Ubuntu Manpage: ltsp image - generate a squashfs image from an image source

NAME

       ltsp image - generate a squashfs image from an image source

SYNOPSIS

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

DESCRIPTION

       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.

OPTIONS

       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.

IMAGE TYPES

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

       /srv/ltsp/img_name.img
              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.

       /srv/ltsp/img_name
              Chroot  directories  can  be  used  both as sources for ltsp image and as NFS root exports for the
              clients.

       /srv/ltsp/images/img_name.img
              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

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.

VM IMAGES

       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!

CHROOTS

       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 ⟨https://github.com/ltsp/ltsp/wiki/chroots⟩.  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=192.168.67.1:/srv/ltsp/img_name"

EXAMPLES

       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 /

COPYRIGHT

       Copyright 2019-2022 the LTSP team, see AUTHORS.