U
- U flag (Linux routing table), The Routing Table
- UDP (User Datagram Protocol), A Data Communications Model, User Datagram Protocol
- Transport Layer, User Datagram Protocol
- udp option (fstab file), The vfstab and fstab files
- UID (user ID), The share command, The /etc/exports file, The /etc/exports file
- exports file, The /etc/exports file
- mapping users to, The /etc/exports file
- share command, The share command
- uid field (inet.conf file), The Internet Daemon
- undefine macro (sendmail), m4 sendmail Macros
- unicast addresses, The IP Address
- unicast multicast parameter (gated), The isis Statement
- Unix, TCP/IP and the Internet, Network Access Layer, The Routing Table, Protocol Numbers, Port Numbers, Port Numbers, Print Services, Using Dynamically Loadable Modules–Using Dynamically Loadable Modules, The BSD Kernel Configuration File, The options statement, The pseudo-device statement, The device statement, Startup Files, The ifconfig Command, Troubleshooting Serial Connections, Network Information Service, Secure the r Commands–Secure the r Commands, Secure Shell
- BSD, The BSD Kernel Configuration File, The options statement, The pseudo-device statement, The device statement
- configuration file, The BSD Kernel Configuration File
- devices statement, The device statement
- options statement, The options statement
- pseudo-device statement, The pseudo-device statement
- configuration files, startup, Startup Files
- dynamically loadable modules, Using Dynamically Loadable Modules–Using Dynamically Loadable Modules
- ifconfig command, overview, The ifconfig Command
- lpr command, Print Services
- Network Access Layer, Network Access Layer
- NIS maps, Network Information Service
- port numbers, Port Numbers
- protocol numbers, Protocol Numbers
- r commands, Secure the r Commands–Secure the r Commands, Secure Shell
- disabling, Secure Shell
- security considerations, Secure the r Commands–Secure the r Commands
- routing tables, The Routing Table
- serial ports, troubleshooting, Troubleshooting Serial Connections
- services, Port Numbers
- TCP/IP and, TCP/IP and the Internet
- Unknown host error (ping command), Testing Basic Connectivity
- UNKNOWN keyword (security), tcpd access control files
- Unreachable Port message, Tracing Routes
- UP flag (ifconfig command), Checking the Interface with ifconfig
- update (EGP trace option), The egp Statement
- update keyword (dbmmanage command), Improved user authentication
- UPDATE messages (BGP), Border Gateway Protocol
- updates (EGP), Exterior Gateway Protocol
- updetach option (pppd), The PPP Daemon
- Use field (Linux routing table), The Routing Table, The Routing Table
- Use Nice field (sendmail), Defining Mailers
- use-host-decl-names parameter (dhcpd), Configuration Parameters
- use-id-pool option (named), The options Statement
- use-lease-addr-for-default-route parameter
(dhcpd), Configuration Parameters
- UseCanonicalName directive (httpd.conf file), Basic Configuration Directives
- usehostname option (pppd command), PPP Daemon Security, The PPP Daemon
- usenet mailer, MAILER
- usepeerdns option (pppd), The PPP Daemon
- user (sendmail K command value), The sendmail K Command
- user authentication, User Authentication (see authentication)
- USER command (POP), Post Office Protocol
- User Datagram Protocol, A Data Communications Model (see UDP)
- User directive (Apache), Managing the Swarm
- user option (pppd), The PPP Daemon
- user setting (smb.config file), Configuring a Samba Server
- USERCTL (Linux configuration value), Assigning an Address
- UserDir directive (httpd.conf file), Defining Where Things Are Stored
- Userid field (sendmail), Defining Mailers
- USERID option (xinetd), Controlling Access with xinetd
- use_ct_file (sendmail), FEATURE
- use_cw_file (sendmail), FEATURE
- UUCP protocol, Simple Mail Transfer Protocol
- uucpdomain (sendmail database feature), FEATURE
- UUCPSMTP macro (sendmail), m4 sendmail Macros