Index U

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UDP
    blocking packets on privileged ports 
    probing ports, difficulties of 
    stateful firewall, necessity for 
    testing for open port 
umask
    Linux chmod and umask commands 
    preventing files from being world-writable 
    setting as group writable 
unicast packets 
unique identifier for GnuPG keys 
unsecured IMAP connections 
unshadow command 
urlsnarf command 
Usenet news, tunneling NNTP connections through SSH 
user (inetd.conf file) 
user accounts
    allowing one account to access another with ksu 
    multiple root accounts 
    without a password, finding 
    restricting access to SSH server by 
    restricting hostbased authentication to 
    for SMTP authentication 
    superuser, finding 
    suspicious use, checking for 
        on multiple systems 
    usernames in remote file copying 
    usernames in trusted-host authentication 
user facility, system messages 
user ID of zero (0) (superuser) 
users
    administration of their own machines 
    authorizing to restart sshd 
    changes since last Tripwire check 
    Kerberos credentials for 
    login information about, printing 
    script forcing sudo to prompt for password