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## Index: U

/u directory: 31.11. Finding (Anyone's) Home Directory, Quickly
UAs (User Agents): 46.8. Mail — SMTP, POP, and IMAP
uc operator: 41.5.1. Scalars
UDP (User Datagram Protocol): 46.1. TCP/IP — IP Addresses and Ports
  46.1.2. Layer 4 Protocols: TCP, UDP, and ICMP
UIDs (see user IDs)
ulimit -f command: 15.5.1. limit and ulimit
umask command: 31.13. Automatic Setup When You Enter/Exit a Directory
  default mode for newly created files: 49.4. Setting an Exact umask
  permission values, setting: 50.2.1. User, Group, and World
  setting in shell scripts: 24.4. Subshells
  subshell, running in: 36.27. Shell Lockfile
umount command: 44.6. Mounting and Unmounting Removable Filesystems
unalias command: 29.4. Setting and Unsetting Bourne-Type Aliases
uname -n command: 2.5. How Unix Systems Remember Their Names
uncompressing files: 15.6. Compressing Files to Save Space
  bunzip2 program: 15.6. Compressing Files to Save Space
underscore (_) in filenames: 1.11. Filenames
undoing
  actions in Emacs editor: 19.1. Emacs: The Other Editor
  deletions with vi editor: 17.7. Get Back What You Deleted with Numbered Buffers
  edits in vi editor: 17.29. Finding Your Place with Undo
  search and replace commands with vi editor: 17.9. Confirming Substitutions in vi
unformatted manpage files: 2.4. Searching Online Manual Pages
uniq command: 21.20. What Is (or Isn't) Unique?
  sort -u vs.: 22.6.1. Dealing with Repeated Lines
  testing for duplicate terms: 16.7. Find a a Doubled Word
Universal Serial Bus (USB): 44.12. USB Configuration
Unix
  advantages of: 1.1. What's Special About Unix?
    1.2. Power Grows on You
  communicating with: 1.4. Communication with Unix
  networking and communications utilities: 1.21. Unix Networking and Communications
  priority, definition of: 26.5. Know When to Be "nice" to Other Users...and When Not To
  versions of: 0.6. About Unix Versions
unkillable processes, cleaning up: 24.18. Cleaning Up an Unkillable Process
unless statements: 41.6. Perl Boot Camp, Part 3: Branching and Looping
unlimit coredumpsize command: 15.5.1. limit and ulimit
unlink( ) system call: 14.14. Using unlink to Remove a File with a Strange Name
unlink function: 41.8. Perl Boot Camp, Part 5: Perl Knows Unix
unlocking files (RCS): 39.5. RCS Basics
unmatched pieces of code, errors caused by: 37.1.4. Missing or Extra esac, ;;, fi, etc.
unset -f command, deleting definition of function: 29.11.5. Conclusion
unset variables, errors caused by: 37.3. Stop Syntax Errors in Numeric Tests
unsetenv command: 35.3. What Environment Variables Are Good For
unshift operator (Perl): 41.5.2. Arrays
until loops: 31.6. Loop Control: break and continue
  nonzero exit status: 36.27. Shell Lockfile
  test command used with: 35.26. test: Testing Files and Strings
  testing exit status in Bourne shells: 35.15.1. Looping Until a Command Succeeds
  while loops vs.: 35.15.2. Looping Until a Command Fails
updatedb shell script: 9.20. Finding Files (Much) Faster with a find Database
updating
  CVS files: 39.7. CVS Basics
    39.8. More CVS
  distributed database: 11.11. Even More Uses for make
  information on available packages with apt-get: 40.6.2.1. Updating information on available packages
upgrading installed packages with apt-get: 40.6.2.3. Upgrading installed packages
uppercase (see case)
uptime command: 4.16. Preprompt, Pre-execution, and Periodic Commands
  26.1. Timing Is Everything
  26.4. Checking System Load: uptime
URI for software package source: 40.6.1. Configuring the sources.list File
urllib module: 42.4. Python and the Web
URLs for Java applet VNC desktops: 47.7.1. Connecting to a Windows VNC server
