xenial (1) pax.1posix.gz

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PROLOG

       This  manual  page  is part of the POSIX Programmer's Manual.  The Linux implementation of this interface
       may differ (consult the corresponding Linux manual page for details of Linux behavior), or the  interface
       may not be implemented on Linux.

NAME

       pax — portable archive interchange

SYNOPSIS

       pax [−dv] [−c|−n] [−H|−L] [−o options] [−f archive] [−s replstr]...
           [pattern...]

       pax −r[−c|−n] [−dikuv] [−H|−L] [−f archive] [−o options]... [−p string]...
           [−s replstr]... [pattern...]

       pax −w [−dituvX] [−H|−L] [−b blocksize] [[−a] [−f archive]] [−o options]...
           [−s replstr]... [−x format] [file...]

       pax −r −w [−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 and each  entry  in  this
                 list  shall  be  processed as if it had been a file operand on the command line. 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 a pax format 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  POSIX.1‐2008, 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
       POSIX.1‐2008, 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.

       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. 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  POSIX.1‐2008,  Section  12.2,  Utility
       Syntax Guidelines, except that the order of presentation of the −o, −p, and −s options is significant.

       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  POSIX.1‐2008
                 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, when neither −H or −L are specified, 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,  when  neither −H or −L are specified, 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  POSIX.1‐2008,  Section  3.278,  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  Section  2.13.1,  Patterns  Matching a Single
                       Character and Section 2.13.2, 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 −odelete=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:

                       binary    In  write  mode,  pax shall generate a hdrcharset=BINARY extended header record
                                 for each file with a filename, link name, group name, owner name, or any  other
                                 field  in  an  extended  header  record  that cannot be translated to the UTF‐8
                                 codeset, allowing the archive to contain  the  files  with  unencoded  extended
                                 header  record values. In read or copy mode, pax shall use the values specified
                                 in the header without translation, regardless of whether this may overwrite  an
                                 existing  file with a valid name. In list mode, pax shall behave identically to
                                 the bypass action.

                       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. If a hdrcharset  extended
                                 header  record  is in effect for this file, the character set specified by that
                                 record shall be used instead of UTF‐8. If a hdrcharset=BINARY  extended  header
                                 record is in effect for this file, no translation shall be performed.

                       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 −oinvalid=bypass were
                       specified. Any overwriting of existing files  that  may  be  allowed  by  the  −oinvalid=
                       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  −olistopt=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  <equals-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
                       POSIX.1‐2008, Section 3.169, 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 Section 1.1.1.4, 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) back-references, or subexpression matching. The old string shall  also  be
                 permitted to contain <newline> characters.

                 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.

       −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
                 POSIX.1‐2008, 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
       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  POSIX.1‐2008,
       Chapter  5,  File  Format Notation, with the exceptions 1. through 6. defined in the EXTENDED DESCRIPTION
       section of printf, plus the following exceptions:

       7.    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 Table 4-14, ustar Header Block and Table 4-16, Octet-Oriented
                 cpio Archive Entry.  The implementation may support the cpio keywords without the leading c_ in
                 addition to the form required by Table 4-16, Octet-Oriented cpio Archive Entry.

             --  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  (or
             alternative  encoding  specified  by  any  hdrcharset  extended header record) to the character set
             appropriate for the local file system, user database, and so on, as applicable.

       8.    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:

                 %b %e %H:%M %Y

       9.    An  additional  conversion specifier character, M, shall be used to specify the file mode string as
             defined in ls Standard Output. If (keyword) is  omitted,  the  mode  keyword  shall  be  used.  For
             example,  %.1M  writes  the  single  character corresponding to the <entry type> field of the ls −l
             command.

       10.   An additional conversion specifier character, D, shall be used to specify the device for  block  or
             special files, if applicable, in an implementation-defined format. If not applicable, and (keyword)
             is specified, then this conversion shall be equivalent  to  %(keyword)u.  If  not  applicable,  and
             (keyword) is omitted, then this conversion shall be equivalent to <space>.

       11.   An  additional  conversion  specifier  character,  F,  shall  be  used to specify a pathname. The F
             conversion character can be preceded by a sequence of <comma>-separated keywords:

                 (keyword[,keyword] ... )

             The values for all the keywords that are non-null shall be concatenated together, each separated by
             a '/'.  The default shall be (path) if the keyword path is defined; otherwise, the default shall be
             (prefix,name).

