286 lines
12 KiB
Perl
286 lines
12 KiB
Perl
.\" Copyright (c) 1985 The Regents of the University of California.
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)5.t 5.1 (Berkeley) 4/17/91
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.\"
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.ds RH Functional Extensions
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.NH
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Functional Extensions
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.PP
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Some of the facilities introduced in 4.2BSD were not completely
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implemented. An important part of the effort that went into
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4.3BSD was to clean up and unify both new and old facilities.
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.NH 2
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Kernel Extensions
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.PP
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A significant effort went into improving
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the networking part of the kernel.
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The work consisted of fixing bugs,
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tuning the algorithms,
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and revamping the lowest levels of the system
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to better handle heterogeneous network topologies.
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.NH 3
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Subnets, Broadcasts and Gateways
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.PP
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To allow sites to expand their network in an autonomous
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and orderly fashion, subnetworks have been introduced in 4.3BSD [GADS85].
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This facility allows sites to subdivide their local Internet address
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space into multiple subnetwork address spaces that are visible
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only by hosts at that site. To off-site hosts machines on a site's
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subnetworks appear to reside on a single network. The routing daemon
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has been reworked to provide routing support in this type of
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environment.
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.PP
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The default Internet broadcast address is now specified with a host part
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of all one's, rather than all zero's.
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The broadcast address may be set at boot time on a per-interface basis.
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.NH 3
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Interface Addressing
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.PP
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The organization of network interfaces has been
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reworked to more cleanly support multiple
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network protocols. Network interfaces no longer
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contain a host's address on that network; instead
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each interface contains a pointer to a list of addresses
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assigned to that interface. This permits a single
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interface to support, for example, Internet protocols
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at the same time as XNS protocols.
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.PP
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The Address Resolution Protocol (ARP) support
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for 10 megabyte/second Ethernet\(dg
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.FS
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\(dg Ethernet is a trademark of Xerox.
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.FE
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has been made more flexible by allowing hosts to
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act as an ``clearing house'' for hosts that do
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not support ARP. In addition, system managers have
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more control over the contents of the ARP translation
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cache and may interactively interrogate and modify
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the cache's contents.
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.NH 3
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User Control of Network Buffering
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.PP
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Although the system allocates reasonable default amounts of buffering
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for most connections, certain operations such as file system dumps
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to remote machines benefit from significant increases in buffering [Walsh84].
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The \fIsetsockopt\fP system call has been extended to allow such requests.
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In addition, \fIgetsockopt\fP and \fIsetsockopt\fP,
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are now interfaced to the protocol level allowing protocol-specific
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options to be manipulated by the user.
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.NH 3
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Number of File Descriptors
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.PP
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To allow full use of the many descriptor based services available,
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the previous hard limit of 30 open files per process has been relaxed.
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The changes entailed generalizing \fIselect\fP to handle arrays of
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32-bit words, removing the dependency on file descriptors from
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the page table entries,
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and limiting most of the linear scans of a process's file table.
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The default per-process descriptor limit was raised from 20 to 64,
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though there are no longer any hard upper limits on the number
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of file descriptors.
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.NH 3
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Kernel Limits
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.PP
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Many internal kernel configuration limits have been increased by suitable
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modifications to data structures.
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The limit on physical memory has been changed from 8 megabyte to 64 megabyte,
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and the limit of 15 mounted file systems has been changed to 255.
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The maximum file system size has been increased to 8 gigabyte,
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number of processes to 65536,
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and per process size to 64 megabyte of data and 64 megabyte of stack.
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Note that these are upper bounds,
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the default limits for these quantities are tuned for systems
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with 4-8 megabyte of physical memory.
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.NH 3
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Memory Management
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.PP
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The global clock page replacement algorithm used to have a single
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hand that was used both to mark and to reclaim memory.
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The first time that it encountered a page it would clear its reference bit.
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If the reference bit was still clear on its next pass across the page,
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it would reclaim the page.
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The use of a single hand does not work well with large physical
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memories as the time to complete a single revolution of the hand
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can take up to a minute or more.
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By the time the hand gets around to the marked pages,
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the information is usually no longer pertinent.
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During periods of sudden shortages,
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the page daemon will not be able to find any reclaimable pages until
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it has completed a full revolution.
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To alleviate this problem,
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the clock hand has been split into two separate hands.
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The front hand clears the reference bits,
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the back hand follows a constant number of pages behind
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reclaiming pages that still have cleared reference bits.
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While the code has been written to allow the distance between
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the hands to be varied, we have not found any algorithms
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suitable for determining how to dynamically adjust this distance.
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.PP
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The configuration of the virtual memory system used to require
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a significant understanding of its operation to do such
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simple tasks as increasing the maximum process size.
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This process has been significantly improved so that the most
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common configuration parameters, such as the virtual memory sizes,
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can be specified using a single option in the configuration file.
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Standard configurations support data and stack segments
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of 17, 33 and 64 megabytes.
