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Description of problem:
We'd like the ability to define mount units on the kernel command line. This allows the system to be booted into a snapshot of the system state (for e.g. using LVM2 CoW or thin provisioned snapshots) and enables rollback for system updates by allowing the administrator to preserve a copy of the prior system state and to optionally roll the system back to that state at a later time using the snapshot merge facility.
This would add new kernel command line syntax something like the following:
systemd.mount=what:where:fstype:options
The feature has been proposed to upstream systemd and has received some initial positive comments:
https://github.com/systemd/systemd/issues/27260
The new functionality would be added to the existing systemd-fstab-generator to write out mount units during early boot.
Version-Release number of selected component (if applicable):
systemd-250-12.el9_1
How reproducible:
100%
Steps to Reproduce:
1. man systemd-fstab-generator
Actual results:
No syntax exists for specifying kernel command line mount units.
Expected results:
The ability to specify mount units on the kernel command line
Additional info:
This will be used by Leapp and boom to provide rollback capable upgrades.
Tested with a recent RHEL-9.3 compose and systemd-252-18.el9.
Using the following command line:
systemd.mount-extra=/dev/rhel/root-snap:/:xfs:defaults rd.lvm.lv=rhel/root-snap crashkernel=1G-4G:192M,4G-64G:256M,64G-:512M fstab=no systemd.mount-extra=/dev/rhel/var-snap:/var:xfs:defaults systemd.mount-extra=/dev/rhel/home:/home:xfs:defaults console=tty1 console=ttyS1
The system boots correctly into the snapshot environment and the generated mount units all look correct:
# ls /run/systemd/generator/
getty.target.wants home.mount local-fs.target.requires local-fs.target.wants -.mount var.mount
# cat /run/systemd/generator/-.mount
# Automatically generated by systemd-fstab-generator
[Unit]
Documentation=man:fstab(5) man:systemd-fstab-generator(8)
SourcePath=/proc/cmdline
Before=local-fs.target
After=blockdev@dev-rhel-root\x2dsnap.target
[Mount]
What=/dev/rhel/root-snap
Where=/
Type=xfs
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.
For information on the advisory (systemd bug fix and enhancement update), and where to find the updated
files, follow the link below.
If the solution does not work for you, open a new bug report.
https://access.redhat.com/errata/RHBA-2023:6640