       12.   An additional conversion specifier  character,  L,  shall  be  used  to  specify  a  symbolic  link
             expansion. If the current file is a symbolic link, then %L shall expand to:

                 "%s −> %s", <value of keyword>, <contents of link>

             Otherwise, the %L conversion specification shall be the equivalent of %F.

OPERANDS

       The following operands shall be supported:

       directory The destination directory pathname for copy mode.

       file      A pathname of a file to be copied or archived.

       pattern   A  pattern  matching  one  or more pathnames of archive members. A pattern must be given in the
                 name-generating notation of the pattern matching notation in  Section  2.13,  Pattern  Matching
                 Notation,  including the filename expansion rules in Section 2.13.3, Patterns Used for Filename
                 Expansion.  The default, if no pattern is specified, is to select all members in the archive.

STDIN

       In write mode, the standard input shall be used only if no file operands are specified.  It  shall  be  a
       file containing a list of pathnames, each terminated by a <newline> character.

       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.

INPUT FILES

       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.

ENVIRONMENT VARIABLES

       The following environment variables shall affect the execution of pax:

       LANG      Provide a default value for the internationalization variables that are unset or null. (See the
                 Base Definitions volume  of  POSIX.1‐2008,  Section  8.2,  Internationalization  Variables  the
                 precedence   of   internationalization  variables  used  to  determine  the  values  of  locale
                 categories.)

       LC_ALL    If set to a non-empty string value, override the values of all the  other  internationalization
                 variables.

       LC_COLLATE
                 Determine  the  locale  for  the  behavior  of ranges, equivalence classes, and multi-character
                 collating elements used in the pattern matching expressions for the pattern operand, the  basic
                 regular  expression  for  the  −s  option,  and the extended regular expression defined for the
                 yesexpr locale keyword in the LC_MESSAGES category.

       LC_CTYPE  Determine the locale for the interpretation of sequences of bytes of text  data  as  characters
                 (for  example,  single-byte  as opposed to multi-byte characters in arguments and input files),
                 the behavior of character classes used in the  extended  regular  expression  defined  for  the
                 yesexpr locale keyword in the LC_MESSAGES category, and pattern matching.

       LC_MESSAGES
                 Determine  the  locale used to process affirmative responses, and the locale used to affect the
                 format and contents of diagnostic messages and prompts written to standard error.

       LC_TIME   Determine the format and contents of date and time strings when the −v option is specified.

       NLSPATH   Determine the location of message catalogs for the processing of LC_MESSAGES.

       TMPDIR    Determine the pathname that provides part of the default global extended header record file, as
                 described for the −o globexthdr= keyword in the OPTIONS section.

       TZ        Determine the timezone used to calculate date and time strings when the −v option is specified.
                 If TZ is unset or null, an unspecified default timezone shall be used.

ASYNCHRONOUS EVENTS

       Default.

STDOUT

       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 −olistopt=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 −olistopt=format option, the table of contents of  the  selected  archive  members  shall  be
       written to standard output using the following format:

           "%s\n", <pathname>

       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:

           "%s == %s\n", <ls −l listing>, <linkname>

       For all other pathnames:

           "%s\n", <ls −l listing>

       where <ls −l listing> shall be the format specified by the ls 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 pathname (plus any associated information
       and a <newline> terminator) at a time.

STDERR

       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:

           "%s\n", <pathname>

       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:

           "%s >> %s\n", <original pathname>, <new pathname>

       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 using the −xpax archive format, if a filename, link name, group name, owner name, or any other field
       in an extended header record cannot be translated between the codeset in use  for  that  extended  header
       record  and  the  character  set  of the current locale, pax shall write a diagnostic message to standard
       error, shall process the file as described for the −o invalid= option, and then shall continue processing
       with the next file.

OUTPUT FILES

       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 (−oinvalid=) 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.

EXTENDED DESCRIPTION

   pax Interchange Format
       A  pax  archive  tape or file produced in the −xpax 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:

        *  An  optional header block with extended header records. This header block is of the form described in
           pax Header Block, with a typeflag value of x or g.  The extended header  records,  described  in  pax
           Extended Header, shall be included as the data for this header block.

