spax (1) - Linux Manuals
spax: portable archive interchange
NAME
pax - portable archive interchangeSYNOPSIS
- spax
-
[other options] [-cdnv] [-H|-L] [-f archive] [-o options]... [-s replstr]... [pattern...] - spax
- -r
[other options] [-cdiknuv] [-H|-L] [-f archive] [-o options]... [-p string]... [-s replstr]... [pattern...] - spax
- -w
[other options] [-dituvX] [-H|-L] [-b blocksize] [-a] [-f archive] [-o options]... [-s replstr]... [-x format] [file...] - spax
- -r -w[other options] [-diklntuvX] [-H|-L] [-o
options]... [-p string]... [-s replstr]... [file...] directory
DESCRIPTION
The pax utility shall read, write, and write lists of the members of archive files and copy directory hierarchies. A variety of archive formats shall be supported; see the -x format option.
The action to be taken depends on the presence of the -r and -w options. The four combinations of -r and -w are referred to as the four modes of operation: list, read, write, and copy modes, corresponding respectively to the four forms shown in the SYNOPSIS section.
- list
- In list mode (when neither -r nor -w are specified), pax shall write the names of the members of the archive file read from the standard input, with pathnames matching the specified patterns, to standard output. If a named file is of type directory, the file hierarchy rooted at that file shall be listed as well.
- read
-
In
read
mode (when
-r
is specified, but
-w
is not),
pax
shall extract the members of the archive file read from the
standard input, with pathnames matching the specified
patterns.
If an extracted file is of type directory, the file
hierarchy rooted at that file shall be extracted as well. The
extracted files shall be created performing pathname
resolution with the directory in which
pax
was invoked as the
current working directory.
If an attempt is made to extract a directory when the directory already exists, this shall not be considered an error. If an attempt is made to extract a FIFO when the FIFO already exists, this shall not be considered an error.
The ownership, access, and modification times, and file mode of the restored files are discussed under the -p option.
- write
- In write mode (when -w is specified, but -r is not), pax shall write the contents of the file operands to the standard output in an archive format. If no file operands are specified, a list of files to copy, one per line, shall be read from the standard input. A file of type directory shall include all of the files in the file hierarchy rooted at the file.
- copy
-
In
copy
mode (when both
-r
and
-w
are specified),
pax
shall copy the file operands to the destination directory.
If no file operands are specified, a list of files to copy, one per line, shall be read from the standard input. A file of type directory shall include all of the files in the file hierarchy rooted at the file.
The effect of the copy shall be as if the copied files were written to an archive file and then subsequently extracted, except that there may be hard links between the original and the copied files. If the destination directory is a subdirectory of one of the files to be copied, the results are unspecified. If the destination directory is a file of a type not defined by the System Interfaces volume of IEEE Std 1003.1-2001, the results are implementation-defined; otherwise, it shall be an error for the file named by the directory operand not to exist, not be writable by the user, or not be a file of type directory.
In read or copy modes, if intermediate directories are necessary to extract an archive member, pax shall perform actions equivalent to the mkdir() function defined in the System Interfaces volume of IEEE Std 1003.1-2001, called with the following arguments:
- •
- The intermediate directory used as the path argument.
- •
- The value of the bitwise-inclusive OR of S_IRWXU, S_IRWXG, and S_IRWXO as the mode argument.
If any specified pattern or file operands are not matched by at least one file or archive member, pax shall write a diagnostic message to standard error for each one that did not match and exit with a non-zero exit status.
The archive formats described in the EXTENDED DESCRIPTION section shall be automatically detected on input. The default output archive format shall be implementation-defined.
The spax implementation defaults to -x ustar.
A single archive can span multiple files. The pax utility shall determine, in an implementation-defined manner, what file to read or write as the next file.
If the selected archive format supports the specification of linked files, it shall be an error if these files cannot be linked when the archive is extracted, except that if the files to be linked are symbolic links and the system is not capable of making hard links to symbolic links, then separate copies of the symbolic link shall be created instead. For archive formats that do not store file contents with each name that causes a hard link, if the file that contains the data is not extracted during this pax session, either the data shall be restored from the original file, or a diagnostic message shall be displayed with the name of a file that can be used to extract the data. In traversing directories, pax shall detect infinite loops; that is, entering a previously visited directory that is an ancestor of the last file visited. When it detects an infinite loop, pax shall write a diagnostic message to standard error and shall terminate.
OPTIONS
The pax utility shall conform to the Base Definitions volume of IEEE Std 1003.1-2001, Section 12.2, Utility Syntax Guidelines, except that the order of presentation of the -o, -p, and -s options is significant.
See also the "OTHER OPTIONS" section.
The following options shall be supported:
- -r
- Read an archive file from standard input.
- -w
- Write files to the standard output in the specified archive format.
- -a
- Append files to the end of the archive. It is implementation-defined which devices on the system support appending. Additional file formats unspecified by this volume of IEEE Std 1003.1-2001 may impose restrictions on appending.
- -b blocksize
- Block the output at a positive decimal integer number of bytes per write to the archive file. Devices and archive formats may impose restrictions on blocking. Blocking shall be automatically determined on input. Conforming applications shall not specify a blocksize value larger than 32256. Default blocking when creating archives depends on the archive format. (See the -x option below.)
- -c
- Match all file or archive members except those specified by the pattern or file operands.
- -d
- Cause files of type directory being copied or archived or archive members of type directory being extracted or listed to match only the file or archive member itself and not the file hierarchy rooted at the file.
- -f archive
- Specify the pathname of the input or output archive, overriding the default standard input (in list or read modes) or standard output (write mode).
- -H
- If a symbolic link referencing a file of type directory is specified on the command line, pax shall archive the file hierarchy rooted in the file referenced by the link, using the name of the link as the root of the file hierarchy. Otherwise, if a symbolic link referencing a file of any other file type which pax can normally archive is specified on the command line, then pax shall archive the file referenced by the link, using the name of the link. The default behavior shall be to archive the symbolic link itself.
- -i
-
Interactively rename files or archive members. For each
archive member matching a pattern operand or file matching a
file operand, a prompt shall be written to the file /dev/tty.
The prompt shall contain the name of the file or archive
member, but the format is otherwise unspecified. A line shall
then be read from /dev/tty. If this line is blank, the file
or archive member shall be skipped. If this line consists of
a single period, the file or archive member shall be
processed with no modification to its name. Otherwise, its
name shall be replaced with the contents of the line. The
pax
utility shall immediately exit with a non-zero exit status if
end-of-file is encountered when reading a response or if
/dev/tty cannot be opened for reading and writing.
The results of extracting a hard link to a file that has been renamed during extraction are unspecified.
- -k
- Prevent the overwriting of existing files.
- -l
- (The letter ell.) In copy mode, hard links shall be made between the source and destination file hierarchies whenever possible. If specified in conjunction with -H or -L, when a symbolic link is encountered, the hard link created in the destination file hierarchy shall be to the file referenced by the symbolic link. If specified when neither -H nor -L is specified, when a symbolic link is encountered, the implementation shall create a hard link to the symbolic link in the source file hierarchy or copy the symbolic link to the destination.
- -L
- If a symbolic link referencing a file of type directory is specified on the command line or encountered during the traversal of a file hierarchy, pax shall archive the file hierarchy rooted in the file referenced by the link, using the name of the link as the root of the file hierarchy. Otherwise, if a symbolic link referencing a file of any other file type which pax can normally archive is specified on the command line or encountered during the traversal of a file hierarchy, pax shall archive the file referenced by the link, using the name of the link. The default behavior shall be to archive the symbolic link itself.
- -n
- Select the first archive member that matches each pattern operand. No more than one archive member shall be matched for each pattern (although members of type directory shall still match the file hierarchy rooted at that file).
- -o options
-
Provide information to the implementation to modify the
algorithm for extracting or writing files. The value of
options shall consist of one or more comma-separated keywords
of the form:
-
keyword[[:]=value][,keyword[[:]=value],...]
Some keywords apply only to certain file formats, as indicated with each description. Use of keywords that are inapplicable to the file format being processed produces undefined results.
Keywords in the options argument shall be a string that would be a valid portable filename as described in the Base Definitions volume of IEEE Std 1003.1-2001, Section 3.276, Portable Filename Character Set.
- Note:
- Keywords are not expected to be filenames, merely to follow the same character composition rules as portable filenames.
Keywords can be preceded with white space. The value field shall consist of zero or more characters; within value, the application shall precede any literal comma with a backslash, which shall be ignored, but preserves the comma as part of value. A comma as the final character, or a comma followed solely by white space as the final characters, in options shall be ignored. Multiple -o options can be specified; if keywords given to these multiple -o options conflict, the keywords and values appearing later in command line sequence shall take precedence and the earlier shall be silently ignored. The following keyword values of options shall be supported for the file formats as indicated:
- delete=pattern
-
(Applicable only to the
-x pax
format.) When used in
write or copy mode,
pax
shall omit from extended header
records that it produces any keywords matching the
string pattern. When used in read or list mode,
pax
shall ignore any keywords matching the string pattern in
the extended header records. In both cases, matching
shall be performed using the pattern matching notation
described in Patterns Matching a Single Character and
Patterns Matching Multiple Characters. For example:
-
-o delete=security.*
would suppress security-related information. See pax Extended Header for extended header record keyword usage.
When multiple -o delete=pattern options are specified, the patterns shall be additive; all keywords matching the specified string patterns shall be omitted from extended header records that pax produces.
-
- exthdr.name=string
-
(Applicable only to the
-x pax
format.) This keyword
allows user control over the name that is written into
the ustar header blocks for the extended header produced
under the circumstances described in
pax Header Block.
