Note: If you installed by using the debian package and answered the configuration questions you already have a working setup. If you skipped the questions you will still already have the PAM module itself already setup. Continue with "Setting up Devices and Users" in that case.

Setting up pam_usb requires the following, once pam_usb is installed:

1. Set up devices and users
2. Configuring PAM for system authentication
3. (Optional) Configuring pamusb-agent to run programs when the device is inserted or removed

Once you've connected your USB device to the computer, use pamusb-conf to add it to the configuration file:

# pamusb-conf --add-device MyDevice
Please select the device you wish to add.
* Using "SanDisk Corp. Cruzer Titanium (SNDKXXXXXXXXXXXXXXXX)" (only option)
Which volume would you like to use for storing data ?
* Using "/dev/sda1 (UUID: <6F6B-42FC>)" (only option)
Name            : MyDevice
Vendor          : SanDisk Corp.
Model           : Cruzer Titanium
Serial          : SNDKXXXXXXXXXXXXXXXX
Volume UUID     : 6F6B-42FC (/dev/sda1)
Save to /etc/security/pam_usb.conf ?
[Y/n] y
Done.

Note that MyDevice can be any arbitrary name you'd like, but will be used as an XML attribute value so stay away from any special characters and stick to A-Z.

Also, you can add as many devices as you want. However, in versions prior to v0.8.5 each user can only use a single device. So additional devices can only be used for additional users. Starting from v0.8.5 a single user can have multiple devices assigned as well.

Next, configure users you want to be able to authenticate with pam_usb:

# pamusb-conf --add-user username
Which device would you like to use for authentication ?
* Using "MyDevice" (only option)
User            : username
Device          : MyDevice
Save to /etc/security/pam_usb.conf ?
[Y/n] y
Done.

You can run pamusb-check anytime to check if everything is correctly worked. This tool will simulate an authentication request (requires your device to be connected, otherwise it will fail).

# pamusb-check username
* Authentication request for user "username" (pamusb-check)
* Device "MyDevice" is connected (good).
* Performing one time pad verification...
* Verification match, updating one time pads...
* Access granted.

Before you do this step you should read into how pam.d configuration works. If you make the wrong changes you could easily end up with a system where you can't login at all - requiring you to use recovery mode to revert your changes.

See https://manpages.ubuntu.com/manpages/impish/en/man7/PAM.7.html for a quick explanation of PAM and https://manpages.ubuntu.com/manpages/impish/man5/pam.d.5.html for a configuration file guide. If you aren't on a Debian based distro check your system man pages for them since there will be some differences most likely.

To add pam_usb into the system authentication process, we need to edit /etc/pam.d/common-auth

NOTE: If you are using RedHat, Arch or Fedora this file can be known as `/etc/pam.d/system-auth`.
Some distributions also require you to additionally insert the line into `/etc/pam.d/password-auth`.

Your default PAM common-auth configuration should include the following line:

auth    required        pam_unix.so nullok_secure

This is a current standard which uses passwords to authenticate a user.

Alter your /etc/pam.d/common-auth configuration to:

auth    sufficient      pam_usb.so
auth    required        pam_unix.so nullok_secure

Remember what we've learned in the pam manpages (you've read them, riiiight?): pam rules are a stack, order of the rules is important and makes a difference in behavior.

The sufficient keyword means that if pam_usb allows the authentication, then no password will be asked. If the authentication fails, then the default password-based authentication will be used as fallback.

If you change it to required, it means that both the USB flash drive and the password will be required to grant access to the system.

At this point, you should be able to authenticate with the relevant removable device plugged-in.

scox $ sudo bash
* Authentication request for user "scox" (sudo)
* Authentication device "MyDevice" is connected.
* Performing one time pad verification...
* Regenerating new pads...
* Access granted.

If you want to use pamusb with run0 from systemd, you will have to add it to the file systemd-run0 in your PAM configuration. At least according to its manpage, I haven't tested it.

The pam_usb agent (pamusb-agent) allows you to automatically execute commands upon locking and unlocking events. Those events are generated when you insert or remove your authentication device. To configure the commands, you have to edit pam_usb's configuration file (/etc/security/pam_usb.conf) and add agent entries into your user section.