        *  A  header  block  that describes the file. Any fields in the preceding optional extended header shall
           override the associated fields in this header block for this file.

        *  Zero or more blocks that contain the contents of the file.

       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
       Figure 4-1, 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.

                                        Figure 4-1: pax Format Archive Example

   pax Header Block
       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:

       x     Represents extended header records for the following file in the archive (which shall have its  own
             ustar  header  block).  The  format  of  these extended header records shall be as described in pax
             Extended Header.

       g     Represents global extended header records for the following files in the  archive.  The  format  of
             these  extended  header  records  shall  be  as described in pax Extended Header.  Each value shall
             affect all subsequent files that do not override that value in their own extended header record and
             until  another  global  extended  header record is reached that provides another value for the same
             field. The typeflag g global headers should not be used with interchange media  that  could  suffer
             partial data loss in transporting the archive.

       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.

   pax Extended Header
       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:

           "%d %s=%s\n", <length>, <keyword>, <value>

       The  extended  header  records  shall  be  encoded  according  to the ISO/IEC 10646‐1:2000 standard UTF‐8
       encoding. The <length> field, <blank>, <equals-sign>,  and  <newline>  shown  shall  be  limited  to  the
       portable  character  set,  as  encoded  in  UTF‐8. The <keyword> 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>.   If there is a hdrcharset extended header in effect for a file, the value field for
       any gname, linkpath, path, and uname extended header records shall be encoded  using  the  character  set
       specified  by  the  hdrcharset  extended header record; otherwise, the value field shall be encoded using
       UTF‐8. The value field for all other keywords specified by POSIX.1‐2008 shall be encoded using UTF‐8.

       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.)

       atime     The file access time for the following file(s), equivalent to the value of the st_atime  member
                 of the stat structure for a file, as described by the stat() function. The access time shall be
                 restored if the process has appropriate privileges required to do so. The format of the <value>
                 shall be as described in pax Extended Header File Times.

       charset   The  name of the character set used to encode the data in the following file(s). The entries in
                 the following table are defined to refer to known standards; additional names may be agreed  on
                 between the originator and recipient.

                                    ┌────────────────────────┬───────────────────────────────┐
                                    │        <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.                         │
                                    └────────────────────────┴───────────────────────────────┘
                 The  encoding  is  included  in  an  extended  header for information only; when pax is used as
                 described in POSIX.1‐2008, 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.

       comment   A series of characters used as a comment. All characters in the <value> field shall be  ignored
                 by pax.

       gid       The  group  ID of the group that owns the file, expressed as a decimal number using digits from
                 the ISO/IEC 646:1991 standard. This record shall override the gid field in the following header
                 block(s).  When  used in write or copy mode, pax shall include a gid extended header record for
                 each file whose group ID is greater than 2097151 (octal 7777777).

       gname     The group of the file(s), formatted as a group name in the group database.  This  record  shall
                 override the gid and gname fields in the following header block(s), and any gid extended header
                 record. When used in read, copy, or list mode, pax shall translate the name from  the  encoding
                 in  the  header record to the character set appropriate for the group database on the receiving
                 system. If any of the characters cannot be  translated,  and  if  neither  the  −oinvalid=UTF‐8
                 option  nor  the  −oinvalid=binary option is specified, the results are implementation-defined.
                 When used in write or copy mode, pax shall include a gname extended header record for each file
                 whose  group  name  cannot  be represented entirely with the letters and digits of the portable
                 character set.

       hdrcharset
                 The name of the character set used to encode the value field of the gname, linkpath, path,  and
                 uname  pax  extended header records. The entries in the following table are defined to refer to
                 known standards; additional names may be agreed between the originator and the recipient.

                                    ┌────────────────────────┬───────────────────────────────┐
                                    │        <value>Formal Standard        │
                                    ├────────────────────────┼───────────────────────────────┤
                                    │ISO-IR 10646 2000 UTF-8 │ ISO/IEC 10646, UTF-8 encoding │
                                    │BINARY                  │ None.                         │
                                    └────────────────────────┴───────────────────────────────┘
                 If no hdrcharset extended header record is specified, the default character set used to  encode
                 all  values  in  extended  header  records  shall  be  the  ISO/IEC 10646‐1:2000 standard UTF‐8
                 encoding.