The name shall be the contents of string, after the
following character substitutions have been made:
-
string Includes: Replaced By: %d The directory name of the file, equivalent to the result of the dirname utility on the translated pathname. %f The filename of the file, equivalent to the result of the basename utility on the translated pathname. %p The process ID of the pax process. %% A '%' character. Any other '%' characters in string produce undefined results.
If no -o exthdr.name= string is specified, pax shall use the following default value:
%d/PaxHeaders.%p/%f
-
- globexthdr.name=string
-
(Applicable only to the
-x pax
format.) When used in
write or copy mode with the appropriate options,
pax
shall create global extended header records with ustar
header blocks that will be treated as regular files by
previous versions of
pax.
This keyword allows user
control over the name that is written into the ustar
header blocks for global extended header records. The
name shall be the contents of string, after the
following character substitutions have been made:
-
string Includes: Replaced By: %n An integer that represents the sequence number of the global extended header record in the archive, starting at 1. %p The process ID of the pax process. %% A '%' character. Any other '%' characters in string produce undefined results.
If no -o globexthdr.name=string is specified, pax shall use the following default value:
$TMPDIR/GlobalHead.%p.%n
where $TMPDIR represents the value of the TMPDIR environment variable. If TMPDIR is not set, pax shall use /tmp.
-
- invalid=action
-
(Applicable only to the
-x pax
format.) This keyword
allows user control over the action
pax
takes upon
encountering values in an extended header record that,
in read or copy mode, are invalid in the destination
hierarchy or, in list mode, cannot be written in the
codeset and current locale of the implementation. The
following are invalid values that shall be recognized by
pax:
-
- +
- In read or copy mode, a filename or link name that contains character encodings invalid in the destination hierarchy. (For example, the name may contain embedded NULs.)
- +
- In read or copy mode, a filename or link name that is longer than the maximum allowed in the destination hierarchy (for either a pathname component or the entire pathname).
- +
- In list mode, any character string value (filename, link name, user name, and so on) that cannot be written in the codeset and current locale of the implementation.
The following mutually-exclusive values of the action argument are supported:
- bypass
- In read or copy mode, pax shall bypass the file, causing no change to the destination hierarchy. In list mode, pax shall write all requested valid values for the file, but its method for writing invalid values is unspecified.
- rename
- In read or copy mode, pax shall act as if the -i option were in effect for each file with invalid filename or link name values, allowing the user to provide a replacement name interactively. In list mode, pax shall behave identically to the bypass action.
- UTF-8
- When used in read, copy, or list mode and a filename, link name, owner name, or any other field in an extended header record cannot be translated from the pax UTF-8 codeset format to the codeset and current locale of the implementation, pax shall use the actual UTF-8 encoding for the name.
- write
- In read or copy mode, pax shall write the file, translating the name, regardless of whether this may overwrite an existing file with a valid name. In list mode, pax shall behave identically to the bypass action.
If no -o invalid=option is specified, pax shall act as if -o invalid= bypass were specified. Any overwriting of existing files that may be allowed by the -o invalid= actions shall be subject to permission(-p) and modification time (-u) restrictions, and shall be suppressed if the -k option is also specified.
-
- linkdata
- (Applicable only to the -x pax format.) In write mode, pax shall write the contents of a file to the archive even when that file is merely a hard link to a file whose contents have already been written to the archive.
- listopt=format
- This keyword specifies the output format of the table of contents produced when the -v option is specified in list mode. See List Mode Format Specifications. To avoid ambiguity, the listopt= format shall be the only or final keyword= value pair in a -o option-argument; all characters in the remainder of the option-argument shall be considered part of the format string. When multiple -o listopt= format options are specified, the format strings shall be considered a single, concatenated string, evaluated in command line order.
- times
- (Applicable only to the -x pax format.) When used in write or copy mode, pax shall include atime and mtime extended header records for each file. See pax Extended Header File Times.
In addition to these keywords, if the -x pax format is specified, any of the keywords and values defined in pax Extended Header, including implementation extensions, can be used in -o option-arguments, in either of two modes:
- keyword=value
- When used in write or copy mode, these keyword/value pairs shall be included at the beginning of the archive as typeflag g global extended header records. When used in read or list mode, these keyword/value pairs shall act as if they had been at the beginning of the archive as typeflag g global extended header records.
- keyword:=value
-
When used in write or copy mode, these keyword/value
pairs shall be included as records at the beginning of a
typeflag x extended header for each file. (This shall be
equivalent to the equal-sign form except that it creates
no typeflag g global extended header records.) When used
in read or list mode, these keyword/value pairs shall
act as if they were included as records at the end of
each extended header; thus, they shall override any
global or file-specific extended header record keywords
of the same names. For example, in the command:
-
pax -r -o "gname:=mygroup," <archive
the group name will be forced to a new value for all files read from the archive.
-
The precedence of -o keywords over various fields in the archive is described in pax Extended Header Keyword Precedence.
-
- -p string
-
Specify one or more file characteristic options (privileges).
The string option-argument shall be a string specifying file
characteristics to be retained or discarded on extraction.
The string shall consist of the specification characters a ,
e, m, o, and p. Other implementation-defined characters can
be included. Multiple characteristics can be concatenated
within the same string and multiple
-p
options can be
specified. The meaning of the specification characters are as
follows:
-
- a
- Do not preserve file access times.
- e
- Preserve the user ID, group ID, file mode bits (see the Base Definitions volume of IEEE Std 1003.1-2001, Section 3.168, File Mode Bits), access time, modification time, and any other implementation-defined file characteristics.
- m
-
Do not preserve file modification times.
- o
- Preserve the user ID and group ID.
- p
- Preserve the file mode bits. Other implementation-defined file mode attributes may be preserved.
In the preceding list, "preserve" indicates that an attribute stored in the archive shall be given to the extracted file, subject to the permissions of the invoking process. The access and modification times of the file shall be preserved unless otherwise specified with the -p option or not stored in the archive. All attributes that are not preserved shall be determined as part of the normal file creation action (see File Read, Write, and Creation).
If neither the e nor the o specification character is specified, or the user ID and group ID are not preserved for any reason, pax shall not set the S_ISUID and S_ISGID bits of the file mode.
If the preservation of any of these items fails for any reason, pax shall write a diagnostic message to standard error. Failure to preserve these items shall affect the final exit status, but shall not cause the extracted file to be deleted.
If file characteristic letters in any of the string option-arguments are duplicated or conflict with each other, the ones given last shall take precedence. For example, if -p eme is specified, file modification times are preserved.
-
- -s replstr
-
Modify file or archive member names named by pattern or file
operands according to the substitution expression replstr,
using the syntax of the ed utility. The concepts of "address"
and "line" are meaningless in the context of the
pax
utility,
and shall not be supplied. The format shall be:
-
-s /old/new/[gp]
where as in ed, old is a basic regular expression and new can contain an ampersand, '\n' (where n is a digit) backreferences, or subexpression matching. The old string shall also be permitted to contain <newline>s.
Any non-null character can be used as a delimiter ( '/' shown here). Multiple -s expressions can be specified; the expressions shall be applied in the order specified, terminating with the first successful substitution. The optional trailing 'g' is as defined in the ed utility. The optional trailing 'p' shall cause successful substitutions to be written to standard error. File or archive member names that substitute to the empty string shall be ignored when reading and writing archives.
-
- -t
- When reading files from the file system, and if the user has the permissions required by utime() to do so, set the access time of each file read to the access time that it had before being read by pax.
- -u
- Ignore files that are older (having a less recent file modification time) than a pre-existing file or archive member with the same name. In read mode, an archive member with the same name as a file in the file system shall be extracted if the archive member is newer than the file. In write mode, an archive file member with the same name as a file in the file system shall be superseded if the file is newer than the archive member. If -a is also specified, this is accomplished by appending to the archive; otherwise, it is unspecified whether this is accomplished by actual replacement in the archive or by appending to the archive. In copy mode, the file in the destination hierarchy shall be replaced by the file in the source hierarchy or by a link to the file in the source hierarchy if the file in the source hierarchy is newer.
- -v
- In list mode, produce a verbose table of contents (see the STDOUT section). Otherwise, write archive member pathnames to standard error (see the STDERR section).
- -x format
-
Specify the output archive format. The
pax
utility shall
support the following formats:
-
- cpio
- The cpio interchange format; see the EXTENDED DESCRIPTION section. The default blocksize for this format for character special archive files shall be 5120. Implementations shall support all blocksize values less than or equal to 32256 that are multiples of 512.
- pax
- The pax interchange format; see the EXTENDED DESCRIPTION section. The default blocksize for this format for character special archive files shall be 5120. Implementations shall support all blocksize values less than or equal to 32256 that are multiples of 512.
- ustar
- The tar interchange format; see the EXTENDED DESCRIPTION section. The default blocksize for this format for character special archive files shall be 10240. Implementations shall support all blocksize values less than or equal to 32256 that are multiples of 512.
Implementation-defined formats shall specify a default block size as well as any other block sizes supported for character special archive files.
Any attempt to append to an archive file in a format different from the existing archive format shall cause pax to exit immediately with a non-zero exit status.
In copy mode, if no -x format is specified, pax shall behave as if -x pax were specified.
-
- -X
- When traversing the file hierarchy specified by a pathname, pax shall not descend into directories that have a different device ID ( st_dev; see the System Interfaces volume of IEEE Std 1003.1-2001, stat()).
Specifying more than one of the mutually-exclusive options -H and -L shall not be considered an error and the last option specified shall determine the behavior of the utility.
