initramfs-tools

root@kali:~# update-initramfs -h

Usage: update-initramfs {-c|-d|-u} [-k version] [-v] [-b directory]

Options:
 -k version	Specify kernel version or 'all'
 -c		Create a new initramfs
 -u		Update an existing initramfs
 -d		Remove an existing initramfs
 -b directory	Set alternate boot directory
 -v		Be verbose

See update-initramfs(8) for further details.

root@kali:~# lsinitramfs -h

Usage: lsinitramfs [-l] initramfs-file...

Options:
  -l   Display long and more verbose listing of initramfs content

See lsinitramfs(8) for further details.

root@kali:~# mkinitramfs -h

Usage: mkinitramfs [option]... -o outfile [version]

Options:
  -c compress	Override COMPRESS setting in initramfs.conf.
  -d confdir	Specify an alternative configuration directory.
  -l level	Override COMPRESSLEVEL setting in initramfs.conf.
  -k		Keep temporary directory used to make the image.
  -o outfile	Write to outfile.
  -r root	Override ROOT setting in initramfs.conf.

See mkinitramfs(8) for further details.

root@kali:~# unmkinitramfs -h

Usage: unmkinitramfs [-v] initramfs-file directory

Options:
  -v   Display verbose messages about extraction

See unmkinitramfs(8) for further details.