Arch Linux

Description:

At early boot time there is a warnig message:
"WARNING

The root device is not configured to be mounted
read-write! It may be fsck'd again later."

$ cat /run/initramfs/init.log (attachment: run-initramfs-init.log-with-error)
...
+ echo ********************** WARNING **********************
********************** WARNING **********************
+ echo * *
* *
+ echo * The root device is not configured to be mounted *
* The root device is not configured to be mounted *
+ echo * read-write! It may be fsck'd again later. *
* read-write! It may be fsck'd again later. *
+ echo * *
* *
+ echo *****************************************************
...

$ cat /etc/fstab
...
/dev/sda2 / ext4 rw,relatime,data=ordered 0 1
...

$ cat /etc/mkinitcpio.conf
...
HOOKS="base udev autodetect modconf block filesystems keyboard fsck"
...

$ cat /etc/default/grub
...
GRUB_CMDLINE_LINUX_DEFAULT="quiet"
GRUB_CMDLINE_LINUX=""
...

Originally, I installed Fedora first, with its grub bootloader in MBR.
Later I installed Arch (but, without the grub package, which I did not notice).
Fedora's grub picked up Arch into its bootloader menu (as shown below).
This is the situation in which when booting Arch I am getting the fsck warning.

Fedora's /etc/default/grub shows:
GRUB_CMDLINE_LINUX="... quiet"
Fedora's /boot/grub2/grub.cfg shows:
- Fedora
linux /boot/vmlinuz-3.15.10-201.fc20.i686 ... ro
Notice the "ro" on boot line.
- Arch probed by os-prober
linux /boot/vmlinuz-linux root=/dev/sda2
Notice the lack of "ro" or "rw" on boot line ! This is surprising.
- Slackware probed by os-prober
linux /boot/vmlinuz root=/dev/sda3 ro ...
Notice the "ro" on boot line.

In the meantime, I noticed that my Arch installation does not have grub installed.
So, I installed it to Arch's partition (/dev/sda2) as required.
Arch's /boot/grub/grub.cfg shows:
- Arch
linux /boot/vmlinuz-linux root=UUID=38f0621f-5e39-4a84-9203-f10f56271833 rw quiet
Notice the "rw" on boot line !
- Fedora probed by os-prober
linux /boot/vmlinuz-3.15.10-201.fc20.i686 ... ro ...
Notice the "ro" on boot line.
- Slackware probed by os-prober
linux /boot/vmlinuz root=/dev/sda3 ro ...
Notice the "ro" on boot line.

The above shows the difference in Arch's kernel boot line as generated by os-prober in Fedora's grub, and Arch's own grub.

Now I went back to Fedora and regenerated its grub.cfg to see if there is any difference to its previous one.
Fedora's /boot/grub2/grub.cfg shows:
- Fedora
linux /boot/vmlinuz-3.15.10-201.fc20.i686 ... ro
Notice the "ro" on boot line.
- Arch probed by os-prober
linux /boot/vmlinuz-linux root=UUID=38f0621f-5e39-4a84-9203-f10f56271833 rw ...
There is the difference: "rw" on boot line ! I verified it at boot time too.
- Slackware probed by os-prober
linux /boot/vmlinuz root=/dev/sda3 ro ...
Notice the "ro" on boot line.

The result: no more warning message when booting Arch.
So, I found the cause of it - it looks like os-prober is doing funny dance (here discovered in Fedora because of this Arch's grub missing first; I did not test the same situation in reverse, that is, Arch's grub in MBR and Fedora's grub missing).

Also see comparison of attachments:
$ diff run-initramfs-init.log-with-error run-initramfs-init.log-without-error

Additional info:
* package version(s)
* config and/or log files etc.

community/os-prober 1.58-1
core/grub 1:2.02.beta2-4
core/mkinitcpio 18-2

Steps to reproduce:
As above.