The options that operate on the names of files or archive members (-c, -i, -n, -s, -u, and -v) shall interact as follows. In read mode, the archive members shall be selected based on the user-specified pattern operands as modified by the -c, -n, and -u options. Then, any -s and -i options shall modify, in that order, the names of the selected files. The -v option shall write names resulting from these modifications.
In write mode, the files shall be selected based on the user-specified pathnames as modified by the -n and -u options. Then, any -s and -i options shall modify, in that order, the names of these selected files. The -v option shall write names resulting from these modifications.
If both the -u and -n options are specified, pax shall not consider a file selected unless it is newer than the file to which it is compared.
List Mode Format Specifications
The manual page for spax is not yet ready. The following text is a quotation from the POSIX.1-2001 standard.
In list mode with the -o listopt=format option, the format argument shall be applied for each selected file. The pax utility shall append a <newline> to the listopt output for each selected file. The format argument shall be used as the format string described in the Base Definitions volume of IEEE Std 1003.1-2001, Chapter 5, File Format Notation, with the exceptions 1. through 5. defined in the EXTENDED DESCRIPTION section of printf(3), plus the following exceptions:
- 6.
-
The sequence
(keyword)
can occur before a format conversion
specifier. The conversion argument is defined by the value of
keyword.
The implementation shall support the following
keywords:
-
- •
- Any of the Field Name entries in ustar Header Block and Octet-Oriented cpio Archive Entry. The implementation may support the cpio keywords without the leading c_ in addition to the form required by Values for cpio c_mode Field.
- •
- Any keyword defined for the extended header in pax Extended Header.
- •
- Any keyword provided as an implementation-defined extension within the extended header defined in pax Extended Header.
For example, the sequence "%(charset)s" is the string value of the name of the character set in the extended header.
The result of the keyword conversion argument shall be the value from the applicable header field or extended header, without any trailing NULs.
All keyword values used as conversion arguments shall be translated from the UTF-8 encoding to the character set appropriate for the local file system, user database, and so on, as applicable.
-
- 7.
- An additional conversion specifier character, T, shall be used to specify time formats. The T conversion specifier character can be preceded by the sequence (keyword=subformat), where subformat is a date format as defined by date operands. The default keyword shall be mtime and the default subformat shall be:
Otherwise, the
%L
conversion specification shall be the
equivalent of
%F.
The following operands shall be supported:
In
write
mode, the standard input shall be used only if no
file
operands are specified. It shall be a text file containing a list
of pathnames, one per line, without leading or trailing <blank>s.
In
list
and
read
modes, if
-f
is not specified, the standard input
shall be an archive file.
Otherwise, the standard input shall not be used.
The input file named by the
archive
option-argument, or standard
input when the archive is read from there, shall be a file
formatted according to one of the specifications in the EXTENDED
DESCRIPTION section or some other implementation-defined format.
The file
/dev/tty
shall be used to write prompts and read
responses.
The following environment variables shall affect the execution of
pax:
Default.
In
write
mode, if
-f
is not specified, the standard output shall
be the archive formatted according to one of the specifications in
the EXTENDED DESCRIPTION section, or some other
implementation-defined format (see
-x format).
In
list
mode, when the
-o listopt=
format has been specified, the
selected archive members shall be written to standard output using
the format described under List Mode Format Specifications. In
list
mode without the
-o listopt=
format option, the table of
contents of the selected archive members shall be written to
standard output using the following format:
If the
-v
option is specified in
list
mode, the table of contents
of the selected archive members shall be written to standard
output using the following formats.
For pathnames representing hard links to previous members of the
archive:
For all other pathnames:
where
<ls -l listing>
shall be the format specified by the
ls(1)
utility with the
-l
option. When writing pathnames in this format,
it is unspecified what is written for fields for which the
underlying archive format does not have the correct information,
although the correct number of <blank>-separated fields shall be
written.
In
list
mode, standard output shall not be buffered more than a
line at a time.
If
-v
is specified in
read,
write,
or
copy
modes,
pax
shall write
the pathnames it processes to the standard error output using the
following format:
These pathnames shall be written as soon as processing is begun on
the file or archive member, and shall be flushed to standard
error. The trailing <newline>, which shall not be buffered, is
written when the file has been read or written.
If the
-s
option is specified, and the replacement string has a
trailing
'p',
substitutions shall be written to standard error in
the following format:
In all operating modes of
pax,
optional messages of unspecified
format concerning the input archive format and volume number, the
number of files, blocks, volumes, and media parts as well as other
diagnostic messages may be written to standard error.
In all formats, for both standard output and standard error, it is
unspecified how non-printable characters in pathnames or link
names are written.
When
pax
is in
read
mode or
list
mode, using the
-x pax
archive
format, and a filename, link name, owner name, or any other field
in an extended header record cannot be translated from the
pax
UTF-8 codeset format to the codeset and current locale of the
implementation,
pax
shall write a diagnostic message to standard
error, shall process the file as described for the
-o invalid=
option, and then shall process the next file in the archive.
In
read
mode, the extracted output files shall be of the archived
file type. In
copy
mode, the copied output files shall be the type
of the file being copied. In either mode, existing files in the
destination hierarchy shall be overwritten only when all
permission
(-p),
modification time
(-u),
and invalid-value
(-o invalid=)
tests allow it.
In
write
mode, the output file named by the
-f
option-argument
shall be a file formatted according to one of the specifications
in the EXTENDED DESCRIPTION section, or some other
implementation-defined format.
A
pax
archive tape or file produced in the
-x pax
format shall
contain a series of blocks. The physical layout of the archive
shall be identical to the
ustar
format described in ustar
Interchange Format. Each file archived shall be represented by the
following sequence:
At the end of the archive file there shall be two 512-byte blocks
filled with binary zeros, interpreted as an end-of-archive
indicator.
A schematic of an example archive with global extended header
records and two actual files is shown in
pax Format Archive
Example. In the example, the second file in the archive has no
extended header preceding it, presumably because it has no need
for extended attributes.
The
pax
header block shall be identical to the
ustar
header block
described in
ustar Interchange Format,
except that two additional
typeflag
values are defined:
For both of these types, the size field shall be the size of the
extended header records in octets. The other fields in the header
block are not meaningful to this version of the
pax
utility.
However, if this archive is read by a
pax
utility conforming to
the ISO POSIX-2:1993 standard, the header block fields are used to
create a regular file that contains the extended header records as
data. Therefore, header block field values should be selected to
provide reasonable file access to this regular file.
A further difference from the
ustar
header block is that data
blocks for files of
typeflag
1
(the digit one) (hard link) may be
included, which means that the size field may be greater than
zero. Archives created by
pax -o linkdata
shall include these data
blocks with the hard links.
A
pax
extended header contains values that are inappropriate for
the
ustar
header block because of limitations in that format:
fields requiring a character encoding other than that described in
the ISO/IEC 646:1991 standard, fields representing file attributes
not described in the
ustar
header, and fields whose format or
length do not fit the requirements of the
ustar
header. The values
in an extended header add attributes to the following file (or
files; see the description of the
typeflag
g
header block) or
override values in the following header block(s), as indicated in
the following list of keywords.
An extended header shall consist of one or more records, each
constructed as follows:
The extended header records shall be encoded according to the
ISO/IEC 10646-1:2000 standard (UTF-8). The
<length>
field,
<blank>, equals sign, and <newline> shown shall be limited to the
portable character set, as encoded in UTF-8. The
<keyword>
and
<value>
fields can be any UTF-8 characters. The
<length>
field
shall be the decimal length of the extended header record in
octets, including the trailing <newline>.
The
<keyword>
field shall be one of the entries from the following
list or a keyword provided as an implementation extension.
Keywords consisting entirely of lowercase letters, digits, and
periods are reserved for future standardization. A keyword shall
not include an equals sign. (In the following list, the notations
"file(s)" or "block(s)" is used to acknowledge that a keyword
affects the following single file after a
typeflag
x
extended
header, but possibly multiple files after
typeflag
g.
Any requirements in the list for
pax
to include a record when in
write
or
copy
mode shall apply only when such a record has not already
been provided through the use of the
-o
option. When used in
copy
mode,
pax
shall behave as if an archive had been created with
applicable extended header records and then extracted.)
The encoding is included in an extended header for
information only; when
pax
is used as described in
IEEE Std 1003.1-2001, it shall not translate the file data
into any other encoding. The
BINARY
entry indicates unencoded binary data.
When used in
write
or
copy
mode, it is implementation-defined
whether
pax
includes a charset extended header record for a file.
When used in
write
or
copy
mode,
pax
shall include a
path
extended header record for each file whose pathname cannot be
represented entirely with the members of the portable
character set other than NUL.
If the
<value>
field is zero length, it shall delete any header
block field, previously entered extended header value, or global
extended header value of the same name.
If a keyword in an extended header record (or in a
-o
option-argument) overrides or deletes a corresponding field in the
ustar
header block,
pax
shall ignore the contents of that header block field.
Unlike the
ustar
header block fields, NULs shall not delimit
<value>s;
all characters within the
<value>
field shall be
considered data for the field. None of the length limitations of
the
ustar
header block fields in
ustar Header Block
shall apply to the extended header records.
This section describes the precedence in which the various header
records and fields and command line options are selected to apply
to a file in the archive. When
pax
is used in
read
or
list
modes, it shall determine a file attribute in the following sequence:
The
pax
utility shall write an
mtime
record for each file in
write
or
copy
modes if the file's modification time cannot be
represented exactly in the
ustar
header logical record described
in
ustar Interchange Format.