                 The BINARY entry indicates that all values recorded in extended headers for affected files  are
                 unencoded binary data from the underlying system.

       linkpath  The  pathname  of  a link being created to another file, of any type, previously archived. This
                 record shall override the linkname field in the following ustar header block(s). The  following
                 ustar  header  block  shall  determine  the  type of link created. If typeflag of the following
                 header block is 1, it shall be a hard link. If typeflag is 2, it shall be a symbolic  link  and
                 the  linkpath value shall be the contents of the symbolic link. The pax utility shall translate
                 the name of the link (contents of the symbolic link) from the encoding in  the  header  to  the
                 character set appropriate for the local file system. When used in write or copy mode, pax shall
                 include a linkpath extended header record for each link whose pathname  cannot  be  represented
                 entirely with the members of the portable character set other than NUL.

       mtime     The  file  modification  time of the following file(s), equivalent to the value of the st_mtime
                 member of the stat structure for a file, as described in the stat() function. This record shall
                 override  the  mtime  field  in  the  following header block(s). The modification time shall be
                 restored if the process has appropriate privileges required to do so. The format of the <value>
                 shall be as described in pax Extended Header File Times.

       path      The pathname of the following file(s). This record shall override the name and prefix fields in
                 the following header block(s). The pax utility shall translate the pathname of  the  file  from
                 the encoding in the header to the character set appropriate for the local file system.

                 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.

       realtime.any
                 The keywords prefixed by ``realtime.'' are reserved for future standardization.

       security.any
                 The keywords prefixed by ``security.'' are reserved for future standardization.

       size      The  size  of  the  file  in  octets,  expressed  as  a  decimal  number  using digits from the
                 ISO/IEC 646:1991 standard. This record shall override the size field in  the  following  header
                 block(s).  When used in write or copy mode, pax shall include a size extended header record for
                 each file with a size value greater than 8589934591 (octal 77777777777).

       uid       The user ID  of  the  file  owner,  expressed  as  a  decimal  number  using  digits  from  the
                 ISO/IEC 646:1991  standard.  This  record  shall override the uid field in the following header
                 block(s). When used in write or copy mode, pax shall include a uid extended header  record  for
                 each file whose owner ID is greater than 2097151 (octal 7777777).

       uname     The  owner of the following file(s), formatted as a user name in the user database. This record
                 shall override the uid and uname fields in the following header block(s), and any uid  extended
                 header  record.  When  used  in read, copy, or list mode, pax shall translate the name from the
                 encoding in the header record to the character set appropriate for the  user  database  on  the
                 receiving  system.  If  any  of  the  characters  cannot  be  translated,  and  if  neither the
                 −oinvalid=UTF‐8  option  nor  the  −oinvalid=binary  option  is  specified,  the  results   are
                 implementation-defined.   When  used  in write or copy mode, pax shall include a uname extended
                 header record for each file whose user name cannot be represented entirely with the letters and
                 digits of the portable character set.

       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 Table 4-14, ustar Header Block shall apply to the extended header records.

   pax Extended Header Keyword Precedence
       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:

        1. If  −odelete=keyword-prefix  is  used,  the  affected attributes shall be determined from step 7., if
           applicable, or ignored otherwise.

        2. If −okeyword:= is used, the affected attributes shall be ignored.

        3. If −okeyword:=value is used, the affected attribute shall be assigned the value.

        4. If there is a typeflag x extended header  record,  the  affected  attribute  shall  be  assigned  the
           <value>.  When  extended  header  records  conflict,  the  last  one  given  in the header shall take
           precedence.

        5. If −okeyword=value is used, the affected attribute shall be assigned the value.

        6. If there is a typeflag g global extended header record, the affected attribute shall be assigned  the
           <value>.  When global extended header records conflict, the last one given in the global header shall
           take precedence.

        7. Otherwise, the attribute shall be determined from the ustar header block.

   pax Extended Header File Times
       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.

   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.

       The logical records may be grouped for physical I/O operations, as described under the −bblocksize and −x
       ustar options. Each group of logical records may be written with a single  operation  equivalent  to  the
       write()  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.