USB (Universal Serial Bus): 44.12. USB Configuration
Usenet: 1.21. Unix Networking and Communications
  eight-bit text, encoding into seven-bit: 21.12. Encoding "Binary" Files into ASCII
  GNUS client in Emacs: 19.2. Emacs Features: A Laundry List
User Agents (UAs): 46.8. Mail — SMTP, POP, and IMAP
user-based access control: 6.10.2. Starting a Remote Client with rsh and ssh
User Datagram Protocol (see UDP)
user defined subroutines (Perl): 41.4. Perl Boot Camp, Part 1: Typical Script Anatomy
USER environment variable: 35.5. Predefined Environment Variables
user IDs (UIDs): 24.3. Managing Processes: Overall Concepts
  in passwd file: 49.2. When Does a User Become a User
user interfaces (see GUIs)
-user operator (find command): 9.16. Searching by Owner and Group
user-space tools to configure devices: 44.1. Quick Introduction to Hardware
user time: 26.2. Timing Programs
useradd utility: 49.2. When Does a User Become a User
username field in crontab entries: 25.2.1. Execution Scheduling
users
  backing up directories: 38.5.1. What to Back Up
  login shell, killing: 24.12. Destroying Processes with kill
  RCS files, listing for: 39.5. RCS Basics
  UID: 49.2. When Does a User Become a User
  Unix user/group infrastructure: 49.1. Unix User/Group Infrastructure
    adding to Unix systems: 49.2. When Does a User Become a User
    disabling logins: 49.13. Disable logins
    file ownerhsip and: 50.2.1. User, Group, and World
    group permissions in directory with setgid bit: 49.5. Group Permissions in a Directory with the setgid Bit
    groups and group ownership: 49.6. Groups and Group Ownership
    groups that deny permissions: 49.7. Add Users to a Group to Deny Permissions
    substitute identity with su: 49.9. Substitute Identity with su
    SUID and SGID scripts: 49.8. Care and Feeding of SUID and SGID Scripts
    superpowers with sudo application: 49.11. Providing Superpowers with sudo
  usernames: 49.2. When Does a User Become a User
    in shell prompt: 4.2. Static Prompts
users command: 35.25.2. Setting (and Parsing) Parameters
/usr directory: 40.1. /usr/bin and Other Software Directories
  /usr/bin directory: 40.1. /usr/bin and Other Software Directories
    local programs and: 10.7. Linking Directories
    programs in: 1.9. Internal and External Commands
  /usr/bsd directory, remote shell (rsh): 6.10.2. Starting a Remote Client with rsh and ssh
  /usr/dict/words file: 16.3. How Do I Spell That Word?
  /usr/lib/crontab file: 25.2.1. Execution Scheduling
  /usr/lib/crontab.local file: 25.2.1. Execution Scheduling
  /usr/libexec/makewhatis file: 2.2. whatis: One-Line Command Summaries
  /usr/lib/spell directory: 16.4. Inside spell
  /usr/lib/X11/app-defaults file: 6.9. Listing the Current Resources for a Client: appres
  /usr/local directory: 10.7. Linking Directories
  /usr/local/bin directory: 40.1. /usr/bin and Other Software Directories
  /usr/local/man directory: 2.4. Searching Online Manual Pages
  /usr/man directory: 2.4. Searching Online Manual Pages
  /usr/share/man directory: 2.4. Searching Online Manual Pages
utilities: 35.2. Everyone Should Learn Some Shell Programming
  (see also individual utility or command names)
  combining: 35.2. Everyone Should Learn Some Shell Programming
  relationship with kernel, shell, and applications: 1.4. Communication with Unix
UUCP (Unix-to-Unix copy): 1.21. Unix Networking and Communications
uudecode command: 21.12.1. uuencoding
uuencode utility: 21.12.1. uuencoding
uuencoding: 21.12. Encoding "Binary" Files into ASCII
uuname -l command: 2.5. How Unix Systems Remember Their Names

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