This can occur if the time is out of
ustar
range, or if the file system of the underlying
implementation supports non-integer time granularities and the
time is not an integer. All of these time records shall be
formatted as a decimal representation of the time in seconds since
the Epoch. If a period ('.') decimal point character is present,
the digits to the right of the point shall represent the units of
a subsecond timing granularity, where the first digit is tenths of
a second and each subsequent digit is a tenth of the previous
digit. In
read
or
copy
mode, the
pax
utility shall truncate the
time of a file to the greatest value that is not greater than the
input header file time. In
write
or
copy
mode, the
pax
utility
shall output a time exactly if it can be represented exactly as a
decimal number, and otherwise shall generate only enough digits so
that the same time shall be recovered if the file is extracted on
a system whose underlying implementation supports the same time
granularity.
The logical records may be grouped for physical I/O operations, as
described under the
-b blocksize
and
-x ustar
options. Each group
of logical records may be written with a single operation
equivalent to the
write(2)
function. On magnetic tape, the result
of this write shall be a single tape physical block. The last
physical block shall always be the full size, so logical records
after the two zero logical records may contain undefined data.
The header logical record shall be structured as shown in the
following table. All lengths and offsets are in decimal.
All characters in the header logical record shall be represented
in the coded character set of the ISO/IEC 646:1991 standard. For
maximum portability between implementations, names should be
selected from characters represented by the portable filename
character set as octets with the most significant bit zero. If an
implementation supports the use of characters outside of slash and
the portable filename character set in names for files, users, and
groups, one or more implementation-defined encodings of these
characters shall be provided for interchange purposes.
However, the
pax
utility shall never create filenames on the local
system that cannot be accessed via the procedures described in
IEEE Std 1003.1-2001. If a filename is found on the medium that
would create an invalid filename, it is implementation-defined
whether the data from the file is stored on the file hierarchy and
under what name it is stored. The
pax
utility may choose to ignore
these files as long as it produces an error indicating that the
file is being ignored.
Each field within the header logical record is contiguous; that
is, there is no padding used. Each character on the archive medium
shall be stored contiguously.
The fields
magic,
uname,
and
gname
are character strings each
terminated by a NUL character. The fields
name,
linkname,
and
prefix
are NUL-terminated character strings except when all
characters in the array contain non-NUL characters including the
last character. The
version
field is two octets containing the
characters "00" (zero-zero). The
typeflag
contains a single
character. All other fields are leading zero-filled octal numbers
using digits from the ISO/IEC 646:1991 standard IRV. Each numeric
field is terminated by one or more <space> or NUL characters.
The
name
and the
prefix
fields shall produce the pathname of the
file. A new pathname shall be formed, if
prefix
is not an empty
string (its first character is not NUL), by concatenating
prefix
(up to the first NUL character), a slash character, and
name;
otherwise,
name
is used alone. In either case,
name
is terminated
at the first NUL character. If
prefix
begins with a NUL character,
it shall be ignored. In this manner, pathnames of at most 256
characters can be supported. If a pathname does not fit in the
space provided,
pax
shall notify the user of the error, and shall
not store any part of the file-header or data-on the medium.
The
linkname
field, described below, shall not use the
prefix
to
produce a pathname. As such, a
linkname
is limited to 100
characters. If the name does not fit in the space provided,
pax
shall notify the user of the error, and shall not attempt to store
the link on the medium.
The
mode
field provides 12 bits encoded in the ISO/IEC 646:1991
standard octal digit representation. The encoded bits shall
represent the following values:
When appropriate privilege is required to set one of these mode
bits, and the user restoring the files from the archive does not
have the appropriate privilege, the mode bits for which the user
does not have appropriate privilege shall be ignored. Some of the
mode bits in the archive format are not mentioned elsewhere in
this volume of IEEE Std 1003.1-2001. If the implementation does
not support those bits, they may be ignored.
The
uid and
gid
fields are the user and group ID of the owner and
group of the file, respectively.
The
size
field is the size of the file in octets. If the
typeflag
field is set to specify a file to be of type 1 (a link) or 2 (a
symbolic link), the
size
field shall be specified as zero. If the
typeflag
field is set to specify a file of type 5 (directory), the
size field shall be interpreted as described under the definition
of that record type. No data logical records are stored for types
1, 2, or 5. If the typeflag field is set to 3 (character special
file), 4 (block special file), or 6 (FIFO), the meaning of the
size
field is unspecified by this volume of IEEE Std 1003.1-2001,
and no data logical records shall be stored on the medium.
Additionally, for type 6, the
size
field shall be ignored when
reading. If the
typeflag
field is set to any other value, the
number of logical records written following the header shall be
(size+511)/512, ignoring any fraction in the result of the
division.
The
mtime
field shall be the modification time of the file at the
time it was archived. It is the ISO/IEC 646:1991 standard
representation of the octal value of the modification time
obtained from the
stat(2)
function.
The
chksum
field shall be the ISO/IEC 646:1991 standard IRV
representation of the octal value of the simple sum of all octets
in the header logical record. Each octet in the header shall be
treated as an unsigned value. These values shall be added to an
unsigned integer, initialized to zero, the precision of which is
not less than 17 bits. When calculating the checksum, the
chksum
field is treated as if it were all spaces.
The
typeflag
field specifies the type of file archived. If a
particular implementation does not recognize the type, or the user
does not have appropriate privilege to create that type, the file
shall be extracted as if it were a regular file if the file type
is defined to have a meaning for the
size
field that could cause
data logical records to be written on the medium (see the previous
description for
size).
If conversion to a regular file occurs, the
pax
utility shall produce an error indicating that the conversion
took place. All of the
typeflag
fields shall be coded in the
ISO/IEC 646:1991 standard IRV:
It is unspecified whether files with pathnames that refer to the
same directory entry are archived as linked files or as separate
files. If they are archived as linked files, this means that
attempting to extract both pathnames from the resulting archive
will always cause an error (unless the
-u
option is used) because
the link cannot be created.
It is unspecified whether files with the same device and file
serial numbers being appended to an archive are treated as linked
files to members that were in the archive before the append.
Attempts to archive a socket using
ustar
interchange format shall
produce a diagnostic message. Handling of other file types is
implementation-defined.
The
magic
field is the specification that this archive was output
in this archive format. If this field contains
ustar
(the five
characters from the ISO/IEC 646:1991 standard IRV shown followed
by NUL), the
uname
and
gname
fields shall contain the
ISO/IEC 646:1991 standard IRV representation of the owner and
group of the file, respectively (truncated to fit, if necessary).
When the file is restored by a privileged, protection-preserving
version of the utility, the user and group databases shall be
scanned for these names. If found, the user and group IDs
contained within these files shall be used rather than the values
contained within the
uid
and
gid
fields.
The octet-oriented
cpio
archive format shall be a series of
entries, each comprising a header that describes the file, the
name of the file, and then the contents of the file.
An archive may be recorded as a series of fixed-size blocks of
octets. This blocking shall be used only to make physical I/O more
efficient. The last group of blocks shall always be at the full
size.
For the octet-oriented
cpio
archive format, the individual entry
information shall be in the order indicated and described by the
following table; see also the
<cpio.h>
header.
For each file in the archive, a header as defined previously shall
be written. The information in the header fields is written as
streams of the ISO/IEC 646:1991 standard characters interpreted as
octal numbers. The octal numbers shall be extended to the
necessary length by appending the ISO/IEC 646:1991 standard IRV
zeros at the most-significant-digit end of the number; the result
is written to the most-significant digit of the stream of octets
first. The fields shall be interpreted as follows:
Directories, FIFOs, symbolic links, and regular files shall
be supported on a system conforming to this volume of
IEEE Std 1003.1-2001; additional values defined previously
are reserved for compatibility with existing systems.
Additional file types may be supported; however, such files
should not be written to archives intended to be transported
to other systems.
The
c_name
field shall contain the pathname of the file. The
length of this field in octets is the value of
c_namesize.
If a filename is found on the medium that would create an invalid
pathname, it is implementation-defined whether the data from the
file is stored on the file hierarchy and under what name it is
stored.
All characters shall be represented in the ISO/IEC 646:1991
standard IRV. For maximum portability between implementations,
names should be selected from characters represented by the
portable filename character set as octets with the most
significant bit zero. If an implementation supports the use of
characters outside the portable filename character set in names
for files, users, and groups, one or more implementation-defined
encodings of these characters shall be provided for interchange
purposes. However, the
pax
utility shall never create filenames on
the local system that cannot be accessed via the procedures
described previously in this volume of IEEE Std 1003.1-2001. If a
filename is found on the medium that would create an invalid
filename, it is implementation-defined whether the data from the
file is stored on the local file system and under what name it is
stored. The
pax
utility may choose to ignore these files as long
as it produces an error indicating that the file is being ignored.
Following
c_name,
there shall be
c_filesize
octets of data.
Interpretation of such data occurs in a manner dependent on the
file. If
c_filesize
is zero, no data shall be contained in
c_filedata.
When restoring from an archive:
FIFO special files, directories, and the trailer shall be recorded
with
c_filesize
equal to zero. For other special files,
c_filesize
is unspecified by this volume of IEEE Std 1003.1-2001. The header
for the next file entry in the archive shall be written directly
after the last octet of the file entry preceding it. A header
denoting the filename
TRAILER!!!
shall indicate the end of the
archive; the contents of octets in the last block of the archive
following such a header are undefined.
The following exit values shall be returned:
If
pax
cannot create a file or a link when reading an archive or
cannot find a file when writing an archive, or cannot preserve the
user ID, group ID, or file mode when the
-p
option is specified, a
diagnostic message shall be written to standard error and a
non-zero exit status shall be returned, but processing shall
continue. In the case where
pax
cannot create a link to a file,
pax
shall not, by default, create a second copy of the file.
