  IP-  , ,    
     .

TTY. .  ,     
UNIX.    TTY      ( , 
  ),   .     UNIX,  
   Linux     .

tunneling ().     ,  -
 ,       .    -
    ,   , 
     .    -
   ,    internet-,   -
  ssh   -   Internet. roLDOC CM.
 VPN.

UDP.     (User Datagram Protocol). -
    Internet,  ,  -
   . UDP     -
, ,   TCP,     IP.
   TCP,  UDP        -
.      ,      -
      . UDP  
     ,     
  , , -  . roLDOC

UID.   (User ID). ,      
 passwd.

undecillion ().     1036.     -
  . .   .

unicast (). ,      . "-
"      .

unmanaged window (  ). .  .

URI.    (Universal Resource Identifier). 
    ,    ,  
 (  Internet).    URI- URL. roLDOC

URL.  ( "")   (Uniform ( Uni-
versal) Resource Locator).     , 
Web-,  Internet.  URL    URI.

usage message (  ). ,    
     .

usage message (  ). . UDP.

User ID ( ). . UID.

user interface ( ). . .

user mode ( ).   ,   -
   , ,    ( 
    ).   .

userspace ( ).  () ,   -
 . ,    ,   -
         , 
 . .  KernelAnalysis-HOWTO.

UTC.   . UTC   
    (0 ).     (Zulu, -

998                                                         VII. 