U
UDP (User Datagram Protocol)
The Internet Protocol that allows application programs on remote machines to
send datagrams to one another. UDP uses IP to deliver the datagrams.
UFS (UNIX File System)
TBS
uid, UID
See user ID
ULTRIX
One of two UNIX operating system products available from DIGITAL Equipment
Corporation. The ULTRIX operating system runs on VAX and RISC computers,
whereas DIGITAL UNIX runs on Alpha systems.
umask
A three-digit octal number that specifies the default permissions given to a file
when it is created. The umask command sets or changes this number.
UNIX
A trademark of X-Open Company, Ltd., that can be used in names of operating
systems that conform to X/Open UNIX CAE specifications and meet other X/Open
UNIX branding requirements. The UNIX operating system was originally
developed at the Bell Laboratories of AT&T in the late 1960s and early 1970s and
subsequently enhanced by the University of California at Berkeley, AT&T, the
Open Software Foundation (OSF), and others.
UNIX-to-UNIX Copy Program
See UUCP (UNIX-to-UNIX Copy Program)
unlink
The system call used to sever the connection between files that had been created
with the link system call.
unmount
To announce to the system that a file system previously mounted on a specified
directory is to be removed. Only the person who mounted the particular file
system or a superuser can unmount it. A file system is unmounted with the
umount command.
up time
The period during which a machine is available for use.
See also down time
upward compatible
Pertaining to that which is designed for use on small machines, but capable of
running without change on larger machines.
URL (Uniform Resource Locator)
The address of a file or other resource accessible on the Internet. The type of file
or resource depends on the Internet application protocol. For example, using the
HyperText Transfer Protocol (HTTP) , the file can be an HTML page, an image file,
or a program such as a CGI application or Java applet. Such an address would
look like this:
http://www.unix.digital.com/faqs/publications/pub_page/pubs_page.html, which
is the URL for the DIGITAL UNIX documentation Web site.
User Datagram Protocol
See UDP (User Datagram Protocol)
user ID
The number associated with each login name. This number is stored in the
/etc/passwd file.
user name
See login name
/usr
A read-only file system in which some components of the operating system and
of applications are stored. Users' home directories are sometimes also located in
a subdirectory of /usr.
UUCP (UNIX-to-UNIX Copy Program)
A set of programs and protocols developed at the Bell Laboratories of AT&T for
the purpose of connecting computers by means of dial-up lines. The programs
include facilities for copying files, logging in to remote computers, and encoding
binary files for transmission of 7-bit ASCII data lines. The ease of connection and
low cost have made UUCP one of the most popular information networks in the
world.
UUCP network
A term applied to any grouping of computers connected by means of the UUCP
programs.