If the extraction of a file from an archive is prematurely
terminated by a signal or error,
pax
may have only partially
extracted the file or (if the
-n
option was not specified) may
have extracted a file of the same name as that specified by the
user, but which is not the file the user wanted. Additionally, the
file modes of extracted directories may have additional bits from
the S_IRWXU mask set as well as incorrect modification and access
times.
Caution is advised when using the
-a
option to append to a
cpio
format archive. If any of the files being appended happen to be
given the same
c_dev
and
c_ino
values as a file in the existing
part of the archive, then they may be treated as links to that
file on extraction. Thus, it is risky to use
-a
with
cpio
format
except when it is done on the same system that the original
archive was created on, and with the same
pax
utility, and in the
knowledge that there has been little or no file system activity
since the original archive was created that could lead to any of
the files appended being given the same
c_dev
and
c_ino
values as
an unrelated file in the existing part of the archive. Also, when
(intentionally) appending additional links to a file in the
existing part of the archive, the
c_nlink
values in the modified
archive can be smaller than the number of links to the file in the
archive, which may mean that the links are not preserved on
extraction.
The
-p
(privileges) option was invented to reconcile differences
between historical
tar
and
cpio
implementations. In particular,
the two utilities use
-m
in diametrically opposed ways. The
-p
option also provides a consistent means of extending the ways in
which future file attributes can be addressed, such as for
enhanced security systems or high-performance files. Although it
may seem complex, there are really two modes that are most
commonly used:
The one pathname per line format of standard input precludes
pathnames containing <newline>s. Although such pathnames violate
the portable filename guidelines, they may exist and their
presence may inhibit usage of
pax
within shell scripts. This
problem is inherited from historical archive programs. The problem
can be avoided by listing filename arguments on the command line
instead of on standard input.
It is almost certain that appropriate privileges are required for
pax
to accomplish parts of this volume of IEEE Std 1003.1-2001.
Specifically, creating files of type block special or character
special, restoring file access times unless the files are owned by
the user (the
-t
option), or preserving file owner, group, and
mode (the
-p
option) all probably require appropriate privileges.
In
read
mode, implementations are permitted to overwrite files
when the archive has multiple members with the same name. This may
fail if permissions on the first version of the file do not permit
it to be overwritten.
The
cpio
and
ustar
formats can only support files up to 8589934592
bytes (8 * 2^30) in size.
The following command:
copies the contents of the current directory to tape drive 1,
medium density (assuming historical System V device naming
procedures-the historical BSD device name would be /dev/rmt9).
The following commands:
copy the olddir directory hierarchy to newdir.
reads the archive a.pax, with all files rooted in /usr in the
archive extracted relative to the current directory.
Using the option:
overrides the default output description in Standard Output and
instead writes:
Using the options:
overrides the default output description in Standard Output and
instead writes:
/usr/foo/bar -> /tmp 1492
The
pax
utility was new for the ISO POSIX-2:1993 standard. It
represents a peaceful compromise between advocates of the
historical
tar
and
cpio
utilities.
A fundamental difference between
cpio
and
tar
was in the way
directories were treated. The
cpio
utility did not treat
directories differently from other files, and to select a
directory and its contents required that each file in the
hierarchy be explicitly specified. For
tar,
a directory matched
every file in the file hierarchy it rooted.
The
pax
utility offers both interfaces; by default, directories
map into the file hierarchy they root. The
-d
option causes
pax
to
skip any file not explicitly referenced, as
cpio
historically did.
The
tar
- style behavior was chosen as the default because it was
believed that this was the more common usage and because
tar
is
the more commonly available interface, as it was historically
provided on both System V and BSD implementations.
The data interchange format specification in this volume of
IEEE Std 1003.1-2001 requires that processes with "appropriate
privileges" shall always restore the ownership and permissions of
extracted files exactly as archived. If viewed from the historic
equivalence between superuser and "appropriate privileges", there
are two problems with this requirement. First, users running as
superusers may unknowingly set dangerous permissions on extracted
files. Second, it is needlessly limiting, in that superusers
cannot extract files and own them as superuser unless the archive
was created by the superuser. (It should be noted that restoration
of ownerships and permissions for the superuser, by default, is
historical practice in
cpio,
but not in
tar.)
In order to avoid
these two problems, the
pax
specification has an additional
"privilege" mechanism, the
-p
option. Only a
pax
invocation with
the privileges needed, and which has the
-p
option set using the
e
specification character, has the "appropriate privilege" to
restore full ownership and permission information.
Note also that this volume of IEEE Std 1003.1-2001 requires that
the file ownership and access permissions shall be set, on
extraction, in the same fashion as the
creat(2)
function when
provided with the mode stored in the archive. This means that the
file creation mask of the user is applied to the file permissions.
Users should note that directories may be created by
pax
while
extracting files with permissions that are different from those
that existed at the time the archive was created. When extracting
sensitive information into a directory hierarchy that no longer
exists, users are encouraged to set their file creation mask
appropriately to protect these files during extraction.
The table of contents output is written to standard output to
facilitate pipeline processing.
An early proposal had hard links displaying for all pathnames.
This was removed because it complicates the output of the case
where
-v
is not specified and does not match historical
cpio
usage. The hard-link information is available in the
-v
display.
The description of the
-l
option allows implementations to make
hard links to symbolic links. IEEE Std 1003.1-2001 does not
specify any way to create a hard link to a symbolic link, but many
implementations provide this capability as an extension. If there
are hard links to symbolic links when an archive is created, the
implementation is required to archive the hard link in the archive
(unless
-H
or
-L
is specified). When in
read
mode and in
copy
mode, implementations supporting hard links to symbolic links
should use them when appropriate.
The archive formats inherited from the POSIX.1-1990 standard have
certain restrictions that have been brought along from historical
usage. For example, there are restrictions on the length of
pathnames stored in the archive. When
pax is used in
copy (-rw)
mode (copying directory hierarchies), the ability to use
extensions from the
-x pax
format overcomes these restrictions.
The default blocksize value of 5120 bytes for
cpio
was selected
because it is one of the standard block-size values for
cpio,
set
when the
-B
option is specified. (The other default block-size
value for
cpio
is 512 bytes, and this was considered to be too
small.) The default block value of 10240 bytes for
tar
was selected because that is the standard block-size value for BSD
tar.
The maximum block size of 32256 bytes (2^15-512 bytes) is the
largest multiple of 512 bytes that fits into a signed 16-bit tape
controller transfer register. There are known limitations in some
historical systems that would prevent larger blocks from being
accepted. Historical values were chosen to improve compatibility
with historical scripts using
dd(1)
or similar utilities to
manipulate archives. Also, default block sizes for any file type
other than character special file has been deleted from this
volume of IEEE Std 1003.1-2001 as unimportant and not likely to
affect the structure of the resulting archive.
Implementations are permitted to modify the block-size value based
on the archive format or the device to which the archive is being
written. This is to provide implementations with the opportunity
to take advantage of special types of devices, and it should not
be used without a great deal of consideration as it almost
certainly decreases archive portability.
The intended use of the
-n
option was to permit extraction of one
or more files from the archive without processing the entire
archive. This was viewed by the standard developers as offering
significant performance advantages over historical
implementations. The
-n
option in early proposals had three
effects; the first was to cause special characters in patterns to
not be treated specially. The second was to cause only the first
file that matched a pattern to be extracted. The third was to
cause
pax
to write a diagnostic message to standard error when no
file was found matching a specified pattern. Only the second
behavior is retained by this volume of IEEE Std 1003.1-2001, for
many reasons. First, it is in general not acceptable for a single
option to have multiple effects. Second, the ability to make
pattern matching characters act as normal characters is useful for
parts of
pax
other than file extraction. Third, a finer degree of
control over the special characters is useful because users may
wish to normalize only a single special character in a single
filename. Fourth, given a more general escape mechanism, the
previous behavior of the
-n
option can be easily obtained using
the
-s
option or a sed script. Finally, writing a diagnostic
message when a pattern specified by the user is unmatched by any
file is useful behavior in all cases.
In this version, the
-n
was removed from the copy mode synopsis of
pax;
it is inapplicable because there are no pattern operands
specified in this mode.
There is another method than
pax
for copying subtrees in
IEEE Std 1003.1-2001 described as part of the
cp(1)
utility. Both
methods are historical practice:
cp(1)
provides a simpler, more
intuitive interface, while
pax
offers a finer granularity of
control. Each provides additional functionality to the other; in
particular,
pax
maintains the hard-link structure of the hierarchy
while
cp(1)
does not. It is the intention of the standard developers
that the results be similar (using appropriate option combinations
in both utilities). The results are not required to be identical;
there seemed insufficient gain to applications to balance the
difficulty of implementations having to guarantee that the results
would be exactly identical.
A single archive may span more than one file. It is suggested that
implementations provide informative messages to the user on
standard error whenever the archive file is changed.
The
-d
option (do not create intermediate directories not listed
in the archive) found in early proposals was originally provided
as a complement to the historic
-d
option of
cpio.
It has been deleted.
The
-s
option in early proposals specified a subset of the
substitution command from the ed utility. As there was no reason
for only a subset to be supported, the
-s
option is now compatible
with the current ed specification. Since the delimiter can be any
non-null character, the following usage with single spaces is
valid:
The
-t description is worded so as to note that this may cause the
access time update caused by some other activity (which occurs
while the file is being read) to be overwritten.
The default behavior of
pax
with regard to file modification times
is the same as historical implementations of
tar.
It is not the
historical behavior of
cpio.
Because the
-i
option uses
/dev/tty,
utilities without a
controlling terminal are not able to use this option.