                                            Table 4-14: ustar Header Block

                                   ┌───────────┬──────────────┬────────────────────┐
                                   │Field NameOctet OffsetLength (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         │
                                   └───────────┴──────────────┴────────────────────┘
       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 POSIX.1‐2008. 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:

                                                Table: ustar mode Field

                   ┌──────────┬──────────────────┬─────────────────────────────────────────────────┐
                   │Bit ValuePOSIX.1‐2008 BitDescription                   │
                   ├──────────┼──────────────────┼─────────────────────────────────────────────────┤
                   │  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. │
                   └──────────┴──────────────────┴─────────────────────────────────────────────────┘
       When appropriate privileges are required to set one of these mode bits, and the user restoring the  files
       from  the  archive  does  not have appropriate privileges, the mode bits for which the user does not have
       appropriate privileges shall be ignored. Some of the mode bits in the archive format  are  not  mentioned
       elsewhere  in this volume of POSIX.1‐2008. 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 POSIX.1‐2008, 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() 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 <space> characters.

       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 privileges 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:

       0       Represents a regular file. For backwards-compatibility, a typeflag value of  binary  zero  ('\0')
               should  be  recognized as meaning a regular file when extracting files from the archive. Archives
               written with this version of the archive file format create regular files with a  typeflag  value
               of the ISO/IEC 646:1991 standard IRV '0'.

       1       Represents  a  file  linked  to  another  file,  of any type, previously archived. Such files are
               identified by having the same device and  file  serial  numbers,  and  pathnames  that  refer  to
               different  directory  entries.  All  such files shall be archived as linked files.  The linked-to
               name is specified in the linkname field with a NUL-character terminator if it is  less  than  100
               octets in length.

       2       Represents  a  symbolic  link.  The contents of the symbolic link shall be stored in the linkname
               field.

       3,4     Represent character special files and  block  special  files  respectively.   In  this  case  the
               devmajor  and  devminor fields shall contain information defining the device, the format of which
               is unspecified by this volume of POSIX.1‐2008. Implementations may map the device  specifications
               to their own local specification or may ignore the entry.

       5       Specifies  a  directory  or  subdirectory.  On  systems  where  disk allocation is performed on a
               directory basis, the size field shall contain the maximum number of octets (which may be  rounded
               to  the  nearest  disk  block allocation unit) that the directory may hold.  A size field of zero
               indicates no such limiting. Systems that do not support limiting in this manner should ignore the
               size field.

       6       Specifies  a  FIFO special file. Note that the archiving of a FIFO file archives the existence of
               this file and not its contents.

       7       Reserved to represent a file to which an  implementation  has  associated  some  high-performance
               attribute. Implementations without such extensions should treat this file as a regular file (type
               0).

       A‐Z     The letters 'A' to 'Z', inclusive, are reserved for custom implementations. All other values  are
               reserved for future versions of this standard.

       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.

   cpio Interchange Format
       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.

                                     Table 4-16: Octet-Oriented cpio Archive Entry

                             ┌─────────────────────┬────────────────────┬─────────────────┐
                             │ Header Field NameLength (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 NameLengthInterpreted as  │
                             ├─────────────────────┴────────────────────┴─────────────────┤
                             │c_name                 c_namesize           Pathname string │
                             ├─────────────────────┬────────────────────┬─────────────────┤
                             │File Data Field NameLengthInterpreted as  │
                             ├─────────────────────┴────────────────────┴─────────────────┤
                             │c_filedata             c_filesize           Data            │
                             └────────────────────────────────────────────────────────────┘
   cpio 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:

       c_magic   Identify  the  archive  as  being  a  transportable archive by containing the identifying value
                 "070707".

       c_dev, c_ino
                 Contains values that uniquely identify the file within the archive (that is, no  files  contain
                 the  same  pair  of  c_dev and c_ino values unless they are links to the same file). The values
                 shall be determined in an unspecified manner.

       c_mode    Contains the file type and access permissions as defined in the following table.

                                            Table 4-17: Values for cpio c_mode Field

                 │                 ─────┬─────────┬────────────────────────┬──────────────────
--

EXIT STATUS

       The following exit values shall be returned:

        0    All files were processed successfully.

       >0    An error occurred.

CONSEQUENCES OF ERRORS

       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.

       The following sections are informative.

APPLICATION USAGE

       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:

       −p e    ``Preserve  everything''.  This  would  be  used  by  the  historical superuser, someone with all
               appropriate privileges, to preserve all aspects of the files as they are recorded in the archive.
               The e flag is the sum of o and p, and other implementation-defined attributes.