For instance, you could automatically start your screensaver as soon as you remove the device, and deactivate it when you plug the device back.

You can find details in the "Agent" section of Configuration

Security warning: You should think twice before enabling this feature. To use it you need to put your keyring password in cleartext in your home directory. The tool restricts the file to owner-only permissions (0600), but anyone with root/sudo access can still read it. Even worse: if you have Samba user shares enabled, the password file will be accessible to anyone who can reach that share. This is a comfort feature and is insecure by design.

An autostart .desktop entry runs pamusb-keyring-unlock-gnome at the start of every GNOME session. The script calls pamusb-check for the current user; if the USB token is present and valid, it kills any existing gnome-keyring-daemon instance and re-launches it with the stored password supplied over stdin, unlocking your default keyring without a password prompt. If the token is absent or the check fails the script exits silently, leaving the keyring locked.

• pam_usb must already be configured and working for your user (pamusb-check must succeed with the device connected).
• gnome-keyring-daemon must be installed (package gnome-keyring on most distros).

Run as your normal user — do not run as root:

pamusb-keyring-unlock-gnome --install

Follow the prompt to enter your keyring password. The installer:

1. Writes ~/.pamusb/.keyring_unlock_password (mode 0600) with your password.
2. Creates ~/.config/autostart/pamusb-keyring-unlock-gnome.desktop — the unlock autostart entry.
3. Creates ~/.config/autostart/gnome-keyring-secrets.desktop with Hidden=true to disable GNOME's own default keyring autostart, preventing conflicts.

Log out and back in for the autostart to take effect.

pamusb-keyring-unlock-gnome --uninstall

This removes the password file and both .desktop files created above, fully reverting the installation.

pam_usb ships a custom pinentry program — pinentry-pamusb — that supplies your GPG passphrase automatically when your USB token is present and verified.

When GPG needs a passphrase it calls whatever binary is registered as pinentry. pinentry-pamusb intercepts that call, runs pamusb-check for the current user, and — if the token is present and valid — returns the passphrase stored in ~/.pamusb/.pinentry.env. If the token is absent or the check fails it falls back to a regular pinentry program of your choice (e.g. pinentry-gnome3).

• python-dotenv must be installed (preferably via your distro's package manager, e.g., python3-dotenv).
• update-alternatives must be available (standard on Debian/Ubuntu/Fedora; on Arch you may need to perform the registration manually — see below).

Run the installer as root (so it can register the update-alternatives entry system-wide, but the env file is written to the calling user's home via $SUDO_USER):

sudo pinentry-pamusb --install

This does two things:

1. Creates ~/.pamusb/.pinentry.env (mode 0600) with a template you must edit.
2. Registers pinentry-pamusb as a pinentry alternative with priority 100 and activates it.

Now edit the env file and set your actual GPG passphrase:

$EDITOR ~/.pamusb/.pinentry.env

The file looks like this:

# pinentry-pamusb configuration
# Your GPG passphrase for auto-unlock
PINENTRY_PASSWORD=changeme

# Fallback pinentry application (must be an absolute path)
# PINENTRY_FALLBACK_APP=/usr/bin/pinentry-gnome3

Replace changeme with your real passphrase and, if you want a fallback when the token is not present, uncomment and set PINENTRY_FALLBACK_APP to the full path of another pinentry binary.

Security note: ~/.pamusb/.pinentry.env is created with mode 0600 and must remain readable only by you. Do not place it in a world-readable directory or check it into version control. Anyone with root/sudo access will still be able to read it — keep that in mind before using this feature.

To undo the installation (removes the env file and de-registers the alternative):

sudo pinentry-pamusb --uninstall

If update-alternatives is not available (e.g. vanilla Arch Linux), --install will still create the env file but skip alternative registration. You can register the alternative manually or simply symlink:

# Option A – symlink (destructive, replaces the existing pinentry)
sudo ln -sf /usr/bin/pinentry-pamusb /usr/bin/pinentry

# Option B – keep the original and switch back manually later
sudo mv /usr/bin/pinentry /usr/bin/pinentry.bak
sudo ln -sf /usr/bin/pinentry-pamusb /usr/bin/pinentry

There are many options available to configure pam_usb.

Check out the configuration reference.