The
-y
option, found in early proposals, has been deleted because
a line containing a single period for the
-i
option has equivalent
functionality. The special lines for the
-i
option (a single
period and the empty line) are historical practice in
cpio.
In early drafts, a
-e charmap
option was included to increase
portability of files between systems using different coded
character sets. This option was omitted because it was apparent
that consensus could not be formed for it. In this version, the
use of UTF-8 should be an adequate substitute.
The
-k
option was added to address international concerns about
the dangers involved in the character set transformations of
-e
(if the target character set were different from the source, the
filenames might be transformed into names matching existing files)
and also was made more general to protect files transferred
between file systems with different
{NAME_MAX}
values (truncating
a filename on a smaller system might also inadvertently overwrite
existing files). As stated, it prevents any overwriting, even if
the target file is older than the source. This version adds more
granularity of options to solve this problem by introducing the
-o invalid=option
- specifically the UTF-8 action. (Note that an
existing file that is named with a UTF-8 encoding is still subject
to overwriting in this case. The
-k
option closes that loophole.)
Some of the file characteristics referenced in this volume of
IEEE Std 1003.1-2001 might not be supported by some archive
formats. For example, neither the
tar
nor
cpio
formats contain the
file access time. For this reason, the
e
specification character
has been provided, intended to cause all file characteristics
specified in the archive to be retained.
It is required that extracted directories, by default, have their
access and modification times and permissions set to the values
specified in the archive. This has obvious problems in that the
directories are almost certainly modified after being extracted
and that directory permissions may not permit file creation. One
possible solution is to create directories with the mode specified
in the archive, as modified by the
umask
of the user, with
sufficient permissions to allow file creation. After all files
have been extracted,
pax
would then reset the access and
modification times and permissions as necessary.
The list-mode formatting description borrows heavily from the one
defined by the
printf(1)
utility. However, since there is no separate
operand list to get conversion arguments, the format was extended
to allow specifying the name of the conversion argument as part of
the conversion specification.
The
T
conversion specifier allows time fields to be displayed in
any of the date formats. Unlike the
ls(1)
utility,
pax
does not
adjust the format when the date is less than six months in the
past. This makes parsing the output more predictable.
The
D
conversion specifier handles the ability to display the
major/minor or file size, as with
ls(1),
by using %-8(size)D.
The
L
conversion specifier handles the ls display for symbolic
links.
Conversion specifiers were added to generate existing known types
used for
ls(1).
The new POSIX data interchange format was developed primarily to
satisfy international concerns that the
ustar
and
cpio
formats did
not provide for file, user, and group names encoded in characters
outside a subset of the ISO/IEC 646:1991 standard. The standard
developers realized that this new POSIX data interchange format
should be very extensible because there were other requirements
they foresaw in the near future:
The following were not goals for this format because these are
better handled by separate utilities or are inappropriate for a
portable format:
The format chosen to support the goals is an extension of the
ustar
format. Of the two formats previously available, only the
ustar
format was selected for extensions because:
The new format was designed with one additional goal in mind:
reasonable behavior when an older
tar
or
pax
utility happened to
read an archive. Since the POSIX.1-1990 standard mandated that a
"format-reading utility" had to treat unrecognized
typeflag
values
as regular files, this allowed the format to include all the
extended information in a pseudo-regular file that preceded each
real file. An option is given that allows the archive creator to
set up reasonable names for these files on the older systems.
Also, the normative text suggests that reasonable file access
values be used for this
ustar
header block. Making these header
files inaccessible for convenient reading and deleting would not
be reasonable. File permissions of 600 or 700 are suggested.
The ustar
typeflag
field was used to accommodate the additional
functionality of the new format rather than
magic
or
version
because the POSIX.1-1990 standard (and, by reference, the previous
version of
pax),
mandated the behavior of the format-reading
utility when it encountered an unknown
typeflag,
but was silent about the other two fields.
Early proposals of the first revision to IEEE Std 1003.1-2001
contained a proposed archive format that was based on
compatibility with the standard for tape files (ISO 1001, similar
to the format used historically on many mainframes and
minicomputers). This format was overly complex and required
considerable overhead in volume and header records. Furthermore,
the standard developers felt that it would not be acceptable to
the community of POSIX developers, so it was later changed to be a
format more closely related to historical practice on POSIX
systems.
The
prefix
and
name
split of pathnames in
ustar
was replaced by
the single path extended header record for simplicity.
The concept of a global extended header
(typeflag g)
was
controversial. If this were applied to an archive being recorded
on magnetic tape, a few unreadable blocks at the beginning of the
tape could be a serious problem; a utility attempting to extract
as many files as possible from a damaged archive could lose a
large percentage of file header information in this case. However,
if the archive were on a reliable medium, such as a CD-ROM, the
global extended header offers considerable potential size
reductions by eliminating redundant information. Thus, the text
warns against using the global method for unreliable media and
provides a method for implanting global information in the
extended header for each file, rather than in the
typeflag g
records.
No facility for data translation or filtering on a per-file basis
is included because the standard developers could not invent an
interface that would allow this in an efficient manner. If a
filter, such as encryption or compression, is to be applied to all
the files, it is more efficient to apply the filter to the entire
archive as a single file. The standard developers considered
interfaces that would invoke a shell script for each file going
into or out of the archive, but the system overhead in this
approach was considered to be too high.
One such approach would be to have
filter=
records that give a
pathname for an executable. When the program is invoked, the file
and archive would be open for standard input/output and all the
header fields would be available as environment variables or
command-line arguments. The standard developers did discuss such
schemes, but they were omitted from IEEE Std 1003.1-2001 due to
concerns about excessive overhead. Also, the program itself would
need to be in the archive if it were to be used portably.
There is currently no portable means of identifying the character
set(s) used for a file in the file system. Therefore,
pax
has not
been given a mechanism to generate charset records automatically.
The only portable means of doing this is for the user to write the
archive using the
-o charset=string
command line option. This
assumes that all of the files in the archive use the same
encoding. The "implementation-defined" text is included to allow
for a system that can identify the encodings used for each of its
files.
The table of standards that accompanies the charset record
description is acknowledged to be very limited. Only a limited
number of character set standards is reasonable for maximal
interchange. Any character set is, of course, possible by prior
agreement. It was suggested that EBCDIC be listed, but it was
omitted because it is not defined by a formal standard. Formal
standards, and then only those with reasonably large followings,
can be included here, simply as a matter of practicality. The
<value>s
represent names of officially registered character sets
in the format required by the ISO 2375:1985 standard.
The normal comma or <blank>-separated list rules are not followed
in the case of keyword options to allow ease of argument parsing
for
getopts.
Further information on character encodings is in
pax
Archive
Character Set Encoding/Decoding.
The standard developers have reserved keyword name space for
vendor extensions. It is suggested that the format to be used is:
VENDOR.keyword
where
VENDOR
is the name of the vendor or organization in all
uppercase letters. It is further suggested that the keyword
following the period be named differently than any of the standard
keywords so that it could be used for future standardization, if
appropriate, by omitting the
VENDOR
prefix.
The
<length>
field in the extended header record was included to
make it simpler to step through the records, even if a record
contains an unknown format (to a particular
pax)
with complex
interactions of special characters. It also provides a minor
integrity checkpoint within the records to aid a program
attempting to recover files from a damaged archive.
There are no extended header versions of the
devmajor
and
devminor
fields because the unspecified format
ustar
header field should be
sufficient. If they are not, vendor-specific extended keywords
(such as
VENDOR.devmajor)
should be used.
Device and i-number labeling of files was not adopted from
cpio;
files are interchanged strictly on a symbolic name basis, as in
ustar.
Just as with the
ustar
format descriptions, the new format makes
no special arrangements for multi-volume archives. Each of the
pax
archive types is assumed to be inside a single POSIX file and
splitting that file over multiple volumes (diskettes, tape
cartridges, and so on), processing their labels, and mounting each
in the proper sequence are considered to be implementation details
that cannot be described portably.
The
pax
format is intended for interchange, not only for backup on
a single (family of) systems. It is not as densely packed as might
be possible for backup:
The requirements on restoring from an archive are slightly
different from the historical wording, allowing for non-monolithic
privilege to bring forward as much as possible. In particular,
attributes such as "high performance file" might be broadly but
not universally granted while set-user-ID or
chown(2)
might be much
more restricted. There is no implication in IEEE Std 1003.1-2001
that the security information be honored after it is restored to
the file hierarchy, in spite of what might be improperly inferred
by the silence on that topic. That is a topic for another
standard.
Links are recorded in the fashion described here because a link
can be to any file type. It is desirable in general to be able to
restore part of an archive selectively and restore all of those
files completely. If the data is not associated with each link, it
is not possible to do this. However, the data associated with a
file can be large, and when selective restoration is not needed,
this can be a significant burden. The archive is structured so
that files that have no associated data can always be restored by
the name of any link name of any link, and the user may choose
whether data is recorded with each instance of a file that
contains data. The format permits mixing of both types of links in
a single archive; this can be done for special needs, and
pax
is
expected to interpret such archives on input properly, despite the
fact that there is no
pax
option that would force this mixed case
on output. (When
-o linkdata
is used, the output must contain the
duplicate data, but the implementation is free to include it or
omit it when
-o linkdata
is not used.)
The time values are included as extended header records for those
implementations needing more than the eleven octal digits allowed
by the
ustar
format. Portable file timestamps cannot be negative.