       −p p    ``Preserve''  the  file  mode  bits.  This  would be used by the user with regular privileges who
               wished to preserve aspects of the file other than the ownership. The file times are preserved  by
               default, but two other flags are offered to disable these and use the time of extraction.

       The  one  pathname per line format of standard input precludes pathnames containing <newline> characters.
       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 POSIX.1‐2008. 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.

       When archives containing binary header information are listed , the filenames printed may  cause  strange
       behavior on some terminals.

       When all of the following are true:

        1. A file of type directory is being placed into an archive.

        2. The ustar archive format is being used.

        3. The  pathname  of  the  directory  is less than or equal to 155 bytes long (it will fit in the prefix
           field in the ustar header block).

        4. The last component of the pathname of the directory is longer than 100 bytes long (it will not fit in
           the name field in the ustar header block).

       some implementations of the pax utility will place the entire directory pathname in the prefix field, set
       the name field to an empty string, and place the directory in the archive.  Other implementations of  the
       pax  utility will give an error under these conditions because the name field is not large enough to hold
       the last component of the directory name.  This standard allows either behavior. However, when extracting
       a  directory  from  a  ustar  format  archive, this standard requires that all implementations be able to
       extract a directory even if the name field contains an empty string as long as the prefix field does  not
       also contain an empty string.

EXAMPLES

       The following command:

           pax −w −f /dev/rmt/1m .

       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:

           mkdir newdir
           pax −rw olddir newdir

       copy the olddir directory hierarchy to newdir.

           pax −r −s ',^//*usr//*,,' −f a.pax

       reads the archive a.pax, with all files rooted in /usr in the archive extracted relative to  the  current
       directory.

       Using the option:

           −o listopt="%M %(atime)T %(size)D %(name)s"

       overrides the default output description in Standard Output and instead writes:

           −rw−rw−−− Jan 12 15:53 2003 1492 /usr/foo/bar

       Using the options:

           −o listopt='%L\t%(size)D\n%.7' \
           −o listopt='(name)s\n%(atime)T\n%T'

       overrides the default output description in Standard Output and instead writes:

           /usr/foo/bar −> /tmp   1492
           /usr/fo
           Jan 12 15:53 1991
           Jan 31 15:53 2003

RATIONALE

       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 POSIX.1‐2008 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 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 appropriate  privileges  to  restore
       full ownership and permission information.

       Note  also that this volume of POSIX.1‐2008 requires that the file ownership and access permissions shall
       be set, on extraction, in the same fashion as the creat() 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.   Earlier
       versions  of  this  standard  did  not specify any way to create a hard link to a symbolic link, but many
       implementations provided 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 −xpax 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 (215−512 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 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 POSIX.1‐2008  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 POSIX.1‐2008, 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  POSIX.1‐2008  described  as  part  of  the  cp
       utility. Both methods are historical practice: cp 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 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
       <space> characters is valid:

           pax −s " foo bar " ...

       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 −echarmap 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  ISO POSIX‐2:1993  standard  and  ISO POSIX‐1  standard  requirements  for pax, however, made it very
       difficult to create a single archive containing files  created  using  extended  characters  provided  by
       different  locales.   This  version  adds  the hdrcharset keyword to make it possible to archive files in
       these cases without dropping files due to translation errors.

       Translating filenames and other attributes from a locale's encoding to UTF‐8 and then back again can lose
       information,  as  the  resulting filename might not be byte-for-byte equivalent to the original. To avoid
       this problem, users can specify the −o hdrcharset=binary option, which will cause the  resulting  archive
       to  use  binary  format for all names and attributes. Such archives are not portable among hosts that use
       different native encodings (e.g., EBCDIC versus ASCII-based encodings), but they will  allow  interchange
       among  the  vast  majority  of POSIX file systems in practical use. Also, the −o hdrcharset=binary option
       will cause pax in copy mode to behave more like other standard utilities such as cp.

