Mkisofs - OSDev Wiki (2024)

mkisofs is an utility that creates an ISO 9660 image from files on disk.

From the man page for mkisofs, "mkisofs is effectively a pre-mastering program to generate the iso9660 filesystem - it takes a snapshot of a given directory tree, and generates a binary image which will correspond to an iso9660 filesystem when written to a block device."

Developers of operating systems will mainly be interested increating ISO filesystems for bootable CD, DVD, or BD via El-Torito.Nevertheless, ISO filesystems may also be booted from hard disk or USB stick.

Mkisofs, its Clone, and its Emulator

The program mkisofs is part of thecdrtools projectby Joerg Schilling.

prog="mkisofs"

Some quarrels with the GNU/Linux community caused a fork of cdrtools,named cdrkit. The corresponding fork of mkisofsis named genisoimage. You will find it installed as "mkisofs"on many popular GNU/Linux distributions.

prog="genisoimage"

An independent alternative to mkisofs is GNU'sxorriso, which has anemulation mode that understands the options which are used withmkisofs for producing a bootable ISO 9660 image. Most distributionshave it either as package "xorriso" or as part of "libisoburn".GRUB2 script grub-mkrescue depends on xorriso-0.5.6 or newer.

prog="xorriso -as mkisofs"

Even the Linux distributions that ship genisoimage considers itoutdated and bugged. If you arenot using the UDF hybrid feature of genisoimage, you shouldprobably use xorriso on these systems instead. For EFI, xorriso ismandatory.

Warning: Defaults of xorriso -as mkisofs emulation might deviate from those of mkisofs.E.g. up to xorriso version 1.4.8 not specifying -boot-load-size assumed a default of four sectors instead of the entire boot file.

Options and input files

A mkisofs run needs one or more input directories or filesand a name for the emerging filesystem image file.There are options for standards compliance, for filesystemattributes, and -most important here- for setting up boot entrypoints.

-o DISKPATH sets the result file name. E.g. "bootable.iso".

-R enables normal Unix filenames and attributes byRock Ridge extension. -r does the same but also changesaccess permissions to make all files readable by everybody.

-J enables MS-Windows UCS-2 names via Joliet extension.

-iso-level NUMBER sets the ISO 9660 Level of Interchange.Level 1 allows only 8.3 filenames. Level 2 allows up to 30characters in filenames. Level 3 allows data files larger than4 GiB - 1.

-U violates ISO 9660 specs by allowing long case-sensitivefilenames outside of said extensions. If you know that the readercan stand it, then this is a cheap way to get decent file names.But expect standard readers to become confused.

-V TEXT sets the ISO 9660 Volume ID. It can be up to 32characters long and is often used by automounters as name ofthe mount directory for the filesystem.

-hide ISOPATH and -hide-joliet ISOPATH may be usedto exclude a data file from the directory trees while stillhaving its content in data blocks of the filesystem.

-c ISOPATH sets the filename for the El Torito Boot Catalog.The file is created automatically if boot images are announced.If option -c is missing, then the file will not show up in thedirectory trees of the ISO filesystem.

-b ISOPATH announces a data file as El Torito boot imagefor PC-BIOS.

-e ISOPATH announces a data file as El Torito boot imagefor EFI. This is not an option of original mkisofs,but is understood by some variants of genisoimage andby xorriso -as mkisofs.

-no-emul-boot and -hard-disk-boot choose emulationmodes other than the default of floppy emulation. Especially-no-emul-boot is needed for boot images of ISOLINUX and GRUB2.

-boot-load-size NUMBER sets how many blocks of the bootimage are to be loaded by the BIOS. A usual number with-no-emul-boot is 4.

-boot-info-table causes a Boot Info Table to be writteninto the boot image. Needed for boot images of ISOLINUX and GRUB2.

-eltorito-alt-boot ends the range of -b or -e.All further El Torito boot options will apply to the next bootimage given by -b or -e.

-G DISKPATH copies the content of a data file into theSystem Area of the ISO filesystem. This is used to bring MBRor other boot blocks into the filesystem to enable booting fromhard-disk-like devices or booting on exotic hardware.

-isohybrid-mbr DISKPATH copies a SYSLINUX/ISOLINUX MBRtemplate into the System Area and makes it execute the El Toritoboot image for BIOS. This is a speciality of xorriso -as mkisofs.

-isohybrid-gpt-basdat announces the boot image as GPTpartition for booting via EFI and as MBR partition.This is a speciality of xorriso -as mkisofs.

-graft-points enables the interpretation of pathspecswhich give a target path in the ISO filesystem together withthe path of an input directory or file.

A program argument, which is not recognized as option (e.g. because itdoes not begin by a dash "-") and is not parameter of an option,is taken as path to an input directory or file. If it is adirectory, then its content gets merged with the content ofthe root directory of the emerging ISO filesystem. If it isa file of other type, then it gets copied into the root directory.

If enabled, then pathspecs get recognized by an equal signwhich separates target path from source path. E.g.

/boot/readme.txt=/home/me/texts/boot_iso_readme.txt

copies file

/home/me/texts/boot_iso_readme.txt

into the ISO filesystem as

/boot/readme.txt

Hands-on examples

You want to create a bootable iso image?

First you need to build a bootable floppy image which holds f. ex. grub with your menu.lst and your kernel (and additional required modules).

Then, you put this boot floppy image in a temporary directory, say as /tmp/deploy/boot.img.

After that, you copy all your additional files (applications, images, texts, directories too) into the given directory (f. ex. /tmp/deploy).

Finally, you are ready to produce the ISO filesystem imageas /tmp/youriso.iso:

$prog -U -b boot.img -hide boot.img \ -V "Your Name..." -iso-level 3 -o /tmp/youriso.iso /tmp/deploy

Note that the ISOPATH for option -b is relative to theroot directory of the ISO filesystem. By providing the floppy imageas /tmp/deploy/boot.img you managed to let it appear in the ISOfilesystem as /boot.img.

For more examples see El-Torito.

Under Windows

Windows version of mkisofs(through cdrtools) can be downloaded from ftp://ftp.berlios.de/pub/cdrecord/alpha/win32.The following command(inside cygwin) can be used to create bootable iso image without using floopy image.

mkdir -p $ISO_DIR/boot/grubcp $GRUB_BIN/stage2_eltorito $ISO_DIR/boot/grubcp menu.lst $ISO_DIR/boot/grubcp your_kernel $ISO_DIR mkisofs -R -b boot/grub/stage2_eltorito -no-emul-boot -boot-load-size 4 -boot-info-table -o bootcd.iso $ISO_DIR

See Also

Articles

• ISO 9660 - technical properties of ISO 9660 filesystems
• El-Torito - structure of bootable ISO 9660 filesystems with mkisofs examples
• Bootable El-Torito CD with GRUB Legacy - tutorial on how to create a "no emulation" bootable CD
• Bootable CD - tutorial on using floppy disk emulation

Forum

• Thread about making your own .iso image from scratch without tools

External Links

• man 8 mkisofs Manual of mkisofs
• man 1 genisoimage Manual of genisoimage
• man 1 xorrisofs Manual of xorriso's emulation of mkisofs