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.NH 3
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Signals
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.PP
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The 4.2BSD signal implementation would push several words
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onto the normal run-time stack before switching to an
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alternate signal stack.
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The 4.3BSD implementation has been corrected so that
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the entire signal handler's state is now pushed onto the signal stack.
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Another limitation in the original signal implementation was
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that it used an undocumented system call to return from signals.
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Users could not write their own return from exceptions;
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4.3BSD formally specifies the \fIsigreturn\fP system call.
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.PP
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Many existing programs depend on interrupted system calls.
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The restartable system call semantics of 4.2BSD signals caused
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many of these programs to break.
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To simplify porting of programs from inferior versions of
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.UX
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the \fIsigvec\fP system call has been extended so that
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programmers may specify that system calls are not to be
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restarted after particular signals.
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.NH 3
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System Logging
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.PP
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A system logging facility has been added
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that sends kernel messages to the
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syslog daemon for logging in /usr/adm/messages and possibly for
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printing on the system console.
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The revised scheme for logging messages
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eliminates the time lag in updating the messages file,
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unifies the format of kernel messages,
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provides a finer granularity of control over the messages
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that get printed on the console,
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and eliminates the degradation in response during the printing of
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low-priority kernel messages.
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Recoverable system errors and common resource limitations are logged
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using this facility.
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Most system utilities such as init and login,
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have been modified to log errors to syslog
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rather than writing directly on the console.
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.NH 3
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Windows
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.PP
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The tty structure has been augmented to hold
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information about the size
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of an associated window or terminal.
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These sizes can be obtained by programs such as editors that want
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to know the size of the screen they are manipulating.
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When these sizes are changed,
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a new signal, SIGWINCH, is sent the current process group.
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The editors have been modified to catch this signal and reshape
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their view of the world, and the remote login program and server
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now cooperate to propagate window sizes and window size changes
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across a network.
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Other programs and libraries such as curses that need the width
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or height of the screen have been modified to use this facility as well.
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.NH 3
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Configuration of UNIBUS Devices
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.PP
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The UNIBUS configuration routines have been extended to allow auto-configuration
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of dedicated UNIBUS memory held by devices.
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The new routines simplify the configuration of memory-mapped devices
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and correct problems occurring on reset of the UNIBUS.
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.NH 3
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Disk Recovery from Errors
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.PP
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The MASSBUS disk driver's error recovery routines have been fixed to
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retry before correcting ECC errors, support ECC on bad-sector replacements,
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and correctly attempt retries after earlier
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corrective actions in the same transfer.
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The error messages are more accurate.
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.NH 2
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Functional Extensions to Libraries and Utilities
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.PP
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Most of the changes to the utilities and libraries have been to
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allow them to handle a more general set of problems,
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or to handle the same set of problems more quickly.
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.NH 3
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Name Server
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.PP
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In 4.2BSD the name resolution routines (\fIgethostbyname\fP,
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\fIgetservbyname\fP,
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etc.) were implemented by a set of database files maintained on the
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local machine.
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Inconsistencies or obsolescence in these files resulted in inaccessibility of
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hosts or services.
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In 4.3BSD these files may be replaced by a network name server that can
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insure a consistent view of the name space in a multimachine environment.
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This name server operates in accordance with Internet standards
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for service on the ARPANET [Mockapetris83].
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.NH 3
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System Management
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.PP
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A new utility, \fIrdist\fP,
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has been provided to assist system managers in keeping
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all their machines up to date with a consistent set of sources and binaries.
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A master set of sources may reside on a single central machine,
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or be distributed at (known) locations throughout the environment.
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New versions of \fIgetty\fP, \fIinit\fP, and \fIlogin\fP
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merge the functions of several
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files into a single place, and allow more flexibility in the
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startup of processes such as window managers.
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.PP
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The new utility \fItimed\fP keeps the time on a group of cooperating machines
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(within a single LAN) synchronized to within 30 milliseconds.
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It does its corrections using a new system call that changes
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the rate of time advance without stopping or reversing the system clock.
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It normally selects one machine to act as a master.
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If the master dies or is partitioned, a new master is elected.
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Other machines may participate in a purely slave role.
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.NH 3
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Routing
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.PP
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Many bugs in the routing daemon have been fixed;
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it is considerably more robust,
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and now understands how to properly deal with
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subnets and point-to-point networks.
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Its operation has been made more efficient by tuning with the use
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of execution profiles, along with inline expansion of common operations
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using the kernel's \fIinline\fP optimizer.
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.NH 3
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Compilers
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.PP
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The symbolic debugger \fIdbx\fP has had many new features added,
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and all the known bugs fixed. In addition \fIdbx\fP
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has been extended to work with the Pascal compiler.
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The fortran compiler \fIf77\fP has had numerous bugs fixed.
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The C compiler has been modified so that it can, optionally,
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generate single precision floating point instructions when operating
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on single precision variables.
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