initramfs (Dracut) Command Reference

Starting with Ubuntu 26.04, the initramfs build tool changed from initramfs-tools to Dracut. The day-to-day commands change accordingly: the old update-initramfs and lsinitramfs are replaced by dracut and lsinitrd, and the configuration directory becomes /etc/dracut.conf.d/.

Note

Systems upgraded to 26.04 may still keep initramfs-tools, in which case the old commands still work. Fresh installs use Dracut by default. Confirm with which dracut / dracut --version.

Command Mapping

Old (initramfs-tools)	New (Dracut)	Description
`sudo update-initramfs -u`	`sudo dracut -f`	Rebuild the initramfs for the current kernel (`-f` overwrites the existing file)
`sudo update-initramfs -u -k all`	`sudo dracut -f --regenerate-all`	Rebuild for all installed kernels
`sudo update-initramfs -u -k $(uname -r)`	`sudo dracut -f --kver $(uname -r)`	Build for a specific kernel version
`lsinitramfs /boot/initrd.img-$(uname -r)`	`lsinitrd`	List files included in the initramfs
`lsinitramfs … \| grep xxx`	`lsinitrd \| grep xxx`	Check whether a module/file is packed in
`/etc/initramfs-tools/`	`/etc/dracut.conf.d/`	Configuration directory
`/etc/initramfs-tools/modules`	`force_drivers+=" MODULE "` (in conf.d)	Force-include a kernel module

Common Operations


# Rebuild the initramfs for the current kernel
sudo dracut -f
 
# Rebuild for all installed kernels (common after changing drivers, encryption, resume, etc.)
sudo dracut -f --regenerate-all
 
# Build for a specific kernel version to a specific path
sudo dracut -f /boot/initrd.img-7.0.0-10-generic 7.0.0-10-generic

Inspecting the initramfs


# View the contents of the current kernel's initramfs (defaults to the current kernel)
lsinitrd
 
# Inspect a specific file
lsinitrd /boot/initrd.img-$(uname -r)
 
# Confirm whether a kernel module is packed in (e.g. resume, encryption, NIC driver)
lsinitrd | grep -i resume
lsinitrd | grep -i nvme

Configuring Dracut

Dracut configuration lives in *.conf files under /etc/dracut.conf.d/. Changes only take effect after rebuilding the initramfs.


# Example: force-pack certain drivers into the initramfs
echo 'force_drivers+=" nvme nvme_core "' | sudo tee /etc/dracut.conf.d/90-nvme.conf
sudo dracut -f --regenerate-all

Common configuration options:


# /etc/dracut.conf.d/zz-local.conf
 
# Pack only modules needed by this host (smaller, the default behavior)
hostonly="yes"
 
# Force-include specific kernel drivers
force_drivers+=" MODULE "
 
# Add specific dracut modules (such as crypt, lvm, network)
add_dracutmodules+=" crypt lvm "
 
# Include extra executables in the initramfs
install_items+=" /usr/bin/vi "

Tip

After changing resume (hibernation), disk encryption, or the driver for the controller holding the root filesystem, remember to run sudo dracut -f --regenerate-all, or the system may fail to boot.

apt Command Reference — Third-party repo signing and package management
Black Screen / Boot Hang — Rebuild the initramfs to fix booting
Suspend and Hibernate — Rebuild the initramfs after configuring resume