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ARCHIVE_WRITE(3) BSD Library Functions Manual
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ARCHIVE_WRITE(3)
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NAME
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archive_write —
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functions for creating archives
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LIBRARY
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Streaming Archive Library
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(libarchive, -larchive)
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SYNOPSIS
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#include
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<archive.h>
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DESCRIPTION
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These functions provide a
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complete API for creating streaming archive files. The
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general process is to first create the struct archive
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object, set any desired options, initialize the archive,
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append entries, then close the archive and release all
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resources.
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Create
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archive object
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See archive_write_new(3).
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To write an
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archive, you must first obtain an initialized struct archive
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object from archive_write_new().
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Enable
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filters and formats, configure block size and padding
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See archive_write_filter(3), archive_write_format(3) and
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archive_write_blocksize(3).
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You can then
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modify this object for the desired operations with the
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various archive_write_set_XXX() functions. In
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particular, you will need to invoke appropriate
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archive_write_add_XXX() and
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archive_write_set_XXX() functions to enable the
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corresponding compression and format support.
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Set
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options
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See archive_write_set_options(3).
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Open
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archive
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See archive_write_open(3).
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Once you have
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prepared the struct archive object, you call
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archive_write_open() to actually open the archive and
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prepare it for writing. There are several variants of this
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function; the most basic expects you to provide pointers to
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several functions that can provide blocks of bytes from the
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archive. There are convenience forms that allow you to
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specify a filename, file descriptor, FILE * object,
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or a block of memory from which to write the archive
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data.
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Produce
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archive
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See archive_write_header(3) and archive_write_data(3).
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Individual
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archive entries are written in a three-step process: You
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first initialize a struct archive_entry structure with
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information about the new entry. At a minimum, you should
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set the pathname of the entry and provide a struct
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stat with a valid st_mode field, which specifies
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the type of object and st_size field, which specifies
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the size of the data portion of the object.
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Release
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resources
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See archive_write_free(3).
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After all
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entries have been written, use the
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archive_write_free() function to release all
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resources.
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EXAMPLE
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The following sketch illustrates
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basic usage of the library. In this example, the callback
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functions are simply wrappers around the standard open(2),
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write(2), and close(2) system calls.
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#ifdef
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__linux__
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       cellspacing="0" cellpadding="0">
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#define
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_FILE_OFFSET_BITS 64
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#endif
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#include <sys/stat.h>
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#include <archive.h>
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#include <archive_entry.h>
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#include <fcntl.h>
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#include <stdlib.h>
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#include <unistd.h>
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struct mydata {
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const char *name;
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int fd;
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};
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int
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myopen(struct archive *a, void *client_data)
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{
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struct mydata *mydata = client_data;
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mydata->fd =
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open(mydata->name, O_WRONLY | O_CREAT, 0644);
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if (mydata->fd >= 0)
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return (ARCHIVE_OK);
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else
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return (ARCHIVE_FATAL);
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}
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la_ssize_t
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mywrite(struct archive *a, void *client_data, const void
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*buff, size_t n)
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{
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struct mydata *mydata = client_data;
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return
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(write(mydata->fd, buff, n));
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}
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int
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myclose(struct archive *a, void *client_data)
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{
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struct mydata *mydata = client_data;
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if
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(mydata->fd > 0)
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close(mydata->fd);
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return (0);
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}
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void
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write_archive(const char *outname, const char **filename)
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{
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struct mydata *mydata = malloc(sizeof(struct mydata));
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struct archive *a;
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struct archive_entry *entry;
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struct stat st;
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char buff[8192];
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int len;
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int fd;
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a =
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archive_write_new();
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mydata->name = outname;
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/* Set archive format and filter according to output file
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extension.
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* If it fails, set default format. Platform depended
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function.
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* See supported formats in
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archive_write_set_format_filter_by_ext.c */
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if (archive_write_set_format_filter_by_ext(a, outname) !=
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ARCHIVE_OK) {
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archive_write_add_filter_gzip(a);
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archive_write_set_format_ustar(a);
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}
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archive_write_open(a, mydata, myopen, mywrite, myclose);
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while (*filename) {
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stat(*filename, &st);
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entry = archive_entry_new();
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archive_entry_copy_stat(entry, &st);
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archive_entry_set_pathname(entry, *filename);
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archive_write_header(a, entry);
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if ((fd = open(*filename, O_RDONLY)) != -1) {
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len = read(fd, buff, sizeof(buff));
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while (len > 0) {
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archive_write_data(a, buff, len);
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len = read(fd, buff, sizeof(buff));
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}
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close(fd);
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}
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archive_entry_free(entry);
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filename++;
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}
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archive_write_free(a);
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}
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int main(int
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argc, const char **argv)
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{
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const char *outname;
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argv++;
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outname = *argv++;
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write_archive(outname, argv);
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return 0;
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}
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SEE ALSO
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tar(1), libarchive(3),
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archive_write_set_options(3), cpio(5), mtree(5), tar(5)
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HISTORY
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The libarchive library
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first appeared in FreeBSD 5.3.
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AUTHORS
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The libarchive library
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was written by Tim Kientzle <kientzle@acm.org>.
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BUGS
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There are many peculiar bugs in
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historic tar implementations that may cause certain programs
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to reject archives written by this library. For example,
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several historic implementations calculated header checksums
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incorrectly and will thus reject valid archives; GNU tar
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does not fully support pax interchange format; some old tar
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implementations required specific field terminations.
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The default pax
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interchange format eliminates most of the historic tar
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limitations and provides a generic key/value attribute
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facility for vendor-defined extensions. One oversight in
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POSIX is the failure to provide a standard attribute for
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large device numbers. This library uses
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’’SCHILY.devminor’’ and
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’’SCHILY.devmajor’’ for device
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numbers that exceed the range supported by the
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backwards-compatible ustar header. These keys are compatible
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with Joerg Schilling’s star archiver. Other
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implementations may not recognize these keys and will thus
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be unable to correctly restore device nodes with large
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device numbers from archives created by this library.
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BSD
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February 2, 2012 BSD
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