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ltsp image - generate a squashfs image from an image source


ltsp [ltsp-options] image [-b backup] [-c cleanup] [-i ionice] [-k kernel-initrd] [-m mksquashfs-params] [-r revert] [image] ...


Compress a virtual machine image or chroot directory into a squashfs image, to be used as the network root filesystem of LTSP clients. It's used in similar fashion to live CDs, i.e. all clients will boot from this single read only image and then use SSHFS or NFS to mount /home/username from the server.


See the ltsp(8) man page for ltsp-options.

-b, --backup=0|1
Backup /srv/ltsp/images/image.img to image.img.old. Defaults to 1.
-c, --cleanup=0|1
Create a writeable overlay on top of the image source and temporarily remove user accounts and sensitive data before calling mksquashfs. Defaults to 1.
-i, --ionice=cmdline
Set a prefix command to run mksquashfs with a lower priority, or specify "" to disable it completely. Defaults to nice ionice -c3.
-k, --kernel-initrd=glob-regex
Pass this parameter to the ltsp kernel call after the squashfs creation. See ltsp-kernel(8) for more information.
-m, --mksquashfs-params="params"
Pass $params to the mksquashfs call unquoted; so params shouldn't contain spaces. See mksquashfs(1) for more information.
-r, --revert[=0|1]
Move /srv/ltsp/images/image.img.old to image.img and call ltsp kernel image. Useful when the clients won't boot with the new image.


There are three "image" types in LTSP, in the following locations. The /srv/ltsp path can be configured using ltsp --base-dir=:

Source images are placed directly under /srv/ltsp and usually are symlinks to virtual machine raw disk files. They're only used by ltsp image.
Chroot directories can be used both as sources for ltsp image and as NFS root exports for the clients.
Exported images (usually squashfs) are placed under the images directory and the clients can netboot from them.

Images can be specified as simple names like ltsp image img_name, in which case the aforementioned locations are searched, or as or full paths like ltsp image ~/VMs/vm.img.

The supported image types result in the following three methods to use LTSP. You may use either one of the methods or even all of them at the same time.


Chrootless LTSP, previously called "ltsp-pnp", is the recommended way to maintain LTSP if its restrictions are acceptable. In this mode, the server operating system itself is exported into a squashfs file and used for netbooting all the clients. You, the sysadmin, would use the typical GUI tools to manage the server, like software centers or update managers. Then whenever necessary, you'd run:

ltsp image /

This creates or updates /srv/ltsp/images/x86_64.img (the arch name comes from uname -m). Then, all the clients should be able to boot from x86_64.img and have a desktop environment identical to the server.

The big advantage of the chrootless mode is simplicity: there are no virtual machines or chroots involved. You'd maintain the server like any "home desktop PC", and have all clients be exact replicas, which is as simple as it gets.

The disadvantages are that the clients need to have the same architecture as the server (e.g. all x86_64), and that the server can't be a "full blown server" with LDAP and Apache and a lot of other services, without taking care to disable those services on the clients with the MASK_SYSTEM_SERVICES parameter of ltsp.conf. Note that MASK_SYSTEM_SERVICES already includes Apache and MySQL and a few other popular services that we don't want in LTSP clients, so it's not a problem if you install Apache on the LTSP server.

If for some reason you prefer a different name to uname -m, you may create a symlink:

ln -s / ~/amd64

...and run ltsp image ~/amd64 instead.


If the chrootless case doesn't fit you, you may use VirtualBox, virt-manager, KVM, VMWare and similar tools to maintain one or more template images for the clients. As an example, let's suppose you create a VM in VirtualBox and call it "debian". At the disk creation dialog, select "VMDK" type and "Fixed size", not "Dynamically allocated". Proceed with installing Debian on it. In the partitioning step, make sure that the whole operating system goes in the first partition, without extra partitions for /boot etc. BIOS/MBR is easier, while if you have to use GPT/UEFI, put the EFI partition second. When you're done, close VirtualBox and symlink the VM disk so that LTSP finds it more easily:

ln -rs ~/VirtualBox\ VMs/debian/debian-flat.vmdk /srv/ltsp/debian.img

To export this image to the clients, after the initial creation or after updates etc, you'd run:

ltsp image debian

It's also possible to omit the symlink by running:

ltsp image ~/VirtualBox\ VMs/debian/debian-flat.vmdk

...but then the image name shown in the iPXE boot menu would be "debian-flat", which isn't pretty.

In summary, you may symlink raw VM disks in /srv/ltsp/img_name.img, and ltsp image img_name will allow LTSP clients to netboot from them. Please also see the DIRECT IMAGES section of ltsp-kernel(8) for an advanced method of allowing clients to netboot directly from a VM or .iso image without even running ltsp image, and the ADVANCED IMAGE SOURCES section of ltsp-ipxe(8) for extreme cases like telling the LTSP clients to boot from an .iso image inside a local disk partition!


Chroot directories in /srv/ltsp/img_name are properly supported as image sources by LTSP, but their creation and maintenance are left to external tools like debootstrap, lxc etc. The ltsp-build-client LTSPv5 tool no longer exists. LTSP users are invited to create appropriate documentation in the community wiki. As a small example, you can use kvm to netboot a chroot and maintain it if you NFS-export /srv/ltsp/img_name in rw mode for your server IP, and then run

kvm -m 512 -kernel img_name/vmlinuz -initrd img_name/initrd.img \
    -append "rw root=/dev/nfs nfsroot="


Use the server installation as a template to generate a client image (chrootless, previously called ltsp-pnp):

ltsp image /

Inform ltsp image that a chrootless installation uses separate /boot and /opt partitions:

ltsp image /,,/boot,subdir=boot,,/opt,subdir=opt

Compress the /srv/ltsp/x86_64 chroot or the /srv/ltsp/x86_64.img virtual machine image, whichever exists of those two, into /srv/ltsp/images/x86_64.img, while disabling ionice:

ltsp image --ionice="" x86_64

Specify an absolute path to a virtual machine image:

ltsp image /home/user/VirtualBox\ VMs/x86_32/x86_32-flat.vmdk

Revert to the the previous version of the "chrootless" image:

ltsp image -r /