pax Header Block
-The pax header block shall be identical to the ustar header block
-described in ustar Interchange Format, except that two additional
+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
+ Represents extended header records for the following file in
the archive (which shall have its own ustar header block).
g
- Represents global extended header records for the following
-files in the archive. 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
+ Represents global extended header records for the following
+files in the archive. 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
+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
+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.
pax Extended Header
-An extended header shall consist of one or more records, each
+An extended header shall consist of one or more records, each
constructed as follows:
"%d %s=%s\n", <length>, <keyword>, <value>
-The <length> field shall be the decimal length of the extended
-header record in octets, including length string itself and the
+The <length> field shall be the decimal length of the extended
+header record in octets, including length string itself and the
trailing <newline>.
[skip]
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 the appropriate privilege required to
-do so. The format of the <value> shall be as described in pax
+ 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 the appropriate privilege 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
+ The name of the character set used to encode the data in the
following file(s).
- The encoding is included in an extended header for information
-only; when pax is used as described in IEEE Std 1003.1-2001, it
-shall not translate the file data into any other encoding. The
+ The encoding is included in an extended header for information
+only; when pax is used as described in IEEE Std 1003.1-2001, it
+shall not translate the file data into any other encoding. The
BINARY entry indicates unencoded binary data.
- When used in write or copy mode, it is implementation-defined
+ 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
+ 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
+ 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 UTF-8 encoding in the header record to
-the character set appropriate for the group database on the
-receiving system. If any of the UTF-8 characters cannot be
-translated, and if the -o invalid= UTF-8 option is not 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
+ 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 UTF-8 encoding in the header record to
+the character set appropriate for the group database on the
+receiving system. If any of the UTF-8 characters cannot be
+translated, and if the -o invalid= UTF-8 option is not 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.
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 UTF-8 encoding 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
+ 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 UTF-8 encoding 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 the appropriate privilege required to do so. The format of the
+ 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 the appropriate privilege 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 UTF-8 encoding to the character set appropriate for the
+ 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 UTF-8 encoding 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
+ 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
+ The keywords prefixed by "realtime." are reserved for future
standardization.
security.any
- The keywords prefixed by "security." are reserved for future
+ 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
+ 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
+ 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 UTF-8 encoding in the header record to
-the character set appropriate for the user database on the
-receiving system. If any of the UTF-8 characters cannot be
-translated, and if the -o invalid= UTF-8 option is not 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
+ 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 UTF-8 encoding in the header record to
+the character set appropriate for the user database on the
+receiving system. If any of the UTF-8 characters cannot be
+translated, and if the -o invalid= UTF-8 option is not 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
+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
+If a keyword in an extended header record (or in a -o
+option-argument) overrides or deletes a corresponding field in the
+ustar header block, pax shall ignore the contents of that header
block field.
-Unlike the ustar header block fields, NULs shall not delimit
-<value>s; all characters within the <value> field shall be
-considered data for the field. None of the length limitations of
-the ustar header block fields in ustar Header Block shall apply to
+Unlike the ustar header block fields, NULs shall not delimit
+<value>s; all characters within the <value> field shall be
+considered data for the field. None of the length limitations of
+the ustar header block fields in ustar Header Block shall apply to
the extended header records.
pax Extended Header File Times
-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. 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
+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. 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.
Example from Linux kernel archive tarball:
projects / oweals / busybox.git / blobdiff