123 https://api.example.com
When you press Enter, the command will execute perfectly, but it will bypass the history logger entirely. If you press the “Up” arrow immediately afterward, it will skip your secret command and show whatever you typed before it.
Step 1: Ensure the Feature is Enabled
If you are using a rigid server distribution like RHEL or CentOS, this feature might be disabled by default. We need to check an environment variable called HISTCONTROL.
- Open your terminal.
- Type the following command to check your current settings:
echo $HISTCONTROL - Press Enter.
If the output says ignorespace or ignoreboth, the space trick is already active and working. If the output is blank, or if it only says ignoredups, the trick will not work.
Step 2: How to Enable “ignorespace” Permanently
If the feature is disabled, you must edit your user profile configuration file to turn it on permanently.
- Open your bash configuration file in a text editor:
nano ~/.bashrc - Scroll down to the bottom of the file and paste this exact line:
export HISTCONTROL=ignorespace - Save and exit (in nano, press Ctrl+O, Enter, then Ctrl+X).
- Reload the configuration to apply the change immediately:
source ~/.bashrc
From now on, whenever you need to type a highly sensitive database password, an API token, or an SSH key passphrase directly into the command line, just tap the Spacebar first. Your secrets will execute, but leave absolutely no trace behind in the logs.