If
pax
encounters a file with a negative timestamp in
copy
or
write
mode, it can reject the file, substitute a non-negative
timestamp, or generate a non-portable timestamp with a leading
'-'. Even though some implementations can support finer file-time
granularities than seconds, the normative text requires support
only for seconds since the Epoch because the ISO POSIX-1 standard
states them that way. The
ustar
format includes only
mtime;
the
new format adds
atime
and
ctime
for symmetry. The atime access
time restored to the file system will be affected by the
-p a
and
-p e
options. The
ctime
creation time (actually
inode
modification
time) is described with "appropriate privilege" so that it can be
ignored when writing to the file system. POSIX does not provide a
portable means to change file creation time. Nothing is intended
to prevent a non-portable implementation of
pax
from restoring the
value.
The
gid,
size,
and
uid
extended header records were included to
allow expansion beyond the sizes specified in the regular
tar
header. New file system architectures are emerging that will
exhaust the 12-digit size field. There are probably not many
systems requiring more than 8 digits for user and group IDs, but
the extended header values were included for completeness,
allowing overrides for all of the decimal values in the
tar
header.
The standard developers intended to describe the effective results
of
pax
with regard to file ownerships and permissions;
implementations are not restricted in timing or sequencing the
restoration of such, provided the results are as specified.
Much of the text describing the extended headers refers to use in
"write or copy modes". The
copy
mode references are due to the
normative text: "The effect of the copy shall be as if the copied
files were written to an archive file and then subsequently
extracted ...". There is certainly no way to test whether
pax
is
actually generating the extended headers in
copy
mode, but the
effects must be as if it had.
There is a need to exchange archives of files between systems of
different native codesets. Filenames, group names, and user names
must be preserved to the fullest extent possible when an archive
is read on the receiving platform. Translation of the contents of
files is not within the scope of the
pax
utility.
There will also be the need to represent characters that are not
available on the receiving platform. These unsupported characters
cannot be automatically folded to the local set of characters due
to the chance of collisions. This could result in overwriting
previous extracted files from the archive or pre-existing files on
the system.
For these reasons, the codeset used to represent characters within
the extended header records of the
pax
archive must be
sufficiently rich to handle all commonly used character sets. The
fields requiring translation include, at a minimum, filenames,
user names, group names, and link pathnames. Implementations may
wish to have localized extended keywords that use non-portable
characters.
The standard developers considered the following options:
The approach that incorporates the name of the source codeset
poses the problem of codeset name registration, and makes the
archive useless to
pax
archive decoders that do not recognize that
codeset.
Because parts of an archive may be corrupted, the standard
developers felt that including the character map of the source
codeset was too fragile. The loss of this one key component could
result in making the entire archive useless. (The difference
between this and the global extended header decision was that the
latter has a workaround-duplicating extended header records on
unreliable media-but this would be too burdensome for large
character set maps.)
Both of the above approaches also put an undue burden on the
pax
archive receiver to handle the cross-product of all source and
destination codesets.
To simplify the translation from the source codeset to the
canonical form and from the canonical form to the destination
codeset, the standard developers decided that the internal
representation should be a stateless encoding. A stateless
encoding is one where each codepoint has the same meaning, without
regard to the decoder being in a specific state. An example of a
stateful encoding would be the Japanese Shift-JIS; an example of a
stateless encoding would be the ISO/IEC 646:1991 standard
(equivalent to 7-bit ASCII).
For these reasons, the standard developers decided to adopt a
canonical format for the representation of file information
strings. The obvious, well-endorsed candidate is the
ISO/IEC 10646-1:2000 standard (based in part on Unicode), which
can be used to represent the characters of virtually all
standardized character sets. The standard developers initially
agreed upon using UCS2 (16-bit Unicode) as the internal
representation. This repertoire of characters provides a
sufficiently rich set to represent all commonly-used codesets.
However, the standard developers found that the 16-bit Unicode
representation had some problems. It forced the issue of
standardizing byte ordering. The 2-byte length of each character
made the extended header records twice as long for the case of
strings coded entirely from historical 7-bit ASCII. For these
reasons, the standard developers chose the UTF-8 defined in the
ISO/IEC 10646-1:2000 standard. This multi-byte representation
encodes UCS2 or UCS4 characters reliably and deterministically,
eliminating the need for a canonical byte ordering. In addition,
NUL octets and other characters possibly confusing to POSIX file
systems do not appear, except to represent themselves. It was
realized that certain national codesets take up more space after
the encoding, due to their placement within the UCS range; it was
felt that the usefulness of the encoding of the names outweighs
the disadvantage of size increase for file, user, and group names.
The encoding of UTF-8 is as follows:
where each 'x' represents a bit value from the character being
translated.
The description of the
ustar
format reflects numerous enhancements
over pre-1988 versions of the historical
tar
utility. The goal of
these changes was not only to provide the functional enhancements
desired, but also to retain compatibility between new and old
versions. This compatibility has been retained. Archives written
using the old archive format are compatible with the new format.
Implementors should be aware that the previous file format did not
include a mechanism to archive directory type files. For this
reason, the convention of using a filename ending with slash was
adopted to specify a directory on the archive.
The total size of the
name
and
prefix
fields have been set to meet
the minimum requirements for
{PATH_MAX}
If a pathname will fit
within the
name
field, it is recommended that the pathname be
stored there without the use of the
prefix
field. Although the
name field is known to be too small to contain
{PATH_MAX}
characters, the value was not changed in this version of the
archive file format to retain backwards-compatibility, and instead
the
prefix
was introduced. Also, because of the earlier version of
the format, there is no way to remove the restriction on the
linkname
field being limited in size to just that of the
name
field.
The
size
field is required to be meaningful in all implementation
extensions, although it could be zero. This is required so that
the data blocks can always be properly counted.
It is suggested that if device special files need to be
represented that cannot be represented in the standard format,
that one of the extension types
(A-Z)
be used, and that the
additional information for the special file be represented as data
and be reflected in the
size
field.
Attempting to restore a special file type, where it is converted
to ordinary data and conflicts with an existing filename, need not
be specially detected by the utility. If run as an ordinary user,
pax
should not be able to overwrite the entries in, for example,
/dev
in any case (whether the file is converted to another type or
not). If run as a privileged user, it should be able to do so, and
it would be considered a bug if it did not. The same is true of
ordinary data files and similarly named special files; it is
impossible to anticipate the needs of the user (who could really
intend to overwrite the file), so the behavior should be
predictable (and thus regular) and rely on the protection system
as required.
The value
7
in the
typeflag
field is intended to define how
contiguous files can be stored in a
ustar
archive.
IEEE Std 1003.1-2001 does not require the contiguous file
extension, but does define a standard way of archiving such files
so that all conforming systems can interpret these file types in a
meaningful and consistent manner. On a system that does not
support extended file types, the
pax
utility should do the best it
can with the file and go on to the next.
The file protection modes are those conventionally used by the
ls(1)
utility. This is extended beyond the usage in the ISO POSIX-2
standard to support the "shared text" or "sticky" bit. It is
intended that the conformance document should not document
anything beyond the existence of and support of such a mode.
Further extensions are expected to these bits, particularly with
overloading the set-user-ID and set-group-ID flags.
The reference to appropriate privilege in the
cpio
format refers
to an error on standard output; the
ustar
format does not make
comparable statements.
The model for this format was the historical System V
cpio -c
data
interchange format. This model documents the portable version of
the
cpio
format and not the binary version. It has the flexibility
to transfer data of any type described within
IEEE Std 1003.1-2001, yet is extensible to transfer data types
specific to extensions beyond IEEE Std 1003.1-2001 (for example,
contiguous files). Because it describes existing practice, there
is no question of maintaining upwards-compatibility.
There has been some concern that the size of the
c_ino
field of
the header is too small to handle those systems that have very
large inode numbers. However, the
c_ino
field in the header is
used strictly as a hard-link resolution mechanism for archives. It
is not necessarily the same value as the inode number of the file
in the location from which that file is extracted.
The name
c_magic
is based on historical usage.
For most historical implementations of the
cpio
utility,
{PATH_MAX}
octets can be used to describe the pathname without the
addition of any other header fields (the NUL character would be
included in this count).
{PATH_MAX}
is the minimum value for
pathname size, documented as 256 bytes. However, an implementation
may use
c_namesize
to determine the exact length of the pathname.
With the current description of the
<cpio.h>
header, this pathname
size can be as large as a number that is described in six octal
digits.
Two values are documented under the
c_mode
field values to provide
for extensibility for known file types:
This provides for extensibility of the
cpio
format while allowing
for the ability to read old archives. Files of an unknown type may
be read as "regular files" on some implementations. On a system
that does not support extended file types, the
pax
utility should
do the best it can with the file and go on to the next.
None.
First released in Issue 4.
A note is added to the APPLICATION USAGE indicating that the
cpio
and
tar
formats can only support files up to 8 gigabytes in size.
The
pax
utility is aligned with the IEEE P1003.2b draft standard:
The
TZ
entry is added to the ENVIRONMENT VARIABLES section.
IEEE PASC Interpretation 1003.2 #168 is applied, clarifying that
mkdir(2)
and
mkfifo(3)
calls can ignore an [EEXIST] error when
extracting an archive.
IEEE PASC Interpretation 1003.2 #180 is applied, clarifying how
extracted files are created when in
read
mode.
IEEE PASC Interpretation 1003.2 #181 is applied, clarifying the
description of the
-t
option.
IEEE PASC Interpretation 1003.2 #195 is applied.
IEEE PASC Interpretation 1003.2 #206 is applied, clarifying the
handling of links for the
-H,
-L,
and
-l
options.
IEEE Std 1003.1-2001/Cor 1-2002, item XCU/TC1/D6/35 is applied,
adding the process ID of the
pax
process into certain fields. This
change provides a method for the implementation to ensure that
different instances of
pax
extracting a file named
/a/b/foo
will
not collide when processing the extended header information
associated with
foo.