       If the values specified by the −o exthdr.name=value, −o  globexthdr.name=value,  or  by  $TMPDIR  (if  −o
       globexthdr.name  is  not  specified)  require  a  character  encoding  other  than  that described in the
       ISO/IEC 646:1991 standard, a path extended header record will have to be  created  for  the  file.  If  a
       hdrcharset  extended header record is active for such headers, it will determine the codeset used for the
       value field in these extended path header records. These path extended header records always need  to  be
       created  when  writing an archive even if hdrcharset=binary has been specified and would contain the same
       (binary) data that appears in the ustar header record  prefix  and  name  fields.  (In  other  words,  an
       extended  header path record is always required to be generated if the prefix or name fields contain non-
       ASCII characters even when hdrcharset=binary is also in effect for that file.)

       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 −oinvalid=option—specifically the UTF‐8 and  binary  actions.  (Note  that  an
       existing file is still subject to overwriting in this case. The −k option closes that loophole.)

       Some of the file characteristics referenced in this volume of POSIX.1‐2008 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 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
       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, 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.

   pax Interchange Format
       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:

        *  Support international character encodings and locale information

        *  Support security information (ACLs, and so on)

        *  Support future file types, such as realtime or contiguous files

        *  Include data areas for implementation use

        *  Support systems with words larger than 32 bits and timers with subsecond granularity

       The following were not goals for this format because these are better handled by  separate  utilities  or
       are inappropriate for a portable format:

        *  Encryption

        *  Compression

        *  Data translation between locales and codesets

        *  inode storage

       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:

        *  It was easier to extend in an upwards-compatible way. It offered version flags and header block  type
           fields  with  room for future standardization. The cpio format, while possessing a more flexible file
           naming methodology, could not be extended without breaking some theoretical implementation or using a
           dummy filename that could be a legitimate filename.

        *  Industry experience since the original ``tar wars'' fought in developing the ISO POSIX‐1 standard has
           clearly been in favor of the ustar format, which is generally the default output format selected  for
           pax implementations on new systems.

       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 for the first version of this standard 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 (typeflagg) 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 POSIX.1‐2008 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 −ocharset=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:

        *  It contains information as coded characters that could be coded in binary.

        *  It  identifies  extended  records  with  name  fields that could be omitted in favor of a fixed-field
           layout.

        *  It translates names into a portable character set and identifies locale-related information, both  of
           which are probably unnecessary 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() might be much more restricted.  There  is  no  implication  in  POSIX.1‐2008  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 privileges 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.

   pax Archive Character Set Encoding/Decoding
       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 archive creator specifies the well-defined name of the source codeset.  The  receiver  must  then
           recognize the codeset name and perform the appropriate translations to the destination codeset.

        *  The  archive  creator  includes within the archive the character mapping table for the source codeset
           used to encode extended header records.  The receiver must then read the character mapping table  and
           perform the appropriate translations to the destination codeset.

        *  The  archive  creator  translates  the extended header records in the source codeset into a canonical
           form. The receiver must then perform the appropriate translations to the destination codeset.

       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:

           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

       where each 'x' represents a bit value from the character being translated.

   ustar Interchange Format
       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 (AZ) 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. POSIX.1‐2008 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 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.

   cpio Interchange Format
       The  reference  to  appropriate  privileges 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  POSIX.1‐2008,  yet  is  extensible  to  transfer  data  types
       specific to extensions beyond POSIX.1‐2008 (for example, contiguous files). Because it describes existing
       practice, there is no question of maintaining upwards-compatibility.

   cpio Header
       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.

   cpio Filename
       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:

       0110 000  Reserved  for  contiguous  files.  The implementation may treat the rest of the information for
                 this archive like a regular file. If this file type is undefined, the implementation may create
                 the file as a regular file.

       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.

FUTURE DIRECTIONS

       None.

SEE ALSO

       Chapter 2, Shell Command Language, cp, ed, getopts, ls, printf

       The Base Definitions volume of POSIX.1‐2008, Section 3.169,  File  Mode  Bits,  Chapter  5,  File  Format
       Notation, Chapter 8, Environment Variables, Section 12.2, Utility Syntax Guidelines, <cpio.h>

       The  System  Interfaces  volume of POSIX.1‐2008, chown(), creat(), fstatat(), mkdir(), mkfifo(), utime(),
       write()

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition,
       Standard  for  Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electrical and Electronics Engineers,  Inc
       and  The  Open Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the event
       of any discrepancy between this version 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.unix.org/online.html .

       Any typographical or formatting errors that appear in this page are most likely to have  been  introduced
       during   the   conversion  of  the  source  files  to  man  page  format.  To  report  such  errors,  see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .