XORRISOFS(1)

NAME
xorrisofs - Emulation of ISO 9660 program mkisofs by program xorriso

SYNOPSIS
xorrisofs [ options ] [-o filename ] pathspec [pathspecs ...]

DESCRIPTION

xorrisofs produces Rock Ridge enhanced ISO 9660 filesystems and add-on sessions to such filesystems. Optionally it can produce Joliet directory trees too.

xorrisofs understands options of program mkisofs from cdrtools by Joerg Schilling. Its implementation is part of program xorriso which shares no source code with cdrtools.

  ISO 9660, Rock Ridge, Joliet, HFS+:
ISO 9660 (aka ECMA-119) is a read-only filesystem that is mainly used for optical media CD, DVD, BD, but may also reside on other storage devices like disk files, USB sticks or disk partitions. It is widely readable by many operating systems and by boot facilities of personal computers.
ISO 9660 describes directories and data files by very restricted filenames with no distinction of upper case and lower case. Its metadata do not comply to fundamental POSIX specifications.
Rock Ridge is the name of a set of additional information which enhance an ISO 9660 filesystem so that it can represent a POSIX compliant filesystem with ownership, access permissions, symbolic links, and other attributes. Rock Ridge allows filenames of up to 255 bytes and paths of up to 1024 bytes.
xorrisofs produces Rock Ridge information by default. It is strongly discouraged to disable this feature.
Joliet is the name of an additional directory tree which provides filenames up to 64 characters encoded as UTF-16. A Joliet tree is mainly interesting for reading the ISO image by operating systems of Microsoft Corporation. Production of this directory tree may be enabled by option -J.
ISO 9660:1999 is the name of an additional directory tree which provides longer filenames. It allows single file names to have up to 207 characters. It might be of use with some older computer system boot facilities which read neither Rock Ridge nor Joliet but need longer filenames nevertheless. Production of this directory tree may be enabled by option -iso-level 4.
HFS+ is the name of a filesystem which is normally used for writing and reading on hard disks and similar devices. It is possible to embed a HFS+ partition into the emerging ISO 9660 image and to mark it by Apple Partition Map entries. This interferes with options which copy data into the first 32 KiB of the ISO image, like -G or -isohybrid-mbr. See option -hfsplus.
The main purpose for having an embedded HFS+ partition is booting of certain models of Apple computers.

  Inserting files into the ISO image:

xorrisofs deals with two kinds of file addresses:
disk_path is a path to an object in the local filesystem tree.
iso_rr_path is the Rock Ridge address of a file object in the ISO image. If no Rock Ridge information shall be stored in an emerging ISO, then the names will get mapped to ISO 9660 names of limited length and character set.

A program argument is handled as a pathspec, if it is not recognized as original mkisofs option or additional xorrisofs option. A pathspec depicts an input file object by a disk_path. If option -graft-points is not present, then the behavior depends on the file type of disk_path. Directories get merged with the /-directory of the ISO image. Files of other types get copied into the /-directory.
If -graft-points is present then each pathspec gets split at the first occurence of the =-character. The part before the = is taken as target, i.e. the iso_rr_path for the file object in the ISO image. The part after the first = is taken as source, i.e. the disk_path of the input object.
It is possible to make =-characters part of the iso_rr_path by preceding them with a \-character. The same must be done for \-characters which shall be part of the iso_rr_path.

If the source part of the pathspec leads to a directory, then all files underneath this directory get inserted into the image, too. It is possible to exclude particular files from being inserted by help of option -m.
In case that target already exists, the following rules apply: Directories and other files may overwrite existing non-directories. Directories get merged with existing directories. Non-directories may not overwrite existing directories.

  Relation to program xorriso:
xorrisofs is actually a command mode of program xorriso, which gets entered either by xorriso command "-as mkisofs" or by starting the program by one of the names "xorrisofs", "mkisofs", "genisoimage", or "genisofs".
This command mode can be left by argument "--" which leads to generic xorriso command mode. See man xorriso for its description.

xorriso performs image reading and writing by help of libburn, which is mainly intended for optical drives, but also operates on all POSIX file types except directories.
The program messages call any image file a "drive". File types which are not supported for reading are reported as "blank". The reported free media space may be quite fictional.
Nevertheless xorrisofs does not operate directly on optical drives, but rather forces libburn to regard them as general device files. So for writing of sequential optical media (CD, DVD-R, DVD+R, BD-R) one will have to use a burn program. E.g the cdrecord emulation of xorriso. See EXAMPLES.

OPTIONS

  Image loading:

The following options control loading of an existing ISO image for the purpose
    of preparing a suitable add-on session. If they are missing then a new image is composed from scratch.

-M disk_path
    Set the path from which to load the existing ISO image directory tree on which to base the upcomming directory tree as add-on session. The path must lead to a random-access readable file object. On GNU/Linux: regular data files or block device files.
    A special kind of pseudo disk_path has the form "/dev/fd/"number. It depicts the open file descriptor with the given number, regardless whether the operating system supports this feature by file nodes in /dev/fd or not. E.g. /dev/fd/3 is file descriptor 3 which was opened by the program that later started xorriso.

-prev-session disk_path
    Alias of -M.

-dev disk_path
    Alias of -M.

-C last_session_start,next_writeable_address
    Set the 2 KiB block address last_session_start from where to read the ISO image out of the file given by option -M.
    Separated by a comma, set the next_writeable_address to which the add-on session will finally be written. Decisive is actually the block address which the intended readers will have to use as superblock address on the intended medium.
    Both values can be inquired from optical media by help of burn programs and cdrecord option -msinfo. xorriso itself can obtain it in its cdrecord emulation. Do not let it load the drive, but rather do this manually or by a program like dd which reads a few bytes. Only then it is sure that the device driver knows the true readable size of the medium.
      dd if=/dev/... count=1 >/dev/null 2>&1
      values=$(xorriso -as cdrecord dev=/dev/... -msinfo)
      echo $values
    Option -C may be used without option -M to create an ISO image from scratch and prepare it for being finally written to a block address other than 0. Parameter last_session_start must then be set to 0.

-cdrecord-params last_session_start,next_writeable_address
    Alias of -C.

Settings for file insertion:

-path-list disk_path
    Read pathspecs line-by-line from disk_file and insert the depicted file objects into the ISO image. If disk_path is "-" then read the pathspecs from standard input.

--quoted_path_list disk_path
    Like option -path-list but reading quoted words rather than plain lines. Whitespace outside of quotes will be discarded. On the other hand it is possible to represent pathspecs which contain newline characters.
    The double quotation mark " and the single quotation mark ' can be used to enclose whitespace and make it part of pathspecs. Each mark type can enclose the marks of the other type. A trailing backslash \ outside quotations or an open quotation cause the next input line to be appended.

-f
    Resolve symbolic links on disk rather than storing them as symbolic links in the ISO image.

-follow-links
    Alias of -f.

-graft-points
    Enable interpretation of input file pathspecs as combination of iso_rr_path and disk_path, separated by a =-character.

-m disk_pattern
    Exclude files from being inserted into the image. Silently ignored are those files of which the disk_path matches the given shell parser pattern. If no /-character is part of the pattern, then it gets matched against the leaf name of the disk file.
    It is possible to give more than one -m option.

-exclude
    Alias of -m.

-x
    Alias of -m.

-old-exclude
    Alias of -m.

-exclude-list disk_path
    Perform -m using each line out of file disk_path as argument disk_pattern.

-z
    Enable recognition and proper processing of zisofs compressed files as produced by program mkzftree. These files will get equipped with the necessary meta data so that a Linux kernel will recognize them and deliver their content in uncompressed form.

-transparent-compression
    Alias of -z.

-root iso_rr_path
    Insert all files under the given iso_rr_path. If option -graft-points is given, then iso_rr_path is prepended to each target part of a pathspec.
    The default for -root is "/".

-old-root iso_rr_path
    Enable incremental insertion of files into the loaded image. The effective target and source addresses of given pathspecs get compared whether the target already exists in the ISO image and is still identical to the source on disk. Metadata in the ISO image will get adjusted, if they differ from those on disk. New files and files with changed content will get newly added. Target files which do not exist in any of the according pathspec sources will get removed from the ISO directory tree.
    If the effective setting of -root differs from the iso_rr_path given with -old-root, then the files underneath the -old-root directory get cloned underneath the -root directory. Cloning happens before file comparison.

--old-root-no-ino
    Disable recording and use of disk inode numbers. If no disk inode numbers are recorded, then option -old-root will have to read disk file content and compare it with the MD5 checksum that is recorded in the ISO image.
    With recorded disk inode numbers and with credible ctime and mtime, it is possible to detect potential changes in the content without actually reading it. A loophole remains if multiple different filesystems may get mounted at the same directory, like it is habit with /mnt. In this case one has to use option --old-root-devno or disable the inode number shortcut by --old-root-no-ino.

--old-root-devno
    Enable comparison of recorded device numbers together with recorded inode numbers. This works only with good old stable device numbers which get out of fashion, regrettably. If the hard disk has a different device number after each reboot, then this comparison will see all files as changed and thus prevent any incremental size saving.

--old-root-no-md5
    Disable recording and use of MD5 checksums for data file content. If neither checksums and nor disk inode numbers are recorded, then option -old-root will have to read ISO image file content when comparing it with disk file content.

Settings for image production:

-o disk_path
    Set the output file address for the emerging ISO image. If the address exists as regular file, it will be truncated to length 0 when image production begins. It may not already exist as directory. If it does not exist yet then its parent directory must exist and a regular file will get created.
    A special kind of pseudo disk_path has the form "/dev/fd/"number. It depicts the open file descriptor with the given number, regardless whether the operating system supports this feature by file nodes in /dev/fd or not. E.g. /dev/fd/4 is file descriptor 4 which was opened by the program that later started xorriso.
    Default is standard output (/dev/fd/1) which may also be set by disk_path "-".

-output disk_path
    Alias of -o.

--stdio_sync "on"|"off"|number
    Set the number of bytes after which to force output to disk in order to keep the memory from being clogged with lots of pending data for slow devices. Default "on" is the same as "16m". Forced output can be disabled by "off".
    xorriso uses an inner fifo buffer with default size 4 MiB. So forcing the operating system i/o cache to disk does not necessarily block the simultaneous production of more image content.

--emul-toc
    Write a second superblock with the first session into random-access files. If further sessions get appended and the first superblock gets updated, then the second superblock will not be overwritten. This allows to still mount the first session and to find the start blocks of the further sessions.
    The price is 64 KiB extra space consumption. If -partition_offset is non-zero, then it is 128 KiB plus twice the partition setup.

--no-emul-toc
    Do not write a second superblock with the first session into random-access files.
    This is the default.

--sort-weight weight_number iso_rr_path
    Attribute a LBA weight number to regular files. If iso_rr_path leads to a directory then all regular files underneath will get the weight_number.
    The weight_number may range from -2147483648 to 2147483647. The higher it is, the lower will be the block address of the file data in the emerging ISO image. Currently the El Torito boot catalog has a hardcoded weight of 1 billion. Normally it should occupy the block with the lowest possible address. Data files get added or loaded with initial weight 0.

-dir-mode mode
    Set the access permissions for all directories in the image to the given mode which is either an octal number beginning with "0" or a comma separated list of statements of the form [ugoa]*[+-=][rwxst]* . E.g. ug=rx,a-rwx

-file-mode mode
    Like -dir-mode but for all regular data files in the image.

-pad
    Add 300 KiB to the end of the produced ISO image. This circumvents possible read errors from ISO images which have been written to CD media in TAO mode. The additional bytes are claimed as part of the ISO image if not --emul-toc is given.
    Option -pad is the default.

-no-pad
    Disable padding of 300 KiB to the end of the produced ISO image. This is safe if the image is not meant to be written on CD or if it gets written to CD as only track in write mode SAO.

--old-empty
    Use the old way of of giving block addresses in the range of [0,31] to files with no own data content. The new way is to have a dedicated block to which all such files will point.

Settings for standards compliance:

-iso-level number
    Specify the ISO 9660 version which defines the limitations of file naming and data file size. The naming restrictions do not apply to the Rock Ridge names but only to the low-level ISO 9660 names. There are three conformance levels:
    Level 1 allows ISO names of the form 8.3 and file size up to 4 GiB - 1.
    Level 2 allows ISO names with up to 32 characters and file size up to 4 GiB - 1.
    Level 3 allows ISO names with up to 32 characters and file size of up to 400 GiB - 200 KiB. (This size limitation is set by the xorriso implementation and not by ISO 9660 which would allow nearly 8 TiB.)
    Pseudo-level 4 enables production of an additional ISO 9660:1999 directory tree.

-disallow_dir_id_ext
    Do not follow a bad habit of mkisofs which allows dots in the ISO names of directories. On the other hand, some bootable GNU/Linux images depend on this bad habit.

-U
    This option allows ISO file names without dot and up to 37 characters, ISO file paths longer than 255 characters, and all ASCII characters in file names. Further it omits the semicolon and the version numbers at the end of ISO names.
    This all violates ISO 9660 specs.

-untranslated-filenames
    Alias of -U.

-untranslated_name_len number
    Allow ISO file names up to the given number of characters without any character conversion. The maximum number is 96. If a file name has more characters, then image production will fail deliberately.
    This violates ISO 9660 specs.

-allow-lowercase
    Allow lowercase character in ISO file names.
    This violates ISO 9660 specs.

-relaxed-filenames
    Allow nearly all 7-bit characters in ISO file names. Not allowed are 0x0 and '/'. If not option -allow-lowercase is given, then lowercase letters get converted to uppercase.
    This violates ISO 9660 specs.

-d
    Do not add trailing dot to ISO file names without dot.
    This violates ISO 9660 specs.

-omit-period
    Alias of -d.

-l
    Allow up to 31 characters in ISO file names.

-full-iso9660-filenames
    Alias of -l.

-max-iso9660-filenames
    Allow up to 37 characters in ISO file names.
    This violates ISO 9660 specs.

-N
    Omit the semicolon and the version numbers at the end of ISO names.
    This violates ISO 9660 specs.

-omit-version-number
    Alias of -N.

Settings for standards extensions:

-R
    With mkisofs this option enables Rock Ridge extensions. xorrisofs produces them by default. It is strongly discouraged to disable them by option --norock.

-rock
    Alias of -R.

-r
    Set Rock Ridge user and group id of all files in the ISO image to 0. Grant r-permissions to all. Deny all w-permissions. If any x-permission is set, grant x-permission to all. Remove s-bit and t-bit.

-rational-rock
    Alias of -r.

--norock
    This option disables the production of Rock Ridge extensions for the ISO 9660 file objects. The multi-session capabilities of xorrisofs depend much on the naming fidelity of Rock Ridge. So it is strongly discouraged to disable it by this option.

-D  The standard ECMA-119 demands that no path in the image shall have more than 8 name components or 255 characters. Therefore it would be necessary to move deeper directory trees to a higher directory. Rock Ridge offers an opportunity to let these relocated directories appear at their orginal deep position, but this feature might not be implemented properly by operating systems which mount the image.
    Option -D disables this deep directory relocation, and thus violates ISO 9660 specs.
    xorrisofs has -D set by default. If given explicitely then it overrides the options -rr_reloc_dir and -hide-rr-moved.

-disable-deep-relocation
    Alias of -D.

-rr_reloc_dir name
    Enable the relocation of deep directories and thus avoid ECMA-119 file paths of more than 8 name components or 255 characters. Directories which lead to such file paths will get moved to a directory in the root directory of the image. Its name gets set by this option. It is permissible to use the root directory itself.
    The overall directory tree will appear originally deep when interpreted as Rock Ridge tree. It will appear as re-arranged if only ECMA-119 information is considered.
    If the given relocation target directory does not already exist when image production begins, then it will get created and marked for Rock Ridge as relocation artefact. At least on GNU/Linux it will not be displayed in mounted Rock Ridge images.
    The name must not contain a '/' character after its first character and it must not be longer than 255 bytes.
    This option has no effect if option -D is present.

-hide-rr-moved
    Alias of -rr_reloc_dir "/.rr_moved"

--for_backup
    Enable options which improve backup fidelity: --acl, --xattr, --md5, --hardlinks.

--acl
    Enable recording and loading of ACLs from GNU/Linux or FreeBSD (see man getfacl, man acl). They will not be in effect with mounted ISO images. But xorriso can restore them on the same systems when extracting files from the ISO image.

--xattr
    Enable recording and loading of GNU/Linux or FreeBSD extended attributes in user namespace (see man getfattr, man attr, resp. man getextattr, man 9 extattr). They will not be in effect with mounted ISO images. But xorriso can restore them on the same systems when extracting files from the ISO image.

--md5
    Enable recording of MD5 checksums for the overall ISO image and for each single data file in the image. xorriso can check the content of an ISO image with these sums and raise alert on mismatch. See man xorriso, options -check_media, check_md5_r. xorriso can print recorded MD5 checksums. E.g. by:
     -find / -exec get_md5

--hardlinks
    Enable loading and recording of hardlink relations. Search for families of iso_rr files which stem from the same disk file, have identical content filtering and have identical properties. The members of each family get the same inode number in the ISO image.
    Whether these numbers are respected at mount time depends on the operating system. xorriso can create hardlink families when extracting files from the ISO image.

--scdbackup_tag disk_path record_name
    Append a scdbackup checksum record to the image. This works only if the parameter next_writeable_address of option -C is 0. If disk_path is not an empty string, then append a scdbackup checksum record to the end of this file. record_name is a word that gets part of tag and record.
    Program scdbackup_verify will recognize and verify tag resp. record.

-J
    Enable the production of an additional Joliet directory tree along with the ISO 9660 Rock Ridge tree.

-joliet
    Alias of -J.

-joliet-long
    Allow 103 characters in Joliet file names rather than 64 as is prescribed by the specification. Allow Joliet paths longer than the prescribed limit of 240 characters.
    Oversized names get truncated. Without this option, oversized paths get excluded from the Joliet tree.

-hfsplus
    Enable the production of an additional HFS+ filesystem inside the ISO 9660 image and mark it by Apple Partition Map (APM) entries in the System Area, the first 32 KiB of the image.
    This may collide with options like -G or -isohybrid-mbr which submit user data for inclusion in the same address range. The first 8 bytes of the System Area get overwritten by { 0x45, 0x52, 0x08 0x00, 0xeb, 0x02, 0xff, 0xff } which can be executed as x86 machine code without negative effects. So if an MBR gets combined with this feature, then its first 8 bytes should contain no essential commands.
    The next blocks of 2 KiB in the System Area will be occupied by APM entries. The first one covers the part of the ISO image before the HFS+ filesystem metadata. The second one marks the range from HFS+ metadata to the end of file content data. If more ISO image data follow, then a third partition entry gets produced. Other features of xorriso might cause the need for more APM entries.
    Be aware that HFS+ is case-insensitive although it can record file names with upper-case and lower-case letters. Therefore, file names from the iso_rr name tree may collide in the HFS+ name tree. In this case they get changed by adding underscore characters and counting numbers. In case of very long names, it might be necessary to map them to "MANGLED_...".

-hfsplus-serial-no
    Set a string of 16 digits "0" to "9" and letters "a" to "f", which will be used as unique serial number of an emerging HFS+ filesystem.

-hfsplus-block-size number
    Set the allocation block size to be used when producing HFS+ filesystems. Permissible are 512, 2048, or 0. The latter lets the program decide.

-apm-block-size number
    Set the block size to be used when describing partitions by an Apple Partition Map. Permissible are 512, 2048, or 0. The latter lets the program decide.
    Note that size 512 is not compatible with production of GPT, and that size 2048 will not be mountable -t hfsplus at least by older Linux kernels.

-hfsplus-file-creator-type creator type iso_rr_path
    Set the HFS+ creator and type attributes of a file in the emerging image. These are two codes of 4 characters each.

-hfs-bless-by blessing iso_rr_path
    Issue a HFS+ blessing. They are roles which can be attributed to up to four directories and a data file:
    "ppc_bootdir", "intel_bootfile", "show_folder", "os9_folder", "osx_folder".
    They may be abbreviated as "p", "i", "s", "9", and "x".
    Each such role can be attributed to at most one file object. "intel_bootfile" is the one that would apply to a data file. All others apply to directories. No file object can bear more than one blessing.

-hfs-bless disk_path
    Issue HFS+ blessing "ppc_bootdir" to the directory which stems from the directory disk_path in the local filesystem tree.
    This works only if there is at least one data file underneath the directory. disk_path can become ambigous if files from different local filesystem sub-trees are put into the same sub-tree of the ISO image. Consider to use -hfs-bless-by "p" for unambigous addressing via iso_rr_path.

Settings for file hiding:

-hide disk_path_pattern
    Make files invisible in the directory tree of ISO 9660 and Rock Ridge, if their disk_path matches the given shell parser pattern. The data content of such hidden files will be included in the resulting image, even if they do not show up in any directory. But you will need own means to find nameless data in the image.
    This command does not apply to the boot catalog.

-hide-list disk_path
    Perform -hide using each line out of file disk_path as argument disk_path_pattern.

-hide-joliet disk_path_pattern
    Like option -hide but making files invisible in the directory tree of Joliet, if their disk_path matches the given shell parser pattern.

-hide-joliet-list disk_path
    Perform -hide-joliet using each line out of file disk_path as argument disk_path_pattern.

-hide-hfsplus disk_path_pattern
    Like option -hide but making files invisible in the directory tree of HFS+, if their disk_path matches the given shell parser pattern.

-hide-hfsplus-list disk_path
    Perform -hide-hfsplus using each line out of file disk_path as argument disk_path_pattern.

ISO image ID strings:

The following strings and file addresses get stored in the Primary Volume Descriptor of the ISO9660 image. The file addresses are ISO 9660 paths. These files should have iso_rr_paths which consist only of the characters [A-Z0-9_] and exactly one dot which separates at most 8 characters from at most 3 characters.

-V text
    Set the Volume Id of the ISO image. xorriso accepts any text up to 32 characters, but according to rarely obeyed specs stricter rules apply:
    Conformant are ASCII characters out of [A-Z0-9_]. Like: "IMAGE_23"
    Joliet allows 16 UCS-2 characters. Like: "Windows name"
    Be aware that the volume id might get used automatically as name of the mount point when the medium is inserted into a playful computer system.

-volid text
    Alias of -V.

-volset text
    Set the Volume Set Id of the ISO image. Permissible are up to 128 characters.

-p text
    Set the Publisher Id of the ISO image. This may identify the person or organisation who specified what shall be recorded. Permissible are up to 128 characters.

-publisher text
    Alias of -p.

-A text
    Set the Application Id of the ISO image. This may identify the specification of how the data are recorded. Permissible are up to 128 characters.
    The special text "@xorriso@" gets converted to the id string of xorriso which is normally written as Preparer Id. It is a wrong tradition to write the program id as Application Id.

-appid text
    Alias of -A.

-sysid text
    Set the System Id of the ISO image. This may identify the system which can recognize and act upon the content of the System Area in image blocks 0 to 15. Permissible are up to 32 characters.

-p text
    Set the Preparer Id of the ISO image. This may identify the person or other entity which controls the preparation of the data which shall be recorded. Normally this should be the id of xorriso and not of the person or program which operates xorriso. Please avoid to change it. Permissible are up to 128 characters.
    The special text "@xorriso@" gets converted to the id string of xorriso which is default at program startup.

-preparer text
    Alias of -p.

-abstract iso_path
    Set the address of the Abstract File of the ISO image. This should be the ISO 9660 path of a file in the image which contains an abstract statement about the image content. Permissible are up to 37 characters.

-biblio iso_path
    Set the address of the Biblio File of the ISO image. This should be the ISO 9660 path of a file in the image which contains bibliographic records. Permissible are up to 37 characters.

-copyright iso_path
    Set the address of the Copyright File of the ISO image. This should be the ISO 9660 path of a file in the image which contains a copyright statement. Permissible are up to 37 characters.

--modification-date=YYYYMMDDhhmmsscc
    Set a timestring that overrides ISO image creation and modification timestamps literally. It must consist of 16 decimal digits which form YYYYMMDDhhmmsscc, with YYYY between 1970 and 2999. Time zone is GMT. It is supposed to match this GRUB line:
     search --fs-uuid --set YYYY-MM-DD-hh-mm-ss-cc
    E.g. 2010040711405800 is 7 Apr 2010 11:40:58 (+0 centiseconds).

El Torito Bootable ISO images:

The precondition for a bootable ISO image is to have in the ISO image the files of a boot loader. The boot facilities of computers get directed to such files, which usually execute further program files from the ISO image. xorrisofs can produce several kinds of boot block or boot record, which become part of the ISO image, and get interpreted by the according boot facility.

An El Torito boot record points the bootstrapping facility to a boot catalog with one or more boot images, which are binary program files stored in the ISO image. The content of the boot image files is not in the scope of El Torito.
xorriso composes the boot catalog according to the boot image files given and structured by options -b, -e, -el-torito-alt-boot, and --efi-boot. Often it contains only one entry.
El Torito gets interpreted by boot facilities PC-BIOS and EFI. Most bootable GNU/Linux CDs are equipped with ISOLINUX or GRUB boot images for PC-BIOS.
xorrisofs supports the example options out of the ISOLINUX wiki, the options used in GRUB script grub-mkrescue, and the example in the FreeBSD AvgLiveCD wiki.

For CD booting via boot facilities other than PC-BIOS and EFI, and for booting from USB sticks or hard disks, see the next section about the Sytem Area.

-b iso_rr_path
    Specify the boot image file which shall be mentioned in the current entry of the El Torito boot catalog. It will be marked as suitable for PC-BIOS.
    With boot images from ISOLINUX and GRUB this option should be accompanied by options -c , -no-emul-boot , -boot-load-size 4 , -boot-info-table.

-eltorito-boot iso_rr_path
    Alias of -b.

-eltorito-alt-boot
    Finalize the current El Torito boot catalog entry and begin a new one. A boot image file and all its necessary options shall be specified before option -eltorito-alt-boot. All further El Torito boot options apply to the new catalog entry. Up to 32 catalog entries are possible.

-e iso_rr_path
    Specify the boot image file which shall be mentioned in the current entry of the El Torito boot catalog. It will be marked as suitable for EFI.
    Normally no other El Torito options should be used with the catalog entry that points to an EFI image. Consider to use --efi-boot rather than -e.

--efi-boot iso_rr_path
    Perform -eltorito-alt-boot, option -e with the given iso_rr_path, and again -eltorito-alt-boot. This gesture is used for achieving EFI-bootability of the GRUB2 rescue CD.

-boot-load-size number
    Set the number of 512-byte blocks for boot images which emulate a floppy or a hard disk. A safe default for non-emulating boot images is 4.

-hard-disk-boot
    Mark the boot image in the current catalog entry as emulated hard disk. (Not suitable for any known boot loader.)

-no-emul-boot
    Mark the boot image in the current catalog entry as not emulating floppy or hard disk. (This is to be used with all known boot loaders.)
    If neither -hard-disk-boot nor -no-emul-boot is given, then the boot image will be marked as emulating a floppy. (Not suitable for any known boot loader.)

-boot-info-table
    Overwrite certain bytes in the current boot image. The information will be supplied by xorriso in the course of image production: Block address of the Primary Volume Descriptor, block address of the boot image file, size of the boot image file.

-c iso_rr_path
    Set the address of the El Torito boot catalog file within the image. This file address is not significant for the booting PC-BIOS or EFI, but it may later be read by other programs in order to learn about the available boot images.

-eltorito-catalog iso_rr_path
    Alias of -c.

--boot-catalog-hide
    Prevent the El Torito boot catalog from appearing as file in the directory trees of the image.

System Area, MBR, GPT, APM, other boot blocks:

The first 16 blocks of an ISO image are the System Area. It is reserved for system dependent boot software. This may be the boot facilities and partition tables of various hardware architectures.
A MBR (Master Boot Record) contains boot code and a partition table. It is read by PC-BIOS when booting from USB stick or hard disk, and by PowerPC CHRP or PReP when booting. An MBR partiton with type 0xee indicates the presence of GPT.
A GPT (GUID Partition Table) marks partitions in a more modern way. It is read by EFI when booting from USB stick or hard disk, and may be used for finding and mounting a HFS+ partition inside the ISO image.
An APM (Apple Partition Map) marks the HFS+ partition. It is read by Macs for booting and for mounting.
MBR, GPT and APM are combinable. APM occupies the first 8 bytes of MBR boot code. All three do not hamper El Torito booting from CDROM.
xorrisofs supports further boot facilities: MIPS Big Endian (SGI), MIPS Little Endian (DEC), SUN SPARC. Those are mutually not combinable and also not combinable with MBR, GPT, or APM.

-G disk_path
    Copy at most 32768 bytes from the given disk file to the very start of the ISO image.
    Other than a El Torito boot image, the file disk_path needs not to be added to the ISO image. It will not show up as file in the directory trees.

-generic-boot disk_path
    Alias of -G.

--embedded-boot disk_path
    Alias of -G.

-isohybrid-mbr disk_path
    Install disk_path as ISOLINUX isohybrid MBR which makes the boot image given by option -b bootable from USB sticks and hard disks via PC-BIOS. This preparation is normally done by ISOLINUX program isohybrid on the already produced ISO image.
    The disk path should lead to one of the Syslinux files isohdp[fp]x*.bin . The MBR gets patched according to isohybrid needs. The first partition describes the range of the ISO image. Its start is at block 0 by default, but may be set to 64 disk blocks by option -partition_offset 16.

-isohybrid-gpt-basdat
    Mark the current El Torito boot image (see options -b and -e) in GPT as partition of type Basic Data. This works only with -isohybrid-mbr and has the same impact on the system area as -efi-boot-part. It cannot be combined with -efi-boot-part or -hfsplus.

-isohybrid-gpt-hfsplus
    Mark the current El Torito boot image (see options -b and -e) in GPT as partition of type HFS+. Impact and restrictions are like with -isohybrid-gpt-basdat.

-isohybrid-apm-hfsplus
    Mark the current El Torito boot image (see options -b and -e) in Apple Partition Map as partition of type HFS+. This works only with -isohybrid-mbr and has a similar impact on the system area as -hfsplus. It cannot be combined with -efi-boot-part or -hfsplus.
    The ISOLINUX isohybrid MBR file must begin by a known pattern of 32 bytes of x86 machine code which essentially does nothing. It will get overwritten by 32 bytes of APM header mock-up.

--protective-msdos-label
    Patch the System Area by a simple PC-DOS partition table where partition 1 claims the range of the ISO image but leaves the first block unclaimed.

-partition_offset 2kb_block_adr
    Cause a partition table with a single partition that begins at the given block address. This is counted in 2048 byte blocks, not in 512 byte blocks. If the block address is non-zero then it must be at least 16. Values larger than 16 are hardly of use. A non-zero partition offset causes two superblocks to be generated and two sets of directory trees. The image is then mountable from its absolute start as well as from the partition start.
    The offset value of an ISO image gets preserved when a new session is added to a loaded image. So the value defined here is only in effect if a new ISO image gets written.

-partition_hd_cyl number
    Set the number of heads per cylinder for the partition table. 0 chooses a default value. Maximum is 255.

-partition_sec_hd number
    Set the number of sectors per head for the partition table. 0 chooses a default value. Maximum is 63.
    The product partition_sec_hd * partition_hd_cyl * 512 is the cylinder size. It should be divisible by 2048 in order to allow exact alignment. If it is too small to describe the image size by at most 1024 cylinders, then appropriate values of partition_hd_cyl are chosen with partition_sec_hd 32 or 63. If the image is larger than 8,422,686,720 bytes, then the cylinder size constraints cannot be fulfilled. They seem not overly important anyway. Flat block addresses in partition tables are good for 1 TiB.

-partition_cyl_align mode
    Control image size alignment to an integer number of cylinders. It is prescribed by isohybrid specs and it seems to please program fdisk. Cylinder size must be divisible by 2048. Images larger than 8,323,596,288 bytes cannot be aligned.
    Mode "auto" is default. Alignment by padding happens only if option -isohybrid-mbr is given.
    Mode "on" causes alignment by padding with option --protective-msdos-label too. Mode "off" disables alignment unconditionally.

-append_partition partition_number type_code disk_path
    Cause a prepared filesystem image to be appended to the ISO image and to be described by a partition table entry in a boot block at the start of the emerging ISO image. The partition entry will bear the size of the submitted file rounded up to the next multiple of 2048 bytes.
    Beware of subsequent multi-session runs. The appended partition will get overwritten.
    partition_number may be 1 to 4. Number 1 will put the whole ISO image into the unclaimed space before partition 1. So together with most xorriso MBR features, number 2 would be the most natural choice.
    The type_code may be "FAT12", "FAT16", "Linux", or a hexadecimal number between 0x00 and 0xff. Not all those numbers will yield usable results. For a list of codes search the Internet for "Partition Types" or run fdisk command "L".

-efi-boot-part disk_path
    Copy a file from disk into the emerging ISO image and mark it by a GPT entry as EFI System Partition. EFI boot firmware is supposed to use a FAT filesystem image in such a partition for booting from USB stick or hard disk.
    Instead of a disk_path, the word --efi-boot-image may be given. It exposes in GPT the content of the first El Torito EFI boot image as EFI system partition. EFI boot images are introduced by options -e or --efi-boot. The affected EFI boot image cannot show up in HFS+ because it is stored outside the HFS+ partition.

-chrp-boot-part
    Mark the block range of the whole emerging ISO image as MBR partition of type 0x41. This is not compatible with any other feature that produces MBR partition entries. It makes GPT unrecognizable.
    CHRP is used in conjunction with HFS. It is not yet tested whether HFS+ filesystems produced with option -hfsplus would boot on any CHRP capable machine.

-prep-boot-part disk_path
    Copy a file from disk into the emerging ISO image and mark it by a MBR partition entry of type 0x96. PReP boot firmware is supposed to read the content of the partition as single ELF executable file. This option is compatible with other MBR partitions and with GPT.

-mips-boot iso_rr_path
    Declare a data file in the image to be a MIPS Big Endian boot file and cause production of a MIPS Big Endian Volume Header. This is mutually exclusive with production of other boot blocks like MBR. It will overwrite the first 512 bytes of any data provided by -G. Up to 15 boot files can be declared by multiple -mips-boot options.

-mipsel-boot iso_rr_path
    Declare a data file in the image to be the MIPS Little Endian boot file. This is mutually exclusive with other boot blocks. It will overwrite the first 512 bytes of any data provided by -G. Only a single boot file can be declared by -mipsel-boot.

-B disk_path[,disk_path ...]
    Cause one or more data files on disk to be written after the end of the ISO image. A SUN Disk Label will be written into the first 512 bytes of the ISO image which lists this image as partition 1 and the given disk_paths as partition 2 up to 8.
    The disk files should contain suitable boot images for SUN SPARC systems.
    The pseudo disk_path "..." causes that all empty partition entries become copies of the last non-empty entry. If no other disk_path is given before "..." then all partitions describe the ISO image. In this case, the boot loader code has to be imported by option -G.

-sparc-boot disk_path[,disk_path ...]
    Alias of -B.

-sparc-label text
    Set the ASCII label text of a SUN Disk Label.

Character sets:

Character sets should not matter as long as only english alphanumeric characters are used for file names or as long as all writers and readers of the medium use the same character set. Outside these constraints it may be necessary to let xorriso convert byte codes.
A conversion from input character set to the output character set is performed when an ISO image gets written. Vice versa there is a conversion from output character set to the input character set when an ISO image gets loaded. The sets can be defined by options -input-charset and -output-charset, if needed.

-input-charset character_set_name
    Set the character set from which to convert disk file names when inserting them into the ISO image.

-output-charset character_set_name
    Set the character set from which to convert names of loaded ISO images and to which to convert names when writing ISO images.

Jigdo Template Extraction:

From man genisoimage: "Jigdo is a tool to help in the distribution of large files like CD and DVD images; see http://atterer.net/jigdo/ for more details. Debian CDs and DVD ISO images are published on the web in jigdo format to allow end users to download them more efficiently."
If the use of libjte was enabled at compile time of xorriso, then xorrisofs can produce a .jigdo and a .template file together with a single-session ISO image. If not, then Jigdo options will cause a FAILURE event, which normally leads to program abort.
One may determine the ability for Jigdo by:
  $ xorrisofs -version 2>&1 | grep '^libjte' && echo YES

The .jigdo file contains checksums and symbolic file addresses. The .template file contains the compressed ISO image with reference tags instead of the content bytes of the listed files.
Input for this process are the normal arguments for a xorrisofs session with no image loaded, and a .md5 file which lists those data files which may be listed in the .jigdo file and externally referenced in the .template file. Each designated file is represented in the .md5 file by a single text line:
MD5 as 32 hex digits, 2 blanks, size as 12 decimal digits or blanks, 2 blanks, symbolic file address
The file address in an .md5 line has to bear the same basename as the disk_path of the file which it shall match. The directory path of the file address is decisive for To=From mapping, not for file recognition. After To=From mapping, the file address gets written into the .jigdo file. Jigdo restore tools will convert these addresses into really reachable data source addresses from which they can read.
If the list of jigdo parameters is not empty, then padding will be counted as part of the ISO image.

-jigdo-jigdo disk_path
    Set the disk_path for the .jigdo file with the checksums and download addresses for filling the holes in .template.

-jigdo-template disk_path
    Set the disk_path for the .template file with the holed and compressed ISO image copy.

-jigdo-min-file-size size
    Set the minimum size for a data file to be listed in the .jigdo file and being a hole in the .template file. size may be a plain number counting bytes, or a number with appended letter "k", "m", "g" to count KiB (1024 bytes), MiB (1024 KiB), or GiB (1024 MiB).

-jigdo-force-md5 disk_path_pattern
    adds a regular expression pattern which will get compared with the absolute disk_path of any data file that was not found in the .md5 list. A match causes a MISHAP event, which normally does not abort the program run but finally causes a non-zero exit value of the program.

-jigdo-exclude disk_path_pattern
    Add a regular expression pattern which will get compared with the absolute disk_path of any data file. A match causes the file to stay in .template in any case.

-jigdo-map To=From
    Add a string pair of the form To=From to the parameter list. If a data file gets listed in the .jigdo file, then it is referred by the file address from its line in the .md5 file. This file address gets checked whether it begins with the From string. If so, then this string will be replaced by the To string and a ':' character, before it goes into the .jigdo file. The From string should end by a '/' character.

-md5-list disk_path
    Set the disk_path where to find the .md5 input file.

-jigdo-template-compress "gzip"|"bzip2"
    Choose one of "bzip2" or "gzip" for the compression of the template file. The jigdo file is put out uncompressed.

-checksum_algorithm_iso list_of_names
    Choose one or more of "md5", "sha1", "sha256", "sha512" for the auxiliary "# Image Hex" checksums in the .jigdo file. The list_of_names may e.g. look like "md5,sha1,sha512". Value "all" chooses all available algorithms. Note that MD5 stays always enabled.

-checksum_algorithm_template list_of_names
    Choose the algorithms for the "# Template Hex" checksums in the .jigdo file. The rules for list_of_names are the same as with -checksum_algorithm_iso.

Miscellaneous options:

-print-size
    Print to stdandard output the foreseeable number of 2048 byte blocks in the emerging ISO image. Do not produce this image.
    The result depends on several settings.
    If option --emul-toc is given, then padding (see -pad) is not counted as part of the image size. In this case either use -no-pad or add 150 (= 300 KiB) to the resulting number.

--no_rc
    Only if used as first argument this option prevents reading and interpretation of startup files. See section FILES below.

-help
    List supported options to stderr. Original mkisofs options bear their original mkisofs description texts.

-quiet
    Suppress most messages of the program run, except those which indicate problems or errors.

-log-file disk_path
    Truncate file disk_path to 0 size and redirect to it all messages which would normally appear on stderr. -log-file with empty text as disk_path re-enables output to stderr.

-v
    Enable the output of informational program messages.

-verbose
    Alias of -v.

-version
    Print to standard output a text that begins with
     "mkisofs 2.01-Emulation Copyright (C)"
    and to standard error the version information of xorriso.

EXAMPLES

  Overview of examples:
A simple image production run
Set ISO image paths by -graft-points
Perform multi-session runs
Let xorrisofs work underneath growisofs
Incremental backup of a few directory trees
Incremental backup with accumulated trees
Create bootable images for PC-BIOS

  A simple image production run
A prepared file tree in directory ./for_iso gets copied into the root directory of the ISO image. File permissions get set to read-only for everybody. Joliet attributes for Microsoft systems get added. The resulting image gets written as data file ./image.iso on disk.
  $ xorrisofs -r -J -o ./image.iso ./for_iso

  Set ISO image paths by -graft-points
Without option -graft-points each given disk file is copied into the root directory of the ISO image, maintaining its name. If a directory is given, then its files and sub-directories are copied into the root directory, maintaining their names.
  $ xorrisofs ... /home/me/datafile /tmp/directory
yields in the ISO image root directory:
  /datafile
  /file_1_from_directory
  ...
  /file_N_from_directory

With option -graft-points it is possible to put files and directories to arbitrary paths in the ISO image.
  $ xorrisofs ... -graft-points /home/me/datafile /dir=/tmp/directory
yields in the ISO image root directory:
  /datafile
  /dir
Eventually needed parent directories in the image will be created automatically:
  /datafiles/file1=/home/me/datafile
yields in the ISO image:
  /datafiles/file1
The attributes of directory /datafiles get copied from /home/me on disk.

Normally one should avoid = and \ characters in the ISO part of a pathspec. But if it must be, one may escape them:
  /with_\=_and_\\/file=/tmp/directory/file
yields in the ISO image:
  /with_=_and_\/file

  Perform multi-session runs
This example works for multi-session media only: CD-R[W], DVD-R[W], DVD+R, BD-R. Add cdrskin option --grow_overwriteable_iso to all -as cdrecord runs in order to enable multi-session emulation on overwriteable media.
The first session is written like this:
  $ xorrisofs -graft-points \
              /tree1=prepared_for_iso/tree1 \
    | xorriso -as cdrecord -v dev=/dev/sr0 blank=fast -multi -eject -
Follow-up sessions are written like this:
  $ dd if=/dev/sr0 count=1 >/dev/null 2>&1
  $ m=$(xorriso -as cdrecord dev=/dev/sr0 -msinfo)
  $ xorrisofs -M /dev/sr0 -C $m -graft-points \
              /tree2=prepared_for_iso/tree2 \
    | xorriso -as cdrecord -v dev=/dev/sr0 -waiti -multi -eject -
Always eject the drive tray between sessions. The old sessions get read via /dev/sr0. Its device driver might not be aware of the changed content before it loads the medium again. In this case the previous session would not be loaded and the new session would contain only the newly added files.
For the same reason do not let xorriso -as cdrecord load the medium, but rather do this manually or by a program that reads from /dev/sr0.

  Let xorrisofs work underneath growisofs
growisofs expects an ISO formatter program which understands options -C and -M. A variable is defined to override the hardcoded default name.
  $ export MKISOFS="xorrisofs"
  $ growisofs -Z /dev/dvd /some/files
  $ growisofs -M /dev/dvd /more/files
If no "xorrisofs" is available on your system, then you will have to create a link pointing to the xorriso binary and tell growisofs to use it. E.g. by:
  $ ln -s $(which xorriso) "$HOME/xorrisofs"
  $ export MKISOFS="$HOME/xorrisofs"
One may quit mkisofs emulation by argument "--" and make use of all xorriso commands. growisofs dislikes options which start with "-o" but -outdev must be set to "-". So use "outdev" instead:
  $ growisofs -Z /dev/dvd --for_backup -- \
              outdev - -update_r /my/files /files
  $ growisofs -M /dev/dvd --for_backup -- \
              outdev - -update_r /my/files /files
Note that --for_backup is given in the mkisofs emulation. To preserve the recorded extra data it must already be in effect, when the emulation loads the image.

  Incremental backup of a few directory trees
This changes the directory trees /open_source_project and /personal_mail in the ISO image so that they become exact copies of their disk counterparts. ISO file objects get created, deleted or get their attributes adjusted accordingly.
ACL, xattr, hard links and MD5 checksums will be recorded. It is expected that inode numbers in the disk filesystem are persistent over cycles of mounting and booting. Files with names matching *.o or *.swp get excluded explicitly.

To be used several times on the same medium, whenever an update of the two disk trees to the medium is desired. Begin with a blank medium and update it until he run fails gracefully due to lack of remaining space on the old one.
Do not let xorriso -as cdrecord load the medium, but rather do this manually or by a program that reads from /dev/sr0.
  $ dd if=/dev/sr0 count=1 >/dev/null 2>&1
  $ msinfo=$(xorriso -as cdrecord dev=/dev/sr0 -msinfo)
  $ load_opts=
  $ test -n "$msinfo" && load_opts="-M /dev/sr0 -C $msinfo"
  $ xorrisofs $load_opts -o - --for_backup -m '*.o' -m '*.swp' \
    -V PROJ_MAIL_"$(date '+%Y_%m_%d_%H%M%S')" -graft-points \
    -old-root / \
    /projects=/home/thomas/projects \
    /personal_mail=/home/thomas/personal_mail \
    | xorriso -as cdrecord dev=/dev/sr0 -v -multi -waiti -eject -

This makes sense if the full backup leaves substantial remaining capacity on media and if the expected changes are much smaller than the full backup.

Better do not use your youngest backup for -old-root. Have at least two media which you use alternatingly. So only older backups get endangered by the new write operation, while the newest backup is stored safely on a different medium.
Always have a blank medium ready to perform a full backup in case the update attempt fails due to insufficient remaining capacity. This failure will not spoil the old medium, of course.

If inode numbers on disk are not persistent, then use option --old-root-no-ino . In this case an update run will compare recorded MD5 sums against the current file content on hard disk.

With mount option -o "sbsector=" on GNU/Linux resp. -s on FreeBSD it is possible to access the session trees which represent the older backup versions. With CD media, GNU/Linux mount accepts session numbers directly by its option "session=".
Multi-session media and most overwriteable media written by xorriso can tell the sbsectors of their sessions by xorriso option -toc:
  $ xorriso -dev /dev/sr0 -toc
xorriso can print the matching mount command for a session number:
  $ xorriso -mount_cmd /dev/sr0 session 12 /mnt
or for a volume id that matches a search expression:
  $ xorriso -mount_cmd /dev/sr0 volid '*2008_12_05*' /mnt
Both yield on standard output something like:
  mount -t iso9660 -o nodev,noexec,nosuid,ro,sbsector=1460256 '/dev/sr0' '/mnt'
The superuser may let xorriso execute the mount command directly:
  # osirrox -mount /dev/sr0 "volid" '*2008_12_05*' /mnt

  Incremental backup with accumulated trees
Solaris does not offer the option to mount older sessions. In order to keep them accessible, one may map all files to a file tree under a session directory and accumulate those directories from session to session. The -root tree is cloned from the -old-root tree before it gets compared with the appropriate trees on disk.
This demands to know the previously used session directory name.
With the first session:
  $ xorrisofs -root /session1 \
    -o - --for_backup -m '*.o' -m '*.swp' \
    -V PROJ_MAIL_"$(date '+%Y_%m_%d_%H%M%S')" -graft-points \
    /projects=/home/thomas/projects \
    /personal_mail=/home/thomas/personal_mail \
    | xorriso -as cdrecord dev=/dev/sr0 -v blank=as_needed \
              -multi -waiti -eject -

With the second session, option -old-root refers to /session1 and the new -root is /session2.
Do not let xorriso -as cdrecord load the medium, but rather do this manually or by a program that reads from /dev/sr0.
  $ dd if=/dev/sr0 count=1 >/dev/null 2>&1
  $ msinfo=$(xorriso -as cdrecord dev=/dev/sr0 -msinfo)
  $ load_opts=
  $ test -n "$msinfo" && load_opts="-M /dev/sr0 -C $msinfo"
  $ xorrisofs $load_opts -root /session2 -old-root /session1 \
    -o - --for_backup -m '*.o' -m '*.swp' \
    -V PROJ_MAIL_"$(date '+%Y_%m_%d_%H%M%S')" -graft-points \
    /projects=/home/thomas/projects \
    /personal_mail=/home/thomas/personal_mail \
    | xorriso -as cdrecord dev=/dev/sr0 -v -multi -waiti -eject -
With the third session, option -old-root refers to /session2. The new -root is /session3. And so on.

  Create bootable images for PC-BIOS
The ISOLINUX wiki prescribes to create on disk a directory ./CD_root and to copy all desired files underneath that directory. Especially file isolinux.bin shall be copied to ./CD_root/isolinux/isolinux.bin . This is the boot image file.
The prescribed mkisofs options can be used unchanged with xorrisofs:
  $ xorrisofs -o output.iso \
      -b isolinux/isolinux.bin -c isolinux/boot.cat \
      -no-emul-boot -boot-load-size 4 -boot-info-table \
      ./CD_root
Put it on CD by a burn program. E.g.:
  $ xorriso -as cdrecord -v dev=/dev/sr0 blank=as_needed output.iso

The image from above example will boot from CD, DVD or BD, but not from USB stick or other hard-disk-like devices. This can be done by help of an isohybrid MBR. Syslinux provides matching template files as isohdp[fp]x*.bin . E.g. /usr/lib/syslinux/isohdpfx.bin .
If a few hundred KB of size do not matter, then option -partition_offset can be used to create a partition table where partition 1 starts not at block 0. This facilitates later manipulations of the USB stick by tools for partitioning and formatting.
The image from the following example will be prepared for booting via MBR and its first parttion will start at hard disk block 64.
It will also boot from optical media.
  $ xorrisofs -o output.iso \
      -b isolinux/isolinux.bin -c isolinux/boot.cat \
      -no-emul-boot -boot-load-size 4 -boot-info-table \
      -isohybrid-mbr /usr/lib/syslinux/isohdpfx.bin \
      -partition_offset 16 \
      ./CD_root
Become superuser and copy the image to the unpartitioned base device file of the USB stick. On GNU/Linux this is e.g. /dev/sdb, not /dev/sdb1.
CAUTION: This will overwrite any partitioning on the USB stick and make remaining data unaccessible.
So first make sure you got the correct address of the intended device. E.g. by reading 100 MiB data from it and watching it blinking:
  # dd bs=2K if=/dev/sdb count=50K >/dev/null
Now copy the image onto it
  # dd bs=2K if=output.iso of=/dev/sdb

FILES

  Startup files:
If not --no_rc is given as the first argument then xorrisofs attempts on startup to read and execute lines from the following files:
   /etc/default/xorriso
   /etc/opt/xorriso/rc
   /etc/xorriso/xorriso.conf
   $HOME/.xorrisorc
The files are read in the sequence given here, but none of them is required to exist. The lines are not interpreted as xorrisofs options but as generic xorriso commands. See man xorriso.

After the xorriso startup files, the program tries one by one to open for reading:
   ./.mkisofsrc
   $MKISOFSRC
   $HOME/.mkisofsrc
   $(dirname $0)/.mkisofsrc
On success it interprets the file content and does not try further files. The last address is used only if start argument 0 has a non-trivial dirname.
The reader currently interprets the following NAME=VALUE pairs:
 APPI default for -A
 PUBL default for -publisher
 SYSI default for -sysid
 VOLI default for -V
 VOLS default for -volset
Any other lines will be silently ignored.

SEE ALSO

For generic xorriso command mode
    xorriso(1)

For the cdrecord emulation of xorriso
    xorrecord(1)

For mounting xorriso generated ISO 9660 images (-t iso9660)
    mount(8)

Other programs which produce ISO 9660 images
    mkisofs(8), genisoimage(8)

Programs which burn sessions to optical media
    growisofs(1), cdrecord(1), wodim(1), cdrskin(1), xorriso(1)

ACL and xattr
    getfacl(1), setfacl(1), getfattr(1), setfattr(1)

MD5 checksums
    md5sum(1)

On FreeBSD the commands for xattr and MD5 differ
    getextattr(8), setextattr(8), md5(1)

BUGS
To report bugs, request help, or suggest enhancements for xorriso, please send electronic mail to the public list <bug-xorriso@gnu.org>. If more privacy is desired, mail to <scdbackup@gmx.net>.
Please describe what you expect xorriso to do, the program arguments resp. commands by which you tried to achieve it, the messages of xorriso, and the undesirable outcome of your program run.
Expect to get asked more questions before solutions can be proposed.

AUTHOR
Thomas Schmitt <scdbackup@gmx.net>
for libburnia-project.org

COPYRIGHT
Copyright (c) 2011 - 2012 Thomas Schmitt
Permission is granted to distribute this text freely. It shall only be modified in sync with the technical properties of xorriso. If you make use of the license to derive modified versions of xorriso then you are entitled to modify this text under that same license.

CREDITS
xorrisofs is in part based on work by Vreixo Formoso who provides libisofs together with Mario Danic who also leads the libburnia team. Vladimir Serbinenko contributed the HFS+ filesystem code and related knowledge.
Compliments towards Joerg Schilling whose cdrtools served me for ten years.