IEEE Std 1003.1-2001/Cor 1-2002, item XCU/TC1/D6/36 is applied,
changing
-x B
to
-x pax
in the OPTIONS section.
IEEE Std 1003.1-2001/Cor 2-2004, item XCU/TC2/D6/20 is applied,
updating the SYNOPSIS to be consistent with the normative text.
IEEE Std 1003.1-2001/Cor 2-2004, item XCU/TC2/D6/21 is applied,
updating the DESCRIPTION to describe the behavior when files to be
linked are symbolic links and the system is not capable of making
hard links to symbolic links.
IEEE Std 1003.1-2001/Cor 2-2004, item XCU/TC2/D6/22 is applied,
updating the OPTIONS section to describe the behavior for how
multiple
options are to be handled.
IEEE Std 1003.1-2001/Cor 2-2004, item XCU/TC2/D6/23 is applied,
updating the
write
option within the OPTIONS section.
IEEE Std 1003.1-2001/Cor 2-2004, item XCU/TC2/D6/24 is applied,
adding a paragraph into the OPTIONS section that states that
specifying more than one of the mutually-exclusive options
(-H
and
-L)
is not considered an error and that the last option
specified will determine the behavior of the utility.
IEEE Std 1003.1-2001/Cor 2-2004, item XCU/TC2/D6/25 is applied,
removing the
ctime
paragraph within the EXTENDED DESCRIPTION.
There is a contradiction in the definition of the
ctime
keyword
for the
pax
extended header, in that the
st_ctime
member of the
stat
structure does not refer to a file creation time. No field in
the standard stat structure from
<sys/stat.h>
includes a file
creation time.
IEEE Std 1003.1-2001/Cor 2-2004, item XCU/TC2/D6/26 is applied,
making it clear that
typeflag
1
RB ( ustar
Interchange Format)
applies not only to files that are hard-linked, but also to files
that are aliased via symlinks.
IEEE Std 1003.1-2001/Cor 2-2004, item XCU/TC2/D6/27 is applied,
clarifying the
cpio
c_nlink
field.
End of quoted text from the POSIX.1-2001 standard.
The Institute of Electrical and Electronics Engineers and The Open Group,
have given us permission to reprint portions of their documentation. In
the following statement, the phrase ``this text'' refers to portions of
the system documentation.
Portions of this text are reprinted and reproduced in electronic form
in the
sfind
manual,
from IEEE Std 1003.1, 2004 Edition, Standard for
Information Technology -- Portable Operating System Interface (POSIX),
The Open Group Base Specifications Issue 6, Copyright (C) 2001-2004 by
the Institute of Electrical and Electronics Engineers, Inc and The Open
Group. In the event of any discrepancy between these versions and the
original IEEE and The Open Group Standard, the original IEEE and The
Open Group Standard is the referee document. The original Standard can
be obtained online at
http://www.opengroup.org/unix/online.html.
Mail bugs and suggestions to:
schilling [at] fokus.fraunhofer.de
or
js [at] cs.tu-berlin.de
or
joerg [at] schily.isdn.cs.tu-berlin.de
Shell Command Language,
cp(1),
ed(1),
getopts(1),
ls(1),
printf(3),
the Base
Definitions volume of IEEE Std 1003.1-2001,
<cpio.h>,
the System
Interfaces volume of IEEE Std 1003.1-2001,
chown(2),
creat(2),
mkdir(2),
mkfifo(3),
stat(2),
utime(2),
write(2).
OPERANDS
STDIN
INPUT FILES
ENVIRONMENT VARIABLES
ASYNCHRONOUS EVENTS
STDOUT
STDERR
OUTPUT FILES
EXTENDED DESCRIPTION
pax Interchange Format
ustar Header [typeflag = 'g'] Global Extended Header Data ustar Header [typeflag = 'x'] Extended Header Data ustar Header [typeflag = '0'] Data for File 1 ustar Header [typeflag = '0'] Data for File 2 Block of binary Zeroes Block of binary Zeroes pax Header Block
pax Extended Header
<value> Formal Standard ISO-IR 646 1990 ISO/IEC 646:1990 ISO-IR 8859 1 1998 ISO/IEC 8859-1:1998 ISO-IR 8859 2 1999 ISO/IEC 8859-2:1999 ISO-IR 8859 3 1999 ISO/IEC 8859-3:1999 ISO-IR 8859 4 1998 ISO/IEC 8859-4:1998 ISO-IR 8859 5 1999 ISO/IEC 8859-5:1999 ISO-IR 8859 6 1999 ISO/IEC 8859-6:1999 ISO-IR 8859 7 1987 ISO/IEC 8859-7:1987 ISO-IR 8859 8 1999 ISO/IEC 8859-8:1999 ISO-IR 8859 9 1999 ISO/IEC 8859-9:1999 ISO-IR 8859 10 1998 ISO/IEC 8859-10:1998 ISO-IR 8859 13 1998 ISO/IEC 8859-13:1998 ISO-IR 8859 14 1998 ISO/IEC 8859-14:1998 ISO-IR 8859 15 1999 ISO/IEC 8859-15:1999 ISO-IR 10646 2000 ISO/IEC 10646:2000 ISO-IR 10646 2000 UTF-8 ISO/IEC 10646, UTF-8 encoding BINARY None
pax Extended Header Keyword Precedence
pax Extended Header File Times
ustar Interchange Format
A
ustar
archive tape or file shall contain a series of logical
records. Each logical record shall be a fixed-size logical record
of 512 octets (see below). Although this format may be thought of
as being stored on 9-track industry-standard 12.7 mm (0.5 in)
magnetic tape, other types of transportable media are not
excluded. Each file archived shall be represented by a header
logical record that describes the file, followed by zero or more
logical records that give the contents of the file. At the end of
the archive file there shall be two 512-octet logical records
filled with binary zeros, interpreted as an end-of-archive
indicator.
Field Name Octet Offset Length (in Octets) name 0 100 mode 100 8 uid 108 8 gid 116 8 size 124 12 mtime 136 12 chksum 148 8 typeflag 156 1 linkname 157 100 magic 257 6 version 263 2 uname 265 32 gname 297 32 devmajor 329 8 devminor 337 8 prefix 345 155
Bit IEEE Std Description Value 1003.1-2001 Bit 04000 S_ISUID Set UID on execution. 02000 S_ISGID Set GID on execution. 01000 <reserved> Reserved for future standardization. 00400 S_IRUSR Read permission for file owner class. 00200 S_IWUSR Write permission for file owner class. 00100 S_IXUSR Execute/search permission for file owner class. 00040 S_IRGRP Read permission for file group class. 00020 S_IWGRP Write permission for file group class. 00010 S_IXGRP Execute/search permission for file group class. 00004 S_IROTH Read permission for file other class. 00002 S_IWOTH Write permission for file other class. 00001 S_IXOTH Execute/search permission for file other class.
cpio Interchange Format
Header Field Name Length (in Octets) Interpreted as c_magic 6 Octal number c_dev 6 Octal number c_ino 6 Octal number c_mode 6 Octal number c_uid 6 Octal number c_gid 6 Octal number c_nlink 6 Octal number c_rdev 6 Octal number c_mtime 11 Octal number c_namesize 6 Octal number c_filesize 11 Octal number Filename Field Name Length Interpreted as c_name c_namesize Pathname string File Data Field Name Length Interpreted as c_filedata c_filesize Data cpio Header
File Permissions Name Value Indicates C_IRUSR 000400 Read by owner C_IWUSR 000200 Write by owner C_IXUSR 000100 Execute by owner C_IRGRP 000040 Read by group C_IWGRP 000020 Write by group C_IXGRP 000010 Execute by group C_IROTH 000004 Read by others C_IWOTH 000002 Write by others C_IXOTH 000001 Execute by others C_ISUID 004000 Set uid C_ISGID 002000 Set gid C_ISVTX 001000 Reserved File Type Name Value Indicates C_ISDIR 0040000 Directory C_ISFIFO 0010000 FIFO C_ISREG 0100000 Regular file C_ISLNK 0120000 Symbolic link C_ISBLK 0060000 Block special file C_ISCHR 0020000 Character special file C_ISSOCK 0140000 Socket C_ISCTG 0110000 Reserved cpio Filename
cpio File Data
cpio Special Entries
EXIT STATUS
CONSEQUENCES OF ERRORS
The following sections are informative.
APPLICATION USAGE
EXAMPLES
/usr/fo
Jan 12 1991
Jan 31 15:53
RATIONALE
pax Interchange Format
pax Archive Character Set Encoding/Decoding
UCS4 Hex Encoding UTF-8 Binary Encoding 00000000-0000007F 0xxxxxxx 00000080-000007FF 110xxxxx 10xxxxxx 00000800-0000FFFF 1110xxxx 10xxxxxx 10xxxxxx 00010000-001FFFFF 11110xxx 10xxxxxx 10xxxxxx 10xxxxxx 00200000-03FFFFFF 111110xx 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx 04000000-7FFFFFFF 1111110x 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx ustar Interchange Format
cpio Interchange Format
cpio Header
cpio Filename
FUTURE DIRECTIONS
End of informative sections.
CHANGE HISTORY
Issue 5
Issue 6
OTHER OPTIONS
The following
other options
are implemented as extension to the POSIX standard. Note that some other
non-POSIX options are mentioned in -help and -xhelp output
- these are also supported in
spax(1)
and are well described in
star(1)
manual page.
EXAMPLES
ENVIRONMENT
FILES
DIAGNOSTICS
NOTES
BUGS
AUTHOR
Joerg Schilling
Seestr. 110
D-13353 Berlin
Germany
SEE ALSO
SEE ALSO