When user smithj attempts to execute sudo commands on CentOS 6, the system behaves unexpectedly:

$ sudo adduser jonesjp
Sorry, try again.
Sorry, try again.
Sorry, try again.
sudo: 3 incorrect password attempts

Notably absent is the password prompt that should appear before these rejection messages. The user is properly configured in /etc/sudoers:

root ALL=(ALL) ALL
smithj ALL=(ALL) ALL

Several system components could be responsible for this behavior:

1. PAM Configuration: The Pluggable Authentication Modules stack handles sudo authentication
2. Terminal Settings: PTY allocation issues with remote sessions
3. Sudoers Configuration: Potential NOPASSWD directives or syntax errors
4. System Logs: Authentication attempts might reveal more details

First, check relevant system logs:

# tail -f /var/log/secure
# journalctl -xe (for newer systems)

Inspect the PAM configuration for sudo:

# cat /etc/pam.d/sudo
# Check for any unusual modules or broken dependencies

Based on similar cases, here's the most effective resolution sequence:

# Verify sudo binary integrity
rpm -V sudo

# Reinstall PAM modules (CentOS 6 specific)
yum reinstall pam*

# Check terminal permissions
ls -l /dev/pts/

# Test with local console session
su - smithj
sudo -l

If PAM configuration is corrupted, restore the default:

# Backup current config
cp /etc/pam.d/sudo /etc/pam.d/sudo.bak

# Apply known working configuration
cat > /etc/pam.d/sudo << 'EOF'
auth       include    system-auth
account    include    system-auth
password   include    system-auth
session    optional   pam_keyinit.so revoke
session    required   pam_limits.so
EOF

After making changes, verify the fix:

# As the affected user
sudo -k  # Clear any cached credentials
sudo -l  # Should now prompt properly

If issues persist, consider these advanced checks:

# Check SELinux context
ls -Z /usr/bin/sudo

# Verify tty allocation
stty -a

Remember that CentOS 6 reached EOL in November 2020, so upgrading should be considered for security reasons.

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When smithj attempts to execute sudo adduser jonesjp on a CentOS 6 system, something unusual happens:

$ sudo adduser jonesjp
Sorry, try again.
Sorry, try again.
Sorry, try again.
sudo: 3 incorrect password attempts

Notice two critical anomalies:

• No password prompt appears before the error messages
• The system immediately fails with 3 attempts counted

First, verify the sudoers configuration is actually being loaded:

# Verify sudoers syntax
$ sudo visudo -c
/etc/sudoers: parsed OK

# Check effective privileges
$ sudo -l

The reported /etc/sudoers content shows proper configuration:

root ALL=(ALL) ALL
smithj ALL=(ALL) ALL

The most likely culprit is PAM (Pluggable Authentication Modules) configuration. Check these files:

# Examine PAM stack for sudo
$ cat /etc/pam.d/sudo

# Common problematic patterns to look for:
auth sufficient pam_permit.so
auth required pam_deny.so

Here's what a healthy PAM configuration should resemble:

auth       include      system-auth
account    include      system-auth
session    include      system-auth

Since the user connects via PuTTY, TTY allocation might be involved. Test with:

# Force pseudo-tty allocation
$ ssh -tt user@host sudo whoami

# Check TTY settings
$ stty -a

Certain environment variables can interfere with sudo's operation:

# Check for problematic variables
$ env | grep -i 'sudo\|tty\|term'

# Test with clean environment
$ env -i sudo -k whoami

Enable sudo debugging to gather more information:

# Temporary debug mode
$ sudo -D adduser jonesjp

# Permanent debugging (add to /etc/sudo.conf)
Debug sudo /var/log/sudo_debug all@debug

For legacy systems, sometimes the solution involves:

# Reinstall PAM and sudo packages
$ yum reinstall pam sudo

# Verify SELinux context
$ restorecon -v /etc/pam.d/*